To describe large momentum distributions of charged particles observed at RHIC, a diffusion equation in the three dimensional hyperbolic space is introduced.
In order to describe large transverse momentum ($p_T$) distributions observed in high energy nucleus-nucleus collisions, a stochastic model in the three dimensional rapidity space is introduced. The fundamental solution of the radial symmetric diffusion equation is Gaussian-like in radial rapidity. We can also derive a $p_T$ or radial rapidity distribution function, where a distribution of emission center is taken into account. It is applied to the analysis of observed large $p_T$ distributions of charged particles. It is shown that our model approaches to a power function of $p_T$ in the high transverse momentum limit.
The transverse momentum distributions of various hadrons produced in most central Pb+Pb collisions at LHC energy Root(s_NN) = 2.76 TeV have been studied using our earlier proposed unified statistical thermal freeze-out model. The calculated results are found to be in good agreement with the experimental data measured by the ALICE experiment. The model calculation fits provide the thermal freeze-out conditions in terms of the temperature and collective flow effect parameters for different particle species. Interestingly the model parameter fits reveal a strong collective flow in the system which appears to be a consequence of the increasing particle density at LHC. The model used incorporates a longitudinal as well as transverse hydrodynamic flow. The chemical potential has been assumed to be nearly equal to zero for the bulk of the matter owing to a high degree of nuclear transparency effect at such energies. The contributions from heavier decay resonances are also taken into account in our calculations.
Transverse momentum spectra of protons and anti-protons from RHIC ($sqrt{s}$ = 62 and 200 GeV) and LHC experiments ($sqrt{s}$= 0.9 and 7 TeV) have been considered. The data are fitted in the low $p_T$ region with the universal formula that includes the value of exponent slope as a main parameter. It is seen that the slope of low-$p_T$ distributions is changing with energy. This effect impacts on the energy dependence of average transverse momenta, which behaves approximately as $s^{0.06}$ that is similar to the previously observed behavior for $Lambda^0$-baryon spectra. In addition, the available data on $Lambda_c$ production from LHCb at $sqrt{s}= 7$ TeV were also studied. The estimated average $<p_T>$ is bigger than this value for protons proportionally to masses. The preliminary dependence of hadron average transverse momenta on their masses at LHC energy is presented.
It has long been debated whether the hydrodynamics is suitable for the smaller colliding systems such as p+p collisions. In this paper, by assuming the existence of longitudinal collective motion and long-range interactions in the hot and dense matter created in p+p collisions, the relativistic hydrodynamics incorporating with the nonextensive statistics is used to analyze the transverse momentum distributions of the particles. The investigations of present paper show that the hybrid model can give a good description of the currently available experimental data obtained in p+p collisions at RHIC and LHC energies, except for p and p^bar produced in the range of p_T> 3.0 GeV/c at sqrt(s)=200 GeV.
The new data on k_t distributions obtained at RHIC are analysed by means of selected models of statistical and stochastic origin in order to estimate their importance in providing new information on hadronization process, in particular on the value of the temperature at freeze-out to hadronic phase.
N.Suzuki
,M.Biyajima
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(2003)
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"Analysis of transverse momentum distributions observed at RHIC by a stochastic model in hyperbolic space"
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Naomichi Suzuki
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