Strangeness enhancement in sulphur—Nucleus collisions at 200 A GeV/c

The NA35 experiment used several independent methods to determine the strange particle production in p+S and S+A collisions. The different techniques show consistent results. Strangeness conservation in full phase space is used as an additional check of the consistency of the data. On the base of the analysis in full phase space it could be shown that strangeness conservation is fullfilled. The NA35K _S ⁰ in S+S and S+Ag are consistent with the NA44 results forK ⁺ andK ^?. The results of the NA36 collaboration for S+Pb collisions were extrapolated to full phase space. The comparison with the NA35 results shows more than two times lower yields. The ratio of Λ to $\bar \Lambda $ at midrapidity of NA36 is inconsistent with the high baryon density determind by NA35. The strange particle production is compared to the abundance of non strange particles, especially negatively charged pions which are measured in full phase space in the same experiment. A clear enhanced strange hadron production relative to σ^? is observed in S+Ag collisions compared to p+S reactions at the same energy. TheK _S ⁰ multiplicity in full phase space per negative hadron (h ^?) in S+S, S+Ag and Pb+Pb is enhanced by about a factor 1.6 compared to N+N and p+S collisions. The NA36 result for theK _S ⁰ multiplicity perh ^? in S+Pb is below the N+N value.     

Transverse mass spectra of strange and multi–strange particles in Pb–Pb collisions at 158 A GeV/c

The WA97 experiment has measured the transverse mass spectra for negative hadrons () and strange particles produced at mid–rapidity in Pb–Pb collisions. The increased statistics of analysed data samples allowed us to perform a study of the spectra of , , , and as a function of the collision centrality. The data, which correspond to the most central 40% of the total inelastic cross section, have been divided into four centrality classes according to the estimated number of nucleons taking part in the collision. The spectra, analysed separately for each centrality bin, exhibit only weak ( 15%) centrality dependence. The deviation of the inverse slope from the linear dependence on the particle mass is confirmed even for the most central Pb–Pb collisions. Received: 5 January 2000 / Revised version: 28 February 2000 / Published online: 14 April 2000     

Strangeness enhancement in Cu-Cu and Au-Au collisions at √S(NN)=200 GeV

We report new STAR measurements of midrapidity yields for the Λ, Λ[over ˉ], K(S)(0), Ξ(-), Ξ[over ˉ](+), Ω(-), Ω[over ˉ](+) particles in Cu+Cu collisions at √S(NN)==200 GeV, and midrapidity yields for the Λ, Λ[over ˉ], K(S)(0) particles in Au+Au at √S(NN)==200 GeV. We show that, at a given number of participating nucleons, the production of strange hadrons is higher in Cu+Cu collisions than in Au+Au collisions at the same center-of-mass energy. We find that aspects of the enhancement factors for all particles can be described by a parametrization based on the fraction of participants that undergo multiple collisions.     

φ production in In–In collisions at 158 A GeV

The NA60 experiment has measured muon pair production in In–In collisions at 158 AGeV at the CERN SPS. This paper presents a high statistics measurement of φ→μ μ meson production. Differential spectra, yields, mass and width are measured as a function of centrality and compared to previous measurements in other colliding systems at the same energy. The width of the rapidity distribution is found to be constant as a function of centrality, compatible with previous results. The decay muon polar angle distribution is measured in several reference frames. No evidence of polarization is found as a function of transverse momentum and centrality. The analysis of the p _T spectra shows that the φ has a small radial flow, implying a weak coupling to the medium. The T _eff parameter measured in In–In collisions suggests that the high value observed in Pb–Pb in the kaon channel is difficult to reconcile with radial flow alone. The absolute yield is compared to results in Pb–Pb collisions: though significantly smaller than measured by NA50 in the muon channel, it is found to exceed the NA49 and CERES data in the kaon channel at any centrality. The mass and width are found to be compatible with the PDG values at any centrality and at any p _T : no evidence for in-medium modifications is observed.     

Flow effects in nucleus-nucleus collisions at (4.5×A) GeV/c

The multiplicity distributions of the negative particles are analysed using the moments method, for obtaining some experimental information on the possibility to observe flow processes and correlation between the particles in nucleus-nucleus collisions. The role of the collision geometry is important. The calculations are compared with experimental results for nucleus-nucleus collisions at (4.5×A) GeV/c obtained at the Synchrophasotron from JINR Dubna.Presented (by the first author) at the International School-Workshop Relativistic Heavy-Ion Physics, Prague (Czech Republic), 19–23 September 1994.     

Evidence for the production of thermal muon pairs with masses above 1 GeV/c 2 in 158 A GeV indium-indium collisions

The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c ² produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions. In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson production, but made of prompt muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass and significantly lower than those found at masses below 1 GeV/c ², rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c ² to be of largely partonic origin, when radial flow has not yet built up.     

K − and\bar p Production in Au + Pb Collisions at 11.5 A GeV/cProduction in Au + Pb Collisions at 11.5 A GeV/c

I will present the first results from the E864 collaboration on the production of negative kaons and antiprotons in 10% central 11.5 A GeV/c Au+Pb nucleus collisions at the Brookhaven AGS. E864 is a high rate, open geometry spectrometer, capable of measuring particle production in a range of rapidities and transverse momenta at a single setting of the spectrometer magnets. The results are derived from the analysis of over 20 million central interactions collected in the Fall 1994 run. I will report onK ^? production in a rapidity range from 1.9<y<2.2 (y _cm=1.6) and 25<pT<150 MeV/c, and $\bar p$ production from 1.2<y<2.2 and 50<pT<400 MeV/c. A comparison with previously published results from E878 is presented and the implications for $\bar \Lambda $ production are discussed.     

Multiplicity distributions of shower particles and target fragments in 7Li–Em collisions at 3 A GeV/c

Multiplicity distributions of shower particles and target fragments in ⁷Li–Em (emulsion) collisions at 3 A GeV/c are experimentally studied. In the framework of the multisource thermal model, the multicomponent Erlang distribution is used to describe the experimental multiplicity distributions of shower particles, grey fragments, black fragments, and heavily ionized fragments. The correlations between these multiplicities are experimentally reported. With the increase of impacting centrality (or the target fragment multiplicity), a saturation phenomenon for shower particle multiplicity is observed in the experiment.     

158GeV/c的Pb–Pb碰撞中的J/ψ抑制现象研究

在Blaizot等人建立的模型基础上,我们考虑了核–核碰撞中的参与者数与核子–核子碰撞数的起伏效应对J/?ψ产生的影响,并对NA50合作组在入射动量为158GeV/c的Pb-Pb碰撞中的实验数据进行了分析,理论结果与实验数据符合的很好     

2.22 GeV ηη′ structure observed in 38 GeV / c and 100 GeV / c π−p collisions

A structure has been observed at 2220 MeV in the mass spectrum of ηη′ systems produced by 38GeV/c and 100 GeV/c′ negative pions on protons. The angular distribution of the decay products shows that this structure is presumably a spin J ⩾ 2 meson.     

158A GeV/c Pb+Pb碰撞可能有QGP的一旁证

用不含QGP假设的强子和弦级联模型(JPCIAE) ,研究了CERNWA98实验组新近发表的158 AGeV/c Pb+Pb中心碰撞中直接光子和π⁰粒子的横动量分布:两者的理论结果均一致的低于实验值.联系到JPCIAE能成功解释无直接光子超出确切迹象的WA80和WA93对200A GeV/c S+Au中心碰撞测量得出的结果:因而为158A GeV/c Pb+Pb中心碰撞中可能有QGP生成提供了一个旁证.     

On coherent particle production in central 4.3A GeV/c Mg–Mg collisions

Features of dense groups, or spikes, of negative pions produced in Mg–Mg collisions at 4.3 GeV/c/nucleon are studied to search for a coherent, Čerenkov-like, mechanism of multihadron production. We investigate the distributions of spike centers and, for the first time, the energy spectra of particles in spikes. The spike-center distributions are obtained to exhibit the structure expected from coherent gluon-jet emission dynamics. This structure is similar to that observed recently for all-charged-particle spikes in hadronic and nuclear interactions. The energy distribution within spikes is found to have a significant peak over the inclusive background, while the inclusive spectrum shows exponential decrease with two characteristic values of average kinetic energy. The value of the peak energy and its width are in a good agreement with those expected for pions produced in a nuclear medium in the framework of the Čerenkov quantum approach. The peak energy obtained is consistent with the value of the cross-section maximum observed in coincidence experiments of nucleon-nucleus interactions.     

Inclusive production of protons, anti-protons and neutrons in p+p collisions at 158 GeV/c beam momentum

New data on the production of protons, anti-protons and neutrons in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The charged baryons are identified by energy loss measurement in a large TPC tracking system. Neutrons are detected in a forward hadronic calorimeter. Inclusive invariant cross sections are obtained in intervals from 0 to 1.9 GeV/c (0 to 1.5 GeV/c) in transverse momentum and from ?0.05 to 0.95 (?0.05 to 0.4) in Feynman x for protons (anti-protons), respectively. p _T integrated neutron cross sections are given in the interval from 0.1 to 0.9 in Feynman x. The data are compared to a wide sample of existing results in the SPS and ISR energy ranges as well as to proton and neutron measurements from HERA and RHIC.     

Prompt photon production in proton–nucleus collisions at LHC: a comparison among color dipole models

The nuclear modification factor for prompt photon production in proton–nucleus collisions is investigated within color dipole formalism. By means of the Glauber–Gribov approach, the nuclear effects are studied in various rapidity bins with the evolution equation-based saturation models and the phenomenological dipole models. The theoretical results are compared with the experimental data provided by PHENIX, ATLAS and CMS Collaborations. At forward rapidity and midrapidity, a reasonable agreement...     

Light-front analysis of π− mesons produced in MgMg collisions at 4.3A GeV/c

Light-front analysis of π⁻ mesons in MgMg collisions is carried out. The phase space of secondary pions is naturally divided into two parts in one of which the thermal equilibration assumption seems to be in good agreement with the data. Corresponding temperatures are extracted and compared to the results of other experiments. The experimental results have been compared with the predictions of the Quark-Gluon String Model (QGSM) and satisfactory agreement between the experimental data and the model has been found.     

Neutral strange particle production inK + andπ + collisions with Al and Au nuclei at 250 GeV/c

Data are presented on inclusiveK _s ⁰ and production inK ⁺ and ⁺ collisions with Al and Au nuclei at 250 GeV/c. Results are given on total inclusive cross sections and theA dependence, as well as on distributions in Feynman-x _F , rapidityy and transverse momentum. Ratios ofK _S ⁰ and of to ⁺ production are presented. The data are compared with predictions of the quark-parton model FRITIOF.     

Higher order bose-einstein correlations in π+p and K+p collisions at 250 GeV/c

Bose-Einstein correlations up to fourth order are presented at $\sqrt s = 22GeV$ . Genuine third-order correlations are observed. The experimental data are compared with predictions from a quantum statistical approach of radiation from a partially coherent source and with the FRITIOF model.