Showing papers on "Strangeness published in 1985"

Meson exchange calculation of the p ¯ p →Λ¯Λ reaction

Abstract: The process p\ifmmode\bar\else\textasciimacron\fi{}p\ensuremath{\rightarrow}\ensuremath{\Lambda}\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\Lambda} is studied using a one-boson t-channel strangeness exchange mechanism incorporating pseudoscalar, vector, and tensor mesons. Particular attention is paid to the spin degrees of freedom in the calculation. Initial and final state interactions, including the spin-orbit interaction and absorption, are taken into account using simple phenomenological models. The calculations are performed using density matrix ideas in the helicity basis, and the most important contributing amplitudes are identified. A reasonable fit to existing data can be obtained by allowing a smooth variation of the final state parameters with laboratory momentum. The effect of each of the exchanged mesons, and of the initial- and final-state baryon-baryon interactions on the cross sections and spin observables, is discussed. It is found that the tensor meson exchange plays an essential role even near threshold, which indicates the need for a detailed understanding of the short-range spin dynamics, perhaps as provided by future quark model studies.

Strangeness abundances in p¯-nucleus annihilations

Abstract: In the annihilation of antiprotons of low kinetic energy on light nuclei, substantial transfer of annihilation energy to spectator nucleons and distribution of the available energy over the transversal degrees of freedom is observed.' Furthermore, strange particles produced in hot matter carry information about the dense phase of the annihilation reaction, because strangeness is mostly produced in the hot and dense Zone and it is not depleted again during the lifetime of the hadronic fireball. The abundance of strange particles has therefore been suggested to be a signal in the search for quark matter possibly existing in the hot region.2 The aim of this paper is to calculate in a statistical model the abundance of strangeness produced in an antiproton annihilation on light nuclei or protons. The conservation of ~ t r a n ~ e n e s s ~ , ~ and baryon number in strong interactions is an essential ingredient constraining the particle production in our m ~ d e l . ~ We further apply our model to the currently available pd data5 and show that the substantial high momentum component observed corresponds to the expected distribution from hot hadronic matter. Certain applications for PA collisions are also presented. Our initial hypothesis is that hadronic matter inside the annihilation Zone in p nucleus reactions can be described by a statistical model, as is, e.g., indicated by the experimentally observed exponential shape of the p spectra from which the temperature Parameter can be obtained. Assuming (relative) chemical equilibrium, the mean multiplicity of the different hadronic components produced can then be determined. However, we should not expect perfect chemical or thermal equilibrium to exist for several reasons: (1) the reaction volume is expanding; (2) the temperature decreases due to the expansion and radiation energy losses; and (3) the fireball does not exist long enough to reach the phase space limit of strangeness abundance. But within the strangeness carrying particles a relative chemical equilibrium is possible, as strangeness exchange reactions (e.g., K-~-AT') have relatively large Cross sections. Therefore, while absolute multiplicities may be difficult to interpret, ratios of multiplicities of strange particles can be predicted well in our approach.3 The following assumption is furthermore made: The expansion of the reaction volume and the decrease of temperature are sufficiently slow for the temporary thermal equilibrium and relative chemical equilibrium among strange particles to hold. This picture of the hadronic fireball created in annihilations is directly applicable for arbitrary nuclear target Systems, but only for light targets will it be likely that all target baryons participate in the annihilation process in that they share its energy.

TheK0/π- ratio and strangeness supression inv p and\(\bar vp\) charged current interactions

Abstract: Neutral kaon to negative pion production ratios fromvp and\(\bar vp\) charged current interactions in BEBC are presented and compared with LUND fragmentation model predictions. Good agreement is obtained with a strangeness suppression factor λ=0.203±0.014(stat)±0.010(sys). No evidence is seen for an energy dependence of λ in our kinematic region.

Strangeness production as a signal for quark-gluon plasma formation in high energy particle collisions

Abstract: Strangeness production in hot nuclear matter in the non-interacting gas approximation with anUB(1)×US(1) internal symmetry group is discussed. It is argued that the strangeness abundancy ratio in the quark-gluon plasma as compared to the hadron gas strongly depends on under which thermodynamical circumstances it has been computed.

Search for a strangeness‐2 dibaryon

Abstract: The existing data on the strangeness ‐2 two‐baryon mass spectrum is reviewed and a new experiment is proposed to explore this spectrum from 100 MeV below the mass of the lightest known two‐baryon strangeness ‐2 system, ΛΛ, to 20 MeV above the ΛΛ mass. The proposed experiment is motivated by Jaffe’s 1977 prediction of a six‐quark object with strangeness −2 and Jπ=0+ at a mass of 2150. This particle, called the ‘‘H’’, has been predicted by later bag models as well. Calculations indicate the proposed experiment will be a sensitive test of the dibaryon theories.

Strangeness Suppression and Recombination Effect in Large Transverse Momentum Dependent Quark Statistics

Abstract: The quark statistics has successfully described the variation of the ratios π±/p, K±/p and\(p/\bar p\) with energy purely statistically and the variation of π-/π+, K−/K+ and\(p/\bar p\) with largepT by means of the leading-quark effect. This model is now further enhanced by thepT-dependent strangeness suppression mechanism and recombination effect, so that the characteristics exhibited by the ratios K+/π+, K-/π-, ϕ/π-, p/π+ and\(\bar p/\pi ^ - \) could be studied phenomenologically.