Intriguing aspects of strangeness production at CERN energies

Strange particle production in pp, pA and AA collisions at CERN SPS energies is reviewed. First results from Pb beam experiments are briefly presented. The emerging picture (still incomplete) is discussed.     

Precision measurements of strangeness photoproduction at threshold energies with the Crystal Ball at MAMI-C

The photoproduction of K＋ mesons from the nucleon provides important constraints on the nucleon excitation spectrum and at threshold energies challenges effective field theories based on chiral perturbation in the strange quark sector. Preliminary cross-section measurements for γ（P, K＋）A are presented at an unprecedented beam energy resolution. The data was collected at the MAMI-C facility in Mainz using the Crystal Ball Detector. A new method of K＋ detection was used in which the K＋ is tagged from its weak decay products in the detector crystals. This technique has application with other calorimeters at present and future hadron facilities.     

Precision measurements of strangeness photoproduction at threshold energies with the Crystal Ball at MAMI-C

The photoproduction of K~+ mesons from the nucleon provides important constraints on the nucleon excitation spectrum and at threshold energies challenges effective field theories based on chiral perturbation in the strange quark sector. Preliminary cross-section measurements for γ(p, K~+)A are presented at an unprece-dented beam energy resolution. The data was collected at the MAMI-C facility in Mainz using the Crystal Ball Detector. A new method of K~+ detection was used in which the K~+ is tagged from its weak decay products in the detector crystals. This technique has application with other calorimeters at present and future hadron facilities.     

Rapid hadronization and strangeness production

A fast hadronization scenario is presented where a central role is played by the chiral symmetry break-down in the expanding Quark-Gluon Plasma. This mechanism can become effective when thermal damping ceases after the thermal freeze-out of the quark system. We estimate time scales and spatial characteristics of chiral-symmetry breaking instabilities on the basis of an effective field-theoretical model. It is argued that this fast process provides a basis to understand the measured large abundances of strange antibaryons in heavy ion collisions.     

Recent results on strangeness,charm and beauty production at HERA

Based on the data collected with the H1 and ZEUS detectors at HERA,recent results on strangeness,charm and beauty production in ep collision are presented.     

Recent results on strangeness,charm and beauty production at HERA

Based on the data collected with the H1 and ZEUS detectors at HERA, recent results on strangeness, charm and beauty production in ep collision are presented.     

Threshold strangeness production in pp interactions

During the actual lectures, features of the COSY-Jülich accelerator were presented, followed by a short summary of ongoing experiments at the COoler SYnchrotron COSY using internal as well as external beams in the range of 45 MeV to 2.5 GeV. Here the research of the COSY-11 collaboration is presented. This °⁰ facility studies the hidden and open strangeness production observing the ν and η′ as well the K⁺Y and K⁺K^? production in the proton—proton interactions at the respective thresholds.     

Charge and strangeness transfer in multiparticle production

A simple explicit model for charge production is found to agree well with available data. This model combined with unitarity gives a realistic estimate for the suppression of two-body charge exchange scattering. Similar considerations are applied to strangeness transfer.     

Dilepton and strangeness production probed with HADES

With the High Acceptance Di-Electron Spectrometer (HADES) at GSI we have studied dilepton production in the few-GeV energy regime in various collisions systems, from elementary NN, over pA, up to the medium-heavy Ar + KCl system. We have thus confirmed the puzzling results of the former DLS Collaboration at the Bevalac. While we have traced the origin of the excess pair yield in CC collisions to elementary pp and pn processes, in our Ar + KCl data a contribution from the dense phase of the collision has been identified. Together with the e ⁺ e ^? pairs, we have also obtained in the Ar + KCl system at 1.76 A GeV a high-statistics data set on open and hidden strangeness, i.e. K ^±, K _s ⁰ , ??, ?, and ??^?, allowing for a comprehensive discussion of strangeness production in this system.     

Top-quark pair production near threshold at LHC

The next-to-leading order analysis for the cross section for hadroproduction of top-quark pairs close to threshold is presented. Within the framework of non-relativistic QCD a significant enhancement compared to fixed-order perturbation theory is observed which originates from the characteristic remnant of the 1S peak below production threshold of top-quark pairs. The analysis includes all color-singlet and color-octet configurations of top-quark pairs in S-wave states and, for the dominant configurations, it employs all-order soft-gluon resummation for the hard parton cross section. Numerical results for the Large Hadron Collider at TeV and TeV and also for the Tevatron are presented. The possibility of a top-quark mass measurement from the invariant-mass distribution of top-quark pairs is discussed.     

Double strangeness production in antiproton annihilation on nuclei

The recent data on double strangeness production after antiproton annihilation on nuclei are analyzed within the conventional picture of the reaction, namely annihilation on a single nucleon, followed by rescattering of the products in the nucleus, assumed to proceed in a hadronic phase. General expressions for single and double strangeness are derived within this picture. The relevant parameters are determined, as far as possible, from the single strangeness production yields and are used to predict double strangeness production yields. The later are compared with experiment and found consistent with the conventional picture. However, the data seem to indicate that the strangeness production in the primordial annihilation is different from what it is in nucleon-antinucleon reactions. An estimate of theΞ production rate is also performed. It is shown that the latter is much less sensitive to the rescattering process than in theΛ production case.     

System-size dependence of strangeness production in nucleus-nucleus collisions at squareroot[sNN]=17.3 GeV

Emission of pi+/-, K+/-, phi, and Lambda was measured in near-central C+C and Si+Si collisions at 158 AGeV beam energy. Together with earlier data for p+p, S+S, and Pb+Pb, the system-size dependence of relative strangeness production in nucleus-nucleus collisions is obtained. Its fast rise and the saturation observed at about 60 participating nucleons can be understood as the onset of the formation of coherent systems of increasing size.     

Hypernuclear and strangeness physics program at J-PARC

The inauguration ceremony of the Japan Proton Accelerator Research Complex (J-PARC) was held on 6 July 2009, celebrating the completion of its construction. Now, the beam commissioning of the 50-GeV main proton synchrotron is in progress to improve the beam intensity and quality. Many important experimental programs are planned with the improved beams. In this report, some of them are introduced.     

Resonance model study of strangeness production in pp collisions

Results for the energy dependence of the elementary kaon production cross sections in proton-proton collisions are reported. Calculations are performed within an extended version of the resonance model which was used for the previous studies of elementary kaon production in pion-nucleon and pion-Δ collisions. Although the model treatment is within theempirical tree level (observed widths for the resonances are used), it is fully relativistic, and includes all relevant baryon resonances up to 2 GeV. One of the purposes of this study is to provide the results for the simulation codes of subthreshold kaon production in heavy ion collisions. This is the first, consistent study of the elementary kaon production reactions including both πB and BB (B = N,Δ) collisions on the same footing. Comparisons are made between the calculated results and the existing semi-empirical parametrizations which are widely used for the simulation codes, as well as the experimental data.     

Probing dense matter with strangeness production in nuclear collisions

Experiments on strangeness production in nucleus–nucleus collisions at SIS energies address fundamental questions of modern nuclear physics: the determination of the nuclear equation-of-state at high baryon densities and the properties of hadrons in dense nuclear matter. From the yields of K⁺ mesons measured in heavy-ion collisions a value for the nuclear compressibility of is extracted for nuclear densities around twice saturation density using different microscopic transport models. Both the yield of K⁺ mesons and their anisotropic azimuthal angular distribution (elliptic flow) exhibit strong evidence for a repulsive K⁺N potential. The yields of K⁺ and K⁻ mesons measured in proton–nucleus collisions can be reproduced by transport calculations assuming at saturation density a repulsive K⁺N potential of and an attractive K⁻N potential of .     

Neutrino dimuon production and the strangeness asymmetry of the nucleon

We have performed the first global QCD analysis to include the CCFR and NuTeV dimuon data, which provide direct constraints on the strange and antistrange parton distributions, s(x) and . To explore the strangeness sector, we adopt a general parametrization of the non-perturbative functions satisfying basic QCD requirements. We find that the strangeness asymmetry, as represented by the momentum integral , is sensitive to the dimuon data provided the theoretical QCD constraints are enforced. We use the Lagrange multiplier method to probe the quality of the global fit as a function of [S ^-] and find -0.001 < [S ^-] < 0.004. Representative parton distribution sets spanning this range are given. Comparisons with previous work are made.Received: 15 January 2004, Revised: 23 November 2004, Published online: 15 February 2005PACS: 11.30.Hv, 12.15.-y, 13.15. + g, 12.38.-t, 13.60.Hb