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  • 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<

    04/28/20
    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.

    2
    JAXA GINGA

    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 .


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  • 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<

    04/15/20
    Emily Ayshford

    1
    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

    3
    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 .


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

    From Symmetry: “Dark matter decoys” 

    Symmetry Mag
    From Symmetry<

    04/07/20
    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


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  • richardmitnick 2:11 pm on March 24, 2020 Permalink | Reply
    Tags: "Scientists search for origin of proton mass", , , Chirality is related to a quantum mechanical property called spin., , Higgs is responsible for the mass of the quarks. The rest of it has a different origin., Ninety-nine percent of mass might originate from this process of chirality flipping in the vacuum., Only 1% of the mass of the proton comes from the Higgs field. ALICE scientists examine a process that could help explain the rest., , , , Protons are made up of fundamental particles called quarks and gluons. Quarks are very light and as far as scientists know gluons have no mass at all., Quarks like people can be left- or right-handed- a concept called chirality., Symmetry Magazine, The constant flipping of quarks from one handedness to the other is how theorists explain the majority of the proton’s mass.   

    From Symmetry: “Scientists search for origin of proton mass” 

    Symmetry Mag
    From Symmetry<

    03/24/20
    Sarah Charley

    1
    Courtesy of CERN

    Only 1% of the mass of the proton comes from the Higgs field. ALICE scientists examine a process that could help explain the rest.

    When protons and nuclei inside the Large Hadron Collider smash directly into each other, their energy can transform into new types of matter such as the famed Higgs boson, known for its association with a field that gives fundamental particles mass. But when nuclei merely graze each other, a different amazing thing happens: They generate some of the strongest magnetic fields in the universe.

    These ultra-intense magnetic fields are enabling scientists to peer inside atoms to answer a fundamental question: How do protons get most of their mass?

    Protons are made up of fundamental particles called quarks and gluons. Quarks are very light, and, as far as scientists know, gluons have no mass at all. Yet protons are much heavier than the combined masses of the three quarks they each contain.

    “There is a lot of publicity about the origin of mass because of the Higgs boson,” says Dmitri Kharzeev, a theorist with a joint appointment at Stony Brook University and the Department of Energy’s Brookhaven National Laboratory. “But the Higgs is responsible for the mass of the quarks. The rest of it has a different origin.”

    The origin of mass

    Quarks are very light, accounting for only about 1% of the proton’s overall mass. The plausible—yet still unproven—theoretical explanation for this discrepancy is related to how quarks move through the vacuum.

    This vacuum is not empty, says Sergei Voloshin, a professor at Wayne State University and a member of the ALICE experiment at CERN. The vacuum is actually filled with undulating fields that constantly burp particle-antiparticle pairs into and out of existence.

    The three quarks that give protons their identity are forever jostling with these ethereal particle-antiparticle pairs. When one of these quarks gets too close to a vacuum-produced antiquark, it is annihilated and disappears in a burst of energy.

    But the proton doesn’t wither and die when its quark is zapped out of existence; rather, the partner quark from the vacuum-produced particle-antiparticle pair steps in and takes the annihilated quark’s place (a plot twist straight out of The Talented Mr. Ripley).

    Scientists think that this incessant interchange of quarks is responsible for making a proton appear more massive than the sum of its quarks.

    A matter of handedness

    From the outside, not much appears to change in this swap. The annihilated quark is immediately replaced by a seemingly identical twin, making this process difficult to observe. Luckily for LHC scientists, they are not exactly identical: Quarks, like people, can be left- or right-handed, a concept called chirality.

    Chirality is related to a quantum mechanical property called spin and roughly translates to whether the quark spins clockwise or counterclockwise as it moves along a particular direction through space. (Visualize beads spinning as they slide along a wire.)

    Because of the properties of the vacuum, the replacement quark will always have the opposite handedness from the original. That constant flipping of quarks from one handedness to the other is how theorists explain the majority of the proton’s mass.

    “Ninety-nine percent of mass might originate from this process of chirality flipping in the vacuum,” Kharzeev says. “When we step on a scale, the number we see might be the result of these chirality-flipping transitions.”

    Physics inside a magnetic field

    In 2004, when Kharzeev was the head of the Nuclear Theory Group at Brookhaven Lab, he had an idea for how they could experimentally search for evidence of quark chirality flipping, which had never been observed.

    Because quarks are charged, they should interact with a magnetic field. “Normally, we never think about this interaction, because the magnetic fields we can create in the laboratory are extremely weak compared to the strength of quarks’ interactions with each other,” Kharzeev says. “However, we realized that when charged ions are colliding, they are accompanied by an electromagnetic field, and this field can be used to probe the chirality of quarks.”

    When they did the math, they found that positively charged ions grazing each other inside a particle collider like the LHC will generate a magnetic field two orders of magnitude stronger than the one at the surface of the strongest magnetic field known to exist. This would be enough to override the quarks’ strong attraction to each other.

    “Measuring the magnetic field’s strength and its lifetime was the primary goal of a recent ALICE data analysis,” says Voloshin. “The study yielded somewhat unexpected results, but they were still consistent with the existence of the strong magnetic field required for sorting of quarks according to their handedness.”

    Within a strong magnetic field, a quark’s motion is no longer random. The magnetic field automatically sorts quarks according to their chirality, with their handedness steering them toward either the field’s north or south pole.

    A hearty, hot soup of quarks

    It’s nearly impossible to catch a quark flipping its chirality inside a proton, Kharzeev says.

    “Inside a proton, left-handed quarks transition into right-handed quarks, and right-handed quarks transition back into left-handed quarks,” he says. “We will always see a mixture of left- and right-handed quarks.”

    To study whether quark chirality flipping happens, physicists need to catch several large and unexpected imbalances between the number of right- and left-handed quarks.

    Luckily, heavy nuclei collisions produce the perfect conditions for quarks to change their handedness. When two nuclei hit each other at high speeds, their protons and neutrons melt into a quark-gluon plasma, which is one of the hottest and densest materials known to exist in the universe. The liberated quarks swimming through this plasma can shift their identities with ease.

    “It’s like pretzels before they’re baked,” Kharzeev says. “You can easily mold the dough and change the twist.”

    The vacuum of space is not homogeneous—there are knots of gluon field that preferentially twist these doughy quarks one way or the other. If chirality flipping is happening, then scientists should catch an imbalance in the number of left- and right-handed quarks that shoot out from the plasma.

    “The average handedness over all the collisions should be the same,” Kharzeev says, “but the fluctuations from collision to collision should be very large; we should see some quark-gluon plasmas that are preferentially righted-handed and others that are preferentially left-handed.” Due to the presence of magnetic field, the handedness of the plasma translates into observable charge asymmetry of produced particles—this is the “chiral magnetic effect” proposed by Kharzeev.

    Shortly after Kharzeev proposed the idea of sorting quarks according to their handedness in the strong magnetic field of colliding nuclei, Voloshin designed a way to test this theory using the ALICE experiment, whose US participation is funded by the Department of Energy. The initial results show evidence for quarks sorting themselves according to chirality. But more research needs to be done before scientists can be sure.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:14 pm on March 10, 2020 Permalink | Reply
    Tags: "Accounting for the Higgs", , , , , , , , , Symmetry Magazine   

    From Symmetry: “Accounting for the Higgs” 

    Symmetry Mag
    From Symmetry<

    03/10/20
    Sarah Charley

    Only a fraction of collision events that look like they produce a Higgs boson actually produce a Higgs boson. Luckily, it doesn’t matter.

    CERN CMS Higgs Event May 27, 2012

    LHC

    CERN map


    CERN LHC Maximilien Brice and Julien Marius Ordan


    CERN LHC particles

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    I’ll let you in on a little secret: Even though physicists have produced millions of Higgs bosons at the Large Hadron Collider, they’ve never actually seen one. Higgs bosons are fragile things that dissolve immediately after they’re born. But as they die, they produce other particles, which, if they’re created at the LHC, can travel through a particle detector and leave recognizable signatures.

    Here’s another secret: Higgs signatures are identical to the signatures of numerous other processes. In fact, every time the Higgs signs its name in a detector, there are many more background processes leaving the exact same marks.

    For instance, one of the Higgs boson’s cleanest signatures is two photons with a combined mass of around 125 billion electronvolts. But for every 10 diphotons that look like a Higgs signature, only about one event actually belongs to a Higgs.

    So how can scientists study something that they cannot see and cannot isolate? They employ the same technique FBI agents use to uncover illegal money laundering schemes: accounting.

    In money laundering, “dirty” money (from illegal activities) is mixed with “clean” money from a legitimate business like a car wash. It all looks the same, so determining which Benjamins came from drugs versus which came from detailing is impossible. But agents don’t need to look at the individual dollars; they just need to look for suspiciously large spikes in profit that cannot be explained by regular business activities.

    In physics, the accounting comes from a much-loved set of equations called the Standard Model.

    Standard Model of Particle Physics, Quantum Diaries

    Physicists have spent decades building and perfecting the Standard Model, which tells them what percentage of the time different subatomic processes should happen. Scientists know which signatures are associated with which processes, so if they see a signature more often than expected, it means there is something happening outside the purview of the Standard Model: a new process.

    Clever accounting is how scientists originally discovered the Higgs boson in 2012. Theorists predicted what the Higgs signatures should look like, and when physicists went searching, they consistently saw some of these signatures more frequently than they could explain without the Higgs boson. When scientists added the mathematics for the Higgs boson into the equations, the predictions matched the data.

    Today, physicists use this accounting method to search for new particles. Many of these new particles are predicted to be rarer than Higgs bosons (for reference, Higgs bosons are produced in about one in a billion collisions). Many processes are also less clear-cut, and just the act of standardizing the accounting is a challenge. (To return to the money laundering analogy, it would be like FBI agents investigating an upscale bar, where a sudden excess could be explained by a generous tip.)

    To find these complex and subtle signs of mischief, scientists need a huge amount of data and a finely tuned model. Future runs of the LHC will be dedicated to building up these enormous datasets so that scientists can dig through the books for numbers that the Standard Model cannot explain.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:40 pm on February 27, 2020 Permalink | Reply
    Tags: "‘Flash photography’ at the LHC", , , , , , , , Symmetry Magazine   

    From Symmetry: “‘Flash photography’ at the LHC” 

    Symmetry Mag
    From Symmetry<

    02/27/20
    Sarah Charley

    1
    Photo by Tom Bullock

    An extremely fast new detector inside the CMS detector will allow physicists to get a sharper image of particle collisions.

    Some of the best commercially available high-speed cameras can capture thousands of frames every second. They produce startling videos of water balloons popping and hummingbirds flying in ultra-slow motion.

    But what if you want to capture an image of a process so fast that it looks blurry if the shutter is open for even a billionth of a second? This is the type of challenge scientists on experiments like CMS and ATLAS face as they study particle collisions at CERN’s Large Hadron Collider.

    When the LHC is operating to its full potential, bunches of about 100 billion protons cross each other’s paths every 25 nanoseconds. During each crossing, which lasts about 2 nanoseconds, about 50 protons collide and produce new particles. Figuring out which particle came from which collision can be a daunting task.

    “Usually in ATLAS and CMS, we measure the charge, energy and momentum of a particle, and also try to infer where it was produced,” says Karri DiPetrillo, a postdoctoral fellow working on the CMS experiment at the US Department of Energy’s Fermilab. “We’ve had timing measurements before—on the order of nanoseconds, which is sufficient to assign particles to the correct bunch crossing, but not enough to resolve the individual collisions within the same bunch.”

    Thanks to a new type of detector DiPetrillo and her collaborators are building for the CMS experiment, this is about to change.

    CERN/CMS Detector

    Physicists on the CMS experiment are devising a new detector capable of creating a more accurate timestamp for passing particles. The detector will separate the 2-nanosecond bursts of particles into several consecutive snapshots—a feat a bit like taking 30 billion pictures a second.

    This will help physicists with a mounting challenge at the LHC: collision pileup.

    Picking apart which particle tracks came from which collision is a challenge. A planned upgrade to the intensity of the LHC will increase the number of collisions per bunch crossing by a factor of four—that is from 50 to 200 proton collisions—making that challenge even greater.

    Currently, physicists look at where the collisions occurred along the beamline as a way to identify which particular tracks came from which collision. The new timing detector will add another dimension to that.

    “These time stamps will enable us to determine when in time different collisions occurred, effectively separating individual bunch crossings into multiple ‘frames,’” says DiPetrillo.

    DiPetrillo and fellow US scientists working on the project are supported by DOE’s Office of Science, which is also contributing support for the detector development.

    According to DiPetrillo, being able to separate the collisions based on when they occur will have huge downstream impacts on every aspect of the research. “Disentangling different collisions cleans up our understanding of an event so well that we’ll effectively gain three more years of data at the High-Luminosity LHC. This increase in statistics will give us more precise measurements, and more chances to find new particles we’ve never seen before,” she says.

    The precise time stamps will also help physicists search for heavy, slow moving particles they might have missed in the past.

    “Most particles produced at the LHC travel at close to the speed of light,” DiPetrillo says. “But a very heavy particle would travel slower. If we see a particle arriving much later than expected, our timing detector could flag that for us.”

    The new timing detector inside CMS will consist of a 5-meter-long cylindrical barrel made from 160,000 individual scintillating crystals, each approximately the width and length of a matchstick. This crystal barrel will be capped on its open ends with disks containing delicately layered radiation-hard silicon sensors. The barrel, about 2 meters in diameter, will surround the inner detectors that compose CMS’s tracking system closest to the collision point. DiPetrillo and her colleagues are currently working out how the various sensors and electronics at each end of the barrel will coordinate to give a time stamp within 30 to 50 picoseconds.

    “Normally when a particle passes through a detector, the energy it deposits is converted into an electrical pulse that rises steeply and the falls slowly over the course of a few nanoseconds,” says Joel Butler, the Fermilab scientist coordinating this project. “To register one of these passing particles in under 50 picoseconds, we need a signal that reaches its peaks even faster.”

    Scientists can use the steep rising slopes of these signals to separate the collisions not only in space, but also in time. In the barrel of the detector, a particle passing through the crystals will release a burst of light that will be recorded by specialized electronics. Based on when the intense flash of light arrives at each sensor, physicists will be able to calculate the particle’s exact location and when it passed. Particles will also produce a quick pulse in the endcaps, which are made from a new type of silicon sensor that amplifies the signal. Each silicon sensor is about the size of a domino and can determine the location of a passing particle to within 1.3 millimeters.

    The physicists working on the timing detector plan to have all the components ready and installed inside CMS for the start-up of the High Luminosity LHC in 2027

    “High-precision timing is a new concept in high-energy physics,” says DiPetrillo. “I think it will be the direction we pursue for future detectors and colliders because of its huge physics potential. For me, it’s an incredibly exciting and novel project to be on right now.”

    LHC

    CERN map


    CERN LHC Maximilien Brice and Julien Marius Ordan


    CERN LHC particles

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:54 pm on February 11, 2020 Permalink | Reply
    Tags: Although scientists have yet to find the spooky stuff they aren’t completely in the dark., , , , It all adds up to 85% of the universe., It shaped entire galaxies without touching a thing., It’s built to last., Natalia Toro, Symmetry Magazine,   

    From Symmetry: “What we know about dark matter” 

    Symmetry Mag
    From Symmetry<

    02/11/20
    Jim Daley

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    Although scientists have yet to find the spooky stuff, they aren’t completely in the dark.

    There are a lot of things scientists don’t know about dark matter: Can we catch it in a detector? Can we make it in a lab? What kinds of particles is it made of? Is it made of more than one kind of particle? Is it even made of particles at all?

    In short, dark matter is still pretty mysterious. The term is really just the name scientists gave to an ingredient that seems to be missing from our understanding of the universe.

    But there are some things scientists can definitively say about the stuff.

    Natalia Toro is a theoretical physicist at the US Department of Energy’s SLAC National Accelerator Laboratory and a member of the Light Dark Matter Experiment (LDMX) and the Beam Dump Experiment (BDX) dark matter search. She gave a talk at the 2019 meeting of the American Physical Society’s Division of Particles and Fields about the short list of things we do know about dark matter.

    2
    Light Dark Matter Experiment (LDMX).https://www.researchgate.net/figure/The-LDMX-experiment-layout_fig4_330726206

    3
    Beam Dump Experiment. https://www.jlab.org/accel/ops/ops_liaison/BDX/BDX.html

    1. It’s built to last.

    Dark matter formed very early on in the universe’s history. The evidence of this is apparent in the cosmic microwave background, or CMB—the ethereal layer of radiation left over from the universe’s searingly hot first moments.

    The fact that so much dark matter still seems to be around some 13.7 billion years later tells us right away that it has a lifetime of at least 1017 seconds (or about 3 billion years), Toro says.

    But there is another, more obvious clue that the lifetime of dark matter is much longer than that: We don’t see any evidence of dark matter decay.

    The heaviest particles in the Standard Model of particle physics break down, releasing their energy in the form of lighter particles. Dark matter doesn’t seem to do that, Toro says. “Whatever dark matter is made of, it lasts a really long time.”

    This property isn’t unheard of—electrons, protons and neutrinos all have extremely long lifespans—but it would be unusual, especially if dark matter turns out to be heavier than those light, stable particles.

    “One possibility is that there’s some kind of charge in nature, and dark matter is the lightest thing that carries that charge,” Toro says.

    In particle physics, charge must be conserved—meaning it cannot be created or destroyed. Take the decay of a muon, a heavier version of an electron. A muon often decays into a pair of neutrinos, one positively charged and one negatively charged, and an electron, which shares the muon’s negative charge. The charges of the neutrinos cancel one another out. So even though the muon has fallen apart into three other particles, its electromagnetic charge is conserved overall in the results of the decay.

    The electron is the lightest particle with a negative electromagnetic charge. Since there’s nothing with a smaller mass for it to decay into, it remains stable.

    But the electromagnetic charge is not the only type of charge. Protons, for example, are the lightest particle to carry a charge called the baryon number, which is related to the fact that they’re made of particles called quarks (but not anti-quarks). Quarks and gluons have what physicists call color charge, which seems to be conserved in particle interactions.

    It could be that dark matter particles are the most stable particles with a new kind of charge.

    2. It shaped entire galaxies without touching a thing.

    Dark matter’s apparent stability seems to have been key to another of its qualities: its ability to influence the evolution of the universe. Astrophysicists think that most galaxies would probably not have formed as they did without the help of dark matter.

    In the 1930s Swiss astrophysicist Fritz Zwicky noted that something seemed to be causing galaxies in the Coma Cluster to behave as if they were 400 times heavier than they would if they contained only luminous material. That discrepancy has today been calculated to be smaller, but it still exists. Zwicky coined the term “dark matter” to describe whatever could be giving the galaxies their extra mass.

    In the 1970s Vera Rubin, an astronomer at the Carnegie Institution in Washington, used spectrographic evidence to determine that spiral galaxies such as our own also seemed to be acting more massive than they appeared. They were rotating far more quickly than expected, something that could happen if they were, for example, sitting in invisible halos of dark matter.

    Fritz Zwicky discovered Dark Matter 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

    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 LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

    LSST telescope, The Vera Rubin Survey Telescope 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

    Dark Matter Research

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

    Scientists studying the cosmic microwave background [CMB]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.

    [caption id="attachment_73741" align="alignnone" width="632"] CMB per ESA/Planck

    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


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

    Scientists have seen another effect of dark matter on luminous material. Clusters of dark matter act as cosmic potholes on the path that light travels through the cosmos, bending and distorting it in a process called “gravitational lensing.” Astronomers can map the distribution of otherwise invisible dark matter by studying this lensing.

    Just like regular matter, dark matter isn’t evenly distributed across the universe. Astrophysicists think that when the galaxies first formed, areas of the universe that had slightly more dark matter (and thus more gravitational pull) attracted more matter, leading to the distribution of galaxies that we now see.

    Had there been a different pattern of dark matter throughout the universe—or slightly more or less of it—then galaxies might have formed later, formed with different densities or never formed at all, Toro says. “Galaxies become a lot denser, and you could end up in a situation where lots of black holes form, or you could end up with much more dark matter.”

    Despite being massively (forgive the pun) influential, dark matter is famously standoffish, avoiding most of the kinds of interactions that Standard Model particles commonly undergo from the very beginning. “One thing that we know concretely from looking at the CMB is that there was a component of that plasma that was not interacting with the electrons and protons,” she says. “That’s one very clear constraint—that the constituents of dark matter interacted less than electrons and protons.”

    Dark matter is so nonreactive that it may not even interact with itself; when two galaxies merge, their respective dark matter halos simply pass through one another like ghosts.

    3. It all adds up to 85%.

    Amazingly, despite being unclear on precisely what dark matter is, astrophysicists do know pretty well how much of it there is—which is why we can say that it accounts for 85% of the known matter in the universe. Physicists call that amount the “cosmological abundance” of dark matter.

    Cosmological abundance can tell us a great deal about the makeup of the universe, Toro says—particularly in its earliest days, when it was much smaller and denser. During the evolution of the early universe, “average density was very representative” of the actual dark matter present in any area of it, she says.

    Currently, Toro says, dark matter’s cosmological abundance is “the only number physicists can hang our hat on.” Scientists have proposed—and are actively searching for—a number of different possible dark matter candidates. Whether dark matter is made up of a smaller number of heavy WIMPs or a larger number of light axions, its total mass must add up to the measure of the cosmological abundance.

    Toro says it’s important to take that number as far as it can be taken and to try to extrapolate different strategies for looking for dark matter from it.

    Quantifying anything else about dark matter—its interaction strength, its scattering rate and a laundry list of other potential properties—would be “amazing,” she says. “Having any confirmation, finding one more property of dark matter that we could actually quantify, would be a huge jump.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:33 am on February 4, 2020 Permalink | Reply
    Tags: "On background", , , , Symmetry Magazine   

    From Symmetry: “On background” 

    Symmetry Mag
    From Symmetry

    02/04/20
    Jim Daley

    Physicists deal with background in their experiments in two ways: by reducing it and by rejecting it.

    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy


    One site where “background” is well blocked.

    To some degree, scientists on all of today’s particle physics experiments share a common challenge: How can they pick out the evidence they are looking for from the overwhelming abundance of all the other stuff in the universe getting in their way?

    Physicists refer to that stuff—the unwelcome clamor of gamma rays, cosmic rays and radiation crowding particle detectors—as background.

    “You’re trying to find a signal that is small and that has a lot of stuff around it that could fake it,” says Rupak Mahapatra, an experimental particle physicist at Texas A&M University, who battles background while developing next-generation dark matter detectors for the Super Cryogenic Dark Matter Search, or SuperCDMS.

    SLAC SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

    Mahapatra sums up the strategies for mitigating background in two words: reduction and rejection. To reduce backgrounds, physicists build shielding around detectors and construct them from materials that are as unreactive as possible. To reject background, they use complex analyses to filter signal from noise.

    Shielding often comes in the form of lead or water—or even a mile or so of rock. Detectors looking for hard-to-spot targets such as neutrinos or dark matter are often built far underground to protect them from cosmic rays. That works pretty well. For SuperCDMS, going underground results in a reduction of background events in the detector each day from around a billion to about one.

    A scientist’s dream is to design experiments that have no background at all, says Lindley Winslow, an experimental nuclear and particle physicist at MIT. She works on the Cryogenic Underground Observatory for Rare Event Neutrinos (CUORE) experiment, which uses tellurium dioxide crystals to search for evidence of a phenomenon called neutrinoless double-beta decay.

    CUORE experiment,at the Italian National Institute for Nuclear Physics’ (INFN’s) Gran Sasso National Laboratories (LNGS) in located in the Abruzzo region of central Italy,a search for neutrinoless double beta decay

    Finding neutrinoless double-beta decay would be a sign that neutrino particles are their own antiparticles. Like SuperCDMS, CUORE is located deep underground to shield it from cosmic rays. The main background for CUORE is gamma rays, which can be produced by cosmic rays. But gamma rays don’t only rain down from interactions between cosmic rays and Earth’s atmosphere. They are also emitted by the materials that make up the CUORE detector itself.

    The main background for CUORE is gamma rays, which can be produced by cosmic rays. But gamma rays don’t only rain down from interactions between cosmic rays and Earth’s atmosphere. They are also emitted by the materials that make up the CUORE detector itself.

    Winslow works on both CUORE and a dark matter experiment with the especially long name “A Broadband/Resonant Approach to Cosmic Axion Detection with an Amplifying B-field Ring Apparatus,”—or ABRACADABRA for short.

    “At some level, you can’t get rid of all the background,” she says. “What you need, then, is to get smarter” about designing the experiment.

    For Michelle Dolinski, an experimental particle physicist at Drexel University, background includes anything that can deposit similar levels of energy in detectors as the kinds of particles she and her colleagues are looking for. She works with the EXO-200 and nEXO detectors, liquid xenon detectors used to search for neutrinoless double-beta decay. “We’re very sensitive to even tiny backgrounds that wouldn’t make a difference to many other experiments,” Dolinski says.

    “Even though we strive to find materials with some of the lowest radioactivity content anywhere, there’s still a tiny bit of radioactivity that can deposit energy in our detector,” Dolinski says.

    For its part, EXO-200 uses innovations both in how the detector is designed and built and in how researchers analyze the data. “We’ve developed a number of metrics that help us distinguish signal from background,” Dolinski says.

    For one thing, a signal coming from neutrinoless double-beta decay would most likely come from a single site in the detector, whereas background signals often come from multiple sites. Scientists can use this distinction to roughly identify each. “It’s not a perfect discriminator, but it gives us some ability to distinguish signal and background,” Dolinski says.

    Any gamma rays that do sneak in are most likely to come from the walls of the detector, which gives the researchers a clue to identify them. “We can look at the distribution of events, and if they’re concentrated more towards the wall, that’s more likely to be background than signal,” Dolinski explains.

    Dolinski and her colleagues plug all of these clues into a neural network for analysis. “We construct an optimal discriminator that says, on an event-by-event basis, what looks more like signal or background,” she says. “And we use that as a parameter when we do our final analysis.”

    As physicists continue to search for dark matter and rare physics events that could change our understanding of the Standard Model, the challenge of dealing with background will always be there. The good news is that scientists continue to get better and better at filtering it out.

    Until they discover what they’re looking for, “particle physicists will never stop building the next generation of detectors,” Mahapatra says. “We’ll always have to come up with new technologies to bypass what appears to be irreducible background.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:19 pm on January 21, 2020 Permalink | Reply
    Tags: , , , , , , Symmetry Magazine,   

    From Symmetry: “The other dark matter candidate” 

    Symmetry Mag
    From Symmetry<

    01/21/20
    Laura Dattaro

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

    CERN CAST Axion Solar Telescope

    As technology improves, scientists discover new ways to search for theorized dark matter particles called axions.

    In the early 1970s, physics had a symmetry problem. According to the Standard Model, the guiding framework of particle physics, a symmetry between particles and forces in our universe and a mirror version should be broken.

    Standard Model of Particle Physics

    It was broken by the weak force, a fundamental force involved in processes like radioactive decay.

    This breaking should feed into the interactions mediated by another fundamental force, the strong force. But experiments show that, unlike the weak force, the strong force obeys mirror symmetry perfectly. No one could explain it.

    The problem confounded physicists for years. Then, in 1977, physicists Roberto Peccei and Helen Quinn found a solution: a mechanism that, if it existed, would cause the strong force to obey this symmetry and right the Standard Model.

    Shortly after, Frank Wilczek and Steven Weinberg—both of whom went on to win the Nobel Prize—realized that this mechanism creates an entirely new particle. Wilczek ultimately dubbed this new particle the axion, after a dish detergent with the same name, for its ability to “clean up” the symmetry problem.

    Several years later, the theoretical axion was found not only to solve the symmetry problem, but also to be a possible candidate for dark matter, the missing matter that scientists think makes up 85% of the universe but the true nature of which is unknown.

    Fritz Zwicky discovered Dark Matter 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

    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 LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

    LSST telescope, The Vera Rubin Survey Telescope 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

    Dark Matter Research

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

    Scientists studying the cosmic microwave background [CMB]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.

    [caption id="attachment_73741" align="alignnone" width="632"] CMB per ESA/Planck

    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


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

    Despite its theoretical promise, though, the axion stayed in relative obscurity, due to a combination of its strange nature and being outshone by another new dark matter candidate, called a WIMP, that seemed even more like a sure thing.

    But today, four decades after they were first theorized, axions are once again enjoying a moment in the sun, and may even be on the verge of detection, poised to solve two major problems in physics at once.

    “I think WIMPs have one last hurrah as these multiton experiments come online,” says MIT physicist Lindley Winslow. “Since they’re not done building those yet, we have to take a deep breath and see if we find something.

    “But if you ask me the thing we need to be ramping up, it’s axions. Because the axion has to be there, or we have other problems.”

    Around the time the axion was proposed, physicists were developing a theory called Supersymmetry, which called for a partner for every known particle.

    Standard Model of Supersymmetry via DESY

    The newly proposed dark matter candidate called a WIMP—or weakly interacting massive particle—fit beautifully with the theory of Supersymmetry, making physicists all but certain they’d both be discovered.

    Even more promising was that both the supersymmetric particles and the theorized WIMPs could be detected at the Large Hadron Collider at CERN.

    LHC

    CERN map


    CERN LHC Maximilien Brice and Julien Marius Ordan


    CERN LHC particles

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    “People just knew nature was going to deliver supersymmetric particles at the LHC,” says University of Washington physicist Leslie Rosenberg. “The LHC was a machine built to get a Nobel Prize for detecting Supersymmetry.”

    Experiments at the LHC made another Nobel-worthy discovery: the Higgs boson. But evidence of both WIMPS and Supersymmetry has yet to appear.

    Peter Higgs

    CERN CMS Higgs Event May 27, 2012

    CERN ATLAS Higgs Event

    Axions are even trickier than WIMPs. They’re theorized to be extremely light—a millionth of an electronvolt or so, about a trillion times lighter than the already tiny electron—making them next to impossible to produce or study in a traditional particle physics experiment. They even earned the nickname “invisible axion” for the unlikeliness they’d ever be seen.

    But axions don’t need to be made in a detector to be discovered. If axions are dark matter, they were created at the beginning of the universe and exist, free-floating, throughout space. Theorists believe they also should be created inside of stars, and because they’re so light and weakly interacting, they’d be able to escape into space, much like other lightweight particles called neutrinos. That means they exist all around us, as many as 10 trillion per cubic centimeter, waiting to be detected.

    In 1983, newly minted physics professor Pierre Sikivie decided to tackle this problem, taking inspiration from a course he had just taught on electromagnetism. Sikivie discovered that axions have another unusual property: In the presence of an electromagnetic field, they should sometimes spontaneously convert to easily detectable photons.

    “What I found is that it was impossible or extremely difficult to produce and detect axions,” Sikivie says. “But if you ask a less ambitious goal of detecting the axions that are already there, axions already there either as dark matter or as axions emitted by the sun, that actually became feasible.”

    When Rosenberg, then a postdoc working on cosmic rays at the University of Chicago, heard about Sikivie’s breakthrough—what he calls “Pierre’s Great Idea”—he knew he wanted to dedicate his work to the search.

    “Pierre’s paper hit me like a rock in the head,” Rosenberg says. “Suddenly, this thing that was the invisible axion, which I thought was so compelling, is detectable.”

    Rosenberg began work on what’s now called the Axion Dark Matter Experiment, or ADMX. The concept behind the experiment is relatively simple: Use a large magnet to create an electromagnetic field, and wait for the axions to convert to photons, which can then be detected with quantum sensors.

    When work on ADMX began, the technology wasn’t sensitive enough to pick up the extremely light axions. While Rosenberg kept the project moving forward, much of the field has focused on WIMPs, building ever-larger dark matter detectors to find them.

    But neither WIMPs nor supersymmetric particles have been discovered, pushing scientists to think creatively about what happens next.

    “That’s caused a lot of people to re-evaluate what other dark matter models we have,” says University of Michigan theorist Ben Safdi. “And when people have done that re-evaluation, the axion is the natural candidate that’s still floating around. The downfall of the WIMP has been matched exactly by the rise of axions in terms of popularity.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:46 pm on January 9, 2020 Permalink | Reply
    Tags: , , , , , , Symmetry Magazine,   

    From Symmetry: “Expanding a neutrino hunt in the South Pole” 

    Symmetry Mag
    From Symmetry<

    01/09/20
    Diana Kwon

    1
    Photo by Martin Wolf, IceCube/NSF

    A forthcoming upgrade to the IceCube detector will provide deeper insights into the elusive particles.

    Underneath the vast, frozen landscape of the South Pole lies IceCube, a gigantic observatory dedicated to finding ghostly subatomic particles called neutrinos. Neutrinos stream through the Earth from all directions, but they are lightweight, abundant and hardly interact with their surroundings.

    The IceCube detector consists of an array of 86 strings festooned with more than 5000 sensors, like round, basketball-sized Christmas lights. They reach more than 2 kilometers (more than 1 mile) down through layers of Antarctic ice that have accumulated over hundreds of thousands of years.

    A small fraction of the neutrinos that pass through the ice collide with its atoms and spit out showers of particles, some of which can be spotted by IceCube’s sensors as sparks of blue light. By probing the light patterns, scientists can identify and assess the elusive particles, some of which originate beyond our solar system.

    In July 2019 the IceCube collaboration announced that the US National Science Foundation had granted it $23 million to put toward a $37 million upgrade, with additional financial support coming from Michigan State University, the University of Wisconsin–Madison, and agencies in Germany and Japan.

    The upgrade will add seven more strings of sensors to the detector, along with new instruments meant to characterize the ice. This extension will allow physicists to better understand how neutrinos oscillate between their three flavors: electron, muon and tau. Scientists also plan to make more precise measurements of IceCube’s icy interior to get a closer look at neutrinos from far out in the universe.

    U Wisconsin IceCube neutrino observatory

    U Wisconsin ICECUBE neutrino detector at the South Pole

    U Wisconsin IceCube experiment at the South Pole



    U Wisconsin ICECUBE neutrino detector at the South Pole


    IceCube Gen-2 DeepCore PINGU


    IceCube reveals interesting high-energy neutrino events

    3
    When cosmic neutrinos crash into the IceCube detector, the interactions generate secondary particles that travel faster than the speed of light through the ice, producing a detectable faint blue glow. Courtesy of Nicolle R. Fuller/NSF/IceCube

    Extraterrestrial signals

    One of the main aims of IceCube, which is run by an international group of more than 300 scientists from 12 different countries, is to identify cosmic neutrinos. They know which neutrinos come from afar by the extraordinarily high levels of energy they have when they crash into the Earth, compared to their more local counterparts. By studying these alien particles, physicists hope to identify the powerful cosmic accelerators that form beams of ultra-high energy particles.

    IceCube had its first major breakthrough in 2013 when it identified two ultra-high energy neutrinos from outside the solar system. These events, dubbed Bert and Ernie, became the first of many cosmic neutrino detections, says Olga Botner, a physicist at Uppsala University in Sweden and former spokesperson of IceCube.

    “We knew we were in business,” she says. “We could observe not only the atmosphere but also neutrinos from outside our own galaxy. That was huge.”

    Four years later, IceCube physicists made a detection of an extraterrestrial neutrino that sparked a search for a glimpse of its source by scientists at astronomical observatories around the globe. This worldwide hunt allowed scientists to pinpoint the particle’s birthplace: an extremely luminous galaxy called a blazar. A blazar acts like a cosmic accelerator, spitting out a constant stream of particles from its core.

    “Working on IceCube is very exciting,” says Delia Tosi, an assistant scientist at the Wisconsin IceCube Particle Astrophysics Center (WIPAC). “There is no space for boredom.”

    Where most cosmic neutrinos come from remains a mystery. But IceCube’s scientific repertoire has expanded since those first discoveries. Scientists also use IceCube to examine how neutrinos change from one type to another—which could help determine whether there are new types of neutrinos that we don’t yet know about—as well as to search for dark matter and characterize how light travels though Antarctic ice.

    “When we started IceCube, we were 90% focused on finding point sources of astrophysical neutrinos,” says Kael Hanson, a physicist and director of WIPAC. “We really had no idea, when we were designing the experiment, how rich the science program would eventually become.”

    An upgrade on ice

    With the forthcoming upgrade, more than 700 new sensors spread across seven strings will be added to the center of IceCube.

    The core is already more densely packed with strings than the rest of the detector, which makes it better able to detect particles at low energies. The new sensors will push that sensitivity even further. “We’re pushing the energy threshold down by a factor of 10,” Hanson says.

    The denser core will make it possible for the scientists to examine the hundreds of thousands of atmospheric neutrinos that bombard the detector each year in more detail. This will allow physicists to make more accurate measurements of the tau neutrino, which can then be used to better understand neutrino oscillations—specifically, how muon neutrinos convert to tau neutrinos.

    “We don’t quite understand how neutrinos can spontaneously morph from one flavor to another,” Botner says. “If discrepancies exist between our predictions and what we observe, this would be a hint of unknown neutrino kinds—the so-called sterile neutrino.”

    To insert new strings into the detector, scientists must drill deep holes into the ice using a high-pressure stream of hot water. During the upgrade, scientists will deploy additional calibration instruments, such as cameras and light sources, along with the detectors to help them characterize the ice.

    When water refreezes around the strings—a process that can take several weeks—the ice that forms can contain dust and bubbles. These imperfections make it more difficult to see signs of neutrinos.

    Not only will characterizing the ice make it possible for scientists to more accurately assess future observations, researchers will also be able to apply this new knowledge to previously collected data. “In principle, we can recalibrate all the data and improve our ability to point back to a source,” says Dawn Williams, a particle astrophysicist at the University of Alabama.

    The IceCube collaboration plans to start drilling in late 2022. In the meantime, the group is preparing the sensors and other components of the upgrade as well as the software that will be used to run the upgraded detector. The team expects to start collecting data in the spring of 2023.

    The upgrade also serves an additional purpose: to test new sensor designs that scientists hope might be deployed in IceCube-Gen2, a proposed detector that would be 10 times the size of the current one. The super-sized observatory would allow scientists to conduct even more precise measurements of neutrinos and detect more ultra-high-energy particles from outer space, heightening the possibly of pinpointing their sources.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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