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  • richardmitnick 1:46 pm on September 23, 2020 Permalink | Reply
    Tags: A chiral twin has been found for every matter and antimatter particle in the Standard Model—with the exception of neutrinos., An object that can coincide with its mirror-image twin in every coordinate such as a dumbbell or a spoon is not chiral., Another broken symmetry: the current predominance of matter over antimatter in our universe., , Chirality is of the universe., , Chirality was discovered in 1848 by biomedical scientist Louis Pasteur., Every time an elementary particle is detected an intrinsic property called its spin must be in one of two possible states., For a completely unknown reason the weak nuclear force only interacts with left-handed particles., Maybe the neutrino masses come from a special Higgs boson that only talks to neutrinos., , Physicists often talk about three mirror symmetries in nature: charge (which can be positive or negative); time (which can go forward or backward) and parity (which can be right- or left-handed)., , Researchers have only ever observed left-handed neutrinos and right-handed antineutrinos., Symmetry Magazine, Understanding the difference between right-chiral and left-chiral objects is important for many scientific applications., You will find chirality in things like proteins; spiral galaxies and most elementary particles.   

    From Symmetry: “Nature through the looking glass” 

    Symmetry Mag
    From Symmetry

    Oscar Miyamoto Gomez

    Illustration by Sandbox Studio, Chicago.

    Handedness—and the related concept of chirality—are double-sided ways of understanding how matter breaks symmetries.

    Our right and left hands are reflections of one another, but they are not equal. To hide one hand perfectly behind the other, we must face our palms in opposite directions.

    In physics, the concept of handedness (or chirality) works similarly: It is a property of objects that are not dynamically equivalent to their mirror images. An object that can coincide with its mirror-image twin in every coordinate, such as a dumbbell or a spoon, is not chiral.

    Because our hands are chiral, they do not interact with other objects and space in the exact same way. In nature, you will find this property in things like proteins, spiral galaxies and most elementary particles.

    These different-handed object pairs reveal some puzzling asymmetries in the way our universe works. For example, the weak force—the force responsible for nuclear decay— has an effect only on particles that are left-handed. Also, life itself—every plant and creature we know—is built almost exclusively with right-handed sugars and left-handed amino acids.

    “If you have anything with a dual principle, it can be related to chirality,” says Penélope Rodríguez, a postdoctoral researcher at the Physics Institute of the National Autonomous University of Mexico. “This is not exclusive to biology, chemistry or physics. Chirality is of the universe.”

    Reflections of life

    Chirality was discovered in 1848 by biomedical scientist Louis Pasteur. He noticed that right-handed and left-handed crystals formed when racemic acid dried out.

    He separated them, one by one, into two samples, and dissolved them again. Although both were chemically identical, one sample consistently rotated polarized light clockwise, while the other did it counterclockwise.

    Pasteur referred to chirality as “dissymmetry” at the time, and he speculated that this phenomenon—consistently found in organic compounds—was a prerequisite for the handed chemistry of life. He was right.

    In 1904, scientist Lord Kelvin introduced the word “chirality” into chemistry, borrowing it from the Greek kheír, or hand.

    “Chirality is an intrinsic property of nature,” says Riina Aav, Professor at Tallinn University of Technology in Estonia. “Molecules in our bodily receptors are chiral. This means that our organism reacts selectively to the spatial configuration of molecules it interacts with.”

    Understanding the difference between right-chiral and left-chiral objects is important for many scientific applications. Scientists use the property of chirality to produce safer pharmaceuticals, build biocompatible metallic nanomaterials, and send binary messages in quantum computing (a field called spintronics).

    Broken mirrors

    Physicists often talk about three mirror symmetries in nature: charge (which can be positive or negative), time (which can go forward or backward) and parity (which can be right- or left-handed).

    Gravity, electromagnetism and the strong nuclear force are ambidextrous, treating particles equally regardless of their handedness. But, as physicist Chien-Shiung Wu experimentally proved in 1956, the weak nuclear force plays favorites.

    “For a completely unknown reason, the weak nuclear force only interacts with left-handed particles,” says Marco Drewes, a professor at Catholic University of Louvain in Belgium. “Why that might be is one of the big questions in physics.”

    Research groups are exploring the idea that such an asymmetry could have influenced the origin of the preferred handedness in biomolecules observed by Pasteur. “There is a symmetry breaking that gives birth to a molecular arrangement, which eventually evolves until it forms DNA, right-handed sugars and left-handed amino acids,” Rodríguez says.

    From an evolutionary perspective, this would mean that chirality is a useful feature for living organisms, making it easier for proteins and nucleic acids to self-replicate due to the preferred handedness of their constituent biomolecules.

    Missing twins

    Every time an elementary particle is detected, an intrinsic property called its spin must be in one of two possible states. The spin of a right-chiral particle points along the particle’s direction of motion, while the spin of a left-chiral particle points opposite to the particle’s direction of motion.

    A chiral twin has been found for every matter and antimatter particle in the Standard Model—with the exception of neutrinos. Researchers have only ever observed left-handed neutrinos and right-handed antineutrinos. If no right-handed neutrinos exist, the fact that neutrinos have mass could indicate that they function as their own antiparticles. It could also mean that neutrinos get their mass in a different way from the other particles.

    “Maybe the neutrino masses come from a special Higgs boson that only talks to neutrinos,” says, André de Gouvêa, a professor at Northwestern University. “There are many other kinds of possible answers, but they all indicate that there are other particles out there.”

    The difference between left- and right-handed could have influenced another broken symmetry: the current predominance of matter over antimatter in our universe.

    “Right-handed neutrinos could be responsible for the fact that there is matter in the universe at all,” Drewes says. “It could be that they prefer to decay into matter over antimatter.”

    According to de Gouvêa, the main lesson that chirality teaches scientists is that we should always be prepared to be surprised. “The big question is whether asymmetry is a property of our universe, or a property of the laws of nature,” he says. “We should always be willing to admit that our best ideas are wrong; nature does not do what we think is best.”

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:50 pm on August 24, 2020 Permalink | Reply
    Tags: "LHC creates matter from light", , , E = mc², Forces that seem separate in our everyday lives—electromagnetism and the weak force—are united., From massless to massive, , Last year the ATLAS experiment at the LHC observed two photons- particles of light- ricocheting off one another and producing two new photons., , , , Scientists on an experiment at the Large Hadron Collider see massive W particles emerging from collisions with electromagnetic fields., Symmetry Magazine, The LHC is the only place where scientists have seen two energetic photons merging and transforming into massive W bosons., The reason photons can collide and produce W bosons in the LHC is that at the highest energies those forces combine to make the electroweak force.   

    From Symmetry: “LHC creates matter from light” 

    Symmetry Mag
    From Symmetry<

    Sarah Charley

    Scientists on an experiment at the Large Hadron Collider see massive W particles emerging from collisions with electromagnetic fields. How can this happen?

    Illustration by Sandbox Studio, Chicago

    The Large Hadron Collider plays with Albert Einstein’s famous equation, E = mc², to transform matter into energy and then back into different forms of matter. But on rare occasions, it can skip the first step and collide pure energy—in the form of electromagnetic waves.

    CERN LHC Map

    Last year, the ATLAS experiment at the LHC observed two photons, particles of light, ricocheting off one another and producing two new photons.


    This year, they’ve taken that research a step further and discovered photons merging and transforming into something even more interesting: W bosons, particles that carry the weak force, which governs nuclear decay.

    This research doesn’t just illustrate the central concept governing processes inside the LHC: that energy and matter are two sides of the same coin. It also confirms that at high enough energies, forces that seem separate in our everyday lives—electromagnetism and the weak force—are united.

    From massless to massive

    If you try to replicate this photon-colliding experiment at home by crossing the beams of two laser pointers, you won’t be able to create new, massive particles. Instead, you’ll see the two beams combine to form an even brighter beam of light.

    “If you go back and look at Maxwell’s equations for classical electromagnetism, you’ll see that two colliding waves sum up to a bigger wave,” says Simone Pagan Griso, a researcher at the US Department of Energy’s Lawrence Berkeley National Laboratory. “We only see these two phenomena recently observed by ATLAS when we put together Maxwell’s equations with special relativity and quantum mechanics in the so-called theory of quantum electrodynamics.”

    Inside CERN’s accelerator complex, protons are accelerated close to the speed of light. Their normally rounded forms squish along the direction of motion as special relativity supersedes the classical laws of motion for processes taking place at the LHC. The two incoming protons see each other as compressed pancakes accompanied by an equally squeezed electromagnetic field (protons are charged, and all charged particles have an electromagnetic field). The energy of the LHC combined with the length contraction boosts the strength of the protons’ electromagnetic fields by a factor of 7500.

    When two protons graze each other, their squished electromagnetic fields intersect. These fields skip the classical “amplify” etiquette that applies at low energies and instead follow the rules outlined by quantum electrodynamics. Through these new laws, the two fields can merge and become the “E” in E=mc².

    “If you read the equation E=mc² from right to left, you’ll see that a small amount of mass produces a huge amount of energy because of the c² constant, which is the speed of light squared,” says Alessandro Tricoli, a researcher at Brookhaven National Laboratory—the US headquarters for the ATLAS experiment, which receives funding from DOE’s Office of Science. “But if you look at the formula the other way around, you’ll see that you need to start with a huge amount of energy to produce even a tiny amount of mass.”

    The LHC is one of the few places on Earth that can produce and collide energetic photons, and it’s the only place where scientists have seen two energetic photons merging and transforming into massive W bosons.

    A unification of forces

    The generation of W bosons from high-energy photons exemplifies the discovery that won Sheldon Glashow, Abdus Salam and Steven Weinberg the 1979 Nobel Prize in physics: At high energies, electromagnetism and the weak force are one in the same.

    Electricity and magnetism often feel like separate forces. One normally does not worry about getting shocked while handling a refrigerator magnet. And light bulbs, even while lit up with electricity, don’t stick to the refrigerator door. So why do electrical stations sport signs warning about their high magnetic fields?

    “A magnet is one manifestation of electromagnetism, and electricity is another,” Tricoli says. “But it’s all electromagnetic waves, and we see this unification in our everyday technologies, such as cell phones that communicate through electromagnetic waves.”

    At extremely high energies, electromagnetism combines with yet another fundamental force: the weak force. The weak force governs nuclear reactions, including the fusion of hydrogen into helium that powers the sun and the decay of radioactive atoms.

    Just as photons carry the electromagnetic force, the W and Z bosons carry the weak force. The reason photons can collide and produce W bosons in the LHC is that at the highest energies, those forces combine to make the electroweak force.

    “Both photons and W bosons are force carriers, and they both carry the electroweak force,” Griso says. “This phenomenon is really happening because nature is quantum mechanical.”

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 10:09 am on August 18, 2020 Permalink | Reply
    Tags: "Long-lived particles get their moment", , ATLAS and CMS experiments at CERN LHC, , , , , , , Symmetry Magazine   

    From Symmetry: “Long-lived particles get their moment” 

    Symmetry Mag
    From Symmetry

    Sarah Charley

    Scientists on experiments at the LHC are redesigning their methods and building supplemental detectors to look for new particles that might be evading them.

    Illustration by Sandbox Studio, Chicago with Ariel Davis.

    Duke University postdoc Katherine Pachal has spent the last ten years—from undergraduate on—searching for new particles with the ATLAS experiment at the Large Hadron Collider. “I’ve always been a search person,” she says.

    CERN ATLAS Image Claudia Marcelloni

    Physicists discovered the Higgs boson in 2012, but since then the list of known fundamental particles has remained static.

    CERN CMS Higgs Event May 27, 2012

    CERN ATLAS Higgs Event June 12, 2012

    This hasn’t dampened Pachal’s enthusiasm for the search for new particles. Rather, she sees it as an indication that physicists need to look for them in an innovative new way.

    When scientists designed detectors for the LHC, they wagered that new forces, fields and physics would come in the form of extremely short-lived particles that decay almost precisely at their points of origin. Scientists catch the particles that behave this way—such as the aforementioned Higgs bosons—in detectors surrounding the collision points.

    “The primary goal of ATLAS [above] and CMS was to find the Higgs, and we built darn good experiments to do that,” Pachal says.

    CERN/CMS Detector

    With many unanswered questions still looming in the field, LHC physicists are revisiting their original assumptions and reinventing their tools and techniques to reach for long-lived particles—ones that could travel long distances before becoming detectable.

    Illustration by Sandbox Studio, Chicago with Ariel Davis.

    Long-lived particles

    “We already have long-lived particles in the Standard Model,” says Jingyu Luo, a graduate student at Princeton University.

    Standard Model of Particle Physics, Quantum Diaries

    Muons, for instance, can travel several kilometers before decaying (which is the main reason the particle detectors at CERN are so enormous). Protons and electrons may not decay at all.

    According to theorist Jonathan Feng at the University of California, Irvine, physicists were originally hesitant to search for additional long-lived particles because there seemed to be no real need for them in the theory.

    “If you want to come up with a theory with long-lived particles, it’s extremely easy,” he says. “You could add an arbitrarily long-lived particle to any theory and put it in by hand, but there was no rhyme or reason to it.”

    Feng’s feelings changed in 2003 when he was building upon a popular set of theories called supersymmetry, and a long-lived particle popped out of his equations. “There was no way around it, we needed long-lived particles,” he says. “This was different than putting it in by hand. It was coming out of a very well-structured theory.”

    But these theoretical particles seemed out of the grasp of the experiments running at the LHC.

    The detectors for the ATLAS and CMS experiments—funded by CERN member states and other contributing countries including the United States, via the US Department of Energy’s Office of Science and the National Science Foundation—generate about 50 terabytes of data a second. Most of this data comes from already well-understood subatomic processes, and a series of increasingly selective trigger systems evaluate the onslaught of hits and only pass along events that they pre-approve as “high quality and potentially interesting.” But a new type of long-lived particle wouldn’t necessarily have any of these pre-defined ‘interesting’ characteristics.

    “Our trigger systems are lacking a lot of the information that is core to many of our long-lived particle searchers,” Pachal says.

    These systems make snap judgments based on factors such as the amount of energy a collision leaves in the detector (a good indicator of the presence of a rare, massive particle). Scientists have already developed software that helps their trigger systems scan parts of the detector for signs of long-lived particles. But for a truly comprehensive search, they need to consider detailed particle tracks.

    “In the past, we were restricted by how time-consuming it is to reconstruct all the tracks,” Pachal says. In the next run of the LHC, “we’re improving our software so that we can use more of the detector to look for particle tracks in the trigger, and this will help us make these more subtle decisions.”

    Illustration by Sandbox Studio, Chicago with Ariel Davis.


    Even if long-lived particles are out there waiting to be found, there is still the question of whether scientists can find enough of them to claim a discovery.

    Traditional techniques to pick out possible sightings of new particles involve a series of strict cuts, removing giant chunks of the dataset at a time. “For instance, if I had a room full of people and wanted to find fans of the Italian composer Ennio Morricone, I could make a series of judgements such as, ‘people between 50 and 70 are good candidates to like this kind of music’ and focus my attention on them,” Luo says. “But in reality, it’s so much more complicated than that.”

    To separate long-lived particle candidates from an ocean of look-alikes, Luo is incorporating machine earning.

    Traditional techniques rely on a series of pre-programed “yes” or “no” check boxes to determine which events to keep. Machine-learning algorithms, on the contrary, examine thousands of collision events to build a deep understanding of how different variables interplay with one another to create the kind of particle signatures physicists are looking for.

    By the time physicists look at the data deemed “interesting,” their machine-learning framework is already a collision connoisseur. Like an expert judge scoring rhythmic gymnastics at the Olympics, it has built up enough specialized knowledge to rate each contender.

    The avoidance of strict cuts gives physicists increased flexibility to conduct these kinds of blue-sky searches.

    “There’s what we know and what we don’t know,” Luo says. “What we know is that there is a group of models that predict the existence of long-lived particles. But what we don’t know is which model is right.”

    Luo and his colleagues are working on model-independent searches at the LHC. Their goal is to stay sensitive to many types of potential long-lived particles, with a wide range of characteristics. “Leave no stone unturned,” he says.

    Particle escape artists

    While CMS and ATLAS search for long-lived particles inside their detectors, other teams of scientists are considering how to capture long-lived particles that could travel beyond them.

    “Upgrading existing experiments is one method,” Feng says. “The other method involves building supplemental detectors.”

    In fall of 2017, Feng and colleagues proposed building one such detector, which they named FASER.

    CERN FASER experiment schematic

    To catch long-lived particles that might escape the ATLAS experiment, FASER will sit in an unused tunnel that just happens to be right along the path they expect particles to follow, 480 meters from the ATLAS detector.

    Construction for FASER started in 2019. It is scheduled to start operation when collisions resume at the LHC, foreseen for late 2021 or early 2022.

    Teams of scientists are designing other, larger detectors—with names such as CODEX-b and MATHUSLA—to be built near other LHC collision points.

    With the help of these improved tools and techniques, the LHC physics community will be poised to jump on new physics. “There’s a moment for everything, and the moment for long-lived particles is starting,” Pachal says.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 12:39 pm on July 30, 2020 Permalink | Reply
    Tags: "Boosting the representation of African American students", , , , Next stop-Women in STEM, , Symmetry Magazine   

    From Symmetry: “Boosting the representation of African American students” Next stop-Women in STEM 

    Symmetry Mag
    From Symmetry<

    Diana Kwon

    Illustration by Sandbox Studio, Chicago with Ana Kova

    A study conducted by the TEAM-UP task force provides a road map for doubling the number of African Americans obtaining bachelor’s degrees in physics and astronomy.

    On June 10, thousands of academics around the globe halted their usual work to reflect on the systemic racism present in their fields and communities and plan ways to eradicate it. Scientific societies, universities and publishers joined in on the strike, which adopted the hashtags #ShutDownSTEM, #ShutDownAcademia and #Strike4BlackLives.

    The strike, which occurred in the wake of the recent Black Lives Matter protests ignited by the murder of George Floyd, has brought conversations about the racism facing African American academics to the fore.

    “We recognize that our academic institutions and research collaborations—despite big talk about diversity, equity and inclusion—have ultimately failed African American people,” wrote members of Particles for Justice, one of the groups that organized the strike, in a statement. “African American representation among physics faculty is non-existent at most institutions, and it is widely known that African American students often feel unwelcome, unsupported and even unsafe in their physics departments and predominantly white campuses.”

    African American students face obstacles throughout academia, but many of these issues are particularly pronounced in physics. The figures paint a telling picture: Although the number of African American undergraduates earning bachelor’s degrees more than doubled between 1995 and 2015, in physics, the number of degrees awarded to African American students dropped from 5% in the late 1990s to 4% in recent years.

    TEAM-UP—a task force put together by the American Institute of Physics, a federation of physics societies—recently completed a two-year study aimed at investigating the key factors stymieing the success of African American students in physics. The group’s detailed findings and recommendations, which were published this January, provide insights as the scientific community grapples with ways to stamp out systemic racism in academia.

    “It has been heartening to see so many copies of the report downloaded from our website and for its recommendations to become part of our community’s dialog on racial justice in the physical sciences,” says Arlene Modeste Knowles, TEAM-UP’s project manager at AIP.

    The TEAM-UP task force, which convened at the end of 2017, included two AIP staff members and 10 academics from various backgrounds, disciplines and career stages. Their study involved multiple lines of assessment, including surveys and interviews with students, visits to physics departments with a good track-record of attracting and retaining African American students, and an extensive review of the literature. The primary goal of the report was to provide a roadmap for community-wide efforts to double the number of bachelor’s degrees in physics and astronomy awarded to African American students by 2030.

    Brian Beckford, a particle and nuclear physicist at the University of Michigan, says that one of his main reasons for joining the task force was that he believes that persistent underrepresentation of African American undergraduate students in physics is a solvable problem.

    “If we just take some of the effort that we put into our experiments—trying to detect undetectable particles like neutrinos, searching for rare processes—and we put it into trying to figure out solutions to a needed systemic change, we would be very far along in solving this,” he says.

    In their report, the task force concludes that African American students do not lack the drive, motivation, intellect or capabilities to obtain degrees in physics or astronomy. Instead, they are turning away from astronomy and physics because of a lack of supportive environments and because of the financial challenges facing both students and the departments that have consistently demonstrated the best practices in supporting their success.

    From “The Time Is Now: Systemic Changes to Increase African Americans with Bachelor’s Degrees in Physics and Astronomy”
    Illustration by Sandbox Studio, Chicago with Ana Kova







    The team pinpointed five key factors contributing to the success of African American students: belonging (feelings of inclusion or exclusion within a department), physics identity (students’ ability to perceive themselves as future physicists or astronomers), academic support (effective teaching, mentoring and strengths-based support that enables student success), personal support (means to lift the burden of financial stress, which disproportionally affect African American students) and leadership and structures (university departments prioritizing and creating supportive environments for African American students).

    Beckford says that one of the responses he found most striking was a student who said they felt a “constant feeling that I am a representative, therefore I must be flawless.”

    Beckford says he has heard this time and time again from African American students he’s mentored—and has felt it himself. “I think it’s a culture issue that makes students feel this pressure to be exceptional, out of the fear that [their performance] reflects on every other student that may be given the opportunity to join the department, to get this fellowship,” he says. “It’s quite a bit of pressure that they’re carrying around.”

    The task force provided specific recommendations about how to effectively address each of these factors. These include: creating and communicating norms that boost a student’s sense of belonging and eliminate identity-based harassment, providing services to African American students that focus on their strengths, and establishing a $50 million endowment to provide support for students facing financial hardship and for departments implementing the report’s recommendations.

    “I hope that people will take away the important message that African American students are as capable of successfully earning their physics and astronomy bachelor’s degrees as other students … [and] come to understand that the environment, culture and available resources for these students must change in order to better support them,” says Modeste Knowles. “I hope that departments will be motivated to implement the recommendations so we can increase not only the number of African American bachelor’s degrees in physics and astronomy, but also the participation and success of African American students in these fields.”

    Although it is too early to assess the full impact of TEAM-UP’s report, there are already signs that the group’s recommendations are being both considered and implemented.

    Several institutions—including historically black colleges and universities—are already practicing many of the recommendations in the report, and faculty members in physics and astronomy departments are reading and discussing the report with their colleagues, Modeste Knowles says.

    Using funds provided by the Heising-Simons Foundation, the group now plans to run two workshops to discuss and share strategies to pursue the goal of doubling the number of African Americans earning bachelor’s degrees in physics and astronomy by 2030. Participants will include AIP and its affiliate societies, other scientific societies and faculty members from university physics and astronomy departments.

    “What I hope people take away from the report is that there are really no more excuses,” Beckford says. “The only thing left to do is act.”

    Next stop, Women in STEM, a huge problem where the lack of acceptance of women in some of our most important institutions represents not only a bias but a waste of talent. There are brilliant women in all of he sciences and we are not only disparaging them. We are also losing their abilities to contribute to our growth of scientific knowledge.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:24 pm on June 30, 2020 Permalink | Reply
    Tags: "Hundreds of hadrons", , , Symmetry Magazine   

    From Symmetry: “Hundreds of hadrons” 

    Symmetry Mag
    From Symmetry<

    Jerald Pinson

    Illustration by Sandbox Studio, Chicago with Ana Kova

    Hadrons count among their number the familiar protons and neutrons that make up our atoms, but they are much more than that.

    In the early 1900s, physicists were trying to find the source of a low-level buzz of radiation that seemed to be present at all times, everywhere around the world. The reigning theory was that all of it came from the Earth itself.

    That quickly changed, however, when the Swiss physicist Albert Gockel used a hot air balloon to take measurements of the radiation far above sea level. To his surprise, it actually increased with altitude. This strange, pervasive energy, it seemed, was coming from above even more than from below. The source? High-energy particles from space called cosmic rays.

    To detect these particles, physicists began taking to the skies in balloons and refitted war planes; hiking up precarious mountainsides; and side-stepping gaping crevasses in high-elevation glaciers. They brought with them cloud chambers, transparent containers full of dense water or alcohol vapor.

    When a cosmic ray collides with an atom in a cloud chamber, a shower of smaller subatomic particles careen off in all directions. These charged particles ionize vapor molecules, which become visible as thin wisps of condensation. (See our article on how to make your own cloud chamber.)

    Using cloud chambers—and later detectors filled with liquid hydrogen—physicists began to realize that there are far more particles than they had initially suspected.

    They discovered muons, pions, kaons and lambda particles. Then, starting in the 1930s when the first particle accelerators began operation, physicists found themselves inundated with even more new subatomic particles.

    “There were so many of these particles,” says Brian Shuve, a physicist at Harvey Mudd College, “that it seemed very unlikely that they were all elementary.”

    That hunch turned out to be correct. Most of the new particles would eventually be classified as “hadrons,” composite particles made up of even tinier constituents called quarks.

    Hadrons include such all-star members as the protons and neutrons that make up the nuclei of atoms, but the group is much larger than that. Through decades of meticulous study, we now know that there are more than 100 different hadrons. By studying them, physicists have been able to paint a clearer picture of the four fundamental forces that explain our universe.

    The periodic table of hadrons

    It’s hard out there for a massive particle. Generally, the more massive a particle is, the faster it decays, releasing its energy as it falls apart into less massive particles.

    Knowing this, physicists were baffled by the behavior of the some of the new particles they saw. Some of them, such as the kaons, were sticking around much longer than expected, based on their masses.

    In 1952, physicists Murray Gell-Mann, Abraham Pais and Kazuhiko Nishijima introduced the concept of ‘strangeness’ to describe this property.

    In 1961, Gell-Mann and physicist Yuval Ne’eman discovered that by charting a particle’s strangeness along one axis in a graph and its isospin—a quantum number related to the particle’s interaction with the strong force—along the other, they could group them into precise geometric figures.

    Gell-Mann called this organization scheme the “Eightfold Way,” a term he borrowed from the Buddhist path to awakening. It allowed him to create a kind of periodic table for the hadrons.

    Just as chemist Dmitri Mendeleev’s periodic table of elements initially contained gaps that allowed him to predict the existence of undiscovered elements, the Eightfold Way also contained gaps that led physicists to the discovery of new particles.

    The case for quarks

    In developing the Eightfold Way, Gell-Mann had crafted a puzzle with an intricate design. He knew roughly where the missing pieces were, but he couldn’t immediately make sense of the pattern.

    Gell-Mann and the physicist George Zweig independently realized that the way in which hadrons were related to one another could be explained if they were actually made up of even smaller particles. Gell-Mann whimsically termed these theoretical elementary particles “quarks,” while Zweig called them “aces.”

    But there were two problems with this theory.

    First, in their experiments physicists had never detected anything even remotely resembling a quark. Second, and just as dire: Up until that point, the charges of all of the known particles came in whole numbers (i.e. 1, -1, 0). To make the theory of quarks or aces work, they had to have charges that were fractional.

    This didn’t sit well with the established physics community, nor even with Gell-Mann himself. He ended his publication outlining the predicted properties of quarks by asking experimentalists to prove him wrong, saying, “A search for stable quarks… would help to reassure us of the non-existence of real quarks.”

    Experimentalists obliged this request for several years without luck. But physicists persisted, and a series of experiments performed in the early 1970s at the US Department of Energy’s SLAC National Accelerator Laboratory—then called Stanford Linear Accelerator Center—finally drummed up evidence for the existence of these elementary particles.

    Gell-Mann and Zweig were vindicated (though Gell-Mann’s name, “quarks,” won the day), and physicists had a new model for understanding the subatomic realm.

    Researchers initially worked under the assumption that there were three quarks, although we now know that there are at least six, called up, down, top, bottom, charm and strange.

    Most hadrons are made up of either two or three quarks.

    Hadrons made up of three quarks—such as the proton and the neutron—are called baryons. (Protons contain two up quarks and a down quark, while neutrons have two down quarks and an up quark.)

    Hadrons made up of two quarks are called mesons. These are bit more exotic; one of their two quarks is always an antimatter particle. Pions, for example, can either be positive, negative or neutral. Positive pions contain an up quark and an anti-down quark that are briefly pulled together in a delicate dance before decaying into a more stable form of matter.

    All in all, physicists have either directly detected or otherwise inferred the existence of more than 100 different hadrons, including a few varieties of four- and even five-quark particles.

    An unstable partnership

    If there are so many different types of hadrons in the universe, why are protons and neutrons the only two that seem to constitute visible matter? To answer this question, we have to return to the question of stability.

    Each of the six types of quark has its own mass, ranging from the light up and down quarks, each of which has a mass equal to less than a percent of the proton’s, to the top quark, which is a whopping 175 times more massive than a proton. To put that into perspective, the difference between the mass of the up quark and the top quark is roughly the difference in weight between a tennis ball and an elephant.

    Since protons are made up of extremely small quarks, you might be asking where the proton gets most of its mass. You’re not alone.

    “The majority of a hadron’s mass actually comes from the energy of the gluons that bind quarks together,” says Cesar Luis Da Silva, a physicist at Los Alamos National Laboratory. “But exactly how the energy of gluons translates to the mass of hadrons is a question physicists are still trying to answer.”

    Hadrons made up of heavier quarks tend to be unstable due to their excess energy and thus exist only briefly before decaying into smaller particles. But the rate at which hadrons decay is governed by which force they interact with.

    “Neutral pions decay 300 million times faster than charged pions, even though they have the same mass,” says Da Silva. “That’s because neutral pions decay via the electromagnetic interactions, whereas charged pions decay through the weak force.”

    The proton and neutron, made up of the lightest quarks, tend to stick around. But not even those particles are necessarily safe from the ravages of time, points out Dmitri Denisov, the deputy associate lab director for High-Energy Physics at Brookhaven National Laboratory.

    “Neutrons in the nucleus of atoms can live for quite a long time—up to billions of years—but as soon as they’re free of the nucleus, they decay in about 15 minutes,” he says.

    No one has ever observed a proton decay, but that may only be because they remain relatively stable for such a long time. It’s possible that in the far, distant future, all protons will have decayed into other forms of matter and energy.

    New combinations

    As newer particle accelerators harness higher energies than their predecessors, physicists are able to create increasingly exotic particles. This has been a staple for researchers on the LHCb experiment at the Large Hadron Collider, Denisov says.

    “The LHC—because it has such high energy—can create particles which contain more than two or three quarks,” he says. “Some can have four, called tetraquarks, or five—the pentaquarks.”

    “Like most other hadrons, these particles are unstable and exist for mere billionths of a second,” Denisov says. “There are only a handful of them detected, and some of their properties are puzzling.”

    Hadrons are still taking us to the edge of known physics and beyond. Just as the disorienting discovery of new hadrons in cloud chambers led to the theory of quarks, the new tetra- and pentaquarks may lead us to an even deeper understanding of how the universe works.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 11:17 am on June 17, 2020 Permalink | Reply
    Tags: "The stories a muon could tell", , Brookhaven Muon g-2, , , Muons- a lot like an electron just more massive., , Symmetry Magazine   

    From Symmetry: “The stories a muon could tell” 

    Symmetry Mag
    From Symmetry<

    Jerald Pinson

    Illustration by Sandbox Studio, Chicago with Steve Shanabruch

    Muons Transforming

    The discovery of the muon originally confounded physicists. Today international experiments are using the previously perplexing particle to gain a new understanding of our world.

    At the beginning of the 20th century, physicists were aware of a pervasive shower of particles that seemed to rain down from space. By filling glass chambers with highly condensed vapor, they could indirectly see tracks left by these highly energetic particles now known as cosmic rays.

    Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet)

    In doing so, they quickly discovered the subatomic world was more complex than initially suspected.

    The first new matter particle they discovered was the muon. It was a lot like an electron, just more massive. At first, no one knew what to make of it.

    Some thought it might be a particle theorized to hold protons and neutrons together in an atom. But a pair of Italians conducting experiments in Rome during World War II proved otherwise.

    After discarding a few alternative theories—including one that posited that this particle might be a new kind of electron—physicists were left with one conclusion: They had discovered a particle that nobody had predicted. As Nobel Laureate I.I. Rabi famously quipped, “Who ordered that?”

    Although scientists hadn’t realized muons would be on the menu, the discovery of muons eventually led to a discovery about how that menu was set up: Particles can come in different versions, each alike in charge, spin and interactions but different in mass. The muon, for example, has the same charge, spin and electroweak interactions as the electron, but is about 200 times heavier, and there’s an even heavier version of the electron and muon, called the tau.

    Physicists built on this principle to predict the existence of generations of other particles, such as neutrinos, which with electrons, muons and taus round out the set of particles called leptons. Eventually, scientists would find that all of the matter particles in the Standard Model, including quarks, could be organized into three generations, though only the lightest are stable.

    Standard Model of Particle Physics, Quantum Diaries

    Muons continue to be useful tools for discovery to this day. Two international experiments, one currently underway and the other slated to begin in the early 2020s, are using the previously perplexing particles to push the boundaries of physics.

    Flavor physics and the Mu2e experiment

    Each of the three generations is called a different “flavor” of particle.

    At first, scientists assumed that flavor was a property that, like mass or energy, had to be conserved when particles interacted with each other. That wasn’t quite right, but in their defense, they did find this to be true almost all of the time.

    “When you have some kind of an interaction that involves charged leptons, such as nuclear or particle decay or some type of high-energy particle interaction, the number of a given flavor of charged leptons remains the same,” says Jim Miller, a professor of physics at Boston University.

    When muons decay, for example, they transform into an electron, an anti-electron neutrino, and a muon neutrino. The electron and anti-electron neutrino cancel each other out, flavor-wise, leaving just the muon neutrino, which has the same flavor as the original muon.

    Flavor conservation was useful; it allowed physicists to predict the interactions they would observe in particle accelerators and nuclear reactions. And those predictions proved to be correct.

    But then physicists discovered that the group of (uncharged lepton) particles called neutrinos are unaware they are expected to follow the rules. On their long journey to Earth from the center of the sun, where they are created in fusion reactions, neutrinos freely oscillate between generations, transforming from electron neutrinos to muon neutrinos to tau neutrinos and back without releasing any additional particles.

    This phenomenon, which won researchers Takaaki Kajita and Arthur B. McDonald the Nobel Prize for Physics in 2015, left scientists with a question: If neutrinos could violate flavor conservation, could other particles do it, too?

    Physicists hope to answer that exact question with Mu2e, an experiment scheduled to start generating data in the next few years at the US Department of Energy’s Fermi National Accelerator Laboratory.

    FNAL Mu2e facility under construction

    FNAL Mu2e solenoid

    The experiment is supported by funding from DOE’s Office of Science.

    Mu2e will search for muons converting into electrons without releasing other particles, a process that would clearly violate flavor conservation.

    But why use muons? It’s because they’re the just-right middle of the lepton family. Not too big or too small, muons are a sort of Goldilocks particle that are perfectly suited to aid physicists in their search for new physics.

    Electrons, the least massive charged leptons, are small and stable. Taus, the most massive ones, are so massive and short-lived that they decay far too quickly for physicists to effectively study. Muons, however, are massive enough to decay but not massive enough to decay too quickly, making them the perfect tool in the search for new physics.

    In the Mu2e experiment, physicists will accelerate a beam of low-energy muons toward a target made of aluminum. In the resulting collisions, muons will knock electrons out of their orbits around the aluminum nuclei and take their place, creating muonic atoms for a brief moment in time.

    “Since the mass of the muon is 200 times greater than the mass of the electron, and its average distance from the nucleus is 200 times smaller, there’s an overlap between the muon’s position and the position of the aluminum nucleus, allowing them to interact,” Miller says.

    As the muon decays into an electron, physicists predict that the extra energy that usually goes into creating two neutrinos in a typical muon decay will instead be transferred to the atom’s nucleus. This would allow the conversion from one flavor to another, muon to electron, without any neutrinos or antineutrinos to provide balance. If observed, this direct transition of a muon into an electron would be the hoped-for discovery of flavor violation among charged leptons.

    Magnetic moment of fame

    Mu2e is not the only experiment that will use muons to test our understanding of physics.

    Eight years before the discovery of muons, physicist Paul Dirac was developing a theory to describe the motion of electrons. In a single, elegant equation, Dirac successfully described that motion—while simultaneously merging Albert Einstein’s special theory of relativity with quantum mechanics and predicting the existence of antimatter.

    It’s hard to overstate how important and incredibly accurate Dirac’s equation turned out to be. Physicists still act giddy whenever it’s mentioned.

    To understand why it’s important, take a look at the electron.

    Dirac’s equation correctly described exactly how the electromagnetic force worked and gave the correct estimate for how an electron’s spin would shift—or “precess”—if placed in a magnetic field, a measurement known as g. (That prediction was later refined through calculations from the field of quantum electrodynamics.)

    When muons were discovered in 1936, Dirac’s equation was used to calculate what their precession rate would be as well. The value g for muons was predicted to be equal to 2.

    But when physicists began generating muons in accelerators at CERN in the 1950s to test his predictions, the results were not quite what they expected. Had they found a discrepancy between observation and theory? Although physicists worked hard for the next 20 years, they couldn’t generate enough energy with their accelerators to obtain a conclusive answer.

    Scientists at Brookhaven National Laboratory were able to test Dirac’s prediction at higher energies between 1999 and 2001 with an experiment meant to directly determine the anomalous part of the magnetic moment called Muon g-2 (pronounced “Muon g minus 2”).

    Brookhaven Muon g-2 ring

    They found hints of the same anomalous measurement, but even with their improved technology, they lacked sufficient precision to prove a disagreement with theory.

    Could Dirac’s equation turn out to be wrong? Physicists think it could be that their findings in muons are actually hinting at a deeper structure in physics that has yet to be discovered and that studying muons could once again lead to new revelations.

    “The g-2 factor has been measured for other particles,” says Fermilab physicist Tammy Walton. “It’s been very precisely measured for the electron. It’s also been measured for composite particles, like the proton and neutron. But the large mass of muons make them more sensitive to new physics.”

    Fermilab recently began the next generation Muon g-2 experiment, which physicists hope along with J-PARC in Japan will unequivocally confirm whether or not theory agrees with nature. Funded by the DOE’s Office of Science, the experiment at Fermilab has been taking data since 2017.

    FNAL Muon g-2 studio

    “We hope to get 20 times the number of muons, giving us a fourfold reduction in statistical uncertainty,” says Erik Swanson, a research engineer at the University of Washington. “If our central value stays the same as that generated at Brookhaven, then we will have confirmed without a doubt the discrepancy between theory and observation. Otherwise it might just be that theory was right all along.”

    If the theory is broken, physicists will have a lot of explaining to do, which could lead them to a new understanding of the particles and forces that make up our universe and the forces that govern them. Not bad work for a particle nobody ordered.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 10:14 am on June 10, 2020 Permalink | Reply
    Tags: "How do neutrinos get their mass?", , , Symmetry Magazine   

    From Symmetry: “How do neutrinos get their mass?” 

    Symmetry Mag
    From Symmetry<

    Jessica Romeo

    Neutrinos don’t seem to get their mass in the same way as other particles in the Standard Model.

    Standard Model of Particle Physics, Quantum Diaries

    A colorized image shows the tracks of neutrinos as they zoom into a chamber. Illustration based on Fermilab Bubble Chamber image.

    In 1998, researchers made a discovery that challenged their understanding of particle physics and vaulted an unassuming particle into the spotlight for decades to come.

    The Standard Model, the theoretical framework that should explain ordinary matter and its interactions, predicted that particles called neutrinos had no mass. In experiments, neutrinos appeared to move at the speed of light, something only a massless particle can accomplish.

    But then, physicists at the Super-Kamiokande Observatory in Japan collected the first evidence that neutrinos had a mass that was tiny but not zero.

    Super-Kamiokande experiment. located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan

    “This was the first observed phenomenon that we didn’t know how to explain,” says André de Gouvêa, a theoretical physicist and professor at Northwestern University. “Our model failed. That means that there’s some ingredient missing.”

    So now we know: Neutrinos aren’t massless, they’re just incredibly light—a million times lighter than the next lightest particle, the electron. Trillions of neutrinos pass harmlessly through your body each second, and in fact, rarely interact with any matter at all.

    “Because they’re so weakly interacting, we don’t know as much about neutrinos as other Standard Model particles,” says Jessica Turner, a postdoc studying neutrino phenomenology at the US Department of Energy’s Fermi National Accelerator Laboratory. “We know that they’re there. We’ve got many experiments that detect their interactions, but we know relatively little about them.”

    We do know some things. We know neutrinos come in three flavors. And they don’t stick to just one of those flavors; they oscillate from flavor to flavor as they move through space. This feat is only possible because they have non-zero mass.

    But where does that mass come from?

    Neutrinos are a type of fundamental particle known as a fermion. All other fermions, such as leptons and quarks, gain their mass through their interactions with the Higgs boson. But neutrinos don’t seem to follow that trend.

    Physicists have proposed hundreds of theories for how neutrinos might get their mass, and everyone has their favorite. Maybe there’s another source of mass that we do not know about. Maybe the neutrino masses are the interplay of the Higgs boson and this new source of mass. For many, the thrill comes from trying to narrow it down.

    “If we’re lucky, the question becomes: Which is the right answer?” says de Gouvêa. “What is the way that nature chooses to give neutrinos a mass? We still don’t know the answer to that.”

    U Wisconsin IceCube Neutrino Experiment

    The hidden neutrino

    As we experimentally observe them now, neutrinos cannot interact with the Higgs field because they’re are missing something vital: They are not right-handed.

    Particles can be left-handed or right-handed; these designations indicate the orientation of the particle’s spin in relation to the direction of its momentum.

    You might call most particles ambidextrous; they come in both left- and right-handed varieties. When a particle interacts with the Higgs field, it switches its handedness from left to right or right to left. This switch needs to happen for the field to give the particle mass.

    “Left-handed particles behave very differently from right-handed particles,” says Pedro Machado, a physicist at Fermilab. “So you need something to glue them together, which is the Higgs boson.”

    But in the case of neutrinos, this is more complicated. That’s because, confoundingly, all neutrinos appear to be left-handed.

    The apparent lack of right-handed neutrino forms the main mystery of neutrino masses. “We don’t know if this particle actually exists,” says Machado. And if they do exist, it could be that the right-handed neutrino is just so inert that it only interacts with the Higgs boson, making it especially difficult to detect.

    The neutrino as its own opposite

    Although scientists have yet to detect right-handed neutrinos, they already know of a different group of right-handed particles in the neutrino ecosystem: antineutrinos. That brings us to the next theory: It’s possible that a neutrino is actually its own antiparticle.

    Each fundamental particle has an antiparticle counterpart with some mirror attributes, such as opposite charge (for example, negatively charged electrons are paired in this way with positively charged positrons). The antiparticles get mass in the same way the associated particles do.

    The neutrino and its opposite, the antineutrino, are both neutrally charged particles. So here’s a riddle: If it looks like a neutrino and acts like a neutrino, doesn’t it follow that the antineutrino might be the same particle as a neutrino?

    If the antineutrino and neutrino are simply right-handed and left-handed versions of the same particle, then they should be able to marry to get a mass. This would mean neutrinos are something called Majorana fermions, which can only occur when both the particle and antiparticle are identical.

    In this scenario, the neutrino would get its mass through an interaction with its antineutrino. To make this work, theorists would need to invent something else, like a unique form of the Higgs boson especially to interact with neutrinos.

    An alternative to the Higgs

    The most popular theory proposes a completely new mass mechanism at play that is not within the Standard Model, one which introduces an entirely new particle.

    According to de Gouvêa, this new entity could be a super-heavy particle, one that looks like a right-handed neutrino but with a mass of its own. It could be something that looks like a Higgs boson or a kind of electron-like particle. It could even be multiple particles whose collected effect gives neutrinos their mass.

    One of the most popular forms of this theory is the Seesaw Mechanism, which accounts for the teeny-tiny size of the neutrino.

    If there’s a heavy particle involved in the mechanism that creates neutrino mass, its heaviness might be what causes left-handed neutrinos to be so light.

    Experiments weigh in

    Physicists are testing these theories in experiments, trying to rule out the ones that don’t work.

    The first and most important question to answer is: Are neutrinos Majorana fermions? Experiments like GERDA (for GERmanium Detector Array) at Gran Sasso Underground Laboratory in Italy are trying to determine whether neutrinos are their own antiparticles by searching for a phenomenon called neutrinoless double beta decay.

    MPG GERmanium Detector Array (GERDA) at Gran Sasso, Italy

    In this process, a neutron inside an isotope, in this case a germanium isotope, decays and spits out an electron and neutrino. If two neutrons inside the same isotope decay at the same time, it’s called a double beta decay. Scientists are looking for neutrinoless double beta decay, in which the nucleus seems to emit only two electrons and no neutrinos because the neutrinos have paired (Majorana-style) and been annihilated.

    Observing double beta decay is extremely rare. Neutrinoless double beta decay—if it occurs—would be even rarer.

    “We haven’t seen it yet, but we’re not worried,” de Gouvêa says.

    He predicts that physicists will have an answer, one way or the other, in around 10 years (though he admits that since it’s hard to prove a negative, neutrinoless double-beta decay might always seem just out of reach).

    The fruits of this research wouldn’t end with neutrinos, Turner says. “If we understand them better we can connect with these other open questions in particle physics,” she says.

    Questions like: Why is there more matter in the universe than antimatter? Why is the expansion of the universe accelerating? Where does dark matter come from?

    “We’re in the process of getting as much information about neutrino masses as we can,” de Gouvêa says, “because it will help shape our understanding of particle physics in a way that’s qualitatively different than what we have now. That’s the hope.”

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 1:51 pm on April 28, 2020 Permalink | Reply
    Tags: , , , , , SN1987a -"The supernova that keeps on giving", Symmetry Magazine   

    From Symmetry: “The supernova that keeps on giving” 

    Symmetry Mag
    From Symmetry<

    Shannon Hall

    Supernova 1987A, the closest supernova observed with modern technology, excited the world more than 30 years ago—and it remains an intriguing subject of study even today.

    This is an artist’s impression of the SN 1987A remnant. The image is based on real data and reveals the cold, inner regions of the remnant, in red, where tremendous amounts of dust were detected and imaged by ALMA. This inner region is contrasted with the outer shell, lacy white and blue circles, where the blast wave from the supernova is colliding with the envelope of gas ejected from the star prior to its powerful detonation. Image credit: ALMA / ESO / NAOJ / NRAO / Alexandra Angelich, NRAO / AUI / NSF.

    SN1987a from NASA/ESA Hubble Space Telescope in Jan. 2017 using its Wide Field Camera 3 (WFC3).

    Astronomer Robert Kirshner didn’t believe the news. It was early one morning in February 1987 and a colleague was recounting an unthinkable rumor: A star had exploded in a galaxy next door.

    If it were a prank, it wouldn’t be the first time, so Kirshner wasn’t alone in his skepticism. “It was so unexpected and outrageous that I think for a few hours, we discounted it,” says Stan Woosley, an astronomer at UC Santa Cruz. “But then the messages kept pouring in from all over the world. It was clear that it was real and our lives were all going to change.”

    Although astronomers now spot thousands of supernovae every year, an explosion close enough to be seen with the unaided eye is still a rare event. In fact, the cosmic explosion—dubbed SN1987A or just 87A for short—remains the closest supernova that has been seen in nearly four centuries. Its proximity, plus the use of modern technology, allowed astronomers across the globe to catch an incredible show—one that continues today.

    Supernovae change the fate of entire galaxies, altering the chemical make-up of the interstellar medium and prompting the formation of new stars. They have even had quite an effect on you; the calcium in your bones, the oxygen you breathe and the iron in your hemoglobin were all elements originally unleashed in these massive stellar explosions.

    We know this now. Before 1987, however, much of our understanding of supernovae was based solely on theory. So astronomers around the world scrambled to observe the live event.

    The Russian space station literally rocked back and forth to catch gamma-rays from the explosion. NASA looked for gamma-rays as well, launching high-altitude balloons from Australia to observe them. The Japanese satellite GINGA successfully detected X-rays.


    Observatories in South Africa, Chile and Australia kept track of the supernova’s light curve. And huge underground detectors in Japan, the United States and Russia detected subatomic particles known as neutrinos.

    “It was a big party, a worldwide party, and stayed that way all year long,” Woosley says.

    But it didn’t end there. Nearly any time a new observatory has come online over the last 33 years, it has swiveled toward the dying explosion. “All the instruments of modern astronomy have been used, by and large,” says Adam Burrows from Princeton University. “There isn’t any class of instrumentation that hasn’t been employed to study 87A.”
    Early insights

    A type II supernova erupts when a heavyweight star runs out of fuel and can no longer support itself against gravity. The bulk of the star comes crashing down toward its core, forcing it to collapse into one of the densest astrophysical objects known, a neutron star. A neutron star squeezes a few solar masses’ worth of star into an orb the size of a city. Meanwhile, the onrush of gas from the rest of the star rebounds against that core, sending a shock wave back toward the surface, which ultimately tears the star apart.

    At least that was the theory. If true, the action would release a huge stream of particles called neutrinos. And because they would pass through the bulk of the star unimpeded, they would arrive at Earth even before the explosion could be seen as a blast of light. (In fact scientists now think that it’s not the bounce that blows up the star, but the neutrinos.)

    To check, scientists began poring over data from the Kamiokande II neutrino detector in Japan as soon as they heard about the eruption.

    Kamiokande-II operated 1985-1990, Japan

    It was painstaking work, but after a few days they spotted nearly a dozen neutrinos that had arrived a few hours before the flash of light—a Nobel Prize-winning discovery that confirmed a neutron star had formed within the blast. “It was the best time so far in my life,” says Masayuki Nakahata, who as a graduate student helped make the detection.

    In total, the Kamiokande II detector in Japan counted 11 neutrinos, the IMB facility in Ohio reported eight and the Baksan Neutrino Observatory in Russia reported five more.

    INR RAS – Baksan Neutrino Observatory (BNO). The Underground Scintillation Telescope in Baksan Gorge at the Northern Caucasus
    (Kabarda-Balkar Republic)

    Neutrino detectors haven’t seen so many particles at once since.

    But while the observation of neutrinos confirmed theories, the observation of the type of star that went supernova went against them. Before SN1987A, textbooks asserted that only puffy red stars known as red supergiants could end their lives in such an explosion. But when scientists peered through past images of the location of the supernova, they found that 87A’s progenitor was a hotter and more compact blue supergiant.

    Astronomers were baffled until the Hubble Space Telescope was launched in 1990. Its early images revealed what other telescopes had only hinted at: a thin ring of glowing gas that encircled the dying ember that 87A left behind, with two fainter rings above and below. These were clues that the star had dumped a lot of gas into space tens of thousands of years before it exploded. A previous outburst, likely from a red supergiant, could have whittled the star down to expose its hotter, bluer innards. Or perhaps two stars had collided together; this would have shed a lot of gas and left behind a hot mess.

    An ongoing event

    To this day, astronomers continue to pivot the Hubble Space Telescope toward SN1987A nearly every year—and for good reason. As the ejecta from the explosion continue to expand outward, they slam into the surrounding medium, lighting up previously unseen material that was emitted in winds before the supernova eruption. “We see something new every time we take an image,” says Josefin Larsson from the KTH Royal Institute of Technology in Sweden.

    They’re not the only ones. The Atacama Large Millimeter/submillimeter Array (ALMA) in Chile recently claimed to have spotted telltale evidence of the “missing” neutron star.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    Although the detection of neutrinos indicated that a neutron star had formed within the embers, there was one major snag: Scientists have yet to actually spot the star itself. That’s a problem, given that the neutron star should finally be visible—unless of course there is too much dust surrounding the explosion. “It’s like trying to observe something through a Sahara Desert storm,” Woosley says.

    Finally, there is a hint that the neutron star is there. Using ALMA, Phil Cigan, an astronomer from Cardiff University in the United Kingdom, and his colleagues spotted a small bright patch—affectionally dubbed “the blob”—within the dust of 87A consistent with where scientists predicted the neutron star should be.

    They’re not calling the case closed, though; without being able to see the star directly, no one can prove that the supernova had the predicted effect. “It’s only tantalizing,” Burrows says. “We have to watch for a much longer time to see what’s left emerge.”

    One hypothesis suggests that perhaps a neutron star formed but that it was only short-lived. If more material rained down in the aftermath of the explosion, the star could have gained so much weight that it collapsed further to form a black hole. “Suppose that happened, let’s say, in five days after the explosion,” says Kirshner, who is still at Harvard University and also works full-time as head of science philanthropy for the Gordon and Betty Moore Foundation. “I don’t think we would have any way to know whether that was true or not.”

    Mikako Matsuura, an astronomer who worked on the ALMA observations at Cardiff, agrees that we cannot exclude this hypothesis. But Woosley says he doubts it, arguing that the most natural time to make a black hole would have been within seconds—a hypothesis that’s discounted by the length of the neutrino arrival.

    Whether or not the supernova created a neutron star is “the biggest remaining question in 1987A right now,” Burrows says. And that means that observations won’t stop anytime soon, he says. “It has been a moveable feast—and continues to be.”

    Astronomers hope it’s just a taste of what’s to come. Supernovae likely erupt every 50 years in a galaxy like ours, yet one hasn’t been seen since 1604 (SN1987A was not actually in our galaxy; it was nearby). “We feel as if we’re due for one,” Kirshner says.

    It’s an exciting prospect, given the number of new observatories that have come online in recent years or are scheduled to begin operation soon. The James Webb Space Telescope would be able to image a supernova in the infrared. Radio telescopes like the upcoming Square Kilometer Array in South Africa and ALMA would collect radio waves. The Athena X-ray observatory, which is scheduled to be launched by the European Space Agency in the early 2030s, would image the energetic emission from the supernova.

    ESA/Athena spacecraft depiction

    Gravitational wave facilities such as LIGO in North America, Virgo in Europe and KAGRA in Asia would detect ripples in space-time from such a supernova.

    MIT /Caltech Advanced aLigo

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    KAGRA gravitational wave detector, Kamioka mine in Kamioka-cho, Hida-city, Gifu-prefecture, Japan

    Neutrino facilities such as IceCube at the South Pole, the NOvA detector (and an even larger upcoming project, the DUNE detector) in the United States, and the Super-Kamiokande detector (and an even larger upcoming project, the Hyper-Kamiokande detector) in Japan would be much more sensitive to the influx of neutrinos.

    U Wisconsin ICECUBE neutrino detector at the South Pole

    NOvA Far Detector Block

    FNAL/NOvA experiment map

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

    Surf-Dune/LBNF Caverns at Sanford

    Super-Kamiokande experiment. located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan

    Hyper-Kamiokande, a neutrino physics laboratory to be located underground in the Mozumi Mine of the Kamioka Mining and Smelting Co. near the Kamioka section of the city of Hida in Gifu Prefecture, Japan.

    Nakahata, who owes his career to 87A and today works as a neutrino physicist, notes that the Hyper-Kamiokande detector alone would be able to witness tens of thousands of the particles in such an instance, a major upgrade from Kamiokande II’s previous record of 11. That would allow scientists to pin down further details behind the neutron star, like how much energy it might emit and the mass of the star itself. While the Hyper-Kamiokande detector would primarily be sensitive to antimatter particles—antineutrinos—the DUNE detector is complementary in that it would primarily be sensitive to matter particles—neutrinos. And additional observations from other detectors across the spectrum would provide even further insights.

    “We should be treated to an incredible show,” Burrows says. “It would dwarf 87A in importance.”

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 11:47 am on April 15, 2020 Permalink | Reply
    Tags: "T2K advances investigation of matter-antimatter imbalance", , , , , Symmetry Magazine, Why is the universe filled with matter and not antimatter?   

    From Symmetry: “T2K advances investigation of matter-antimatter imbalance” 

    Symmetry Mag
    From Symmetry<

    Emily Ayshford

    Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo

    New results from the T2K experiment in Japan rule out with 99.7% confidence nearly half of the possible range of values that could indicate how neutrinos behave compared to their antimatter counterparts [Nature].

    Physicists are closer than ever to measuring a value that could help answer one of the field’s longstanding questions: Why is the universe filled with matter, and not antimatter?

    Why, after the Big Bang should have produced equal amounts of matter and antimatter, did the two fail to cancel one another out entirely, leaving nothing but energy behind? The answer may lie in physics’ most mysterious particle—the ghostly neutrino—and understanding just how it acts compared to its mirror-twin, the antineutrino.

    Scientists involved in the T2K Experiment in Japan have reported new results that eliminate, with 99.7% confidence, nearly half of the possible values of a measurement that could finally tell us whether neutrinos are involved in the imbalance.

    Along with the NOvA experiment in the United States, T2K has been homing in on this value, called the CP violating phase of neutrinos. There’s more work to do to finally determine this value, but these latest results are the strongest constraint yet.

    FNAL NOvA Near Detector

    FNAL/NOvA experiment map

    “T2K now has more data with better algorithms and better analysis techniques,” than ever before, says Chang Kee Jung, US principal investigator for the experiment and a professor at Stony Brook University.

    If neutrinos and antineutrinos behave differently, it would be an extremely rare feature in the symmetrical world of physics. It could provide some explanation for why there is more matter than antimatter and offer us a new understanding of the universe.

    Changing flavors

    Neutrinos are the most abundant matter particle in the universe: About 100 trillion pass through your body each second. They come from nuclear reactions, like those in the sun and supernovae. As they travel through the universe, they barely interact with matter. That makes them extremely difficult to study.

    Like all other subatomic particles, they have an antimatter particle; theirs is called the antineutrino. These twins behave as mirror opposites to their counterparts, with an opposing electric charge and opposing internal quantum numbers. This is called charge-parity (CP) symmetry.

    But what is special about neutrinos is that when they travel, they oscillate, meaning they change from one “flavor” to another. At the T2K experiment, physicists can send a beam of either muon neutrinos or muon antineutrinos from the Japan Proton Accelerator Research Complex (J-PARC) in Tokai, Japan, nearly 300 kilometers away to the Super-Kamiokande detector.

    T2K map, T2K Experiment, Tokai to Kamioka, Japan

    As they travel, some oscillate and change their flavor, with muon neutrinos changing to electron neutrinos and muon antineutrinos changing to electron antineutrinos. Jung likens it to ice cream suddenly changing its flavor from chocolate to strawberry. T2K measures just how many of these flavor changes occur and compares the transformations of the neutrino beam to the transformations of the antineutrino beam.

    If neutrinos and antineutrinos change flavors differently, that could be evidence of an imbalance called CP violation, which could help them understand why there is so much matter in the universe. It is generally assumed that the Big Bang should have produced equal amounts of matter and antimatter. But if that were the case, all the particles and antiparticles would have met and annihilated each other.

    “The whole universe would just be filled with light,” Jung says. “If we have CP violation, then very early in the Big Bang there could have been a process to allow it to eliminate all the antimatter,” leaving just enough matter behind to form our universe.

    Process of elimination

    The amount of CP violation in neutrinos could be described as a specific number, which could be anywhere from -180 to 180. Any number other than 0, -180 or 180 would indicate that there is a difference between the matter and antimatter versions of neutrinos. Neutrino physicists are working to determine this measurement at a confidence level of 5 sigma, at which point physicists would feel comfortable calling it a new discovery.

    After years of taking data, T2K has now eliminated the range of values from -2 to 165 with a confidence level of nearly 3 sigma. “If humankind is making a journey to discover CP violation at a 5-sigma level, T2K is now almost halfway there,” Jung says.

    In fact, with many of the positive values close to 0 and 180 starting to be ruled out, the measurement could eventually show that CP violation in neutrinos is as big as possible. Considering the only types of particles known to violate CP, quarks, have only a very small imbalance between the behavior of their matter and antimatter particles, this result could be very interesting, says André de Gouvêa, a professor at Northwestern University and a neutrino theorist. “Why would that be? It might say something about how these two values are related to each other. There’s a lot we don’t yet know.”

    The NOvA experiment, which is managed by the US Department of Energy’s Fermi National Accelerator Laboratory, is also measuring neutrino oscillations in hopes of narrowing down the potential range of values. NOvA and T2K are slightly different: T2K uses neutrinos with smaller energies, detects them 300 kilometers (about 190 miles) away, and uses a large water tank to detect them. NOvA uses higher energy neutrinos, detects them about 800 kilometers (about 500 miles) away, and uses a detector filled with liquid scintillator.

    It’s important to have multiple experiments looking for the same phenomenon, because “if they get a different answer, that could be a sign that there is some physics that we could have missed,” de Gouvêa says.

    In fact, Jung says, the two experiments are now working together to combine data. “So many people are needed to work on efforts like these,” he says. “Hundreds of people at all different levels, from leaders to people who work directly on the accelerator, beams, detectors and analysis. It takes that kind of collaboration for discovery. Combining our data will give us more confidence as a community in our results.”

    Both T2K and NOvA are looking to take data for several more years before two even more powerful neutrino experiments come online: the Deep Underground Neutrino Experiment (DUNE) in the United States and Hyper-Kamiokande (Hyper-K) in Japan.

    “In the best of all worlds, T2K and NOVA will have a big hint that CP is violated, and the new experiments will measure the value,” de Gouvêa says.

    These results won’t tell us exactly how the universe manages to have more matter than antimatter, he says, but knowing how neutrinos are involved will be key to understanding particle physics going forward. “It will be very important for making progress,” he says.

    T2K Press Release

    Fig.1 The arrow indicates the value most compatible with the data. The gray region is disfavored at 99.7% (3σ) confidence level. Nearly half of the possible values are excluded. Credit: T2K International Collaboration

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 5:14 pm on April 7, 2020 Permalink | Reply
    Tags: , , , , Symmetry Magazine   

    From Symmetry: “Dark matter decoys” 

    Symmetry Mag
    From Symmetry<

    Evelyn Lamb

    Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington. Axion Dark Matter Experiment

    The ADMX experiment trains scientists to deal with real signals—by creating fake ones.

    The Axion Dark Matter Experiment searches for dark matter the way you might search for a radio station in an unfamiliar location. In a process that takes quite a bit longer than simply turning the dial, it scans across frequency bands that correspond to the possible masses of the particle they’re looking for. If they get a hint on their first pass—metaphorically, a few notes that sound like the kind of music they’d like to hear—they conduct a more thorough analysis of that frequency.

    They usually do get a few hints on each pass, says University of Washington physicist Gray Rybka, co-spokesperson of ADMX. Some of this is due to random signal fluctuation. Some of it is due to leaky radio signals. (At one point it was a local religious broadcaster. “We received a message from God,” Rybka jokes.)

    And some of it is actually a test: A small subset of ADMX scientists are responsible for injecting synthetic signals into the data.

    A tricky signal

    Dark matter, so called because it does not interact with light or other electromagnetic radiation, explains many observations about the distribution and movements of stars and galaxies. Astrophysicists estimate that it makes up 85% of the total matter of the universe, but they don’t know what it is. “Everything in our zoo of particle physics—every particle we know of—does not fit the bill,” Rybka says

    The axion is one of several dark matter candidates. The particle was originally proposed in the 1970s as a potential solution to the strong CP problem in particle physics. Later, researchers saw that the particle could also explain dark matter.

    “This is two for one,” says ADMX analysis team member Leanne Duffy of the US Department of Energy’s Los Alamos National Laboratory. “Not only do you solve this existing problem with the Standard Model, but you also get an excellent dark matter candidate out of it.”

    Assuming dark matter axions exist, the Earth and everyone on it is traveling through a “galactic halo” that is thick with them. To touch an axion, we don’t need to do anything.

    ADMX is the only one of DOE’s flagship dark matter searches looking for axions. The question is how to detect them. ADMX scientists hope to do it by converting them into particles that are much easier to detect: photons, quanta of light.

    In the presence of a strong magnetic field, axions should convert into photons. ADMX creates a magnetic field and isolates waves of specific frequencies in a microwave cavity where they can record any axions-turned-photons they come across.

    Passing the test

    Keeping the experiment cold (less than 100 millikelvins above absolute 0) helps separate the signal from the noise by decreasing the number of background photons coming from other sources. But some still do sneak in.

    To make sure the scientists are up to the task of eliminating those background signals, ADMX scientists do something that other experiments do as well—they regularly inject false signals into their data.

    “There is always a part of us that is excited to see a signal because you don’t know if it’s an axion signal or an injected signal.” says Rakshya Khatiwada, a physicist at Fermilab.

    When they inject synthetic signals, the team members responsible for injecting them usually reveal them after the second pass. One time in late 2018, the test proceeded further than that. Only Noah Oblath, a researcher at the Pacific Northwest National Laboratory, and one other colleague knew. “It was a little bit strange,” Oblath says. “I like generally being honest with people.”

    The team proceeded with the next steps of the analysis. When the signal persisted, they had a meeting to discuss how to proceed. “Fortunately this was a teleconference, and I didn’t have any video on, so I didn’t have to worry about covering my grin or anything,” Oblath says.

    They kept up the ruse this time in order to test the scientists’ reactions.

    Rybka says he was doubtful. “There was nothing strange about it,” he says.

    And that was the problem. The signal had been perfectly clear, and its shape was exactly what they had predicted. “When I looked at it, I said, ‘This might be too good to be true.’”

    Duffy had her suspicions as well. And unlike Rybka, she had the tools to test them.

    The high-resolution analysis would have exposed the injections as false immediately. But going to the high-resolution channel wasn’t part of the analysis protocol. Still, she admits, “If I hadn’t been so busy, I probably would have gone and looked at it and just not told anyone.”

    On the call, the doubtful scientists couldn’t let their suspicions guide their actions. If it was a test, it was a test of their process. They began to discuss the next step: Turning the detector’s magnet off to see whether changing the magnetic field affected the signal, as they would expect if it came from a real axion.

    “At that point, Gray paused and gave me a chance to reveal whether it was an injection or not,” Oblath says.

    Powering the magnet down would delay the rest of the experiment, so it was time for Oblath to confess. The test had gone according to plan.

    “It was a great way to test that our axion detection procedure works,” Duffy says. “But it would be nice to actually detect a real axion at some point.”

    See the full article here .

    Dark Matter Research

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Scientists studying the cosmic microwave background hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LBNL LZ Dark Matter project at SURF, Lead, SD, USA

    Dark Matter Background

    Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.

    Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.

    Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)

    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    The Vera C. Rubin Observatory currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    LSST Data Journey, Illustration by Sandbox Studio, Chicago with Ana Kova


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

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