Measurement of high p_T isolated prompt photons in lead-lead collisions at sqrt(s_NN)=2.76 TeV with the ATLAS detector at the LHC

Prompt photons are a powerful tool to study heavy ion collisions. Their production rates provide access to the initial state parton distribution functions and also provide a means to calibrate the expected energy of jets that are produced in the medium. The ATLAS detector measures photons with its hermetic, longitudinally segmented calorimeter, which gives excellent spatial and energy resolutions, and detailed information about the shower shape of each measured photon. This provides significant rejection against the expected background from the decays of neutral pions in jets. Rejection against jet fragmentation products is further enhanced by requiring candidate photons to be isolated. First results on the spectra of isolated prompt photons from a dataset with an integrated luminosity of approximately 0.13 nb^-1 of lead-lead collisions at sqrt(s_NN)=2.76 TeV are shown as a function of transverse momentum and centrality. The measured spectra are compared to expectations from perturbative QCD calculations.Comment: Proceedings for Hard Probes 2012, May 27 - June 1, 2012, Cagliari, Sardinia, Ital

Thoughts on Heavy Quark Production

Various aspects of heavy flavor production in heavy ion collisions in the context of elementary collisions are reviewed. The interplay between theory in experiment in \epem and \pbarp data is been found to be non-trivial, even with new NLO calculations. Quarkonium suppression in p+A and A+A show puzzling features, apparently connected to features of inclusive particle production. Open charm is found to scale as expected for a hard process, but strangeness is also found to share these features. These features contribute to heavy flavor as a interesting probe of strong interactions.Comment: 16 Pages, 17 figures, invited talk at Hot Quarks 2004, Taos, New Mexico, July 18-24, 200

Global Observables at RHIC

The first three measurements from the RHIC program were results on global observables: charged particle multiplicity (N_ch), transverse energy (E_T) and elliptic flow (v_2). They offer a look at the large-scale features of particle production in high-energy nuclear collisions, with particular insight into entropy production and collective behavior. Results from all of the RHIC experiments are discussed in light of data from lower energy nuclear collisions as well as from high-energy hadronic collisions to test our current understanding of the collision dynamics.Comment: 9 Pages, 12 Figures, for QM2001, Stony Broo

Systematics of Charged Particle Production in Heavy-Ion Collisions with the PHOBOS Detector at RHIC

The multiplicity of charged particles produced in Au+Au collisions as a function of energy, centrality, rapidity and azimuthal angle has been measured with the PHOBOS detector at RHIC. These results contribute to our understanding of the initial state of heavy ion collisions and provide a means to compare basic features of particle production in nuclear collisions with more elementary systems.Comment: 4 pages, 4 figures (in eps) talk given at XXXI International Symposium on Multiparticle Dynamics, Sep. 1-7, 2001, Datong China URL http://ismd31.ccnu.edu.cn

Bidirectional transport and pulsing states in a multi-lane ASEP model

In this paper, we introduce an ASEP-like transport model for bidirectional motion of particles on a multi-lane lattice. The model is motivated by {\em in vivo} experiments on organelle motility along a microtubule (MT), consisting of thirteen protofilaments, where particles are propelled by molecular motors (dynein and kinesin). In the model, organelles (particles) can switch directions of motion due to "tug-of-war" events between counteracting motors. Collisions of particles on the same lane can be cleared by switching to adjacent protofilaments (lane changes). We analyze transport properties of the model with no-flux boundary conditions at one end of a MT ("plus-end" or tip). We show that the ability of lane changes can affect the transport efficiency and the particle-direction change rate obtained from experiments is close to optimal in order to achieve efficient motor and organelle transport in a living cell. In particular, we find a nonlinear scaling of the mean {\em tip size} (the number of particles accumulated at the tip) with injection rate and an associated phase transition leading to {\em pulsing states} characterized by periodic filling and emptying of the system.Comment: 11 figure