Clusters of matter and antimatter

Physical Review C, 2005

We study the possibility of producing a new kind of nuclear systems which in addition to ordinary nucleons contain a few antibaryons (B = p, Λ, etc.). The properties of such systems are described within the relativistic mean-field model by employing G-parity transformed interactions for antibaryons. Calculations are first done for infinite systems and then for finite nuclei from 4 He to 208 Pb. It is demonstrated that the presence of a real antibaryon leads to a strong rearrangement of a target nucleus resulting in a significant increase of its binding energy and local compression. Noticeable effects remain even after the antibaryon coupling constants are reduced by factor 3 − 4 compared to G-parity motivated values. We have performed detailed calculations of the antibaryon annihilation rates in the nuclear environment by applying a kinetic approach. It is shown that due to significant reduction of the reaction Q-values, the in-medium annihilation rates should be strongly suppressed leading to relatively long-lived antibaryonnucleus systems. Multi-nucleon annihilation channels are analyzed too. We have also estimated formation probabilities of bound B + A systems in pA reactions and have found that their observation will be feasible at the future GSI antiproton facility. Several observable signatures are proposed. The possibility of producing multi-quark-antiquark clusters is discussed.

Physics Letters B, 2002

We discuss the possibility of producing a new kind of nuclear system by putting a few antibaryons inside ordinary nuclei. The structure of such systems is calculated within the relativistic mean-field model assuming that the nucleon and antinucleon potentials are related by the G-parity transformation. The presence of antinucleons leads to decreasing vector potential and increasing scalar potential for the nucleons. As a result, a strongly bound system of high density is formed. Due to the significant reduction of the available phase space the annihilation probability might be strongly suppressed in such systems.

A brief review of antiproton--nucleus physics is presented. Some topics are related to early LEAR experiments, and others to more recent measurements or proposals. These include: exotic molecules, elastic and inelastic scattering, deep annihilation, strangeness production, neutron--antineutron oscillations, halo nuclei, antiproton production in nuclear reactions etc.

Science, 2010

Nuclear collisions recreate conditions in the universe microseconds after the Big Bang. Only a very small fraction of the emitted fragments are light nuclei, but these states are of fundamental interest. We report the observation of antihypertritons - composed of an antiproton, antineutron, and antilambda hyperon - produced by colliding gold nuclei at high energy. Our analysis yields 70 +- 17 antihypertritons and 157 +- 30 hypertritons. The measured yields of hypertriton (antihypertriton) and helium3 (antihelium3) are similar, suggesting an equilibrium in coordinate and momentum space populations of up, down, and strange quarks and antiquarks, unlike the pattern observed at lower collision energies. The production and properties of antinuclei, and nuclei containing strange quarks, have implications spanning nuclear/particle physics, astrophysics, and cosmology.

Proceedings of 27th European Cosmic Ray Symposium — PoS(ECRS)

Physical Review C, 2012

Inclusive cross sections σ A = Ed 3 σ(X, P 2 t)/d 3 p of antiproton and negative pion production on Be, Al, Cu and Ta targets hit by 10 GeV protons were measured at the laboratory angles of 10.5 • and 59 •. Antiproton cross sections were obtained in both kinematically allowed and kinematically forbidden regions for antiproton production on a free nucleon. The antiproton cross section ratio as a function of the longitudinal variable X exhibits three separate plateaus which gives evidence for the existence of compact baryon configurations in nuclei-small-distance scaled objects of nuclear structure. Comparability of the measured cross section ratios with those obtained in the inclusive electron scattering off nuclei suggests a weak antiproton absorption in nuclei. Observed behavior of the cross section ratios is interpreted in the framework of a model considering the hadron production as a fragmentation of quarks (antiquarks) into hadrons. It has been established that the antiproton formation length in nuclear matter can reach the magnitude of 4.5 fm.

2017

Stored antiprotons beams in the GeV range represent a unparalleled factory for hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of strange hadronic systems with unprecedented precision. The behavior of hyperons and -- for the first time -- of antihyperons in nuclear systems can be studied under well controlled conditions. The exclusive production of $\Lambda\bar{\Lambda}$ and $\Sigma^-\bar{\Lambda}$ pairs in antiproton-nucleus interactions probe the neutron and proton distribution in the nuclear periphery and will help to sample the neutron skin. For the first time, high resolution $\gamma$-spectroscopy of doubly strange nuclei will be performed, thus complementing measurements of ground state decays of double hypernuclei with mesons beams at J-PARC or possible decays of particle unstable hypernuclei in heavy ion reactions. High resolution spectroscopy of multistrange $\Xi$-atoms a...

Nature, 2011

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.

Journal of Physics: Conference Series, 2012

Within the next six years, the Facility for Antiproton and Ion Research (FAIR) is built adjacent to the existing accelerator complex of the GSI Helmholtz Center for Heavy Ion Research at Darmstadt, Germany. Thus, the current research goals and the technical possibilities are substantially expanded. With its worldwide unique accelerator and experimental facilities, FAIR will provide a wide range of unprecedented fore-front research in the fields of hadron, nuclear, atomic, plasma physics and applied sciences which are summarized in this article. As an example this article presents research efforts on strangeness at FAIR using heavy ion collisions, exotic nuclei from fragmentation and antiprotons to tackle various topics in this area. In particular, the creation of hypernuclei and antimatter is investigated.

Physical Review C, 2009

Properties of multi-antikaonic nuclei (MKN), where several numbers of K − mesons are bound, are studied in the relativistic mean-field model, combined with chiral dynamics for kaonic part of the thermodynamic potential. The density profiles for nucleons and K − mesons, the single particle energy of the K − mesons, and binding energy of the MKN are obtained. The effects of theK −K interactions on these quantities are discussed in comparison with other meson (σ, ω, and ρ)-exchange models. It is shown that theK − K interactions originate from two contributions: One is the contact interaction between antikaons inherent in chiral symmetry, and the other is the one generated through coupling between the K − and meson mean fields. Both effects of theK −K repulsive interactions become large on the ground state properties of the MKN as the number of the embedded K − mesons increases. A relation between the multi-antikaonic nuclei and kaon condensation in infinite and uniform matter is mentioned.