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  • richardmitnick 3:11 pm on July 28, 2016 Permalink | Reply
    Tags: , , Symmetry Magazine, The Standard Model   

    From Symmetry: “The deconstructed Standard Model equation” 

    Symmetry Mag


    Rashmi Shivni

    Yvonne Tang, SLAC National Accelerator Laboratory

    The Standard Model is far more than elementary particles arranged in a table.

    The Standard Model of particle physics is often visualized as a table, similar to the periodic table of elements, and used to describe particle properties, such as mass, charge and spin.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The table is also organized to represent how these teeny, tiny bits of matter interact with the fundamental forces of nature.

    But it didn’t begin as a table. The grand theory of almost everything actually represents a collection of several mathematical models that proved to be timeless interpretations of the laws of physics.

    Here is a brief tour of the topics covered in this gargantuan equation.

    The whole thing

    This version of the Standard Model is written in the Lagrangian form. The Lagrangian is a fancy way of writing an equation to determine the state of a changing system and explain the maximum possible energy the system can maintain.

    Technically, the Standard Model can be written in several different formulations, but, despite appearances, the Lagrangian is one of the easiest and most compact ways of presenting the theory.


    Section 1

    These three lines in the Standard Model are ultraspecific to the gluon, the boson that carries the strong force. Gluons come in eight types, interact among themselves and have what’s called a color charge.


    Section 2

    Almost half of this equation is dedicated to explaining interactions between bosons, particularly W and Z bosons.

    Bosons are force-carrying particles, and there are four species of bosons that interact with other particles using three fundamental forces. Photons carry electromagnetism, gluons carry the strong force and W and Z bosons carry the weak force. The most recently discovered boson, the Higgs boson, is a bit different; its interactions appear in the next part of the equation.


    Section 3

    This part of the equation describes how elementary matter particles interact with the weak force. According to this formulation, matter particles come in three generations, each with different masses. The weak force helps massive matter particles decay into less massive matter particles.

    This section also includes basic interactions with the Higgs field, from which some elementary particles receive their mass.

    Intriguingly, this part of the equation makes an assumption that contradicts discoveries made by physicists in recent years. It incorrectly assumes that particles called neutrinos have no mass.


    Section 4

    In quantum mechanics, there is no single path or trajectory a particle can take, which means that sometimes redundancies appear in this type of mathematical formulation. To clean up these redundancies, theorists use virtual particles they call ghosts.

    This part of the equation describes how matter particles interact with Higgs ghosts, virtual artifacts from the Higgs field.


    Section 5

    This last part of the equation includes more ghosts. These ones are called Faddeev-Popov ghosts, and they cancel out redundancies that occur in interactions through the weak force.


    Note: Thomas Gutierrez, an assistant professor of Physics at California Polytechnic State University, transcribed the Standard Model Lagrangian for the web. He derived it from Diagrammatica, a theoretical physics reference written by Nobel Laureate Martinus Veltman. In Gutierrez’s dissemination of the transcript, he noted a sign error he made somewhere in the equation. Good luck finding it!

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 12:59 pm on July 26, 2016 Permalink | Reply
    Tags: , , inSPIRE - HEP High-Energy Physics Literature Database, , , Symmetry Magazine   

    From Symmetry: “The most important website in particle physics” 

    Symmetry Mag


    Matthew R. Francis

    The first website to be hosted in the US has grown to be an invaluable hub for open science.

    Sandbox Studio, Chicago with Lexi Fodor

    With tens of thousands of particle physicists working in the world today, the biggest challenge a researcher can have is keeping track of what everyone else is doing. The articles they write, the collaborations they form, the experiments they run—all of those things are part of being current. After all, high-energy particle physics is a big enterprise, not the province of a few isolated people working out of basement laboratories.

    Particle physicists have a tool that helps them with that. The INSPIRE database allows scientists to search for published papers by topic, author, scholarly journal, what previous papers the authors cited and which newer papers have used it as a reference.


    “I don’t know any other discipline with such a central tool as INSPIRE,” says Sünje Dallmeier-Tiessen, an information scientist at CERN who manages INSPIRE’s open-access initiative. If you’re a high-energy physicist, “everything that relates to your daily work-life, you can find there.”

    Researchers in high-energy physics and related fields use INSPIRE for their professional profiles, job-hunting and promotional materials. They use it to keep track of other people’s research in their disciplines and for finding good resources to cite in their own papers.

    INSPIRE has been around in one form or another since 1969, says Bernard Hecker, who is in charge of SLAC’s portion of INSPIRE. “So we have a high level of credibility with people who use the service.” It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1970s.

    INSPIRE contains up-to-date information about over a million papers, including those published in the major journals. INSPIRE’s database also interacts with the arXiv, a free-access site that hosts papers independently of whether they’re published in journals or not. “We text-mine everything [on the arXiv], and then provide search to the content, and search based on specific algorithms we run,” Dallmeier-Tiessen says.

    In that way, INSPIRE is a powerful addition to the arXiv, which itself provides access to many articles that would otherwise require expensive journal subscriptions or exorbitant one-time fees.

    A lot of human labor is involved. The arXiv, for example, doesn’t distinguish between two people with the same last name and same first initial. “We have a strong interest in keeping dynamic profiles and disambiguating different researchers with similar names,” Hecker says.

    To that end, the INSPIRE team looks at author lists on published papers to match individual researchers with their correct institutions. This includes collaborating with the Institute of High Energy Physics in China, as well as cross-checking other databases.

    The goal, Hecker says, is “trying to find the stuff that’s directly relevant and not stuff that’s not relevant.” After all, researchers will only use the site if its useful, a complicated challenge that INSPIRE has met consistently. “We’re trying to optimize the time researchers spend on the site.”

    Now That’s What I Call Physics

    Every January, the INSPIRE team releases a list of the top 40 most cited articles in high-energy physics that year.

    Looking over the list for 2015, you might be forgiven for thinking it was a slow year. The most commonly referenced articles were papers from previous years, some just a few years old, a few going back several decades.

    But even in years without a blockbuster discovery such as the Higgs boson or gravitational waves, INSPIRE’s list is still useful a snapshot of where the minds of the research community are focused.

    In 2015, researchers prioritized studying the Higgs boson. The two most widely referenced articles of 2015 were the papers announcing its discovery by researchers at the ATLAS and CMS detectors at the Large Hadron Collider. The INSPIRE “top 40” for 2015 also includes the original 1964 theoretical papers by Peter Higgs, François Englert, and Robert Brout predicting the existence of the Higgs.

    Another topic that stood out in 2015 was the cosmic microwave background, a pattern of light that could tell us about conditions in the universe just after the Big Bang. Four highly cited papers, including the third most-referenced, came from the Planck cosmic microwave background experiment, with a fifth devoted to the final WMAP cosmic microwave background data.

    It seems that cosmology was on physicists’ minds. Two more top papers were the first measurements of dark energy from the late ’90s, while yet two more described results from the dark matter experiments LUX and XENON100.

    Open science, open data, open code

    INSPIRE grew out of the Stanford Public Information Retrieval System (SPIRES), a database started at SLAC National Accelerator Laboratory in 1969 when the internet was in its infancy.

    After Tim Berners-Lee developed the World Wide Web at CERN, SPIRES was the first US-hosted website.

    Like high-energy physics itself, the database is international and cooperative. SLAC joined with Fermi National Accelerator Laboratory in the United States, DESY in Germany, and CERN in Switzerland, which now hosts the site, to create the modern version of INSPIRE. The newest member of the collaboration is IHEP Beijing in China. Institutions in France and Japan also collaborate on particular projects.

    INSPIRE has changed a lot since its inception, and a new version is coming out soon. The biggest change will extend INSPIRE’s database to include repositories for data and computer code.

    Starting later this year, INSPIRE will integrate with the HEPDATA open-data archive and the github code-collaboration system to increase visibility for both data and code that scientists write. The INSPIRE team will also roll out a new interface, so it looks “less like something from 1995,” Hecker says.

    From its inception as a way to share printed articles by mail, INSPIRE continues to be a valuable resource to the community. With more papers coming out every year and no sign of decrease in the number of particle physicists working, the need to build on past research—and construct collaborations—is more important than ever.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:20 pm on July 12, 2016 Permalink | Reply
    Tags: , , , Symmetry Magazine   

    From Symmetry: “Scientists salvage insights from lost satellite” 

    Symmetry Mag


    Manuel Gnida

    Before Hitomi died, it sent X-ray data that could explain why galaxy clusters form far fewer stars than expected.

    Hitomi. A. Ikeshita, JAXA

    Working with information sent from the Japanese Hitomi satellite, an international team of researchers has obtained the first views of a supermassive black hole stirring hot gas at the heart of a galaxy cluster. These motions could explain why galaxy clusters form far fewer stars than expected.

    This image created by physicists at Stanford’s SLAC National Accelerator Laboratory illustrates how supermassive black holes at the center of galaxy clusters could heat intergalactic gas, preventing it from cooling and forming stars. (Image credit: SLAC National Accelerator Laboratory)

    The data, published today in Nature, were recorded with the X-ray satellite during its first month in space earlier this year, just before it spun out of control and disintegrated due to a chain of technical malfunctions.

    “Being able to measure gas motions is a major advance in understanding the dynamic behavior of galaxy clusters and its ties to cosmic evolution,” said study co-author Irina Zhuravleva, a postdoctoral researcher at the Kavli Institute for Particle Astrophysics and Cosmology. “Although the Hitomi mission ended tragically after a very short period of time, it’s fair to say that it has opened a new chapter in X-ray astronomy.” KIPAC is a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory.

    Galaxy clusters, which consist of hundreds to thousands of individual galaxies held together by gravity, also contain large amounts of gas. Over time, the gas should cool down and clump together to form stars. Yet there is very little star formation in galaxy clusters, and until now scientists were not sure why.

    “We already knew that supermassive black holes, which are found at the center of all galaxy clusters and are tens of billions of times more massive than the sun, could play a major role in keeping the gas from cooling by somehow injecting energy into it,” said Norbert Werner, a research associate at KIPAC involved in the data analysis. “Now we understand this mechanism better and see that there is just the right amount of stirring motion to produce enough heat.”

    Plasma bubbles stir and heat intergalactic gas

    About 15 percent of the mass of galaxy clusters is gas that is so hot – tens of millions of degrees Fahrenheit – that it shines in bright X-rays. In their study, the Hitomi researchers looked at the Perseus cluster, one of the most massive astronomical objects and the brightest in the X-ray sky.

    Perseus cluster. NASA Chandra.

    Other space missions before Hitomi, including NASA’s Chandra X-ray Observatory, had taken precise X-ray images of the Perseus cluster. These snapshots revealed how giant bubbles of ultrahot, ionized gas, or plasma, rise from the central supermassive black hole as it catapults streams of particles tens of thousands of light-years into space. At the same time, streaks of cold gas appear to be pulled away from the center of the galaxy cluster, according to additional images of visible light. Until now, it has been unclear whether these two actions were connected.

    To find out, the researchers pointed one of Hitomi’s instruments – the soft X-ray spectrometer (SXS) – at the center of the Perseus cluster and analyzed its X-ray emissions.

    Perseus cluster. Hitomi Collaboration/JAXA, NASA, ESA, SRON, CSA

    “Since the SXS had 30 times better energy resolution than the instruments of previous missions, we were able to resolve details of the X-ray signals that weren’t accessible before,” said co-principal investigator Steve Allen, a professor of physics at Stanford and of particle physics and astrophysics at SLAC. “These new details resulted in the very first velocity map of the cluster center, showing the speed and turbulence of the hot gas.”

    By superimposing this map onto the other images, the researchers were able to link the observed motions of the cold gas to the hot plasma bubbles.

    According to the data, the rising plasma bubbles drag cold gas away from the cluster center. Researchers see this in the form of stretched filaments in the optical images. The bubbles also transfer energy to the gas, which causes turbulence, Zhuravleva said.

    “In a way, the bubbles are like spoons that stir milk into a cup of coffee and cause eddies,” she said. “The turbulence heats the gas, and it appears that this is enough to work against star formation in the cluster.”

    Hitomi’s legacy

    Astrophysicists can use the new information to fine-tune models that describe how galaxy clusters change over time.

    One important factor in these models is the mass of galaxy clusters, which researchers typically calculate from the gas pressure in the cluster. However, motions cause additional pressure, and before this study it was unclear if the calculations need to be corrected for turbulent gas.

    “Although the motions heat the gas at the center of the Perseus cluster, their speed is only about 100 miles per second, which is surprisingly slow considering how disturbed the region looks in X-ray images,” said co-principal investigator Roger Blandford, the Luke Blossom Professor of Physics at Stanford and a professor for particle physics and astrophysics at SLAC. “One consequence is that corrections for these motions are only very small and don’t affect our mass calculations much.”

    Although the loss of Hitomi cut most of the planned science program short – it was supposed to run for at least three years – the researchers hope their results will convince the international community to plan another X-ray space mission.

    “The data Hitomi sent back to Earth are just beautiful,” Werner said. “They demonstrate what’s possible in the field and give us a taste of all the great science that should have come out of the mission over the years.”

    Hitomi is a joint project, with the Japan Aerospace Exploration Agency (JAXA) and NASA as the principal partners. Led by Japan, it is a large-scale international collaboration, boasting the participation of eight countries, including the United States, the Netherlands and Canada, with additional partnership by the European Space Agency (ESA). Other KIPAC researchers involved in the project are Tuneyoshi Kamae, Ashley King, Hirokazu Odaka and co-principal investigator Grzegorz Madejski.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:06 pm on July 12, 2016 Permalink | Reply
    Tags: A primer on particle accelerators, , , Symmetry Magazine   

    From Symmetry: “A primer on particle accelerators” 

    Symmetry Mag


    Signe Brewster

    Illustration by Sandbox Studio, Chicago with Jill Preston

    Research in high-energy physics takes many forms. But most experiments in the field rely on accelerators that create and speed up particles on demand.

    What follows is a primer on three different types of particle accelerators: synchrotrons, cyclotrons and linear accelerators, called linacs.

    Synchrotrons: the heavy lifters

    Synchrotrons are the highest-energy particle accelerators in the world. The Large Hadron Collider currently tops the list, with the ability to accelerate particles to an energy of 6.5 trillion electronvolts before colliding them with particles of an equal energy traveling in the opposite direction.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    Synchrotrons typically feature a closed pathway that takes particles around a ring. Other variants are created with straight sections between the curves (similar to a racetrack or in the shape of a triangle or hexagon). Once particles enter the accelerator, they travel around the circular pathway over and over again, always enclosed in a vacuum pipe.

    Radiofrequency cavities at intervals around the ring increase their speed. Several different types of magnets create electromagnetic fields, which can be used to bend and focus the particle beams. The electromagnetic fields slowly build up as the particles are accelerated. Particles pass around the LHC about 14 million times in the 20 minutes they need to reach their intended energy level.

    Researchers send beams of accelerated particles through one another to create collisions in locations surrounded by particle detectors. Relatively few collisions happen each time the beams meet. But because the particles are constantly circulating in a synchrotron, researchers can pass them through one another many times over—creating a large number of collisions over time and more data for observing rare phenomena.

    “The LHC detectors ATLAS and CMS reached about 400 million collisions a second last year,” says Mike Lamont, head of LHC operations at CERN. “This is why this design is so useful.”

    CERN/ATLAS detector
    CERN ATLAS Higgs Event
    CERN/ATLAS detector; CERN ATLAS Higgs Event

    CERN/CMS Detector
    CERN CMS Higgs Event
    CERN/CMS detector; CERN CMS Higgs Event

    Synchrotrons’ power makes them especially suited to studying the building blocks of our universe. For example, physicists were able to witness evidence of the Higgs boson among the LHC’s collisions only because the collider could accelerate particles to such a high energy and produce such high collision rates.

    The LHC primarily collides protons with protons but can also accelerate heavy nuclei such as lead. Other synchrotrons can also be customized to accelerate different types of particles. At Brookhaven National Laboratory [BNL] in New York, the Relativistic Heavy Ion Collider [RHIC] can accelerate everything from protons to uranium nuclei.

    BNL RHIC Campus

    It keeps the proton beams polarized with the use of specially designed magnets, according to RHIC accelerator physicist Angelika Drees. It can also collide heavy ions such as uranium and gold to create quark-gluon plasma—the high-temperature soup that made up the universe just after the Big Bang.

    Cyclotrons: the workhorses
    Synchrotrons are the descendants of another type of circular collider called cyclotrons. Cyclotrons accelerate particles in a spiral pattern, starting at their center.

    Like synchrotrons, cyclotrons use a large electromagnet to bend the particles in a circle. However, they use only one magnet, which limits how large they can be. They use metal electrodes to push particles to travel in increasingly large circles, creating a spiral pathway.

    Cyclotrons are often used to create large amounts of specific types of particles, such as muons or neutrons. They are also popular for medical research because they have the right energy range and intensity to produce medical isotopes.

    The world’s largest cyclotron is located at the TRIUMF laboratory in Vancouver, Canada.

    INSIDE the TRIUMF 520 MeV CYCLOTRON Inside the Cyclotron with the lid raised for servicing

    At the TRIUMF cyclotron, physicists regularly accelerate particles to 520 million electronvolts. They can draw particles from different parts of their accelerator for experiments that require particles at different energies. This makes it an especially adaptable type of accelerator, says physicist Ewart Blackmore, who helped to design and build the TRIUMF accelerator.

    “We certainly make use of that facility every day when we’re running, when we’re typically producing a low-energy but high-current beam for medical isotope production,” Blackmore says. “We’re extracting at fixed energies down one beam for producing pions and muons for research, and on another beam line we’re extracting beams of radioactive nuclei to study their properties.”

    Linacs: straight and to the point
    For physics experiments or applications that require a steady, intense beam of particles, linear accelerators are a favored design. SLAC National Accelerator Laboratory hosts the longest linac in the world, which measures 2 miles long and at one point could accelerate particles up to 50 billion electronvolts.

    SLAC Campus

    Fermi National Accelerator Laboratory uses a shorter linac to speed up protons before sending them into a different accelerator, eventually running the particles into a fixed target to create the world’s most intense neutrino beam.

    While circular accelerators may require many turns to accelerate particles to the desired energy, linacs get particles up to speed in short order. Particles start at one end at a low energy, and electromagnetic fields in the linac accelerate them down its length. When particles travel in a curved path, they release energy in the form of radiation. Traveling in a straight line means keeping their energy for themselves. A series of radiofrequency cavities in SLAC’s linac are used to push particles on the crest of electromagnetic waves, causing them to accelerate forward down the length of the accelerator.

    Like cyclotrons, linacs can be used to produce medical isotopes. They can also be used to create beams of radiation for cancer treatment. Electron linacs for cancer therapy are the most common type of particle accelerator.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 8:59 pm on July 5, 2016 Permalink | Reply
    Tags: , , , Symmetry Magazine   

    From Symmetry: “Incredible hulking facts about gamma rays” 


    Matthew R. Francis


    From lightning to the death of electrons, the highest-energy form of light is everywhere.

    Gamma rays are the most energetic type of light, packing a punch strong enough to pierce through metal or concrete barriers. More energetic than X-rays, they are born in the chaos of exploding stars, the annihilation of electrons and the decay of radioactive atoms. And today, medical scientists have a fine enough control of them to use them for surgery. Here are seven amazing facts about these powerful photons.

    Doctors conduct brain surgery using “gamma ray knives.”


    Gamma rays can be helpful as well as harmful (and are very unlikely to turn you into the Hulk). To destroy brain cancers and other problems, medical scientists sometimes use a “gamma ray knife.” This consists of many beams of gamma rays focused on the cells that need to be destroyed. Because each beam is relatively small, it does little damage to healthy brain tissue. But where they are focused, the amount of radiation is intense enough to kill the cancer cells. Since brains are delicate, the gamma ray knife is a relatively safe way to do certain kinds of surgery that would be a challenge with ordinary scalpels.

    [My wife had gamma-knife brain surgery. Whn I asked her neursurgeon how they got gamma rays, he replied from cobalt.]


    The name “gamma rays” came from Ernest Rutherford.

    French chemist Paul Villard first identified gamma rays in 1900 from the element radium, which had been isolated by Marie and Pierre Curie just two years before. When scientists first studied how atomic nuclei changed form, they identified three types of radiation based on how far they penetrated into a barrier made of lead. Ernest Rutherford named the radiation for the first three letters of the Greek alphabet. Alpha rays bounce right off, beta rays went a little farther, and gamma rays went the farthest. Today we know alpha rays are the same thing as helium nuclei (two protons and two neutrons), beta rays are either electrons or positrons (their antimatter versions), and gamma rays are a kind of light.


    Nuclear reactions are a major source of gamma rays.

    When an unstable uranium nucleus splits in the process of nuclear fission, it releases a lot of gamma rays in the process. Fission is used in both nuclear reactors and nuclear warheads. To monitor nuclear tests in the 1960s, the United States launched gamma radiation detectors on satellites. They found far more explosions than they expected to see. Astronomers eventually realized these explosions were coming from deep space—not the Soviet Union—and named them gamma-ray bursts, or GRBs. Today we know GRBs come in two types: the explosions of extremely massive stars, which pump out gamma rays as they die, and collisions between highly dense relics of stars called neutron stars and something else, probably another neutron star or a black hole.


    Gamma rays played a key role in the discovery of the Higgs boson.

    Most of the particles in the Standard Model of particle physics are unstable; they decay into other particles almost as soon as they come into existence. The Higgs boson, for example, can decay into many different types of particles, including gamma rays. Even though theory predicts that a Higgs boson will decay into gamma rays just 0.2 percent of the time, this type of decay is relatively easy to identify and it was one of the types that scientists observed when they first discovered the Higgs boson.

    NASA Fermi Gamma-ray Space Telescope  Gamma-ray Burst Monitor (GBM)
    NASA Fermi Gamma-ray Space Telescope Gamma-ray Burst Monitor

    To study gamma rays, astronomers build telescopes in space.

    Gamma rays heading toward the Earth from space interact with enough atoms in the atmosphere that almost none of them reach the surface of the planet. That’s good for our health, but not so great for those who want to study GRBs and other sources of gamma rays. To see gamma rays before they reach the atmosphere, astronomers have to build telescopes in space. This is challenging for a number of reasons. For example, you can’t use a normal lens or mirror to focus gamma rays, because the rays punch right through them. Instead an observatory like the Fermi Gamma-ray Space Telescope detects the signal from gamma rays when they hit a detector and convert into pairs of electrons and positrons.

    Some gamma rays come from thunderstorms.

    In the 1990s, observatories in space detected bursts of gamma rays coming from Earth that eventually were traced to thunderclouds. When static electricity builds up inside clouds, the immediate result is lightning. That static electricity also acts like a giant particle accelerator, creating pairs of electrons and positrons, which then annihilate into gamma rays. These bursts happen high enough in the air that only airplanes are exposed—and they’re one reason for flights to steer well away from storms.

    Gamma rays (indirectly) give life to Earth.

    Hydrogen nuclei are always fusing together in the core of the sun. When this happens, one byproduct is gamma rays. The energy of the gamma rays keeps the sun’s core hot. Some of those gamma rays also escape into the sun’s outer layers, where they collide with electrons and protons and lose energy. As they lose energy, they change into ultraviolet, infrared and visible light. The infrared light keeps Earth warm, and the visible light sustains Earth’s plants.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 4:00 pm on June 29, 2016 Permalink | Reply
    Tags: , , , , , , Symmetry Magazine, Tetraquarks? For real?   

    From Symmetry: “LHCb discovers family of tetraquarks” 

    Symmetry Mag


    Sarah Charley

    LHCb. Courtesy of CERN

    Researchers found four new particles made of the same four building blocks.

    It’s quadruplets! Syracuse University researchers on the LHCb experiment confirmed the existence of a new four-quark particle and serendipitously discovered three of its siblings.

    Quarks are the solid scaffolding inside composite particles like protons and neutrons. Normally quarks come in pairs of two or three, but in 2014 LHCb researchers confirmed the existence four-quark particles and, one year later, five-quark particles.

    The particles in this new family were named based on their respective masses, denoted in mega-electronvolts: X(4140), X(4274), X(4500) and X(4700). Each particle contains two charm quarks and two strange quarks arranged in a unique way, making them the first four-quark particles composed entirely of heavy quarks. Researchers also measured each particle’s quantum numbers, which describe their subatomic properties. Theorists will use these new measurements to enhance their understanding of the formation of particles and the fundamental structures of matter.

    “What we have discovered is a unique system,” says Tomasz Skwarnicki, a physics professor at Syracuse University. “We have four exotic particles of the same type; it’s the first time we have seen this and this discovery is already helping us distinguish between the theoretical models.”

    Evidence of the lightest particle in this family of four and a hint of another were first seen by the CDF experiment at the US Department of Energy’s Fermi National Accelerator Lab in 2009.

    FNAL/Tevatron CDF detector
    FNAL/Tevatron machine
    FNAL/Tevatron map
    CDF; Tevatron; Tevtron map

    However, other experiments were unable to confirm this observation until 2012, when the CMS experiment at CERN reported seeing the same particle-like bumps with a much greater statistical certainty.

    CERN/CMS Detector
    CERN/CMS Detector

    Later, the D0 collaboration at Fermilab also reported another observation of this particle.

    FNAL/Tevatron DZero detector

    “It was a long road to get here,” says University of Iowa physicist Kai Yi, who works on both the CDF and CMS experiments. “This has been a collective effort by many complementary experiments. I’m very happy that LHCb has now reconfirmed this particle’s existence and measured its quantum numbers.”

    The US contribution to the LHCb experiment is funded by the National Science Foundation.

    LHCb researcher Thomas Britton performed this analysis as his PhD thesis at Syracuse University.

    “When I first saw the structures jumping out of the data, little did I know this analysis would be such an aporetic saga,” Britton says. “We looked at every known particle and process to make sure these four structures couldn’t be explained by any pre-existing physics. It was like baking a six-dimensional cake with 98 ingredients and no recipe—just a picture of a cake.”

    Even though the four new particles all contain the same quark composition, they each have a unique internal structure, mass and their own sets of quantum numbers. These characteristics are determined by the internal spatial configurations of the quarks.

    “The quarks inside these particles behave like electrons inside atoms,” Skwarnicki says. “They can be ‘excited’ and jump into higher energy orbitals. The energy configuration of the quarks gives each particle its unique mass and identity.”

    According to theoretical predictions, the quarks inside could be tightly bound (like three quarks packed inside a single proton) or loosely bound (like two atoms forming a molecule.) By closely examining each particle’s quantum numbers, scientists were able to narrow down the possible structures.

    “The molecular explanation does not fit with the data,” Skwarnicki says. “But I personally would not conclude that these are definitely tightly bound states of four quarks. It could be possible that these are not even particles. The result could show the complex interplays of known particle pairs flippantly changing their identities.”

    Theorists are currently working on models to explain these new results—be it a family of four new particles or bizarre ripple effects from known particles. Either way, this study will help shape our understanding of the subatomic universe.

    “The huge amount of data generated by the LHC is enabling a resurgence in searches for exotic particles and rare physical phenomena,” Britton says. “There’s so many possible things for us to find and I’m happy to be a part of it.”

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 1:02 pm on June 28, 2016 Permalink | Reply
    Tags: , Brookhaven E821 Muon (g-2), , , Symmetry Magazine   

    From Symmetry: “Preparing for their magnetic moment” 

    Symmetry Mag


    Andre Salles

    Cindy Arnold, Fermilab

    Scientists are using a plastic robot and hair-thin pieces of metal to ready a magnet that will hunt for new physics.

    Three summers ago, a team of scientists and engineers on the Muon g-2 experiment moved a 52-foot-wide circular magnet 3200 miles over land and sea. It traveled in one piece without twisting more than a couple of millimeters, lest the fragile coils inside irreparably break. It was an astonishing feat that took years to plan and immense skill to execute.

    FNAL Muon g-2 studio
    FNAL Muon g-2 studio

    As it turns out, that was the easy part.

    The hard part—creating a magnetic field so precise that even subatomic particles see it as perfectly smooth—has been under way for seven months. It’s a labor-intensive process that has inspired scientists to create clever, often low-tech solutions to unique problems, working from a road map written 30 years ago as they drive forward into the unknown.

    The goal of Muon g-2 is to follow up on a similar experiment conducted at the US Department of Energy’s Brookhaven National Laboratory in New York in the 1990s.

    E821 Muon (g-2) At Brookhaven

    Scientists there built an extraordinary machine that generated a near-perfect magnetic field into which they fired a beam of particles called muons. The magnetic ring serves as a racetrack for the muons, and they zoom around it for as long as they exist—usually about 64 millionths of a second.

    That’s a blink of an eye, but it’s enough time to measure a particular property: the precession frequency of the muons as they hustle around the magnetic field. And when Brookhaven scientists took those measurements, they found something different than the Standard Model, our picture of the universe, predicted they would. They didn’t quite capture enough data to claim a definitive discovery, but the hints were tantalizing.

    Now, 30 years later, some of those same scientists—and dozens of others, from 34 institutions around the world—are conducting a similar experiment with the same magnet, but fed by a more powerful beam of muons at the US Department of Energy’s Fermi National Accelerator Laboratory in Illinois. Moving that magnet from New York caused quite a stir among the science-interested public, but that’s nothing compared with what a discovery from the Muon g-2 experiment would cause.

    “We’re trying to determine if the muon really is behaving differently than expected,” says Dave Hertzog of the University of Washington, one of the spokespeople of the Muon g-2 experiment. “And, if so, that would suggest either new particles popping in and out of the vacuum, or new subatomic forces at work. More likely, it might just be something no one has thought of yet. In any case, it’s all very exciting.”

    Shimming to reduce shimmy

    To start making these measurements, the magnetic field needs to be the same all the way around the ring so that, wherever the muons are in the circle, they will see the same pathway. That’s where Brendan Kiburg of Fermilab and a group of a dozen scientists, post-docs and students come in. For the past six months, they have been “shimming” the magnetic ring, shaping it to an almost inconceivably exact level.

    “The primary goal of shimming is to make the magnetic field as uniform as possible,” Kiburg says. “The muons act like spinning tops, precessing at a rate proportional to the magnetic field. If a section of the field is a little higher or a little lower, the muon sees that, and will go faster or slower.”

    Since the idea is to measure the precession rate to an extremely precise degree, the team needs to shape the magnetic field to a similar degree of uniformity. They want it to vary by no more than ten parts in a billion per centimeter. To put that in perspective, that’s like wanting a variation of no more than one second in nearly 32 years, or one sheet in a roll of toilet paper stretching from New York to London.

    How do they do this? First, they need to measure the field they have. With a powerful electromagnet that will affect any metal object inside it, that’s pretty tricky. The solution is a marriage of high-tech and low-tech: a cart made of sturdy plastic and quartz, moved by a pulley attached to a motor and continuously tracked by a laser. On this cart are probes filled with petroleum jelly, with sensors measuring the rate at which the jelly’s protons spin in the magnetic field.

    The laser can record the position of the cart to 25 microns, half the width of a human hair. Other sensors measure how far apart the top and bottom of the cart are to the magnet, to the micron.

    “The cart moves through the field as it is pulled around the ring,” Kiburg says. “It takes between two and two-and-a-half hours to go around the ring. There are more than 1500 locations around the path, and it stops every three centimeters for a short moment while the field is precisely measured in each location. We then stitch those measurements into a full map of the magnetic field.”

    Erik Swanson of the University of Washington is the run coordinator for this effort, meaning he directs the team as they measure the field and perform the manually intensive shimming. He also designed the new magnetic resonance probes that measure the field, upgrading them from the technology used at Brookhaven.

    “They’re functionally the same,” he says of the probes, “but the Brookhaven experiment started in the 1990s, and the old probes were designed before that. Any electronics that old, there’s the potential that they will stop working.”

    Swanson says that the accuracy to which the team has had to position the magnet’s iron pieces to achieve the desired magnetic field surprised even him. When scientists first turned the magnet on in October, the field, measured at different places around the ring, varied by as much as 1400 parts per million. That may seem smooth, but to a tiny muon it looks like a mountain range of obstacles. In order to even it out, the Muon g-2 team makes hundreds of minuscule adjustments by hand.

    Access mp4 video here .

    Physical physics

    Stationed around the ring are about 1000 knobs that control the ways the field could become non-uniform. But when that isn’t enough, the field can be shaped by taking parts of the magnet apart and inserting extremely small pieces of steel called shims, changing the field by thousandths of an inch.

    There are 12 sections of the magnet, and it takes an entire day to adjust just one of those sections.

    This process relies on simulations, calibrations and iterations, and with each cycle the team inches forward toward their goal, guided by mathematical predictions. Once they’re done with the process of carefully inserting these shims, some as thin as 12.5 microns, they reassemble the magnet and measure the field again, starting the process over, refining and learning as they go.

    “It’s fascinating to me how hard such a simple-seeming problem can be,” says Matthias Smith of the University of Washington, one of the students who helped design the plastic measuring robot. “We’re making very minute adjustments because this is a puzzle that can go together in multiple ways. It’s very complex.”

    His colleague Rachel Osofsky, also of the University of Washington, agrees. Osofsky has helped put in more than 800 shims around the magnet, and says she enjoys the hands-on and collaborative nature of the work.

    “When I first came aboard, I knew I’d be spending time working on the magnet, but I didn’t know what that meant,” she says. “You get your hands dirty, really dirty, and then measure the field to see what you did. Students later will read the reports we’re writing now and refer to them. It’s exciting.”

    Similarly, the Muon g-2 team is constantly consulting the work of their predecessors who conducted the Brookhaven experiment, making improvements where they can. (One upgrade that may not be obvious is the very building that the experiment is housed in, which keeps the temperature steadier than the one used at Brookhaven and reduces shape changes in the magnet itself.)

    Kiburg says the Muon g-2 team should be comfortable with the shape of the magnetic field sometime this summer. With the experiment’s beamline under construction and the detectors to be installed, the collaboration should be ready to start measuring particles by next summer. Swanson says that while the effort has been intense, it has also been inspiring.

    “It’s a big challenge to figure out how to do all this right,” he says. “But if you know scientists, when a challenge seems almost impossible, that’s the one we all go for.”

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:27 pm on June 23, 2016 Permalink | Reply
    Tags: , , Symmetry Magazine, Where are the bottom quarks?   

    From Symmetry: “The Higgs-shaped elephant in the room” 

    Symmetry Mag


    Sarah Charley

    Higgs bosons should mass-produce bottom quarks. So why is it so hard to see it happening?

    Maximilien Brice, CERN

    Higgs bosons are born in a blob of pure concentrated energy and live only one-septillionth of a second before decaying into a cascade of other particles. In 2012, these subatomic offspring were the key to the discovery of the Higgs boson.

    Higgs Boson Event

    So-called daughter particles stick around long enough to show up in the CMS and ATLAS detectors at the Large Hadron Collider. Scientists can follow their tracks and trace the family trees back to the Higgs boson they came from.

    CERN/CMS Detector

    CERN/ATLAS detector

    But the particles that led to the Higgs discovery were actually some of the boson’s less common progeny. After recording several million collisions, scientists identified a handful of Z bosons and photons with a Higgs-like origin. The Standard Model of particle physics predicts that Higgs bosons produce those particles 2.5 and 0.2 percent of the time.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth

    Physicists later identified Higgs bosons decaying into W bosons, which happens about 21 percent of the time.

    According to the Standard Model, the most common decay of the Higgs boson should be a transformation into a pair of bottom quarks. This should happen about 60 percent of the time.

    The strange thing is, scientists have yet to discover it happening (though they have seen evidence).

    According to Harvard researcher John Huth, a member of the ATLAS experiment, seeing the Higgs turning into bottom quarks is priority No. 1 for Higgs boson research.

    “It would behoove us to find the Higgs decaying to bottom quarks because this is the largest interaction,” Huth says, “and it darn well better be there.”

    If the Higgs to bottom quarks decay were not there, scientists would be left completely dumbfounded.

    “I would be shocked if this particle does not couple to bottom quarks,” says Jim Olsen, a Princeton researcher and Physics Coordinator for the CMS experiment. “The absence of this decay would have a very large and direct impact on the relative decay rates of the Higgs boson to all of the other known particles, and the recent ATLAS and CMS combined measurements are in excellent agreement with expectations.”

    To be fair, the decay of a Higgs to two bottom quarks is difficult to spot.

    When a dying Higgs boson produces twin Z or W bosons, they each decay into a pair of muons or electrons. These particles leave crystal clear signals in the detectors, making it easy for scientists to spot them and track their lineage. And because photons are essentially immortal beams of light, scientists can immediately spot them and record their trajectory and energy with electromagnetic detectors.

    But when a Higgs births a pair of bottom quarks, they impulsively marry other quarks, generating huge unstable families which bourgeon, break and reform. This chaotic cascade leaves a messy ancestry.

    Scientists are developing special tools to disentangle the Higgs from this multi-generational subatomic soap opera. Unfortunately, there are no cheek swabs or Maury Povich to announce, Higgs, you are the father! Instead, scientists are working on algorithms that look for patterns in the energy these jets of particles deposit in the detectors.

    “The decay of Higgs bosons to bottom quarks should have different kinematics from the more common processes and leave unique signatures in our detector,” Huth says. “But we need to deeply understand all the variables involved if we want to squeeze the small number of Higgs events from everything else.”

    Physicist Usha Mallik and her ATLAS team of researchers at the University of Iowa have been mapping the complex bottom quark genealogies since shortly after the Higgs discovery in 2012.

    “Bottom quarks produce jets of particles with all kinds and colors and flavors,” Mallik says. “There are fat jets, narrow gets, distinct jets and overlapping jets. Just to find the original bottom quarks, we need to look at all of the jet’s characteristics. This is a complex problem with a lot of people working on it.”

    This year the LHC will produce five times more data than it did last year and will generate Higgs bosons 25 percent faster. Scientists expect that by August they will be able to identify this prominent decay of the Higgs and find out what it can tell them about the properties of this unique particle.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 11:45 am on June 21, 2016 Permalink | Reply
    Tags: , Four fundamental forces of nature, , , Symmetry Magazine   

    From Symmetry: “All four one and one for all” 

    Symmetry Mag

    Matthew R. Francis

    A theory of everything would unite the four forces of nature, but is such a thing possible?


    Over the centuries, physicists have made giant strides in understanding and predicting the physical world by connecting phenomena that look very different on the surface.

    One of the great success stories in physics is the unification of electricity and magnetism into the electromagnetic force in the 19th century. Experiments showed that electrical currents could deflect magnetic compass needles and that moving magnets could produce currents.

    Then physicists linked another force, the weak force, with that electromagnetic force, forming a theory of electroweak interactions. Some physicists think the logical next step is merging all four fundamental forces—gravity, electromagnetism, the weak force and the strong force—into a single mathematical framework: a theory of everything.

    Those four fundamental forces of nature are radically different in strength and behavior. And while reality has cooperated with the human habit of finding patterns so far, creating a theory of everything is perhaps the most difficult endeavor in physics.

    “On some level we don’t necessarily have to expect that [a theory of everything] exists,” says Cynthia Keeler, a string theorist at the Niels Bohr Institute in Denmark. “I have a little optimism about it because historically, we have been able to make various unifications. None of those had to be true.”

    Despite the difficulty, the potential rewards of unification are great enough to keep physicists searching. Along the way, they’ve discovered new things they wouldn’t have learned had it not been for the quest to find a theory of everything.

    CERN/ATLAS http://atlasexperiment.org

    United we hope to stand

    No one has yet crafted a complete theory of everything.

    It’s hard to unify all of the forces when you can’t even get all of them to work at the same scale. Gravity in particular tends to be a tricky force, and no one has come up with a way of describing the force at the smallest (quantum) level.

    Physicists such as Albert Einstein thought seriously about whether gravity could be unified with the electromagnetic force. After all, general relativity had shown that electric and magnetic fields produce gravity and that gravity should also make electromagnetic waves, or light. But combining gravity and electromagnetism, a mission called unified field theory, turned out to be far more complicated than making the electromagnetic theory work. This was partly because there was (and is) no good theory of quantum gravity, but also because physicists needed to incorporate the strong and weak forces.

    A different idea, quantum field theory, combines Einstein’s special theory of relativity with quantum mechanics to explain the behavior of particles, but it fails horribly for gravity. That’s largely because anything with energy (or mass, thanks to relativity) creates a gravitational attraction—including gravity itself. To oversimplify somewhat, the gravitational interaction between two particles has a certain amount of energy, which produces an additional gravitational interaction with its own energy, and so on, spiraling to higher energies with each extra piece.

    “One of the first things you learn about quantum gravity is that quantum field theory probably isn’t the answer,” says Robert McNees, a physicist at Loyola University Chicago. “Quantum gravity is hard because we have to come up with something new.”


    An evolution of theories

    The best-known candidate for a theory of everything is string theory, in which the fundamental objects are not particles but strings that stretch out in one dimension.

    Calabi yau.jpg

    Strings were proposed in the 1970s to try to explain the strong force. This first string theory proved to be unnecessary, but physicists realized it could be joined to the another theory called Kaluza-Klein theory as a possible explanation of quantum gravity.

    String theory expresses quantum gravity in two dimensions rather than the four, bypassing all the problems of the quantum field theory approach but introducing other complications, namely an extra six dimensions that must be curled up on a scale too small to detect.

    Unfortunately, string theory has yet to reproduce the well-tested predictions of the Standard Model.

    Another well-known idea is the sci-fi-sounding “loop quantum gravity,” in which space-time on the smallest scales is made of tiny loops in a flexible mesh that produces gravity as we know it.

    The idea that space-time is made up of smaller objects, just as matter is made of particles, is not unique to the theory. There are many others with equally Jabberwockian names: twistors, causal set theory, quantum graphity and so on. Granular space-time might even explain why our universe has four dimensions rather than some other number.

    Loop quantum gravity’s trouble is that it can’t replicate gravity at large scales, such as the size of the solar system, as described by general relativity.

    None of these theories has yet succeeded in producing a theory of everything, in part because it’s so hard to test them.

    “Quantum gravity is expected to kick in only at energies higher than anything that we can currently produce in a lab,” says Lisa Glaser, who works on causal set quantum gravity at the University of Nottingham. “The hope in many theories is now to predict cumulative effects,” such as unexpected black hole behavior during collisions like the ones detected recently by LIGO.

    Today, many of the theories first proposed as theories of everything have moved beyond unifying the forces. For example, much of the current research in string theory is potentially important for understanding the hot soup of particles known as the quark-gluon plasma, along with the complex behavior of electrons in very cold materials like superconductors—something seemingly as far removed from quantum gravity as could be.

    “On a day-to-day basis, I may not be doing a calculation that has anything directly to do with string theory,” Keeler says. “But it’s all about these ideas that came from string theory.”

    Finding a theory of everything is unlikely to change the way most of us go about our business, even if our business is science. That’s the normal way of things: Chemists and electricians don’t need to use quantum electrodynamics, even though that theory underlies their work. But finding such a theory could change the way we think of the universe on a fundamental level.

    Even a successful theory of everything is unlikely to be a final theory. If we’ve learned anything from 150 years of unification, it’s that each step toward bringing theories together uncovers something new to learn.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:43 pm on June 15, 2016 Permalink | Reply
    Tags: , , , Symmetry Magazine   

    From Symmetry: “Second gravitational wave detection announced” 

    Symmetry Mag


    Kathryn Jepsen

    Courtesy of California Institute of Technology

    For a second time, scientists from the LIGO and Virgo collaborations saw gravitational waves from the merger of two black holes.

    Scientists from the LIGO and Virgo collaborations announced today the observation of gravitational waves from a set of merging black holes.

    This follows their previous announcement, just four months ago, of the first ever detection of gravitational waves, also from a set of merging black holes.

    The detection of gravitational waves confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity. Einstein posited that every object with mass exerts a gravitational pull on everything around it. When a massive object moves, its pull changes, and that change is communicated in the form of gravitational waves.

    Gravity is by far the weakest of the known forces, but if an object is massive enough and accelerates quickly enough, it creates gravitational waves powerful enough to be observed experimentally. LIGO, or Laser Interferometer Gravitational-wave Observatory, caught the two sets of gravitational waves using lasers and mirrors.

    LIGO consists of two huge interferometers in Livingston, Louisiana, and Hanford, Washington.

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector installation  Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    In an interferometer, a laser beam is split and sent down a pair of perpendicular arms. At the end of each arm, the split beams bounce off of mirrors and return to recombine in the center. If a gravitational wave passes through the laser beams as they travel, it stretches space-time in one direction and compresses it in another, creating a mismatch between the two.

    Scientists on the Virgo collaboration have been working with LIGO scientists to analyze their data.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy
    VIRGO Gravitational Wave interferometer, near Pisa, Italy not yet in operation

    With this second observation, “we are now a real observatory,” said Gabriela Gonzalez, LIGO spokesperson and professor of physics and astronomy at Louisiana State University, in a press conference at the annual meeting of the American Astronomical Society.

    The latest discovery was accepted for publication in the journal Physical Review Letters.

    On Christmas evening in 2015, a signal that had traveled about 1.4 billion light years reached the twin LIGO detectors. The distant merging of two black holes caused a slight shift in the fabric of space-time, equivalent to changing the distance between the Earth and the sun by a fraction of an atomic diameter.

    The black holes were 14 and eight times as massive as the sun, and they merged into a single black hole weighing 21 solar masses. That might sound like a lot, but these were relative flyweights compared to the black holes responsible for the original discovery, which weighed 36 and 29 solar masses.

    Cornell SXS team. Two merging black holes simulation
    Cornell SXS team. Two merging black holes simulation

    “It is very significant that these black holes were much less massive than those observed in the first detection,” Gonzalez said in a press release. “Because of their lighter masses compared to the first detection, they spent more time—about one second—in the sensitive band of the detectors.”

    The LIGO detectors saw almost 30 of the last orbits of the black holes before they coalesced, Gonzalez said during the press conference.

    LIGO’s next data-taking run will begin in the fall. The Virgo detector, located near Pisa, Italy, is expected to come online in early 2017. Additional gravitational wave detectors are in the works in Japan and India.

    Additional detectors will make it possible not only to find evidence of gravitational waves, but also to triangulate their origins.

    On its own, LIGO is “more of a microphone,” capturing the “chirps” from these events, Gonzalez said.

    The next event scientists are hoping to “hear” is the merger of a pair of neutron stars, said Caltech’s David Reitze, executive director of the LIGO laboratory, at the press conference.

    Whereas two black holes merging are not expected to release light, a pair of neutron stars in the process of collapsing into one another could produce a plethora of observable gamma rays, X-rays, infrared light and even neutrinos.

    In the future, gravitational wave hunters hope to be able to alert astronomers to an event with enough time and precision to allow them to train their instruments on the area and see those signals.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    Symmetry is a joint Fermilab/SLAC publication.

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