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.
Elliptic flow in Au+Au collisions at RHIC Vale, Carla M; Back, B B; Baker, M D ...
Journal of physics. G, Nuclear and particle physics,
04/2005, Letnik:
31, Številka:
4
Journal Article, Conference Proceeding
The PHOBOS experiment has measured the properties of particle production in heavy ion collisions between sqrt(s_NN) of 20 and 200 GeV. The dependencies of charged particle yield on energy, system ...size, and both longitudinal and transverse momentum have been determined over close to the full kinematic range. Identified charged particles emitted near mid-rapidity have been studied over about 2 orders of magnitude in transverse momentum. This broad data set was found to be characterized by a small number of simple scalings which factorize to a surprising degree. This study has recently been extended by the addition of new data for Cu+Cu as well as new analyses of Au+Au data, including more peripheral collisions. In addition, the exploration of global properties has been expanded with the use of new techniques, including two-particle correlations, more sensitive searches for rare events, and more detailed studies of particles emitted at very forward rapidity. The characteristics of particle production which are revealed by this extensive data set will be described along with the implications for future data from the LHC.
The PHOBOS experiment at the BNL Relativistic Heavy Ion Collider has measured the total multiplicity of primary charged particles as a function of collision centrality in Au+Au collisions at ...{radical}(s{sub NN})= 19.6, 130, and 200 GeV. An approximate independence of <N{sub ch}>/<N{sub part}/2> on the number of participating nucleons is observed, reminiscent of 'wounded nucleon' scaling (N{sub ch}{proportional_to}N{sub part}) observed in proton-nucleus collisions. Unlike p+A, the constant of proportionality does not seem to be set by the pp/pp data at the same energy. Rather, there seems to be a surprising correspondence with the total multiplicity measured in e{sup +}e{sup -} annihilations, as well as the rapidity shape measured over a large range. The energy dependence of the integrated multiplicity per participant pair shows that e{sup +}e{sup -} and A+A data agree over a large range of center-of-mass energies ({radical}(s)>20 GeV), and pp/pp data can be brought to agree approximately with the e{sup +}e{sup -} data by correcting for the typical energy taken away by leading particles. This is suggestive of a mechanism for soft particle production that depends mainly on the amount of available energy. It is conjectured that the dominant distinction between A+A and p+p collisions is the multiple collisions per participant, which appears to be sufficient to substantially reduce the energy taken away by leading particles.
Differential studies of elliptic flow are one of the most powerful tools in studying the initial conditions and dynamical evolution of heavy ion collisions. The comparison of data from Cu+Cu and ...Au+Au collisions taken with the PHOBOS experiment at RHIC provides new information on the interplay between initial geometry and initial particle density in determining the observed final state flow pattern. Studies from PHOBOS point to the importance of fluctuations in the initial state geometry for understanding the Cu+Cu data. We relate the elliptic flow data to the results of our model studies on initial state geometry fluctuations and discuss how we will perform measurements of event-by-event fluctuations in elliptic flow in Au+Au collisions.
Forward calorimetry in the PHOBOS detector has been used to study charged hadron production in d + Au, p + Au, and n + Au collisions at root s(NN) = 200 GeV. The forward proton calorimeter detectors ...are described and a procedure for determining collision centrality with these detectors is detailed. The deposition of energy by deuteron spectator nucleons in the forward calorimeters is used to identify p + Au and n + Au collisions in the data. A weighted combination of the yield of p + Au and n + Au is constructed to build a reference for Au + Au collisions that better matches the isospin composition of the gold nucleus. The p(T) and centrality dependence of the yield of this improved reference system is found to match that of d + Au. The shape of the charged-particle transverse momentum distribution is observed to extrapolate smoothly from p + (p) over bar to central d + Au as a function of the charged-particle pseudorapidity density. The asymmetry of positively and negatively charged hadron production in p + Au is compared to that of n + Au. No significant asymmetry is observed at midrapidity. These studies augment recent results from experiments at the CERN Large Hadron Collider and BNL Relativistic Heavy Ion Collider facilities to give a more complete description of particle production in p + A and d + A collisions, essential for the understanding the medium produced in high-energy nucleus-nucleus collisions.
We have measured transverse momentum distributions of charged hadrons produced in Au+Au collisions at sqrts(NN)=62.4 GeV. The spectra are presented for transverse momenta 0.25<p(T)<4.5 GeV/c, in a ...pseudorapidity range of 0.2<eta<1.4. The nuclear modification factor R(AA) is calculated relative to p+p data at the same collision energy as a function of collision centrality. For 2<p(T)<4.5 GeV/c, R(AA) is found to be significantly larger than in Au+Au collisions at sqrts(NN)= 130 and 200 GeV. In contrast to the large change in R(AA), we observe a very similar centrality evolution of the p(T) spectra at sqrts(NN)=62.4 and 200 GeV. The dynamical origin of this surprising factorization of energy and centrality dependence of particle production in heavy-ion collisions remains to be understood.
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