A Quick Tour of Ultra-Relativistic Heavy-Ion Physics at the LHC

A brief summary of results on Pb+Pb collisions from ALICE, ATLAS, and CMS is presented covering global event properties, anisotropic flow, jet quenching, and quarkonia.Comment: 11 pages, 8 figures, plenary talk given at the DIS2012 conference, Bonn, Germany, 26-30 March 201

Direct-Photon Production in Au+Au Collisions at RHIC

Results from the PHENIX experiment on direct-photon production in Au+Au collisions at sqrt{s_{NN}} = 200 GeV for transverse momenta 1 < p_T < 13 GeV/c are presented. Direct-photon yields at high p_T scale as expected for particle production in hard processes. This supports jet-quenching models which attribute the suppression of high-p_T hadrons to the energy loss of fast partons in the quark-gluon plasma. The low-p_T direct-photon spectra, measured via e+e- pairs with small invariant masses, are possibly related to the production of thermal direct photons in Au+Au collisions at RHIC.Comment: 5 pages, 3 figures, to appear in the proceedings of the 9th Conference on the Intersections of Particle and Nuclear Physics (CIPANP 2006), Puerto Rico, 30 May - 3 June 200

Entropy production in pp and Pb-Pb collisions at energies available at the CERN Large Hadron Collider

We use experimentally measured identified particle spectra and Hanbury Brown-Twiss radii to determine the entropy per unit rapidity $dS/dy$ produced in $\sqrt{s} = 7$ TeV pp and $\sqrt{s_{\rm NN}} = 2.76$ TeV Pb-Pb collisions. We find that $dS/dy = 11335 \pm 1188$ in 0-10% Pb-Pb, $dS/dy = 135.7 \pm 17.9$ in high-multiplicity pp, and $dS/dy = 37.8 \pm 3.7$ in minimum bias pp collisions and compare the corresponding entropy per charged particle $(dS/dy)/(dN_{\rm ch}/dy)$ to predictions of statistical models. Finally, we use the QCD kinetic theory pre-equilibrium and viscous hydrodynamics to model entropy production in the collision and reconstruct the average temperature profile at $\tau_0 = 1$ fm/$c$ for high multiplicity pp and Pb-Pb collisions.Comment: 13 pages, 9 figures; added an appendix on relation between 1D and 3D HBT radii, updated references, small corrections, published versio

Production of Neutral Pions and Eta-mesons in pp Collisions Measured with ALICE

Invariant cross sections for neutral pions and eta mesons in pp collisions at sqrt(s) = 0.9, 2.76, and 7 TeV were measured by the ALICE detector at the Large Hadron Collider. Next-to-leading order (NLO) perturbative QCD calculations describe the pi0 and eta spectra at 0.9 TeV, but overestimate the measured cross sections at 2.76 TeV and 7 TeV. The measured eta/pi0 ratio is consistent with mT scaling at 2.76 TeV. At 7 TeV indications for a violation of mT scaling were found.Comment: 4 pages, 2 figures, to appear in the proceedings of the XXII International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, Quark Matter 2011, Annec

Characteristics of Parton Energy Loss Studied with High-p_T Particle Spectra from PHENIX

In the first three years of the physics program at the Relativistic Heavy Ion Collider (RHIC) a picture was established in which the suppression of hadrons at high transverse momenta (p_T) in central Au+Au collisions is explained by energy loss of quark and gluon jets in a medium of high color-charge density. Measurements of single particle spectra for a smaller nucleus (Cu), for different center-of-mass energies and with higher statistics were performed in the subsequent years and are used to test predictions and assumptions of jet quenching models in more detail. The measurements presented here are consistent with a parton energy loss scenario so that these models can be used to relate the observed suppression to properties of the created medium.Comment: To appear in the proceedings of 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008), Jaipur, India, 04-10 Feb 200