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  • richardmitnick 2:20 pm on November 29, 2016 Permalink | Reply
    Tags: Antimatter, , ,   

    From CERN: “A new ring to slow down antimatter” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead


    28 Nov 2016
    Corinne Pralavorio
    Posted by Harriet Kim Jarlett

    The new deceleration ring ELENA will slow down antimatter particles further than ever to improve the efficiency of experiments studying antimatter. (Image: Maximilien Brice/CERN)

    You could mistake ELENA for a miniature accelerator. But, unlike most accelerators, it’s housed in a hangar and you can take it all in in just a single glance. The biggest difference though, is that it doesn’t accelerate particles, but decelerates them.

    CERN’s brand-new machine measures just 30 metres in circumference and has just begun its first tests with beam.

    The ELENA (Extra Low ENergy Antiproton) deceleration ring will be connected to the Antiproton Decelerator (AD), which has been in service since 2000. The AD is a unique facility that enables the study of antimatter.

    Antimatter can be thought of as a mirror image of matter and it remains a mystery for physicists. For example, matter and antimatter should have been created in equal quantities at the time of the Big Bang— the event at the origin of our Universe. But antimatter seems to have disappeared from the Universe. Where it has gone is one of the many questions physicists are trying to solve with the AD machine.

    The 182-metre-circumference ring decelerates antiprotons (the anti-particles of protons) to 5.3 MeV, the lowest energy possible in a machine of this size. The antiprotons are then sent to experiments where they are studied or used to produce atoms of antimatter. The slower the antiprotons (i.e. the less energy they have), the easier it is for the experiments to study or manipulate them.

    And this is where ELENA comes in. Coupled with the AD, this small ring will slow the antiprotons down even further, reducing their energy by a factor of 50, from 5.3 MeV to just 0.1 MeV. In addition, the density of the beams will be improved. The experiments will be able to trap 10 to 100 times more antiprotons, improving efficiency and paving the way for new studies.

    Decelerating beams is just as complicated as accelerating them. The slower the particles, the harder it is to control their trajectories. At low energy, beams are more sensitive to outside interference, such as the earth’s magnetic field. ELENA is therefore equipped with magnets that are optimised to operate with very weak fields. An electron cooling system concentrates and decelerates the beams.

    Now that the components of the new decelerator have been installed, the teams have begun the first tests with beam.

    “After five years of development and construction, this is a very important stage. We are going to continue the tests over the coming weeks to see if everything is working as planned,” explains Christian Carli, ELENA project leader. “GBAR, the first experiment to be connected to ELENA, should receive its first antiprotons in 2017.”

    The other experiments will be connected during the second long shutdown of CERN’s accelerators in 2019-2020. ELENA will supply antiprotons to four experiments in parallel.

    Several experiments are studying antimatter and its properties: ALPHA, ASACUSA, ATRAP and BASE. GBAR and AEGIS are working more specifically on the effect of gravity on antimatter.

    You can read more about ELENA in the the CERN Courier.

    See the full article here.

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  • richardmitnick 1:40 pm on May 3, 2016 Permalink | Reply
    Tags: Antimatter, , EXO-200 experiment, ,   

    From Symmetry: “EXO-200 resumes its underground quest” 

    Symmetry Mag

    Matthew R. Francis

    EXO-200 Enriched Xenon Observatory near Carlsbad, New Mexico
    SLAC EXO-200 Enriched Xenon Observatory near Carlsbad, New Mexico

    The upgraded experiment aims to discover if neutrinos are their own antiparticles.

    Science is often about serendipity: being open to new results, looking for the unexpected.

    The dark side of serendipity is sheer bad luck, which is what put the Enriched Xenon Observatory experiment, or EXO-200, on hiatus for almost two years.

    Accidents at the Department of Energy’s underground Waste Isolation Pilot Project (WIPP) facility near Carlsbad, New Mexico, kept researchers from continuing their search for signs of neutrinos and their antimatter pairs. Designed as storage for nuclear waste, the site had both a fire and a release of radiation in early 2014 in a distant part of the facility from where the experiment is housed. No one at the site was injured. Nonetheless, the accidents, and the subsequent efforts of repair and remediation, resulted in a nearly two-year suspension of the EXO-200 effort.

    Things are looking up now, though: Repairs to the affected area of the site are complete, new safety measures are in place, and scientists are back at work in their separate area of the site, where the experiment is once again collecting data. That’s good news, since EXO-200 is one of a handful of projects looking to answer a fundamental question in particle physics: Are neutrinos and antineutrinos the same thing?

    The neutrino that wasn’t there

    Each type of particle has its own nemesis: its antimatter partner. Electrons have positrons—which have the same mass but opposite electric charge—quarks have antiquarks and protons have antiprotons. When a particle meets its antimatter version, the result is often mutual annihilation. Neutrinos may also have antimatter counterparts, known as antineutrinos. However, unlike electrons and quarks, neutrinos are electrically neutral, so antineutrinos look a lot like neutrinos in many circumstances.

    In fact, one hypothesis is that they are one and the same. To test this, EXO-200 uses 110 kilograms of liquid xenon (of its 200kg total) as both a particle source and particle detector. The experiment hinges on a process called double beta decay, in which an isotope of xenon has two simultaneous decays, spitting out two electrons and two antineutrinos. (“Beta particle” is a nuclear physics term for electrons and positrons.)

    If neutrinos and antineutrinos are the same thing, sometimes the result will be neutrinoless double beta decay. In that case, the antineutrino from one decay is absorbed by the second decay, canceling out what would normally be another antineutrino emission. The challenge is to determine if neutrinos are there or not, without being able to detect them directly.

    “Neutrinoless double beta decay is kind of a nuclear physics trick to answer a particle physics problem,” says Michelle Dolinski, one of the spokespeople for EXO-200 and a physicist at Drexel University. It’s not an easy experiment to do.

    EXO-200 and similar experiments look for indirect signs of neutrinoless double beta decay. Most of the xenon atoms in EXO-200 are a special isotope containing 82 neutrons, four more than the most common version found in nature. The isotope decays by emitting two electrons, changing the atom from xenon into barium. Detectors in the EXO-200 experiment collect the electrons and measure the light produced when the beta particles are stopped in the xenon. These measurements together are what determine whether double beta decay happened, and whether the decay was likely to be neutrinoless.

    EXO-200 isn’t the only neutrinoless double beta decay experiment, but many of the others use solid detectors instead of liquid xenon. Dolinski got her start on the CUORE experiment, a large solid-state detector, but later changed directions in her research.

    CUORE experiment UC Berkeley
    CUORE experiment UC Berkeley

    “I joined EXO-200 as a postdoc in 2008 because I thought that the large liquid detectors were a more scalable solution,” she says. “If you want a more sensitive liquid-state experiment, you can build a bigger tank and fill it with more xenon.”

    Neutrinoless or not, double beta decay is very rare. A given xenon atom decays randomly, with an average lifetime of a quadrillion times the age of the universe. However, if you use a sufficient number of atoms, a few of them will decay while your experiment is running.

    “We need to sample enough nuclei so that you would detect these putative decays before the researcher retires,” says Martin Breidenbach, one of the EXO-200 project leaders and a physicist at the Department of Energy’s SLAC National Accelerator Laboratory.

    But the experiment is not just detecting neutrinoless events. Heavier neutrinos mean more frequent decays, so measuring the rate reveals the neutrino mass — something very hard to measure otherwise.

    Prior runs of EXO-200 and other experiments failed to see neutrinoless double beta decay, so either neutrinos and antineutrinos aren’t the same particle after all, or the neutrino mass is small enough to make decays too rare to be seen during the experiment’s lifetime. The current limit for the neutrino mass is less than 0.38 electronvolts—for comparison, electrons are about 500,000 electronvolts in mass.

    SLAC National Accelerator Laboratory’s Jon Davis checks the enriched xenon storage bottles before the refilling of the TPC. Brian Dozier, Los Alamos National Laboratory

    Working in the salt mines

    Cindy Lin is a Drexel University graduate student who spends part of her time working on the EXO-200 detector at the mine. Getting to work is fairly involved.

    “In the morning we take the cage elevator half a mile down to the mine,” she says. Additionally, she and the other workers at WIPP have to take a 40-hour safety training to ensure their wellbeing, and wear protective gear in addition to normal lab clothes.

    “As part of the effort to minimize salt dust particles in our cleanroom, EXO-200 scientists also cover our hair and wear coveralls,” Lin adds.

    The sheer amount of earth over the detector shields it from electrons and other charged particles from space, which would make it too hard to spot the signal from double beta decay. WIPP is carved out of a sodium chloride deposit—the same stuff as table salt—that has very little uranium or the other radioactive minerals you find in solid rock caverns. But it has its drawbacks, too.

    “Salt is very dynamic: It moves at the level of centimeters a year, so you can’t build a nice concrete structure,” says Breidenbach. To compensate, the EXO-200 team has opted for a more modular design.

    The inadvertent shutdown provided extra challenges. EXO-200, like most experiments, isn’t well suited for being neglected for more than a few days at a time. However, Lin and other researchers worked hard to get the equipment running for new data this year, and the downtime also allowed researchers to install some upgraded equipment.

    The next phase of the experiment, nEXO, is at a conceptual stage based on what has been learned from EXO200. Experimenters are considering the benefits of moving the project deeper underground, perhaps at a facility like the Sudbury Neutrino Observatory (SNOlab) in Canada.
    SNOLAB, Sudbury, Ontario, Canada.
    SNOLAB, Sudbury, Ontario, Canada

    Dolinski is optimistic that if there are any neutrinoless double beta decays to see, nEXO or similar experiments should see them in the next 15 years or so.

    Then, maybe we’ll know if neutrinos and antineutrinos are the same and find out more about these weird low-mass particles.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 12:30 pm on March 2, 2016 Permalink | Reply
    Tags: Antimatter, , , , , , SuperKEKB reborn   

    From Symmetry: “SuperKEKB reborn” 


    Lauren Biron

    SuperKEKB accelerator
    KEK SuperKEKB accelerator. No image credit found.

    The Japanese accelerator takes its first steps toward resuming its hunt for the universe’s missing antimatter.

    Everyone knows the electron, but in our daily routines of charging laptops and phones, we don’t often think of its antiparticle, the positron. Where has all the antimatter gone, in the long time passing since the dawn of the universe?

    That’s what scientists working on Japan’s electron-positron colliding accelerator, SuperKEKB, hope to find out. They’ll accelerate electrons and their antimatter brothers close to the speed of light before slamming them together. By peering into the debris and searching for rare particle decays, they’ll try to figure out why we live in a world full of matter.

    Japan’s high-energy accelerator research organization, known as KEK, announced today that scientists successfully accelerated and stored electrons and positrons in their separate rings, each nearly 2 miles around. This is the first in several steps to commission the accelerator after a five-year upgrade that included new beam pipes, new magnets (and magnet power supplies) to guide the beam, and a reinforced radio-frequency system that accelerates the particles. Technicians also added a new positron source for the antimatter particles and a new electron gun.

    The improvements should create many more collisions per second than the previous iteration of the accelerator, KEKB, was capable of–and that means a better chance of seeing interesting particle decays. The collisions will create pairs of bottom quarks and bottom antiquarks, hence the “B” in SuperKEKB.

    The project will also involve an upgraded version of the Belle detector that previously recorded the collisions.

    KEK Belle detector

    The initial run of the Belle detector yielded some interesting results, including a difference in the way particles called B mesons decayed. The asymmetry, called CP violation, was an intriguing find.

    “This is still puzzling,” KEK Director-General Masanori Yamauchi said in a Symmetry interview last year. “We still don’t know how it happens. We need at least 10 times more data to find out. That’s why we started the upgrade of KEKB.”

    The rare decays that Belle II will try to capture might also have occurred early in our universe’s history. Replicating them could provide clues to the current matter-antimatter imbalance and help us better understand the physics that underlies our cosmos, which can’t be fully explained by the current Standard Model.

    Standard model with Higgs New
    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.

    Before that can happen, researchers need to tune the accelerator so it operates perfectly, a process slated to take through June. They’ll also add powerful superconducting magnets that will focus the beam and install the Belle II detector. Once it is in place and working properly, they’ll get back to work on the case of the missing antimatter.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:58 pm on January 20, 2016 Permalink | Reply
    Tags: Antimatter, Antineutrinos, , ,   

    From Symmetry: “Is the neutrino its own antiparticle?” 


    Signe Brewster

    The mysterious particle could hold the key to why matter won out over antimatter in the early universe.

    Temp 1
    Artwork by Sandbox Studio, Chicago with Ana Kova

    Almost every particle has an antimatter counterpart: a particle with the same mass but opposite charge, among other qualities.

    This seems to be true of neutrinos, tiny particles that are constantly streaming through us. Judging by the particles released when a neutrino interacts with other matter, scientists can tell when they’ve caught a neutrino versus an antineutrino.

    But certain characteristics of neutrinos and antineutrinos make scientists wonder: Are they one and the same? Are neutrinos their own antiparticles?

    This isn’t unheard of. Gluons and even Higgs bosons are thought to be their own antiparticles. But if scientists discover neutrinos are their own antiparticles, it could be a clue as to where they get their tiny masses—and whether they played a part in the existence of our matter-dominated universe.

    Dirac versus Majorana

    The idea of the antiparticle came about in 1928 when British physicist Paul Dirac developed what became known as the Dirac equation. His work sought to explain what happened when electrons moved at close to the speed of light. But his calculations resulted in a strange requirement: that electrons sometimes have negative energy.

    “When Dirac wrote down his equation, that’s when he learned antiparticles exist,” says André de Gouvêa, a theoretical physicist and professor at Northwestern University. “Antiparticles are a consequence of his equation.”

    Physicist Carl Anderson discovered the antimatter partner of the electron that Dirac foresaw in 1932. He called it the positron—a particle like an electron but with a positive charge.

    Dirac predicted that, in addition to having opposite charges, antimatter partners should have opposite handedness as well.

    A particle is considered right-handed if its spin is in the same direction as its motion. It is considered left-handed if its spin is in the opposite direction.

    Dirac’s equation allowed for neutrinos and anti-neutrinos to be different particles, and, as a result, four types of neutrino were possible: left- and right-handed neutrinos and left- and right-handed antineutrinos. But if the neutrinos had no mass, as scientists thought at the time, only left-handed neutrinos and right-handed antineutrinos needed to exist.

    In 1937, Italian physicist Ettore Majorana debuted another theory: Neutrinos and antineutrinos are actually the same thing. The Majorana equation described neutrinos that, if they happened to have mass after all, could turn into antineutrinos and then back into neutrinos again.

    Temp 2
    Artwork by Sandbox Studio, Chicago with Ana Kova

    The matter-antimatter imbalance

    Whether neutrino masses were zero remained a mystery until 1998, when the Super-Kamiokande and SNO experiments found they do indeed have very small masses—an achievement recognized with the 2015 Nobel Prize for Physics.

    Super-Kamiokande Detector
    Super-Kamiokande neutrino detector

    SNO detector [under construction]

    Since then, experiments have cropped up across Asia, Europe and North America searching for hints that the neutrino is its own antiparticle.

    The key to finding this evidence is something called lepton number conservation. Scientists consider it a fundamental law of nature that lepton number is conserved, meaning that the number of leptons and anti-leptons involved in an interaction should remain the same before and after the interaction occurs.

    Scientists think that, just after the big bang, the universe should have contained equal amounts of matter and antimatter. The two types of particles should have interacted, gradually canceling one another until nothing but energy was left behind. Somehow, that’s not what happened.

    Finding out that lepton number is not conserved would open up a loophole that would allow for the current imbalance between matter and antimatter. And neutrino interactions could be the place to find that loophole.

    Neutrinoless double-beta decay

    Scientists are looking for lepton number violation in a process called double beta decay, says SLAC theorist Alexander Friedland, who specializes in the study of neutrinos.

    In its common form, double beta decay is a process in which a nucleus decays into a different nucleus and emits two electrons and two antineutrinos. This balances leptonic matter and antimatter both before and after the decay process, so it conserves lepton number.

    If neutrinos are their own antiparticles, it’s possible that the antineutrinos emitted during double beta decay could annihilate one another and disappear, violating lepton number conservation. This is called neutrinoless double beta decay.

    Such a process would favor matter over antimatter, creating an imbalance.

    “Theoretically it would cause a profound revolution in our understanding of where particles get their mass,” Friedland says. “It would also tell us there has to be some new physics at very, very high energy scales—that there is something new in addition to the Standard Model we know and love.”

    Standard Model
    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.

    It’s possible that neutrinos and antineutrinos are different, and that there are two neutrino and anti-neutrino states, as called for in Dirac’s equation. The two missing states could be so elusive that physicists have yet to spot them.

    But spotting evidence of neutrinoless double beta decay would be a sign that Majorana had the right idea instead—neutrinos and antineutrinos are the same.

    “These are very difficult experiments,” de Gouvêa says. “They’re similar to dark matter experiments in the sense they have to be done in very quiet environments with very clean detectors and no radioactivity from anything except the nucleus you’re trying to study.”

    Physicists are still evaluating their understanding of the elusive particles.

    “There have been so many surprises coming out of neutrino physics,” says Reina Maruyama, a professor at Yale University associated with the CUORE neutrinoless double beta decay experiment.

    CUORE experiment
    CUORE neutrinoless double beta decay experiment at Gran Sasso in Italy.

    “I think it’s really exciting to think about what we don’t know.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 10:48 am on November 9, 2015 Permalink | Reply
    Tags: Antimatter, , , ,   

    From BNL: “Physicists Measure Force that Makes Antimatter Stick Together” 

    Brookhaven Lab

    November 4, 2015
    Karen McNulty Walsh, (631) 344-8350
    Peter Genzer, (631) 344-3174

    First ever measurement of antiproton interactions that make possible the existence of antimatter nuclei

    Zhengqiao Zhang, a graduate student from the Shanghai Institute of Applied Physics, with STAR physicist Aihong Tang at the STAR detector of the Relativistic Heavy Ion Collider (RHIC).

    Peering at the debris from particle collisions that recreate the conditions of the very early universe, scientists have for the first time measured the force of interaction between pairs of antiprotons. Like the force that holds ordinary protons together within the nuclei of atoms, the force between antiprotons is attractive and strong.

    The experiments were conducted at the Relativistic Heavy Ion Collider (RHIC), a U.S. Department of Energy Office of Science User Facility for nuclear physics research at DOE’s Brookhaven National Laboratory.


    The findings, published in the journal Nature, could offer insight into larger chunks of antimatter, including antimatter nuclei previously detected at RHIC, and may also help scientists explore one of science’s biggest questions: why the universe today consists mainly of ordinary matter with virtually no antimatter to be found.

    “The Big Bang—the beginning of the universe—produced matter and antimatter in equal amounts. But that’s not the world we see today. Antimatter is extremely rare. It’s a huge mystery!” said Aihong Tang, a Brookhaven physicist involved in the analysis, which used data collected by RHIC’s STAR detector.

    BNL Star
    STAR detetctor

    “Although this puzzle has been known for decades and little clues have emerged, it remains one of the big challenges of science. Anything we learn about the nature of antimatter can potentially contribute to solving this puzzle.”

    RHIC is the perfect place to study antimatter because it’s one of the few places on Earth that is able to create the elusive stuff in abundant quantities. It does this by slamming the nuclei of heavy atoms such as gold into one another at nearly the speed of light. These collisions produce conditions very similar to those that filled the universe microseconds after the Big Bang—with temperatures 250,000 times hotter than the center of the sun in a speck the size of a single atomic nucleus. All that energy packed into such a tiny space creates a plasma of matter’s fundamental building blocks, quarks and gluons, and thousands of new particles—matter and antimatter in equal amounts.

    “We are taking advantage of the ability to produce ample amounts of antimatter so we can conduct this study,” said Tang.

    The STAR collaboration has previous experience detecting and studying rare forms of antimatter—including anti-alpha particles, the largest antimatter nuclei ever created in a laboratory, each made of two antiprotons and two antineutrons. Those experiments gave them some insight into how the antiprotons interact within these larger composite objects. But in that case, “the force between the antiprotons is a convolution of the interactions with all the other particles,” Tang said. “We wanted to study the simple interaction of unbound antiprotons to get a ‘cleaner’ view of this force.”

    To do that, they searched the STAR data from gold-gold collisions for pairs of antiprotons that were close enough to interact as they emerged from the fireball of the original collision.

    A new measurement by RHIC’s STAR collaboration reveals that the force between antiprotons (p) is attractive and strong—just like the force that holds ordinary protons (p) together within the nuclei of atoms.

    “We see lots of protons, the basic building blocks of conventional atoms, coming out, and we see almost equal numbers of antiprotons,” said Zhengqiao Zhang, a graduate student in Professor Yu-Gang Ma’s group from the Shanghai Institute of Applied Physics of the Chinese Academy of Sciences, who works under the guidance of Tang when at Brookhaven. “The antiprotons look just like familiar protons, but because they are antimatter, they have a negative charge instead of positive, so they curve the opposite way in the magnetic field of the detector.”

    “By looking at those that strike near one another on the detector, we can measure correlations in certain properties that give us insight into the force between pairs of antiprotons, including its strength and the range over which it acts,” he added.

    The scientists found that the force between antiproton pairs is attractive, just like the strong nuclear force that holds ordinary atoms together. Considering they’d already discovered bound states of antiprotons and antineutrons—those antimatter nuclei—this wasn’t all that surprising. When the antiprotons are close together, the strong force interaction overcomes the tendency of the like (negatively) charged particles to repel one another in the same way it allows positively charged protons to bind to one another within the nuclei of ordinary atoms.

    In fact, the measurements show no difference between matter and antimatter in the way the strong force behaves. That is, within the accuracy of these measurements, matter and antimatter appear to be perfectly symmetric. That means, at least with the precision the scientists were able to achieve, there doesn’t appear to be some asymmetric quirk of the strong force that can account for the continuing existence of matter in the universe and the scarcity of antimatter today.

    But the scientists point out that we wouldn’t know that if they hadn’t done these experiments.

    “There are many ways to test for matter/antimatter asymmetry, and there are more precise tests, but in addition to precision, it’s important to test it in qualitatively different ways. This experiment was a qualitatively new test,” said Richard Lednický, a STAR scientist from the Joint Institute for Nuclear Research, Dubna, and the Institute of Physics, Czech Academy of Sciences, Prague.

    “The successful implementation of the technique used in this analysis opens an exciting possibility for exploring details of the strong interaction between other abundantly produced particle species,” he said, noting that RHIC and the Large Hadron Collider (LHC) are ideally suited for these measurements, which are difficult to assess by other means.

    This research was funded primarily by the DOE Office of Science (NP) and by other funders for STAR listed here.

    See the full article here .

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

  • richardmitnick 10:13 am on May 27, 2015 Permalink | Reply
    Tags: Antimatter, , , , ,   

    From LLNL: “Lawrence Livermore scientists move one step closer to mimicking gamma-ray bursts” 

    Lawrence Livermore National Laboratory

    May. 26, 2015

    Anne M Stark
    stark8@llnl.gov (link sends e-mail)

    The Centaurus A galaxy, at a distance of about 12 million light years from Earth, contains a gargantuan jet blasting away from a central supermassive black hole. In this image, red, green and blue show low, medium and high-energy X-rays. Photo courtesy NASA/CXC/U. Birmingham/M. Burke et al.

    Using ever more energetic lasers, Lawrence Livermore researchers have produced a record high number of electron-positron pairs, opening exciting opportunities to study extreme astrophysical processes, such as black holes and gamma-ray bursts.

    By performing experiments using three laser systems — Titan at Lawrence Livermore, Omega-EP at the Laboratory for Laser Energetics (link is external) and Orion at Atomic Weapons Establishment (link is external) (AWE) in the United Kingdom — LLNL physicist Hui Chen and her colleagues created nearly a trillion positrons (also known as antimatter particles). In previous experiments at the Titan laser in 2008, Chen’s team had created billions of positrons.

    Positrons, or “anti-electrons,” are anti-particles with the same mass as an electron but with opposite charge. The generation of energetic electron-positron pairs is common in extreme astrophysical environments associated with the rapid collapse of stars and formation of black holes. These pairs eventually radiate their energy, producing extremely bright bursts of gamma rays. Gamma-ray bursts (GRBs) are the brightest electromagnetic events known to occur in the universe and can last from ten milliseconds to several minutes. The mechanism of how these GRBs are produced is still a mystery.

    In the laboratory, jets of electron-positron pairs can be generated by shining intense laser light into a gold foil. The interaction produces high-energy radiation that will traverse the material and create electron-positron pairs as it interacts with the nucleus of the gold atoms. The ability to create a large number of positrons in a laboratory, by using energetic lasers, opens the door to several new avenues of antimatter research, including the understanding of the physics underlying extreme astrophysical phenomena such as black holes and gamma-ray bursts.

    “The goal of our experiments was to understand how the flux of electron-positron pairs produced scales with laser energy,” said Chen, who along with former Lawrence Fellow Frederico Fiuza (now at SLAC National Accelerator Laboratory), co-authored the article appearing in the May 18 edition of Physical Review Letters.

    “We have identified the dominant physics associated with the scaling of positron yield with laser and target parameters, and we can now look at its implication for using it to study the physics relevant to gamma-ray bursts,” Chen said. “The favorable scaling of electron-positron pairs with laser energy obtained in our experiments suggests that, at a laser intensity and pulse duration comparable to what is available, near-future 10-kilojoule-class lasers would provide 100 times higher antimatter yield.”

    The team used these scaling results obtained experimentally together with first-principles simulations to model the interaction of two electron positron pairs for future laser parameters. “Our simulations show that with upcoming laser systems, we can study how these energetic pairs of matter-antimatter convert their energy into radiation,” Fiuza said. “Confirming these predictions in an experiment would be extremely exciting.”

    Antimatter research could reveal why more matter than antimatter survived the Big Bang at the start of the universe. There is considerable speculation as to why the observable universe is apparently almost entirely matter, whether other places are almost entirely antimatter, and what might be possible if antimatter could be harnessed. Normal matter and antimatter are thought to have been in balance in the very early universe, but due to an “asymmetry” the antimatter decayed or was annihilated, and today very little antimatter is seen.

    In future work, the researchers plan to use the National Ignition Facility [NIF] to conduct laser antimatter experiments to study the physics of relativistic pair shocks in gamma-ray bursts by creating even higher fluxes of electron-positron pairs.


    The research was funded by LLNL’s Laboratory Directed Research and Development program and the LLNL Lawrence Fellowship.

    Chen and Fiuza were joined by Anthony Link, Andy Hazi, Matt Hill, David Hoarty, Steve James, Shaun Kerr, David Meyerhofer, Jason Myatt, Jaebum Park, Yasuhiko Sentoku and Jackson Williams from LLNL, AWE, University of Alberta, University of Rochester and University of Nevada, Reno.

    See the full article here.

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  • richardmitnick 2:11 pm on May 12, 2015 Permalink | Reply
    Tags: Antimatter, ,   

    From Nature: “Rogue antimatter found in thunderclouds” 

    Nature Mag

    12 May 2015
    Davide Castelvecchi

    Lightning is only the most visible product of clouds’ intense electric fields.

    When Joseph Dwyer’s aeroplane took a wrong turn into a thundercloud, the mistake paid off: the atmospheric physicist flew not only through a frightening storm but also into an unexpected — and mysterious — haze of antimatter.

    Although powerful storms have been known to produce positrons — the antimatter versions of electrons — the antimatter observed by Dwyer and his team cannot be explained by any known processes, they say. “This was so strange that we sat on this observation for several years,” says Dwyer, who is at the University of New Hampshire in Durham.

    The flight took place six years ago, but the team is only now reporting the result (J. R. Dwyer et al. J. Plasma Phys.; in the press). “The observation is a puzzle,” says Michael Briggs, a physicist at the NASA Marshall Space Flight Center in Huntsville, Alabama, who was not involved in the report.

    A key feature of antimatter is that when a particle of it makes contact with its ordinary-matter counterpart, both are instantly transformed into other particles in a process known as annihilation. This makes antimatter exceedingly rare. However, it has long been known that positrons are produced by the decay of radioactive atoms and by astrophysical phenomena, such as cosmic rays plunging into the atmosphere from outer space. In the past decade, research by Dwyer and others has shown that storms also produce positrons, as well as highly energetic photons, or γ-rays [read: gamma rays].

    It was to study such atmospheric γ-rays that Dwyer, then at the Florida Institute of Technology in Melbourne, fitted a particle detector on a Gulfstream V, a type of jet plane typically used by business executives. On 21 August 2009, the pilots turned towards what looked, from its radar profile, to be the Georgia coast. “Instead, it was a line of thunderstorms — and we were flying right through it,” Dwyer says. The plane rolled violently back and forth and plunged suddenly downwards. “I really thought I was going to die.”

    During those frightening minutes, the detector picked up three spikes in γ-rays at an energy of 511 kiloelectronvolts, the signature of a positron annihilating with an electron.

    Each γ-ray spike lasted about one-fifth of a second, Dwyer and his collaborators say, and was accompanied by some γ-rays of slightly lower energy. The team concluded that those γ-rays had lost energy as a result of travelling some distance and calculated that a short-lived cloud of positrons, 1–2 kilometres across, had surrounded the aircraft. But working out what could have produced such a cloud has proved hard. “We tried for five years to model the production of the positrons,” says Dwyer.

    Electrons discharging from charged clouds accelerate to close to the speed of light, and can produce highly energetic γ-rays, which in turn can generate an electron–positron pair when they hit an atomic nucleus. But the team did not detect enough γ-rays with sufficient energy to do this.

    Another possible explanation is that the positrons originated from cosmic rays, particles from outer space that collide with atoms in the upper atmosphere to produce short-lived showers of highly energetic particles, including γ-rays. “There’s always like a light drizzle of positrons,” says Dwyer. In principle, there could be some mechanism that steered the positrons towards the plane, he says. But the motion of positrons would have created other types of radiation, which the team did not see.

    The team’s data are a “cast-iron signature” of positrons, says Jasper Kirkby, a particle physicist who heads an experiment investigating a possible link between cosmic rays and cloud formation at the CERN particle-physics laboratory near Geneva, Switzerland. But “the interpretation needs to be nailed down”. In particular, he says, the team’s estimate of the size of the positron cloud is not convincing.

    If Kirkby is right, and the cloud was smaller than Dwyer’s team estimates, that could imply that the positrons were annihilating only in the immediate vicinity of the aircraft, or even on the craft itself. The wings could have become charged, producing extremely intense electric fields around them and initiating positron production, says Aleksandr Gurevich, an atmospheric physicist at the Lebedev Physical Institute in Moscow.

    To answer these and other questions, Dwyer needs fresh observations of the innards of thunderclouds. To that end, he and others are sending balloons straight into the most violent storms, and the US National Science Foundation even plans to fly a particle detector on an A-10 ‘Warthog’ — an armoured anti-tank plane that could withstand the extreme environment. “The insides of thunder­storms are like bizarre landscapes that we have barely begun to explore,” says Dwyer.

    See the full article here.

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  • richardmitnick 6:46 am on March 7, 2015 Permalink | Reply
    Tags: , Antimatter, , ,   

    From ScienceNews: “Sam Ting tries to expose dark matter’s mysteries” 

    ScienceNews bloc


    March 6, 2015
    Andrew Grant

    Physics Nobel laureate’s space-based detector is analyzing billions of cosmic rays

    EYES ON THE INVISIBLE PRIZE Designed to detect cosmic rays, the Alpha Magnetic Spectrometer cruises above Earth on the International Space Station.


    In the near vacuum of outer space, each rare morsel of matter tells a story. A speedy proton may have been propelled by the shock wave of an exploding star. A stray electron may have teetered on the precipice of a black hole, only to be flung away in a powerful jet of searing gas.

    Since 2011, the International Space Station has housed an experiment that aims to decipher those origin stories. The Alpha Magnetic Spectrometer has already cataloged more than 60 billion protons, electrons and other spaceborne subatomic particles, known as cosmic rays, as they zip by.

    Other experiments sample the shower of particles produced when cosmic rays strike atoms and molecules in Earth’s atmosphere. But the spectrometer scrutinizes pristine cosmic rays — some of which have traveled undisturbed over millions of light-years — from its perch some 400 kilometers above Earth. The Alpha Magnetic Spectrometer is by far the most sensitive cosmic ray detector ever to fly in space, and with a price tag of about $2 billion, it’s also the most expensive.

    The detector’s unprecedented particle census could unmask the identity of dark matter, the mysterious, invisible substance that is five times as abundant in the universe as ordinary matter. Some of the cosmic rays snatched by the instrument may have been produced by particles of dark matter colliding and annihilating each other in the center of the galaxy.

    The spectrometer could also help scientists determine why planets, stars and other structures in the universe are made of matter rather than antimatter. Particles of antimatter have the opposite charge as their matter counterparts but are identical in nearly every other way. It’s uncertain why most of the antimatter particles disappeared just after the Big Bang 13.8 billion years ago. Physicists would love to discover primordial antimatter to test their theories on what hastened its demise.

    Sam Ting

    Nearly four years into the mission, the Alpha Magnetic Spectrometer is delivering precise data and arguably providing a few hints about the nature of dark matter. But it’s unclear whether the mission will ever deliver on its ambitious goals. Cosmic rays are charged particles that get whipped around by magnetic fields, so they don’t travel in straight lines and cannot be traced back to their source. To pin the origin of particular cosmic rays to dark matter, scientists will have to rule out every other possible explanation. Critics say the chances of identifying dark matter are very slim. And finding primordial antimatter, they say, is nearly impossible.

    Such criticism barely registers with the mission’s leader, particle physicist Samuel Ting. The 79-year-old Nobel laureate has made a career of designing elegant experiments and, despite frequent opposition, successfully lobbying to get them built. Then he has patiently collected and analyzed data, meticulous to the extreme, before revealing the often-impressive findings. Though results may come later than most scientists would prefer, Ting is confident that conducting a powerful particle physics experiment in space will expand scientists’ understanding of the cosmos.

    Full focus

    Ting’s home base these days is at CERN, the European physics laboratory outside Geneva that partially funds the Alpha Magnetic Spectrometer and is home to the mission’s command center. But on one afternoon in December, Ting is at MIT, where he still runs a lab. His office is housed in a building marked with a capital J that honors his Nobel Prize–winning discovery, the J particle. The alleged reason for Ting’s U.S. visit was to meet with a contractor to discuss renovating his Cambridge, Mass., home. But the contractor confab was brief. For Ting, matters outside of physics take a backseat.

    “You really can’t get into this field without thinking this is the most important thing in your life,” Ting says.

    Two high-definition monitors on his office wall reinforce his obsession. One shows a live feed from the space station, a grainy black-and-white image capturing the spectrometer and our imperceptibly spinning planet below. The other screen plays a computer reconstruction of the instrument in action. In nearly real time, cosmic rays pass through its magnet, triggering a slate of sensors that determine the particles’ identity, energy and trajectory.

    Ting doesn’t have a background in astrophysics, but he has plenty of experience sorting through a glut of particles to find really cool stuff.

    He pulls up a 1965 New York Times article on his computer. The article describes Ting’s first major discovery, when he, Leon Lederman (who won the 1988 Nobel Prize in physics) and colleagues produced and detected antimatter nuclei for the first time. (A team at CERN made a similar discovery soon after.) It’s difficult enough to observe single particles of antimatter because they disappear in a burst of energy when they encounter ordinary matter. Ting and Lederman managed to observe bound pairs of antimatter particles, called antideuterons, in a particle accelerator at Brookhaven National Laboratory in Upton, N.Y.

    Ting’s childlike curiosity quickly comes across as he describes the possibility that antideuterons and other large chunks of antimatter, relics of the first moments after the Big Bang, could be drifting in the cosmos, waiting to be found. But beneath the inquisitiveness is also an extreme confidence, even an arrogance, that he alone knows the way to probe the big questions.

    Those qualities were on display in the early 1970s when Ting became interested in quarks, tiny parcels that compose such particles as protons and neutrons. Physicists had proposed and discovered evidence for three kinds of quarks. But Ting, eager to unravel every detail about matter’s makeup, joined a group of physicists who wondered whether there were other quark varieties. He proposed colliding particles at high energies, which would create short-lived matter that ultimately decayed into electrons and their antimatter counterparts, positrons. By analyzing the electrons and positrons, he could determine the composition of the intermediate particles.

    Ting says many physicists scoffed at his proposal; they believed that the three quarks could explain all the more complex particles in physics. Multiple labs turned him down before Brookhaven let him give it a try.

    In the summer of 1974, Ting and his team saw convincing signs of a new subatomic particle with an unusual composition. But Ting refused to release the data until he was sure everything was correct. He split his team into two groups that independently analyzed the data again and again. Only in November of that year, when a colleague at a meeting told Ting that particle physicist Burton Richter had seen the same signal at the Stanford Linear Accelerator Center, did Ting share his finding. The confirmation of a fourth quark, the charm, embedded in a particle that Ting called J and Richter called Psi earned Ting a share (with Richter) of the 1976 Nobel Prize in physics. Ting’s experimental design skill, combined with large doses of meticulousness, smarts and stubbornness, had netted him the ultimate physics honor. He was 40 years old.

    From there, Ting kept pursuing big projects. In the late 1980s, he organized a team to design a detector for the multibillion-dollar Superconducting  Super Collider, an 87-kilometer-around particle accelerator slated for construction near Waxahachie, Texas. Ting wanted to build a $750 million instrument; the U.S. Department of Energy said the detector should not cost more than $500 million. So Ting quit. “He was very determined to do it his way,” says Gary Sanders, a high-energy physicist and former Ting graduate student who was part of that team.

    In 1993, Congress dealt American physicists a devastating blow by canceling the Super Collider. Ting, however, had moved on. In 1994, he pitched perhaps the most ambitious project of his career.

    Like his first major experiment, it would hunt for antideuterons and other antimatter nuclei. And similar to his Nobel-winning research, it would use electrons and positrons as probes to identify undiscovered parent particles. Except instead of sorting through shrapnel created in carefully orchestrated particle collisions, he wanted to go after particles produced naturally in the universe. The Alpha Magnetic Spectrometer experiment would collect and analyze particles in space.

    Both NASA and the Department of Energy, the same agency that rejected Ting’s plan for the detector in Texas, pledged their support.

    From lab to liftoff

    Scientists have studied cosmic rays for a century in hope of learning about the objects that produce them. But Ting’s proposal offered the rare chance to create a robust census of cosmic rays from well above Earth’s meddlesome atmosphere. Most previous experiments took place on balloons, which fly only briefly and don’t leave the atmosphere, or on the ground, forcing scientists to analyze cascading showers of particles triggered by cosmic rays striking atoms in the atmosphere.

    Those past experiments still delivered some tantalizing results. In 1997, the High-Energy Antimatter Telescope, or HEAT, a cosmic ray detector tethered to a high-altitude balloon, revealed an unexpectedly high concentration of positrons in space. At the time, physicists didn’t know of many processes in the universe that could produce positrons, so theorists quickly came up with some ideas. The most intriguing possibility was that the positrons were created by particles of dark matter in the galaxy. Though the dark matter particles would be invisible, they would occasionally collide and annihilate each other to produce gamma radiation and detectable particles, including electrons and positrons. If these dark matter theories were correct, then a precise measurement of cosmic ray positrons would enable physicists to pin down the nature and mass of dark matter particles.

    But dark matter wasn’t the only explanation. Other theorists proposed positron-forming mechanisms that have far less relevance for deciphering the universe. Atop the list were pulsars — dense, rapidly spinning cores left over after massive stars explode. A pulsar’s rapid rotational speed generates an intense electromagnetic field strong enough to rip electrons from its surface. Those electrons interact with photons and create pairs of electrons and positrons. Calculations suggested that just one or two pulsars, which are difficult to detect, within hundreds of light-years of the solar system would be enough to litter Earth with positrons.

    Despite the intriguing quandary exposed by HEAT, some scientists doubted that the Alpha Magnetic Spectrometer could add much to the positron origin debate or resolve any big physics mysteries. But Ting was determined to see his project fly. He assembled a 16-country collaboration to divide the work and the ballooning costs. When the 2003 explosion of the space shuttle Columbia led NASA to rescind its offer of a ride to the space station, Ting lobbied members of Congress, teasing at the wonders that could be hidden in cosmic rays and stressing the International Space Station’s not-so-stellar reputation for housing serious science.

    “If you told Sam that to get what he wanted he had to win the Indy 500, he’d become the world’s best race car driver,” says Richard Milner, the director of MIT’s Laboratory for Nuclear Science, who oversees Ting’s group. Ting wouldn’t let up on government officials in Washington, even as many of his collaborators focused on other projects.

    He was very persuasive, says Kay Bailey Hutchison, at the time a U.S. Senator from Texas. She says Ting convinced her and others that the mission was worth the cost and safety concerns of extending the beleaguered shuttle program. “He’s such a visionary,” she says. She was inspired enough to switch appropriations subcommittees to find funding for the project. In October 2008, President George W. Bush signed a bill adding shuttle flights so that the Alpha Magnetic Spectrometer would hitch a ride on one of them. “Without [Ting’s] absolute unwillingness to give up, we would not have gotten it,” Hutchison says.

    By the time Ting’s brainchild reached the space station in May 2011, a couple of space-based cosmic ray experiments had beaten his spectrometer to the punch. In 2008, PAMELA, a cosmic ray detector attached to a Russian reconnaissance satellite, revealed the same positron excess hinted at by HEAT. NASA’s Fermi Gamma-ray Space Telescope, which also carries a cosmic ray detector, came up with similar results in 2011. Neither probe discerned the source of the positrons, however.

    PAMELA Cosmic Ray Detector

    NASA Fermi Telescope
    NASA’s Fermi Gamma-ray Space Telescope

    POSITRON PUZZLE The positron measurements (as a fraction of the total number of positrons and electrons) made by the Alpha Magnetic Spectrometer (AMS) are shown with solid red circles in this graph. Measurements made by previous instruments (see legend) had much larger margins of error, as indicated by the lines above and below each data point. [Source: L. Accardo et al/Phys. Rev. Lett. 2014]

    Ting’s instrument began its cosmic ray survey almost immediately after installation, collecting as much data in one day as PAMELA did in 50. It sifted through positively charged particles, most of which are protons, and picked out the more valuable positrons. Ting, true to form, took his time before releasing the first results. “I doubt in the next 20 years anyone will be able to repeat the experiment,” he says. “There’s nobody to check us. It’s of the utmost importance to get it correct.”

    Ting broke his silence with a news conference at CERN in April 2013. After again employing two separate teams to comb through the data, he confirmed the positron excess detected by HEAT, PAMELA and Fermi (SN: 5/4/13, p. 14). Analyzing the properties of 6.8 million positrons and electrons, Ting’s team found that the number of positrons keeps rising as the particle energies increase. The clear excess of positrons, Ting said, reinforces that something relatively nearby must be producing them. He pushed the dark matter explanation but admitted it was not the only possibility.

    Ting returned for another news conference in September. This time, after poring over 10.9 million positrons and electrons, Ting’s team pinpointed the energy, about 275 billion electron volts, at which the concentration of positrons stops increasing (see graph above). That’s an interesting number, says Peter McIntyre, a high-energy physicist at Texas A&M University in College Station, because it indicates that the mass of hypothetical dark matter particles limits the energy of the positrons they can produce. Theorists could use the peak positron energy to estimate dark matter’s mass. But again, the experiment did not come close to proving that dark matter actually produced the positrons.


    X-ray: NASA/CXC/Univ. of Toronto/M. Durant et al; Optical: DSS/Davide De Martin

    Pulsars, like the Vela pulsar located about 1,000 light-years away, are rapidly spinning dense cores of former stars. Nearby pulsars may produce the unexplained excess of positrons detected by the Alpha Magnetic Spectrometer and other experiments.
    What is it?

    Dark matter A form of matter that accounts for most of the mass in a galaxy but does not consist of the ordinary kind of matter found on Earth.

    Pulsar A dense, rapidly spinning remnant of a star that was initially much more massive than the sun.
    How would it produce positrons?

    Dark matter In theory, two dark matter particles can collide and annihilate each other to produce electrons and positrons.

    Pulsar The collision of photons with speedy electrons ripped from a pulsar’s surface by intense electromagnetic fields produces electrons and positrons.

    What are the implications?

    Dark matter Finding positrons from dark matter would help scientists to determine the type and mass of dark matter particles, resolving a decades-long mystery.

    Pulsar Positrons from pulsars would reveal something about particles that pulsars create. But it would not lead to big-picture understanding of the universe.

    In fact, some physicists argue that the Alpha Magnetic Spectrometer, despite its unmatched particle-detecting prowess, can never definitively distinguish between dark matter annihilation, pulsars or a yet-to-be-discovered process that might be producing those surplus shards of antimatter.

    “A pulsar could explain any observation that AMS could ever make,” says Gregory Tarlé, a particle astrophysicist at the University of Michigan in Ann Arbor. No matter what the positron data, physicists will not be able to definitively isolate the alleged signal of dark matter, he argues.

    Katherine Freese, a theoretical astrophysicist at the Nordic Institute for Theoretical Physics in Stockholm, agrees that conclusively proving dark matter from positrons will be very difficult. “My bet is on pulsars,” she says.

    Other experiments also suggest that AMS has a slim chance of making a compelling case for dark matter. In a study posted online in January at arXiv.org, physicists pored over Fermi telescope measurements to look for gamma radiation, which should also be produced when dark matter particles annihilate each other. The data ruled out most dark matter collision mechanisms proposed by theorists. And in December, scientists with the Planck satellite announced that their survey of the universe’s most ancient light revealed no signs of detritus from colliding dark matter, which if self-annihilating now also should have been when the cosmos was young (SN: 12/27/14, p. 11).

    ESA Planck

    Ting says he pays about as much attention to other experiments as he does to his critics. He monitors the scientific literature, but doesn’t put much stock in blanket conclusions based on one set of data. “I learned a long time ago: Only look at your own experiment,” he says.

    He expects to learn more by studying positrons at higher energies. If the mass of a dark matter particle is, say, one trillion electron volts, then it probably wouldn’t produce positrons with more than a quarter of that energy. So if the positron concentration falls off a cliff after the newly identified peak, Ting says, that would suggest a dark matter origin. Pulsars, on the other hand, should produce positrons with a spectrum of energies that wouldn’t drop so precipitously.

    Within the next year or two, the AMS team will release its first analysis of antiprotons, antimatter particles that Ting says are too heavy to be manufactured by pulsars but should be produced in dark matter collisions. Ting calls the preliminary results “intriguing.” But of course, he won’t offer more until all the cross-checks are complete.

    He’s confident that future measurements will allow him to definitively pin down the origin of positrons, whether from dark matter or something else.

    Even if the dark matter picture remains muddled, there is a possibility that AMS will detect primordial antimatter. One of the biggest mysteries in physics is why matter won out in a universe that presumably began with equal parts of matter and antimatter. Ting hopes to find complex antimatter — perhaps antihelium (two antiprotons and two antineutrons) or antideuterons — that was forged just after the Big Bang. Tarlé and other scientists say the chances of detecting these antinuclei are extremely low because the antimatter would have to navigate through the matter-rich galaxy and solar system without being destroyed.

    Ting is undeterred. Gathering insights about the cosmos takes time. Anticipating that funding will run as long as the space station operates, Ting simply wants to see what nature throws at him. “If you don’t look,” he says, “you do not know.”

    See the full article here.

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  • richardmitnick 3:50 pm on November 20, 2014 Permalink | Reply
    Tags: Antimatter, , ,   

    From NOVA: “Does Antimatter Fall Up or Down?” 



    Wed, 19 Nov 2014
    Matthew Francis

    There are two kinds of matter in the universe: ordinary matter, which makes up all the stuff of everyday life, and antimatter, a sort of mirror image of matter. When the two meet, they annihilate in a flash of energy. It’s our good fortune that, in the early Universe, there was just a tiny bit more matter than antimatter, leaving us with a cosmos almost empty of stuff that could destroy us. Otherwise, we wouldn’t be here to ask what, exactly, antimatter is.

    Here’s what we know: Anti-electrons, known as positrons, are nearly identical to electrons, but instead of being negatively charged they are positively charged. The same goes for other antimatter counterparts: antiprotons are negatively charged and made of the antiquarks corresponding to the quarks in normal protons.

    But physicists think that the other properties of the particles should be the same. Each antimatter particle should have the same mass, spin, and equal but opposite electric charge, and other important properties. But that “should” hides something interesting: In some cases, we simply don’t know the fundamental properties of an antiparticle, because it’s much harder to experiment on antimatter than on matter. For example, it’s possible antimatter doesn’t feel gravity in the same way matter does.

    In other words, antimatter might fall up.

    Up, up and away. Credit: Flickr user Shaun Fisher, adapted under a Creative Commons license.

    Now, that’s a very unlikely possibility. As far as we can tell, the differences between matter and antimatter are confined to interactions involving the weak nuclear force, one of the four fundamental interactions in nature. “Everybody including us would be shocked if we were actually to discover any significant differences” between matter and antimatter, says Joel Fajans, physics professor at the University of California at Berkeley who is studying how gravity affects antimatter. It may be a long shot, but if any experiment showed measurably different behavior, “it would really revolutionize our thinking about how the universe behaves.”

    The effort isn’t easy, though. First, there’s a lot more matter than antimatter in the universe, so any differences in behavior would be very difficult to observe and measure. Second, experiments must be done quickly, before antimatter runs into ordinary matter and everything goes kablooie.

    As a result, we only have rough estimates of some basic properties of antimatter—and some we haven’t measured experimentally at all. Take, for instance, a fundamental quantity called the positron inertial mass, a measure of how difficult it is to accelerate a positron. (The inertial mass is the “m” in E = mc2.) When an electron meets a positron and they annihilate, they give off gamma rays. Researchers can measure the spectrum of gamma rays and figure out how much m was needed to make the E they see. From that, physicists have concluded that the inertial mass of the electron and the positron are very close to equal, if not identical.

    We’d like to do better than “very close,” though. To understand antimatter fully, we need measurements as precise and accurate as our measurements of matter, and that’s a hard goal. Similarly, we don’t yet have precision measurements for the electric charge of the positron and the antiproton, though Fajans and his collaborators have shown that their charges are equal and opposite. This experiment, like many modern antimatter tests, involves atoms of antihydrogen, which are made of a single antiproton and positron. To see if antimatter falls up, Fajans and his colleagues at the ALPHA experiment use strong magnetic fields to trap antihydrogen atoms in a sort of virtual bottle.


    “If we very slowly turn off the ‘walls,’ the magnetic confining field, [the antihydrogen atoms] eventually get out,” Fajans says. “If we do it slowly enough, even though the effects for gravity are subtle, there’ll be a tendency for them to fall downwards presumably, or upwards if things really are weird.” So far, the results aren’t precise enough to distinguish between falling up and falling down, but that’s merely a sign of how inherently difficult the experiment is.

    However, there’s strong indirect evidence that antimatter behaves gravitationally like matter. According to the weak equivalence principle—a key part of the general theory of relativity [Albert Einstein]—the gravitational mass is precisely the same as inertial mass,. (The strong equivalence principle relates to the mathematical structure of gravitational theory.) Researchers have tested the weak equivalence principle to high precision for ordinary matter, using delicate balances capable of detecting tiny variations in gravitational attraction.

    While we can’t yet make the same lab equipment out of anti-atoms to test the weak equivalence principle for antimatter, we know that protons and neutrons contain “virtual” pairs of quarks and antiquarks, which don’t have independent existence but contribute to the particles’ overall structure. As Fajans points out, “Different isotopes have different ratios of virtual antimatter particles, and it’s very well known that there are no anomalies there. If virtual antimatter particles gravitate differently, that would have been noticed in all of these experiments.”

    There are also theoretical reasons to suspect gravity doesn’t work in reverse for antimatter. Raquel Ribeiro, a physicist at Case Western Reserve University, works on possible modifications to general relativity that could solve the riddle of cosmic acceleration. But Ribeiro doesn’t include antigravity antimatter, “because it leads to a number of physical violations of energy principles,” she says. While naively all it would take is turning mass from a positive into a negative number, the reality for stars and other astronomical bodies would be “some serious instabilities in the system.”

    Theory is a good guide, but we still need experiments to see if our theories are right or if they need modification. In fact, theory is so far unable to solve one of the deepest mysteries in physics. “There simply isn’t enough antimatter in the universe,” says Fajans, “and there isn’t a universally accepted reason as to why matter in the universe predominates by such a large ratio over antimatter. The Big Bang should have created exactly equal amounts of matter and antimatter.”

    That’s one reason why researchers will keep studying antimatter, and why some hold out hope for finding even small differences in the behavior of matter and antimatter. Maybe we won’t see antihydrogen falling up, but even a subtle deviation from expectations could open up a new world of possibilities. After all, that’s what the initial discovery of antimatter did.

    See the full article here.

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  • richardmitnick 5:20 pm on October 28, 2014 Permalink | Reply
    Tags: Antimatter, B meson, , , , , , Syracuse University   

    From Syracuse University: “Syracuse Physicists Closer to Understanding Balance of Matter, Antimatter” 

    Syracuse University

    Syracuse University

    Physicists in the College of Arts and Sciences have made important discoveries regarding Bs meson particles—something that may explain why the universe contains more matter than antimatter.

    Sheldon Stone

    Distinguished Professor Sheldon Stone and his colleagues recently announced their findings at a workshop at CERN in Geneva, Switzerland. Titled Implications of LHCb Measurements and Their Future Prospects, the workshop enabled him and other members of the Large Hadron Collider beauty (LHCb) Collaboration to share recent data results.

    CERN LHCb New

    The LHCb Collaboration is a multinational experiment that seeks to explore what happened after the Big Bang, causing matter to survive and flourish in the Universe. LHCb is an international experiment, based at CERN, involving more than 800 scientists and engineers from all over the world. At CERN, Stone heads up a team of 15 physicists from Syracuse.

    “Many international experiments are interested in the Bs meson because it oscillates between a matter particle and an antimatter particle,” says Stone, who heads up Syracuse’s High-Energy Physics Group. “Understanding its properties may shed light on charge-parity [CP] violation, which refers to the balance of matter and antimatter in the universe and is one of the biggest challenges of particle physics.”

    Scientists believe that, 14 billion years ago, energy coalesced to form equal quantities of matter and antimatter. As the universe cooled and expanded, its composition changed. Antimatter all but disappeared after the Big Bang (approximately 3.8 billion years ago), leaving behind matter to create everything from stars and galaxies to life on Earth.

    “Something must have happened to cause extra CP violation and, thus, form the universe as we know it,” Stone says.

    He thinks part of the answer lies in the Bs meson, which contains an antiquark and a strange quark and is bound together by a strong interaction. (A quark is a hard, point-like object found inside a proton and neutron that forms the nucleus of an atom.)

    Enter CERN, a European research organization that operates the world’s largest particle physics laboratory.

    In Geneva, Stone and his research team—which includes Liming Zhang, a former Syracuse research associate who is now a professor at Tsinghua University in Beijing, China—have studied two landmark experiments that took place at Fermilab, a high-energy physics laboratory near Chicago, in 2009.

    The Large Hadron Collider at CERN

    The experiments involved the Collider Detector at Fermilab (CDF) and the DZero (D0), four-story detectors that were part of Fermilab’s now-defunct Tevatron, then one of the world’s highest-energy particle accelerators.

    “Results from D0 and CDF showed that the matter-antimatter oscillations of the Bs meson deviated from the standard model of physics, but the uncertainties of their results were too high to make any solid conclusions,” Stone says.

    He and Zhang had no choice but to devise a technique allowing for more precise measurements of Bs mesons. Their new result shows that the difference in oscillations between the Bs and anti-Bs meson is just as the standard model has predicted.

    Stone says the new measurement dramatically restricts the realms where new physics could be hiding, forcing physicists to expand their searches into other areas. “Everyone knows there is new physics. We just need to perform more sensitive analyses to sniff it out,” he adds.

    See the full article here.

    Syracuse University was officially chartered in 1870 as a private, coeducational institution offering programs in the physical sciences and modern languages. The university is located in the heart of Central New York, is within easy driving distance of Toronto, Boston, Montreal, and New York City. SU offers a rich mix of academic programs, alumni activities, and immersion opportunities in numerous centers in the U.S. and around the globe, including major hubs in New York City, Washington, D.C., and Los Angeles. The total student population at Syracuse University represents all 50 U.S. states and 123 countries.

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