Topic
Antiproton
About: Antiproton is a research topic. Over the lifetime, 4027 publications have been published within this topic receiving 59759 citations.
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TL;DR: This work demonstrates the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment and detects the neutral anti-atoms directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector.
Abstract: A theoretical underpinning of the standard model of fundamental particles and interactions is CPT invariance, which requires that the laws of physics be invariant under the combined discrete operations of charge conjugation, parity and time reversal. Antimatter, the existence of which was predicted by Dirac, can be used to test the CPT theorem—experimental investigations involving comparisons of particles with antiparticles are numerous1. Cold atoms and anti-atoms, such as hydrogen and antihydrogen, could form the basis of a new precise test, as CPT invariance implies that they must have the same spectrum. Observations of antihydrogen in small quantities and at high energies have been reported at the European Organization for Nuclear Research (CERN)2 and at Fermilab3, but these experiments were not suited to precision comparison measurements. Here we demonstrate the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment. The neutral anti-atoms have been detected directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector.
635 citations
TL;DR: A new measurement of the cosmic-ray antiproton-to-proton flux ratio between 1 and 100 GeV is presented, which is a tenfold improvement in statistics with respect to all previously published data.
Abstract: A new measurement of the cosmic-ray antiproton-to-proton flux ratio between 1 and 100 GeV is presented. The results were obtained with the PAMELA experiment, which was launched into low-Earth orbit on-board the Resurs-DK1 satellite on June 15th 2006. During 500 days of data collection a total of about 1000 antiprotons have been identified, including 100 above an energy of 20 GeV. The high-energy results are a tenfold improvement in statistics with respect to all previously published data. The data follow the trend expected from secondary production calculations and significantly constrain contributions from exotic sources, e.g., dark matter particle annihilations.
601 citations
TL;DR: The satellite-borne experiment PAMELA has been used to make a new measurement of the cosmic-ray antiproton flux and the antipropton-to-proton flux ratio which extends previously published measurements down to 60 MeV and up to 180 GeV in kinetic energy.
Abstract: The satellite-borne experiment PAMELA has been used to make a new measurement of the cosmic-ray antiproton flux and the antiproton-to-proton flux ratio which extends previously published measurements down to 60 MeV and up to 180 GeV in kinetic energy. During 850 days of data acquisition approximately 1500 antiprotons were observed. The measurements are consistent with purely secondary production of antiprotons in the Galaxy. More precise secondary production models are required for a complete interpretation of the results.
533 citations
TL;DR: Coalescence of minijet partons with partons from the quark-gluon plasma formed in relativistic heavy ion collisions is suggested as the mechanism for production of hadrons with intermediate transverse momentum, giving a plausible explanation for the observed large antiproton to pion ratio.
Abstract: Coalescence of minijet partons with partons from the quark-gluon plasma formed in relativistic heavy ion collisions is suggested as the mechanism for production of hadrons with intermediate transverse momentum. The resulting enhanced antiproton and pion yields at intermediate transverse momenta give a plausible explanation for the observed large antiproton to pion ratio. With further increasing momentum, the ratio is predicted to decrease and approach the small value given by independent fragmentations of minijet partons after their energy loss in the quark-gluon plasma.
510 citations
TL;DR: In the absolute rigidity range ∼60 to ∼500 GV, the antiproton p[over ¯], proton p, and positron e^{+} fluxes are found to have nearly identical rigidity dependence and the electron e^{-} flux exhibits a different rigidity dependent.
Abstract: A precision measurement by AMS of the antiproton flux and the antiproton-to-proton flux ratio in
primary cosmic rays in the absolute rigidity range from 1 to 450 GV is presented based on 3.49 × 105
antiproton events and 2.42 × 109 proton events. The fluxes and flux ratios of charged elementary particles
in cosmic rays are also presented. In the absolute rigidity range ∼60 to ∼500 GV, the antiproton ¯p, proton
p, and positron eþ fluxes are found to have nearly identical rigidity dependence and the electron e− flux
exhibits a different rigidity dependence. Below 60 GV, the ( ¯ p=p), ( ¯ p=eþ), and (p=eþ) flux ratios each
reaches a maximum. From ∼60 to ∼500 GV, the ( ¯ p=p), ( ¯ p=eþ), and (p=eþ) flux ratios show no rigidity
dependence. These are new observations of the properties of elementary particles in the cosmos.
464 citations