Bulk Observables in pp, dA and AA Collisions at RHIC

Results on charged particle production in p+p, d+Au and Au+Au collisions at RHIC energies (sqrt(s_NN) = 19.6 to 200 GeV) are presented. The data exhibit remarkable, and simple, scaling behaviors, the most prominent of which are discussed.

Overview of ALICE results in pp, pA and AA collisions

The ALICE experiment at the Large Hadron Collider (LHC) at CERN is optimized for recording events in the very large particle multiplicity environment of heavy-ion collisions at LHC energies. The ALICE collaboration has taken data in Pb-Pb collisions in Run I and Run II at nucleon-nucleon center-of-mass energies $sqrt{s_{text{NN}}}$ = 2.76 and mbox{5.02 TeV}, respectively, and in pp collisions at center-of-mass energies $sqrt{s}$ = 0.9, 2.76, 5.02, 7, 8 and 13 TeV. The asymmetric system p-Pb was measured at a center-of-mass energy $sqrt{s_{text{NN}}}$ = 5.02 TeV. Selected physics results from the analysis of these data are presented, and an outline of the ALICE prospects for Run III is given.

Pion spectra and HBT radii at RHIC and LHC

We describe RHIC pion data in central A+A collisions and make predictions for LHC based on hydro-kinetic model, describing continuous 4D particle emission, and initial conditions taken from Color Glass Condensate (CGC) model.

Charm-hadron production in $pp$ and AA collisions

Recent measurements of various charm-hadron ratios in $pp$, $p$-Pb and Pb-Pb collisions at the LHC have posed challenges to the theoretical understanding of heavy-quark hadronization. The $Lambda_c/D^0$ ratio in $pp$ and $p$-Pb collisions shows larger values than those found in $e^+e^-$ and $ep$ collisions and predicted by Monte-Carlo event generators based on string fragmentation, at both low and intermediate transverse momenta ($p_T$). In AA collisions, the $D_s/D$ ratio is significantly enhanced over its values in $pp$, while the $Lambda_c/D^0$ data indicates a further enhancement at intermediate $p_T$. Here, we report on our recent developments for a comprehensive description of the charm hadrochemistry and transport in $pp$ and $AA$ collisions. For $pp$ collisions we find that the discrepancy between the $Lambda_c/D^0$ data and model predictions is much reduced by using a statistical hadronization model augmented by a large set of missing states in the charm-baryon spectrum, contributing to the $Lambda_c$ via decay feeddown. For $AA$ collisions, we develop a 4-momentum conserving resonance recombination model for charm-baryon formation implemented via event-by-event simulations that account for space-momentum correlations (SMCs) in transported charm- and thermal light-quark distributions. The SMCs, together with the augmented charm-baryon states, are found to play an important role in describing the baryon-to-meson enhancement at intermediate momenta. We emphasize the importance of satisfying the correct (relative) chemical equilibrium limit when computing the charm hadrochemistry and its momentum dependence with coalescence models.

Universal anti-baryon density in $e^+e^-$,$gamma p$, pp, pA and AA collisions

We compiled the systematical measurements of anti-nucleus production in ultra-relativistic heavy ion collisions as well as those in $pp$, $pbar{p}$, $gamma p$ and $e^{+}e^{-}$ at various beam energies. The anti-baryon phase space density inferred from $bar{d}/bar{p}$ ratio in $A+A$, $p+A$, $pp(bar{p})$ and $gamma p$ collisions is found to follow a universal distribution as a function of center of mass of beam energy and can be described in a statistical model. We demonstrated that anti-baryon density in all the collisions is the highest when the collisions are dominated by the processes of $g+g$ or $bar{q}+g$. In $e^+e^-$ collisions at LEP, the cross section of $qbar{q}g$ is suppressed by a factor of strong coupling constant $alpha_s$ relative to $qbar{q}$. This can consistently explain the $bar{d}$ suppression observed by ALEPH relative to that in $e^+e^-to ggg$ by ARGUS. We discuss the implications to the baryon enhancement at high transverse momentum at RHIC when jet is quenched.