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Post Info TOPIC: Antimatter
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RE: Antimatter
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Title: Observation of the antimatter helium-4 nucleus
Authors: STAR Collaboration
(Version v2)

High-energy nuclear collisions create an energy density similar to that of the universe microseconds after the Big Bang, and in both cases, matter and antimatter are formed with comparable abundance. However, the relatively short-lived expansion in nuclear collisions allows antimatter to decouple quickly from matter, and avoid annihilation. Thus, a high energy accelerator of heavy nuclei is an efficient means of producing and studying antimatter. The antimatter helium-4 nucleus (^4\bar{He}), also known as the anti-{\alpha} (\bar{\alpha}), consists of two antiprotons and two antineutrons (baryon number B=-4). It has not been observed previously, although the {\alpha} particle was identified a century ago by Rutherford and is present in cosmic radiation at the 10% level. Antimatter nuclei with B < -1 have been observed only as rare products of interactions at particle accelerators, where the rate of antinucleus production in high-energy collisions decreases by about 1000 with each additional antinucleon. We present the observation of the antimatter helium-4 nucleus, the heaviest observed antinucleus. In total 18 ^4\bar{He} counts were detected at the STAR experiment at RHIC in 10^9 recorded Au+Au collisions at center-of-mass energies of 200 GeV and 62 GeV per nucleon-nucleon pair. The yield is consistent with expectations from thermodynamic and coalescent nucleosynthesis models, which has implications beyond nuclear physics.

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Blobrana


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Physicists create heaviest form of antimatter ever seen

A newly created form of antimatter is the heaviest and most complex anti-thing ever seen. Anti-helium nuclei, each containing two anti-protons and two anti-neutrons, have been created and detected at the Relativistic Heavy Ion Collider (RHIC) in Upton, New York.
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Blobrana


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Antimatter caught streaming from thunderstorms on Earth

A space telescope has accidentally spotted thunderstorms on Earth producing beams of antimatter.
Such storms have long been known to give rise to fleeting sparks of light called terrestrial gamma-ray flashes.
But results from the Fermi telescope show they also give out streams of electrons and their antimatter counterparts, positrons.
The surprise result was presented by researchers at the American Astronomical Society meeting in the US.
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Blobrana


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Antimatter atom trapped for first time, say scientists

Antimatter atoms have been trapped for the first time, scientists say.
Researchers at Cern, home of the LHC, have held 38 antihydrogen atoms in place, each for a fraction of a second.
While antihydrogen has been produced before, it is instantly destroyed in a flash of light when it encounters normal matter.
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Blobrana


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New clue to anti-matter mystery

A US-based physics experiment has found a clue as to why the world around us is composed of normal matter and not its shadowy opposite: anti-matter.
Anti-matter is rare today; it can be produced in "atom smashers", in nuclear reactions or by cosmic rays.
But physicists think the Big Bang should have produced equal amounts of matter and its opposite.
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Heavy antimatter created in gold collisions

Collisions between gold nuclei at the Relativistic Heavy Ion Collider (RHIC) on Long Island, New York, have yielded heavy isotopes of antihydrogen that include a subatomic particle known as an antistrange quark, which is heavier than less unusual up or down quarks. The extra mass of the exotic antiquark is enough to make this antihydrogen isotope heavier than the previous record-holder, antihelium. Further studies of the new antinuclei may provide information about the cores of neutron stars, or even insight into the earliest days of the Universe. The work appears online today in the journal Science
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Blobrana


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NASA's space shuttle program is winding down. With only about half a dozen more flights, shuttle crews will put the finishing touches on the International Space Station (ISS), bringing to an end twelve years of unprecedented orbital construction. The icon and workhorse of the American space program will have finished its Great Task.
But, as Apple's CEO Steve Jobs might say, there is one more thing...
An act of Congress in 2008 added another flight to the schedule near the end of the program. Currently scheduled for 2010, this extra flight of the shuttle is going to launch a hunt for antimatter galaxies.
The device that does the actual hunting is called the Alpha Magnetic Spectrometer--or AMS for short. It's a $1.5 billion cosmic ray detector that the shuttle will deliver to the ISS.

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Blobrana


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Positron Annihilation
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Title: Gamma-Rays from Positron Annihilation
Authors: Roland Diehl, Mark Leising
(Version v2)

SPI on INTEGRAL has provided spectra and a map of the sky in the emission from annihilations of positrons in the interstellar medium of our Galaxy. From high-resolution spectra we learned that a warm, partially-ionised medium is the site where the observed gamma-rays originate. The gamma-ray emission map shows a major puzzle for broader astrophysics topics, as it is dominated by a bright and extended apparently spherical emission region centred in the Galaxy's center. Only recently has the disk of the Galaxy been detected with SPI. This may be regarded as confirmation of earlier expectations that positrons should arise predominantly from sources of nucleosynthesis distributed throughout the plane of the Galaxy, which produce proton-rich unstable isotopes. But there are other plausible sources of positrons, among them pulsars and accreting binaries such as microquasars. SPI results may be interpreted also as hints that these are more significant as positron sources on the Galactic scale than thought before, in the plane and therefore also in the bulge of the Galaxy. This is part of the attempt to understand the surprisingly-bright emission from the central region in the Galaxy, which otherwise also could be interpreted as a first rather direct detection of dark matter annihilations in the Galaxy's gravitational well. INTEGRAL has a unique potential to shed light on the various aspects of positron astrophysics, through its capability for imaging spectroscopy.

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Does antimatter fall up?
Gravity, we think, works the same way on all matter. But what about antimatter?
AEGIS, a CERN experiment that has just been given the go-ahead, is designed to find out. Gravity is a relatively weak force, so the experiment will use uncharged particles to prevent electromagnetic forces drowning out gravitational effects. It will first build highly unstable pairings of electrons and positrons, known as positronium, then excite them with lasers to prevent them annihilating too quickly. Clouds of antiprotons will rip these pairs apart, stealing their positrons to create neutral antihydrogen atoms.

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Blobrana


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If you were to list the imperfections of the standard model - physicists' remarkably successful description of matter and its interactions - pretty high up would have to be its prediction that we don't exist.
According to the theory, matter and antimatter were created in equal amounts at the big bang. By rights, they should have annihilated each other totally in the first second or so of the universe's existence. The cosmos should be full of light and little else.

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