Bulletin of the American Physical Society
2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011; East Lansing, Michigan
Session CA: Mini-Symposium on From RHIC to LHC: Lessons Learned about the QGP I |
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Chair: Steffen Bass, Duke University Room: 62 |
Thursday, October 27, 2011 8:30AM - 9:06AM |
CA.00001: From RHIC to LHC: Lessons on the QGP Invited Speaker: Ulrich Heinz Recent data from heavy-ion collisions at RHIC and LHC, together with significant advances in theory, have allowed us to make significant first steps in proceeding from a qualitative understanding of high energy collision dynamics to a quantitative characterization of the transport properties of the hot and dense QCD matter created in these collisions. The almost perfectly liquid nature of the Quark-Gluon Plasma (QGP) created at RHIC has recently also been confirmed at the much higher LHC energies, and we can now constrain the specific QGP shear viscosity $(\eta/s)_{\mathrm{QGP}}$ to within a factor of 2.5 of its conjectured lower quantum bound. Viscous hydrodynamics, coupled to a microscopic hadron cascade at late times, has proven to be an extremely successful and highly predictive model for the QGP evolution at RHIC and LHC. The experimental discovery of higher order harmonic flow coefficients and their theoretically predicted differential sensitivity to shear viscosity promises additional gains in precision by about a factor 5 in $(\eta/s)_{\mathrm{QGP}}$ for the very near future. The observed modification of jets and suppression of high-$p_T$ hadrons confirms the picture of the QGP as a strongly coupled colored liquid, and recent LHC data yield strong constraints on parton energy loss models, putting significant strain on some theoretical approaches, tuned to RHIC data, that are based on leading-order perturbative QCD. Thermal photon radiation provides important cross-checks on the early stages of dynamical evolution models and constrains the initial QGP temperature, but the recently measured strong photon elliptic flow challenges our present understanding of photon emission rates in the hadronic phase. Recent progress in developing a complete theoretical model for all stages of the QGP fireball expansion, from strong fluctuating gluon fields at its beginning to final hadronic freeze-out, and remaining challenges will be discussed. [Preview Abstract] |
Thursday, October 27, 2011 9:06AM - 9:18AM |
CA.00002: Elliptic flow in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$~TeV with the ALICE experiment Alexandru Florin Dobrin The elliptic azimuthal event anisotropy, $v_2$, is an important observable used to study the nature and properties of matter created in heavy-ion collisions. We report on measurements of $v_2$ for inclusive and identified charged particles in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$~TeV recorded by the ALICE experiment at the LHC. $v_2$ is presented for a wide range of particle transverse momenta up to $p_T=20$~GeV/c. The results are compared to the measurements at lower energy reported by RHIC experiments and also to theoretical predictions. [Preview Abstract] |
Thursday, October 27, 2011 9:18AM - 9:30AM |
CA.00003: What kind of sQGP is the matter created at RHIC and LHC? Jinfeng Liao One of the main discoveries at RHIC is the so-called ``perfect fluid,'' and one of the most interesting things to see at LHC is whether and how such ``perfect fluid'' property will change at much higher collisional energies. I argue these will provide unique opportunity to answer theoretical question about the nature of sQGP. I will discuss two very different scenarios for the QGP in the temperature range from RHIC to LHC: (1) sQGP as a ``see-saw''-QGP of its electric and magnetic components, which is inspired by the deep and generic Electric-Magnetic duality in field theories; (2) sQGP as a super-strong-QGP, which may have a holographic dual in one form or another due to the strong coupling. The two scenarios predict different medium properties (viscosity, and opacity to hard probes) with increasing temperature from RHIC to LHC, therefore making them distinguishable at the upcoming LHC top energy PbPb collisions. The first hints of a possible change in created matter's structure at LHC 2.76TeV collisions as well as expectations for 5.5TeV collisions will be discussed. [Preview Abstract] |
Thursday, October 27, 2011 9:30AM - 9:42AM |
CA.00004: Analysis of the inclusive differential jet spectrum in pp collisions at $\sqrt{s}$=2.76 TeV with ALICE at the LHC Rongrong Ma Quantum-Chromodynamics (QCD) predicts that a new state of hot, dense matter, normally referred to as the Quark-Gluon Plasma (QGP), can be created in ultra-relativistic heavy-ion (HI) collisions. Investigating the features of this strongly interacting matter has been the main goal of the field. Full jet reconstruction provides a direct, unbiased probe to study the medium effects. With the advent of the HI run at the Large Hadron Collider (LHC), we are able to measure QGP properties in a new energy domain. In this talk, we present the analysis of the inclusive differential jet spectrum in pp collisions at $\sqrt{s}$=2.76 TeV, which is an essential reference for jet measurements in Pb-Pb collisions at the same $\sqrt{s_{NN}}$. The measurement is based on charged particle tracking in the ALICE central tracking system, and neutral energy measured in the Electromagnetic Calorimeter (EMCal). Especially, high tower triggers provided by the EMCal are used to greatly enhance the kinematic reach of the inclusive jet cross section measurement with ALICE. [Preview Abstract] |
Thursday, October 27, 2011 9:42AM - 9:54AM |
CA.00005: Fluctuation and Correlation Probes of Early Time Dynamics Sean Gavin, George Moschelli Measurements of two-particle correlations in nuclear collisions exhibit a complex pattern of ridges, peaks, and valleys as functions of relative pseudorapidity and azimuthal angle. The azimuthal dependence of these correlations can be described as anisotropic flow by introducing a novel triangular v3 component comparable to the more familiar elliptic v2 contribution. Triangularity has been attributed to by event-wise fluctuations in the initial shape of the collision volume. We ask two questions: 1) How do shape fluctuations impact other event-by-event observables? 2) Can we disentangle fundamental information on the early time behavior that produces these fluctuations from the complex flow that results? We study correlations and fluctuations in a framework in which an early Glasma stage produces fluctuations in the number and position of flux tubes in concert with late-stage hydrodynamic flow. We show how flow observables v1, v2, and v3 can be combined with multiplicity and transverse momentum fluctuations to disentangle Glasma information from hydrodynamic effects. Computations are then compared to a range of LHC and RHIC data [Preview Abstract] |
Thursday, October 27, 2011 9:54AM - 10:06AM |
CA.00006: Measurement of Charge Multiplicity Asymmetry Correlations to Search for Chiral Magnetic Effect in Heavy Ion Collisions Quan Wang It has been suggested that local parity violation in QCD would lead to charge separation of quarks by the Chiral Magnetic Effect (CME) in heavy ion collisions. Charge separation could yield a dynamical charge multiplicity asymmetry with respect to the reaction plane. In this talk, we report results on charge multiplicity asymmetry correlations in $\sqrt{s_{NN}}$ = 200 GeV Au+Au and d+Au collisions by the STAR experiment, as well as from the RHIC beam energy scan. We found that the correlation results could not be explained by CME alone. To gain further insights, we study our results as a function of the measured azimuthal angle range as well as the event-by-event anisotropy parameter $v_2$. The results indicate that the charge separation effect appears to be in-plane rather than out-of-plane. We found that the charge separation effect is proportional to the event-by-event $v_2$ and consistent with zero in events with $v_2 \approx 0$. Our studies suggest that the charge separation effect, within the statistical error, may be a net effect of event anisotropy and correlated particle production. Possible upper limit on the CME imposed by our data will be discussed. [Preview Abstract] |
Thursday, October 27, 2011 10:06AM - 10:18AM |
CA.00007: Local Parity Violation or Local Charge Conservation/Flow? A Reaction-Plane-Dependent Balance Function Study Hui Wang STAR has recently reported charge-dependent azimuthal correlations using a three particle correlator that is sensitive to the charge separation effect in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. Qualitatively, these results agree with some of the theoretical predictions for local parity violation in heavy-ion collisions. However, a study using reaction-plane-dependent balance functions shows an alternative origin of this signal. The balance function, which measures the correlation between oppositely charged pairs, is sensitive to the mechanisms of charge formation and the subsequent relative diffusion of the balancing charges. We report reaction-plane-dependent balance functions for Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV using the STAR detector. The reaction-plane-dependent balance function analysis is consistent with the three particle correlator analysis as expected mathematically. The model of Schlicting and Pratt incorporating local charge conservation and elliptic flow can reproduce most of the three-particle azimuthal correlation results at 200 GeV. [Preview Abstract] |
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