Z. Z. Xu

Distributions of charged hadrons associated with high transverse momentum particles in pp and Au plus Au collisions at root(S)(NN)=200 GeV

Charged hadrons in 0.154 GeV/c are reconstructed in pp and Au+Au collisions at sqrt(s_NN)=200 GeV. The associated multiplicity and pt magnitude sum are found to increase from pp to central Au+Au collisions. The associated pt distributions, while similar in shape on the near side, are significantly softened on the away side 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 away-side fragments approach equilibration with the medium traversed.

Spectra and radial flow in relativistic heavy ion collisions with Tsallis statistics in a blast-wave description

We have implemented the Tsallis statistics in a Blast-Wave model (TBW) and applied it to midrapidity transverse-momentum spectra of identified particles measured at BNL Relativistic Heavy Ion Collider (RHIC). This new TBW function fits the RHIC data very well for p{sub T}<3 GeV/c. We observed that the collective flow velocity starts from zero in p+p and peripheral Au+Au collisions and grows to 0.470{+-}0.009c in central Au+Au collisions. The resulting (q-1) parameter, which characterizes the degree of nonequilibrium in a system, indicates an evolution from a highly nonequilibrated system in p+p collisions toward an almost thermalized system in central Au+Au collisions. The temperature and collective velocity are well described by a quadratic dependence on (q-1). Two sets of parameters in our TBW are required to describe the meson and baryon groups separately in p+p collisions while one set appears to fit all spectra in central Au+Au collisions.

A `soft + hard' model for heavy-ion collisions

We describe the spectra of neutral pions stemming from AuAu collisions at in a soft + hard model. The model is based on the assumptions that hadrons stemming from hard processes are described via perturbative quantum chromodynamics improved parton model calculations, while those stemming from the Quark-Gluon Plasma (we refer to as soft yields) can be described in a super-statistical model induced by multiplicity uctuations. The obtained dependence of the parameters of the model on the event centrality is compared to what is observed in PbPb collisions at .

Systematic study of the experimental measurements on ratios of different

The world data on yields and ratios of different

\Upsilon

ensuremath{Upsilon}

states

states created in hadron collisions at

Systematic study of the experimental measurements on J/ψ cross sections and kinematic distributions in p+p collisions at different energies

sqrt{s}=19text{--}8000

Coherent J/ψ photoproduction in hadronic heavy-ion collisions

GeV are examined in a systematic way. We derive that the ratios of

Net charge fluctuations in Au+Au collisions at root s(NN)=130 GeV

ensuremath{Upsilon}(2S)/ensuremath{Upsilon}(1S)

Onset of radial flow in p+p collisions

and