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

    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.

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  • richardmitnick 2:25 pm on April 14, 2014 Permalink | Reply
    Tags: Antimatter, , ,   

    From PhysicsWorld.com: “Interferometry tips the scales on antimatter” 


    Apr 7, 2014

    Tushna Commissariat

    A new technique for measuring how antimatter falls under gravity has been proposed by researchers in the US. The team says that its device – based on cooling atoms of antimatter and making them interfere – could also help to test Einstein’s equivalence principle with antihydrogen – something that could have far-reaching consequences for cosmology. Finding even the smallest of differences between the behaviour of matter and antimatter could shine a light on why there is more matter than antimatter in the universe today, as well as help us to better understand the nature of the dark universe.

    Trapping potential: The ALPHA experiment at CERN

    Up or down?

    First detected at CERN in 1995, physicists have long wondered how antimatter is affected by gravity – does it fall up or down? Most theoretical and experimental work suggests that gravity probably acts in exactly the same way on antimatter as it does on matter. The problem is that antimatter is difficult to produce and study, meaning that no direct experimental measurements of its behaviour under gravity have been made to date.

    One big step forward took place last year, when researchers at the ALPHA experiment at CERN measured how long it takes atoms of antihydrogen – made up of a positron surrounding an antiproton – to reach the edges of a magnetic trap after it is switched off. Although ALPHA did not find any evidence of the antihydrogen responding differently to gravity, the team was able to rule out the possibility that antimatter responds much more strongly to gravity than matter.

    Alpha Collaboration’s Official image

    Waving matter

    Such experiments are hard to carry out, however – antimatter is difficult to produce on a large scale and it annihilates when it comes into contact with regular matter, making it difficult to trap and hold. The new interferometry technique – proposed by Holger Müller and colleagues at the University of California, Berkeley, and Auburn University in Alabama – exploits the fact that a beam of antimatter atoms can, like light, be split, sent along two paths and made to interfere, with the amount of interference depending on the phase shift between the two beams. The researchers say the light-pulse atom interferometer, which they plan to install at the ALPHA experiment, could work not only with almost any type of atom or anti-atom, but also with electrons and protons.

    In the proposed interferometer, the matter waves would be split and recombined using pulses of laser light. If an atom interacts with the laser beam, it will receive a “kick” from the momentum of a pair of photons, creating the split, explains Müller. By tuning the laser to the correct pulse energy, this process can be made to happen with a probability of 50%, sending the matter waves along either of the two arms of the interferometer. When the paths join again, the probability of detecting the anti-atom depends on the amplitude of the matter wave, which becomes a function of the phase shift.

    Annihilation danger?

    Müller adds that the phase shift depends on the acceleration due to gravity (g), the momentum of the photons (and so the magnitude of the kick) and the time interval between each laser pulse. Measuring the phase shift is therefore a way of measuring g, because the momentum and the time interval are both known. The biggest advantage of the technique is that the anti-atoms will not be in danger of annihilating because they will never come close to any mechanical objects, being moved with light and magnetic fields only.

    Müller’s idea is to combine two proven technologies: light-pulse atom interferometry and ALPHA’s method of producing antihydrogen using its Penning trap. He points out that the team’s proposed method does not assume availability of a laser resonant with the Lyman-alpha transition in hydrogen, which can be very difficult to build. To make the whole experiment even more efficient, the team has also developed what Müller describes as an “atom recycling method”, which allows the researchers to work with “realistic” atom numbers. “The atom is enclosed inside magnetic fields that prevent it from going away. Thus, an atom that hasn’t been hit by the laser on our first attempt has a chance to get hit later. This way, we can use almost every single atom – a crucial feat at a production rate of one every 15 minutes,” he explains. This would let ALPHA measure the gravitational acceleration of antihydrogen to a precision of 1%.

    Precise and accurate

    The team plans to build a demo set-up at Berkeley, which will work with regular hydrogen, and hopes to secure funding for this soon. Müller and colleagues are now also part of the APLHA collaboration. “The work at CERN will proceed in several steps,” he says. “The first is an up/down measurement telling [us] whether the antimatter will go up or down,” he says. This will be followed by a measurement of per-cent-level accuracy. Müller’s long-term aim is get to a precision of 10–6, which would be vastly superior to ALPHA’s measurement last year, which has an error bar of 102. ALPHA can currently trap and hold atoms at the rate of four each hour, but thanks to recent upgrades at its source of antiprotons – the ELENA ring – CERN could theoretically produce nearly 3000 atoms per month. In addition to ALPHA, the GBAR and AEgIS collaborations are also planning to measure gravity’s effects on antimatter.

    While Müller agrees that the gravitational behaviour of antimatter can be studied from experiments with normal matter, a direct observation is essential, and that is what Müller, the ALPHA collaboration and the other teams at CERN are keen to accomplish in the near future. “No matter how sound one’s theory, there is no substitute in science for a direct observation,” he says.

    See the full article here.

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  • richardmitnick 8:21 pm on November 26, 2013 Permalink | Reply
    Tags: Antimatter, , , , ,   

    From NASA/Chandra: “Bullet Cluster: Searching for Primordial Antimatter” 

    NASA Chandra

    This view of the Bullet Cluster, located about 3.8 billion light years from Earth, combines an image from NASA’s Chandra X-ray Observatory with optical data from the Hubble Space Telescope and the Magellan telescope in Chile. This cluster, officially known as 1E 0657-56, was formed after the violent collision of two large clusters of galaxies. It has become an extremely popular object for astrophysical research, including studies of the properties of dark matter and the dynamics of million-degree gas.

    Credit X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.
    Release Date October 30, 2008

    In the latest research, the Bullet Cluster has been used to search for the presence of antimatter leftover from the very early Universe. Antimatter is made up of elementary particles that have the same masses as their corresponding matter counterparts – protons, neutrons and electrons – but the opposite charges and magnetic properties.

    The optical image shows the galaxies in the Bullet Cluster and the X-ray image (red) reveals how much hot gas has collided. If some of the gas from either cluster has particles of antimatter, then there will be annihilation between the matter and antimatter and the X-rays will be accompanied by gamma rays.

    The observed amount of X-rays from Chandra and the non-detection of gamma rays from NASA’s Compton Gamma Ray Observatory show that the antimatter fraction in the Bullet Cluster is less than three parts per million. Moreover, simulations of the Bullet Cluster merger show that these results rule out any significant amounts of antimatter over scales of about 65 million light years, an estimate of the original separation of the two colliding clusters.

    See the full article here.

    Chandra X-ray Center, Operated for NASA by the Smithsonian Astrophysical Observatory
    Smithsonian Astrophysical Observatory

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  • richardmitnick 12:35 pm on June 18, 2013 Permalink | Reply
    Tags: Antimatter, , ,   

    From CERN: “New experiment to gain unparalleled insight into antimatter” 

    CERN New Masthead

    18 June 2013
    Katarina Anthony

    “At last week’s Research Board meeting, the Baryon Antibaryon Symmetry Experiment (BASE) was approved for installation at CERN. The collaboration will be setting up shop in the AD Hall this September with its first CERN-based experimental set-up. Using the novel double-Penning trap set-up developed at the University of Mainz, GSI Darmstadt and the Max Plank Institute for Nuclear Physics (Germany), the BASE team will be able to measure the antiproton magnetic moment with hitherto un’eachable part-per-billion precision.’

    CERN’s AD Hall: the new home of the BASE double Penning trap set-up (Image: CERN)

    ‘We constructed the first double-Penning trap at our companion facility in Germany, and made the first ever direct observations of single spin flips of a single proton,” says Stefan Ulmer from RIKEN, Japan, the spokesperson of the BASE collaboration. ‘We also recently demonstrated the first application of the double Penning trap technique with a single proton. This success means we are now ready to use the technique to measure the proton magnetic moment with ultra-high precision and to apply the technique to the antiproton.’”

    Layout of the new BASE collaboration set-up to be installed in the AD Hall (Image: BASE)

    See the full article here.

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  • richardmitnick 4:57 pm on April 30, 2013 Permalink | Reply
    Tags: , Antimatter, , , ,   

    From Symmetry: “Matter, antimatter, we all fall down—right?” 

    April 30, 2013
    Ashley WennersHerron

    Scientists perform the first direct investigation into how antimatter interacts with gravity.

    What goes up must come down, the saying goes. But things might work a little differently with antimatter.
    A CERN-based experiment has taken the first step in investigating exactly how antimatter interacts with gravity.

    Photo: CERN

    Atimatter particles should mimic those of matter particles. If it turns out that there is a difference, it will be a sign of dramatically new physics.
    CERN ALPHA NewSo far, no one has been able to test directly how antimatter interacts with gravity—but the ALPHA experiment has begun to try.

    The ALPHA experiment’s main purpose is to trap and study antihydrogen atoms, the antimatter partners of hydrogen atoms. The antihydrogen atoms are held in place inside a tube by magnetic forces. Physicists on ALPHA have trapped more than 500 antiatoms since 2010. They keep them in their trap for up to about 16 minutes. When they turn off their magnets, the antiatoms fall out of the trap. A highly sensitive detector tracks the antiatoms and records where they first come in contact with matter and annihilate.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 1:00 pm on April 4, 2013 Permalink | Reply
    Tags: Antimatter, , ,   

    From CERN at Quantum Diaries: “Grey matter confronted to dark matter” 


    April 4th, 2013
    Pauline Gagnon

    Pauline Gagnon

    “After 18 years spent building the experiment and nearly two years taking data from the International Space Station, the Alpha Magnetic Spectrometer or AMS-02 collaboration showed its first results on Wednesday to a packed audience at CERN. But Prof. Sam Ting, one of the 1976 Nobel laureates and spokesperson of the experiment, only revealed part of the positron energy spectrum measured so far by AMS-02.

    Positrons are the antimatter of electrons. Given we live in a world where matter dominates, it is not easy to explain where this excess of positrons comes from. There are currently two popular hypotheses: either the positrons come from pulsars or they originate from the annihilation of dark matter particles into a pair of electron and positron. To tell these two hypotheses apart, one needs to see exactly what happens at the high-energy end of the spectrum. But this is where fewer positrons are found, making it extremely difficult to achieve the needed precision. Yesterday, we learned that AMS-02 might indeed be able to reach the needed accuracy.

    The fraction of positrons (measured with respect to the sum of electrons and positrons) captured by AMS-02 as a function of their energy is shown in red. The vertical bars indicate the size of the uncertainty. The most important part of this spectrum is the high-energy part (above 100 GeV or 102) where the results of two previous experiments are also shown: Fermi in green and PAMELA in blue. Note that the AMS-02 precision exceeds the one obtained by the other experiments. The spectrum also extends to higher energy. The big question now is to see if the red curve will drop sharply at higher energy or not. More data is needed before the AMS-02 can get a definitive answer.

    Only the first part of the story was revealed yesterday. The data shown clearly demonstrated the power of AMS-02. That was the excellent news delivered at the seminar: AMS-02 will be able to measure the energy spectrum accurately enough to eventually be able to tell where the positrons come from.

    But the second part of the story, the punch line everyone was waiting for, will only be delivered at a later time. The data at very high energy will reveal if the observed excess in positrons comes from dark matter annihilation or from “simple” pulsars. How long will it take before the world gets this crucial answer from AMS-02? Prof. Ting would not tell. No matter how long, the whole scientific community will be waiting with great anticipation until the collaboration is confident their measurement is precise enough. And then we will know.

    If AMS-02 does manage to show that the positron excess has a dark matter origin, the consequences would be equivalent to discovering a whole new continent. As it stands, we observe that 26.8% of the content of the Universe comes in the form of a completely unknown type of matter called dark matter but have never been able to catch any of it. We only detect its presence through its gravitational effects. If AMS-02 can prove dark matter particles can annihilate and produce pairs of electrons and positrons, it would be a complete revolution.”

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  • richardmitnick 8:49 am on March 15, 2013 Permalink | Reply
    Tags: Antimatter, , , , ,   

    From CERN: “Still making tracks: Eighty Years of the Positron” 

    CERN New Masthead

    March 15, 2013
    Kelly Ann Izlar

    “Eighty years ago today, the journal Physical Review published a paper by physicist Carl Anderson announcing the discovery of the positron.


    The positron is the antimatter counterpart of the electron. The two particles have identical masses but opposite charges. When an electron and a positron interact, they annihilate in a burst of energy, producing two gamma rays.

    LEP at CERN

    In the early 1930s, Anderson and his mentor, Robert Millikan, were using a cloud chamber to measure high-energy cosmic rays.

    A cloud chamber’s sealed cavity contains a supersaturated vapour, usually water or alcohol, which condenses around ion trails left behind by fast-moving charged particles, allowing them to be seen as they pass through. Physicists can deduce the charge of a particle from the way it curves when the chamber is subjected to a magnetic field.

    In August of 1932, Anderson photographed the track of a high-energy particle with a mass about the same as an electron’s but with a positive charge. By measuring both the energy the particle lost in crossing a lead plate within the chamber and the length of the track on the other side of the lead, he determined an upper limit for the particle’s mass. He found it to be of the same order of magnitude as the electron’s mass.

    Anderson had observed a new kind of particle, which he named the positron. It was soon to be identified as the first antiparticle, the antielectron.”

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  • richardmitnick 8:58 am on January 29, 2013 Permalink | Reply
    Tags: , Antimatter, , , , , ,   

    From CERN: “AEGIS completes installation” 

    CERN New Masthead


    29 Jan 2013
    Katarina Anthony

    The AEGIS experiment plans to make the first direct measurement of Earth’s gravitational effect on antimatter. By sending a beam of antihydrogen atoms through very thin gratings, the experiment will measure how far the antihydrogen atoms fall during their horizontal flight. Combining this with the time each atom takes to fly and fall, the AEGIS team can determine the strength of the gravitational force between the Earth and the antihydrogen atoms.

    The AEGIS experiment in the Antiproton Decelerator Hall at CERN (Image: CERN)

    ‘By the end of 2012, we had finished by putting all the elements of the experiment together,’ says AEGIS spokesperson Michael Doser. ‘Now we have to show that they can all work together and, unfortunately, we will have no antiproton beams for a long period due to the machines’ shutdown.

    But instead of waiting for two years for beams to return to the Antiproton Decelerator Hall, the AEGIS team has come up with an alternative. If they can’t work with antihydrogen, why not try out their experiment with hydrogen?

    The Antiproton Decelerator

    ‘We want to make sure we understand how to make antihydrogen and our diagnostic will be the formation of hydrogen,’ says Doser. ‘If we succeed in making hydrogen this year, that will be a huge step forward; and if we can make hydrogen beams next year, then we’ll really be in business.’

    The AEGIS team will be carrying out this commissioning during the coming months, opening up their setup next month to make any necessary adjustments, and to install a hydrogen detector and proton source.”

    See the full article here. Please follow the links in this article to learn more.

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