High transverse momentum Ξ baryon correlations in p+p collisions at √s=200 GeV

Angular correlations between produced high-p _TΞ^? baryons and unidentified charged and neutral particles are observed in high-tower triggered (on a large electromagnetic energy deposit) √s=200 GeV p+p collisions. This trigger favors events with higher average multiplicity than those in minimum bias. These events are likely to contain jets. The average multiplicity of a high-tower triggered event is similar to that of a minimum bias event containing a Ξ baryon, which implies that Ξ baryons are likely to be produced in jets. Ξ^? <p _T> is higher in the triggered data then in the minimum bias sample.     

High transverse momentum correlations in STAR

Azimuthal correlations of charged hadrons with transverse momenta above 2 GeV/c are measured relative to ≥ GeV/c trigger particle in p+p and Au+Au at $\sqrt {s_{NN} } = 200$ GeV in STAR. The correlations exhibit small relative azimuthal angle correlations characteristic of jets. The p+p and peripheral Au+Au data exhibit a peak on the opposite side of the jet indicating the presence of hard scattering in the form of di-jets. The away-side jet disappears for the most central Au+Au collisions, suggesting jet quenching in a dense medium.     

Search for collective transverse flow using particle transverse momentum spectra in relativistic heavy-ion collisions

The particle transverse momentum spectra recently measured in relativistic heavy-ion collisions at CERN and BNL are analysed within an expanding fireball model. All the particle spectra at a given beam energy can be reproduced simultaneously with a single set of intensive parameters for the initial state of the fireball. As typical freeze-out parameters in this beam energy region we find a freeze-out temperatureT _f?110 MeV for most hadrons, and an average transverse expansion velocity at freeze-out of 〈v/c〉?0.4–0.45. The striking enhancement at transverse momentap _T<200 MeV/c in the CERN pion data cannot be fully explained by the existence of transverse flow.     

Centrality dependence of charged hadron transverse momentum spectra in Au+Au collisions from sqrt[s(NN)]=62.4 to 200 GeV

We have measured transverse momentum distributions of charged hadrons produced in Au+Au collisions at sqrt[s(NN)]=62.4 GeV. The spectra are presented for transverse momenta 0.25相似文献   

Absence of suppression in particle production at large transverse momentum in sqrt[s(NN)]=200 GeV d+Au collisions

Transverse momentum spectra of charged hadrons with p(T)<8 GeV/c and neutral pions with p(T)<10 GeV/c have been measured at midrapidity by the PHENIX experiment at BNL RHIC in d+Au collisions at sqrt[s(NN)]=200 GeV. The measured yields are compared to those in p+p collisions at the same sqrt[s(NN)] scaled up by the number of underlying nucleon-nucleon collisions in d+Au. The yield ratio does not show the suppression observed in central Au+Au collisions at RHIC. Instead, there is a small enhancement in the yield of high momentum particles.     

Strange particle production in nuclear collisions at 200 GeV per nucleon

Multiplicities and spectra of strange particles ( andK ^– produced in central³²S+S,³²S+Ag and³²S+Au collisions at 200 GeV per nucleon are presented and compared with data on strange particle production in protonnucleus and nucleon-nucleon interactions. It is shown that strangeness production in³²S+Ag collisions is enhanced by a factor of two, similar to that found previously in central³²S+S collisions.     

Meson-baryon femtoscopy in Au+Au collisions at 200 GeV measured by STAR experiment

Correlations between non-identical particles at small relative velocity probe asymmetries in the average space-time emission points at freezeout [1]. Such asymmetries may arise from long-lived resonances, bulk collective effects, or differences in the freezeout scenario for the different particle species. STAR has extracted pion-proton correlation functions from a high-statistics dataset of Au+Au collisions at ?{s_NN }\sqrt {s_{NN} } = 200 GeV. We present a femtoscopic analysis of this data for all combinations of charged pions and (anti-) protons, for collisions of different centrality. The measurements are compared with calculations of a simple Blast-wave model, in which asymmetries are driven only by collective flow, as well as with Therminator [2], which also accounts fully for resonance effects.     

A study of final states with a large transverse momentum particle from proton-proton collisions at 24 GeV/c

Events with a large transverse momentum (>1 GeV/c) pion or nucleon have been selected from the data of a high-statistics pp bubble chamber experiment (√s=6.84 GeV). Only events in which all secondary particles could be identified were used. One finds that fewer pions are produced in the azimuthal hemisphere containing the large transverse momentum particle than in the opposite hemisphere. An indication for coplanarity is found. Most pions associated with a large transverse momentum pion are emitted with small absolute c.m. rapidities, whereas those associated with large transverse momentum nucleons show some back-to-back structure. Various results of this investigation are similar to those obtained at the ISR. Most of the findings are compatible with predictions from an independent emission model.     

J/psi production versus transverse momentum and rapidity in p+p collisions at square root s=200 GeV

J/psi production in p+p collisions at square root s=200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over a rapidity range of -2.2相似文献   

Neutral transverse momentum spectra in 60 and 200A·GeV16O+nucleus and proton+nucleus reactions

Transverse momentum (p _T) distributions fo inclusive photons and neutral pions at midrapidity are measured with a lead glass calorimeter in 60 and are measured with a lead glass calorimeter in 60 and 200A·Gev¹⁶O+nucleus and and proton+nucleus reactions. Inclusive photon distributions are compared for central and peripheral reactions. The degree of centrality is determined either from the charged particle multiplicity or from the remaining projectile energy in the forward direction. Deviations from a nucleus+nucleus interaction model based upon linear extrapolation from p+p reactions are observed in central¹⁶O+Au data. The variation of theaverage transverse momentum is investigated as function of centrality. The target-mass and energy dependence of π⁰ p _T distributions are presented. For¹⁶O+Au a change of slope in these distributions is observed atp _t ≈0.8 GeV/c compatible with hydrodynamic expansion models.     

Study of jet fragmentation in p+p collisions at 200 GeV in the STAR experiment

The measurement of jet fragmentation functions in p+p collisions at 200 GeV is of great interest because it provides a baseline to study jet quenching in heavy-ion collisions. It is expected that jet quenching in nuclear matter modifies the jet energy and multiplicity distributions, as well as the jet hadrochemical composition. Therefore, a systematic study of the fragmentation functions for charged hadrons and identified particles is a goal both in p+p and Au+Au collisions at RHIC. Studying fragmentation functions for identified particles is interesting in p+p by itself because it provides a test of NLO calculations at RHIC energies. We present a systematic comparison of jet energy spectra and fragment distributions using different jet-finding algorithms in p+p collisions in STAR. Fragmentation functions of charged and neutral strange particles are also reported for different jet energies.     

Event-by-event fluctuations of mean transverse momentum in AuAu collisions in STAR experiment at relativistic heavy-ion collider

We report results on event-by-event fluctuations in mean transverse momentum in AuAu collisions at GeV measured by the STAR experiment at RHIC. The dynamical fluctuations, is found to be about 1.2 ±02% of the mean transverse momentum for particles in pseudo-rapidity range of −0.5 < η < 0.5 and for the top 6% central collisions.     

Statistical hadronization model and transverse momentum spectra of hadrons in high energy collisions

A detailed analysis of transverse momentum spectra of several identified hadrons in high energy collisions within the canonical framework of the statistical model of hadronization is performed. The study of particle momentum spectra requires an extension of the statistical model formalism used to handle particle multiplicities, which is described in detail starting from a microcanonical treatment of single hadronizing clusters. Also, a new treatment of extra strangeness suppression is presented which is based on the enforcement of fixed numbers of pairs in the primary hadrons. The considered center-of-mass energies range from to 30 GeV in hadronic collisions ( and Kp) and from 15 to 35 GeV in collisions. The effect of the decay chain following hadron generation is accurately and exhaustively taken into account by a newly proposed numerical method. The exact conservation at low energy and the increasing hard parton emission at high energy bound the validity of the presently taken approach within a limited center-of-mass energy range. However, within this region, a clear consistency is found between the temperature parameter extracted from the present analysis and that obtained from fits to average hadron multiplicities in the same collision systems. This finding indicates that in the hadronization process the production of different particle species and their momentum spectra are two closely related phenomena governed by one parameter. Received: 31 October 2001 / Published online: 15 February 2002     

Collective flow model for the pion transverse momentum spectra from relativistic nuclear collisions at CERN

The transverse momentum spectra for pions observed by WA80 and NA35 collaborations are analysed within a fireball model with collective isentropic expansion and a realistic freeze-out criterion. By varing the initial state of the fireball, an excellent fit to the data is achieved for the whole measured range ofP _T . Slight differences in the data for the spectral slopes from central and pheripheral collisions originate in our model from the difference in the size of the fireball and in the number of participating nucleons in central and peripheral collisions. Using additional information from two-pion correlations, we can extrapolate our model back from the freeze-out point (determined from the spectra) to the initial state; we find that an initial energy density of 1.5–2GGeV/fm³ is sufficient to explain the data from central O+Au collisions at 200A GeV.     

System size and centrality dependence of charged hadron transverse momentum spectra in Au + Au and Cu + Cu collisions at square root of SNN = 62.4 and 200 GeV

We present transverse momentum distributions of charged hadrons produced in Cu + Cu collisions at square root of SNN = 62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25 < pT < 5.0 GeV/c at square root of SNN = 62.4 GeV and 0.25 < pT < 7.0 GeV/c at square root of SNN = 200 GeV, in a pseudorapidity range of 0.2 < eta < 1.4. The nuclear modification factor R(AA) is calculated relative to p + p data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross section, R(AA) is observed to be systematically larger in Cu + Cu collisions compared to Au + Au. However, for the same number of participating nucleons, R(AA) is essentially the same in both systems over the measured range of pT, in spite of the significantly different geometries of the Cu + Cu and Au + Au systems.     

J/psi production versus centrality, transverse momentum, and rapidity in Au+Au collisions at square root sNN=200 GeV

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured J/psi production for rapidities -2.2相似文献   

Distributions of charged hadrons associated with high transverse momentum particles in pp and Au+Au collisions at sqrt[sNN]=200 GeV

Charged hadrons in [EQUATION: SEE TEXT] associated with particles of [EQUATION: SEE TEXT] are reconstructed in pp and Au+Au collisions at sqrt[sNN]=200 GeV. The associated multiplicity and p magnitude sum are found to increase from pp to central Au+Au collisions. The associated p distributions, while similar in shape on the nearside, are significantly softened on the awayside in central Au+Au relative to pp and not much harder than that of inclusive hadrons. The results, consistent with jet quenching, suggest that the awayside fragments approach equilibration with the medium traversed.