• Matter and antimatter behave differently in atom smasher

    CERN / Maximilien Brice, Rachel Barbier

    The LHCb team stands in front of its experiment, the LHCb detector, at the Large Hadron Collider in Geneva.

    By Clara Moskowitz
    LiveScience

    Matter and antimatter particles are behaving differently inside a giant atom smasher in Switzerland, physicists announced Wednesday. The discovery could help solve the riddle of why the universe is made of matter and not its strange sibling, antimatter.

    All matter particles are thought to have antimatter counterparts with the same mass but opposite charge and spin. When the universe sprang into being 13.8 billion years ago with the Big Bang, it probably had similar amounts of matter and antimatter. Most of this antimatter is thought to have been destroyed in collisions with matter (when the two meet, they annihilate each other), and all that's left over in the universe today is a small overabundance of matter.

    To understand why matter dominated over antimatter, physicists look for any differences in how the two behave that might explain the discrepancy. These differences are called charge-parity violation (CP violation), and that's just what scientists have found inside the Large Hadron Collider (LHC) in Geneva. [Whoa! The Coolest Little Particles in Nature]

    Inside the 17-mile-long (27 kilometers) underground ring of the machine, protons speed up and smash into each other, creating a shower of daughter particles.  One experiment at the collider called LHCb (it stands for "LHC beauty") studies these daughter particles for signs of CP violation that might help elucidate the nature of antimatter.

    After analyzing about 70 trillion proton-proton collisions, LHCb found that a particle called the B_s meson was created slightly more often in its matter form than in its antimatter counterpart. B_s (pronounced ("B-sub-S") mesons are made of bottom quarks and strange anti-quarks, whereas antimatter B_s mesons have an antimatter bottom quark and a matter strange quark ("bottom" and "strange" are two flavors of quarks, and anti-quarks are the antimatter partner particles of normal matter quarks).

    "The thing about antimatter is it behaves almost identically to normal matter," said Tara Shears, a physicist at England's University of Liverpoolwho works on the LHCb experiment. "But the devil is in the details, and it's this very tiny difference that we're trying to measure."

    B_s mesons are rare, and 70 trillion collisions inside the Large Hadron Collider created only about a thousand of these elusive particles. Yet these were enough to demonstrate a significant abundance of matter B_s mesons compared with antimatter B_s mesons.

    "We expected it to be there, but we've never been able to make a measurement of it before because these particles so rare," Shears told LiveScience.

    The B_sparticle is only the fourth subatomic particle known to exhibit such a matter-antimatter asymmetry.

    CP violation was first discovered in neutral particles called kaons at the Brookhaven National Laboratory in Long Island in the 1960s. It took 40 more years for researchers in the United States and Japan to find the next example of this asymmetry in the B0 meson. After that, the LHCb experiment and others found evidence for CP violation in the B+ meson.

    Yet these instances of CP violation aren't enough to explain the prevalence of matter over antimatter in the universe.

    "We still have a lot to do to understand the real nature of antimatter," Shears said. "We know we don't understand the whole story. We've just filled in a little bit more information — a block in our jigsaw puzzle if you like."

    The researchers hope to make more progress when the LHC starts up again in 2015, at a much higher energy, after its current hiatus.

    The LHCb discovery is detailed in a paper submitted to the journal Physical Review Letters.

    Follow Clara Moskowitz on Twitter and Google+. Follow us @livescience, Facebook  and Google+. Original article on LiveScience.com.

    Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

  • How to prove dark matter particles? Catch one!

    Paolo Lombardi INFN-MI

    Experiments at underground laboratories such as this one in Gran Sasso, Italy could detect WIMPS, the particles that make up elusive dark matter.

    By Tia Ghose
    LiveScience

    Physicists announced Wednesday that a particle detector on the International Space Station has possibly detected signals of dark matter.

    Though exciting, the new results are still uncertain, and scientists can't be sure they actually indicate dark matter, as opposed to some more mundane cosmic phenomenon.

    To definitively expose dark matter, physicists must look deep beneath the Earth to directly detect particles that make up dark matter, called WIMPs (or Weakly Interacting Massive Particles), several experts said. Finding direct evidence of dark matter on Earth would help reinforce the space-station experiment's discovery by showing independent evidence that dark matter particles exist.

    WIMPs
    Scientists proposed the existence of invisible stuff called dark matter to explain why galaxies are rotating so fast, yet aren't flying apart. A strong gravitational force must hold galaxies together, but all the visible matter in galaxies can't account for such an immense gravitational pull. [6 Weird Facts About Gravity]

    To explain this conundrum, scientists suggest the universe is filled with mysterious dark matter that reflects no light (it's invisible) and rarely interacts with normal matter.

    One leading theory holds that dark matter is made up of WIMPs, particles that are their own antimatter counterparts, so when they collide with each other they annihilate, producing electrons and their antimatter partners, positrons.

    Matt Kapust / Sanford Laboratory

    The Large Underground Xenon detector in Homestake mine in South Dakota could reveal the particles that make up dark matter.

    The Alpha Magnetic Spectrometer (AMS), a particle detector aboard the International Space Station, has now detected what may be this positron signature. The detector, which measures cosmic-ray particles in space, detected 400,000 positrons over the last year and a half; and the energies of the positrons match up with what would be expected for positrons created by the annihilation of colliding dark-matter particles.

    However, it's difficult to prove that the positron signature comes from dark matter, rather than from spinning stars called pulsars that spew positrons as they whirl around.

    Direct detection?
    To actually prove that dark matter particles exist, scientists hope to catch these particles directly.

    "There are several ways to do it, but essentially they all boil down to trying to capture a dark matter particle bumping into an atom of real matter," said Simon Fiorucci, a particle physicist at Brown University who works on the Large Underground Xenon detector experiment (LUX) in South Dakota.

    The endeavor is a difficult one, though, because even though millions of dark matter particles may be flying through Earth at any moment, they would only rarely interact with ordinary matter, leaving very few traces of their existence.

    "We already know from these direct detection experiments, they're interacting at a rate of less than 1 per year in a reasonable size target mass," said Dan Bauer, a particle physicist at Fermilab in Illinois.

    The world's largest atom smasher, the Large Hadron Collider (LHC) has also searched for WIMPs but so far failed to find them, which rules out the existence of lower-mass WIMPs, Bauer told LiveScience. If the findings from AMS truly are produced by dark matter, they will narrow down the range of masses at which these particles can exist as well, Bauer said.

    Underground labs
    To find elusive WIMPS in the higher mass range, researchers are conducting studies deep underground, where the Earth's crust shields the experiments from cosmic rays that could drown out evidence of WIMP interactions, Fiorucci told LiveScience.

    Several experiments are searching for WIMPs this way, including LUX in South Dakota's Homestake mine, Xenon100 in Gran Sasso, Italy, and the Cryogenic Dark Matter Search (CDMS) in an underground mine in Soudan, Minn.

    Most of these experiments use a heavy liquid such as xenon or germanium that gives off light when a dark matter particle collides with an atom in the liquid. In the LUX experiment, for instance, WIMP particles bump into the nuclei of xenon atoms like billiard balls, causing both to change their motion a bit. By measuring the xenon atom's recoil, scientists can figure out if it was a WIMP that caused it.

    Physicists can distinguish light emissions produced by WIMP interactions from signatures of other particles, such as gamma rays or neutrons, Fiorucci said.

    Follow Tia Ghose on Twitter @tiaghose. Follow LiveScience @livescience, Facebook and Google+. Original article on LiveScience.com

    Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

  • Antimatter's magnetic charge revealed

    Katie Bertsche

    Antimatter refers to sub-atomic particles that have properties opposite normal sub-atomic particles.

    LiveScience

    Scientists say they've made the most precise measurements to date of the magnetic charge of single particles of matter and its spooky counterpart antimatter.

    A better understanding of the characteristics of these particles could help scientists solve one of the most baffling mysteries in physics: Why is the universe made of matter and not antimatter?

    "According to our theories, the same amount of matter and antimatter was produced during the Big Bang," Harvard physicist Gerald Gabrielse explained in a statement. "When matter and antimatter meet, they are annihilated. As the universe cools down, the big mystery is: Why didn't all the matter find the antimatter and annihilate all of both? There's a lot of matter and no antimatter left, and we don't know why."

    Gabrielse and his team captured individual protons and antiprotons in a trap created by electromagnetic fields that keep these particles suspended in one spot for several minutes, ensuring the two don't annihilate each other before measurements are made. For some of their experiments, the team turned to the extensive tunnels of the Geneva-based CERN (the European Organization for Nuclear Research) laboratory, where antiprotons can be created in high-energy collisions at the Large Hadron Collider (LHC).

    Inside the LHC, protons zip at near light speed around a 17-mille-long (27 kilometers) underground loop on the border between France and Switzerland. Head-on particle collisions between protons can give rise to exotic particles, including the elusive Higgs boson, the particle theorized to explain how other particles get their mass. [LHC Photos: The World's Largest Atom Smasher]

    By looking at the oscillations of the protons and antiprotons created, the scientists measured the size of the magnetic charge of both types of particles more accurately than ever before, boosting the precision of the antiproton measurement by a factor of 680.

    "What we wanted to do with these experiments was to say, 'Let's take a simple system — a single proton and a single antiproton — and let's compare their predicted relationships, and see if our predictions are correct," Gabrielse said.

    Theory suggests that protons and antiprotons should be virtually identical in their mass and magnitude of charge but that they should have opposite charges. While the new measurements fit within this model, better measurements of protons and antiprotons could shed light on why matter came to dominate in the universe.

    "What's also very exciting about this breakthrough is that it now prepares us to continue down this road," Gabrielse said. "I'm confident that, given this start, we're going to be able to increase the accuracy of these measurements by another factor of 1,000, or even 10,000."

    The research was detailed Monday in the journal Physical Review Letters.

    Follow us @livescience, Facebook and Google+. Original article on LiveScience.com.

    Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

  • Coldest antimatter yet is goal of new technique

    Chukman So

    In addition to making antihydrogen easier to study, a new cooling technique could make it last longer in traps. In 2011, scientists trapped antimatter for a record 16 minutes (artist's conception shown here).

    By Clara Moskowitz, LiveScience

    Scientists have devised a new method of cooling down antimatter to make it easier to experiment on than ever before.

    The new technique could help researchers probe the mysteries of antimatter, including why it's so rare compared with matter in the universe.

    Every matter particle has an antimatter partner particle with opposite charge — for example, the antimatter counterpart of an electron is a positron. When matter and antimatter meet, they annihilate each other.

    The new technique is focused on antihydrogen atoms, which contain one positron and one antiproton (regular hydrogen contains one electron and one proton). The first experiments on antihydrogen atoms were just performed last year. [ Wacky Physics: The Coolest Little Particles in Nature ]

    "The ultimate goal of antihydrogen experiments is to compare its properties to those of hydrogen," physicist Francis Robicheaux of Auburn University in Alabama said in a statement. "Colder antihydrogen will be an important step for achieving this."

    That's because antihydrogen atoms are usually relatively hot and energetic, which can distort their properties when measured.

    Robicheaux is the co-author of a paper describing the new cooling method published Jan. 6 in the Journal of Physics B: Atomic, Molecular and Optical Physics.

    The new technique relies on using precision laser beams to "kick" antihydrogen atoms, knocking loose a bit of energy from them and cooling them down. The process should be able to cool antihydrogen atoms to temperatures 25 times chillier than ever before.

    "By reducing the antihydrogen energy, it should be possible to perform more precise measurements of all of its parameters," Robicheaux said. "Our proposed method could reduce the average energy of trapped antihydrogen by a factor of more than 10."

    But to cool down antimatter, scientists must first trap it. This is difficult, because antimatter particles would be destroyed if they touched walls made of matter. Thus, researchers use complicated systems of magnetic fields to contain antimatter.

    In addition to making antihydrogen easier to study, the new cooling technique could make it last longer in traps. In 2011, scientists at the European physics lab CERN trapped antimatter for an amazingly long 16 minutes, setting a record.

    "Whatever the processes are, having slower moving, and more deeply trapped, antihydrogen should decrease the loss rate," Robicheaux said.

    The researchers haven't tried the new tactic out yet on actual antimatter atoms, but they used computer simulations to show that it's possible. Their calculations suggest that the particles can be cooled to around 20 millikelvin; in contrast, most trapped antihydrogen atoms have temperatures of up to 500 millikelvin.

    "It is not trivial to make the necessary amount of laser light at a specific wavelength," Robicheaux said. "Even after making the light, it will be difficult to mesh it with an antihydrogen trapping experiment. By doing the calculations, we've shown that this effort is worthwhile."

    Follow Clara Moskowitz on Twitter @ClaraMoskowitz or LiveScience @livescience. We're also on Facebook & Google+.

     

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