Antiproton


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antiproton

[′an·tē¦prō‚tän]
(particle physics)
The antiparticle to the proton; a strongly interacting baryon which is stable, carries unit negative charge, has the same mass as the proton (938.3 MeV), and has spin ½.

Antiproton

 

symbol ρ̄ or p̄), antiparticle with respect to the proton. The mass and spin of an antiproton are equal to those of a proton, but the electrical charge and magnetic momentum, although identical in absolute value, are opposite in sign. The existence of the antiproton was predicted by contemporary theories of elementary particles, and research for its existence in cosmic rays was conducted for about 20 years. Antiprotons were experimentally discovered in 1955 by O. Chamberlain, E. Segrè, C. Wiegand, and T. Ypsilantis at Berkeley (USA), using a proton accelerator with a maximum energy of 6.3 giga electron volts (GeV).

In accordance with the law of conservation of heavy particles (baryons), antiprotons can be bred only in pairs with protons (or with neutrons, if the law of conservation of electric charge is satisfied). The threshold (minimum) energy for creation of a proton-antiproton pair through the collision of two free protons in the laboratory systems of coordinates—that is, in a system in which one of the protons in the collision is at rest—is ~6.6GeV; for collision with a proton or a neutron that is bound in the atomic nucleus, it is about 4 GeV. Therefore, formation of antiprotons on nuclei was expected in a 6.3 GeV proton accelerator.

In the experiment by Chamberlain and the others, antiprotons were bred through the collisions of protons from the accelerator with a copper target. At least 1011 collisions are required for a minimal antiproton generation. A magnetic deflection system removes the negatively charged particles, the great majority of which are negatively charged pi-mesons. To detect antiprotons—that is, to differentiate them from other negatively charged particles—the mass must be determined. This is done by determining the momentum (by deflection in a magnetic field) and velocity (with the use of a Cherenkov counter) of the particles.

Another notable feature of antiprotons was observed in experiments—their annihilation in collisions with protons and neutrons of nuclear matter. It turns out that four or five high-energy pi-mesons are created as a result of antiproton annihilation.

With the help of accelerators it is now possible to obtain quite intensive beams of antiprotons. In experiments with such beams in the 1960’s a number of short-lived elementary particles (meson resonances) were discovered.

V. P. PAVLOV

References in periodicals archive ?
The debate on the antiproton channel has then included tentative claims of anomalies with respect to the conventional scenario, possibly explained in terms of DM indirect detection.
Before describing this mechanism, the results so far obtained are summarized as follows: (i) each cell is in fact an allowed state for one proton or one antiproton; (ii) (3,14) represents the excitation energy necessary to remove either of them from its own [V.sub.0] and leave behind an empty cell; (iii) the latter represents a vacuum state, whereas either particle present in [V.sub.0] defines an occupied state.
Marshall Center engineers are building a High Performance Antimatter Trap, which will store antiprotons for a 10-day lifetime.
Two posibilities on the horizon are superconducting storage rings and ion-trap "vacuum bottles." Storage devices are considered a critical "enabling tool" for antiproton research, as they would allow the antimatter produced at a source facility to be transported to academic, government, and industrial laboratories conducting the experiments.
In order to make their measurements, the researchers used protons generated by CERN's antiproton decelerator and placed them in Penning traps, which use a strong magnetic field to trap particles.
The measurements on proton and antiproton in [40] are expected to give strong constraints on the noncommutative parameters.
Ulmer's next goal is to measure the intrinsic magnetism of the antiproton, which, like charge, should be equal but opposite that of the proton (SN: 6/28/14, p.
Among specific topics are super-heavy and giant nuclear systems, an experimental program with rare-isotope beams at the international Facility for Antiproton and Ion Research (FAIR), quantum Monte Carlo calculations of light nuclei, tests of clustering in light nuclei and applications to nuclear astrophysics, shell-model calculations with low-momentum realistic interactions, studying nuclear structure by means of Coulomb energy differences, symmetry and super-symmetry in nuclear physics, and the microscopic study of multi-photon excitations in nuclei.
In order for the paper to be self-contained let's recall that the pionium is formed by a [[pi].sup.+] and [[pi].sup.-] mesons, the positronium is formed by an antielectron (positron) and an electron in a semi-stable arrangement, the protonium is formed by a proton and an antiproton also semi-stable, the antiprotonic helium is formed by an antiproton and electron together with the helium nucleus (semi-stable), and muonium is formed by a positive muon and an electron.
An atom of antihydrogen, or anti-H, consists of a negatively charged antiproton and a positively charged antielectron (a.k.a.
He says the work's most significant contribution is the Penning trap setup: It should also be able to measure the magnetic moment of the antiproton. The 1972 measurement required a low-energy laser fueled by a gas of hydrogen atoms (whose nuclei consist of a single proton each).
This research paves the way for further UK science programs at the future international FAIR accelerator (Facility for Antiproton and Ion Research) at GSI, where the UK will play a significant role in this growing area of atomic science through a collaboration called NuSTAR (Nuclear Structure, Astrophysics and Reactions).