Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session NB: Mini-Symposium on Initial-State Fluctuations in Relativistic Heavy Ion Collisions |
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Chair: Agnes Mocsy, Pratt Institute Room: Plaza II |
Saturday, October 27, 2012 8:30AM - 9:06AM |
NB.00001: Initial State and Hydrodynamic Models for Particle Production from the Little Bangs Invited Speaker: Bjoern Schenke The understanding of the initial state and its fluctuations in heavy-ion collision experiments is of great importance for determining properties of the created system from the produced particle distributions. One example is the shear-viscosity to entropy density ratio of the quark-gluon plasma, which can be constrained by studying moments of azimuthal particle distributions and comparing to theoretical models. I will review recent developments in the theoretical description of particle production in heavy-ion collisions, focusing on models for the fluctuating initial state and event-by-event hydrodynamic evolution. [Preview Abstract] |
Saturday, October 27, 2012 9:06AM - 9:18AM |
NB.00002: Fluctuating Hydrodynamics Confronts the Rapidity Dependence of Transverse Momentum Fluctuations Rajendra Pokharel, Sean Gavin, George Moschelli Interest in the development of the theory of fluctuating hydrodynamics is growing [1]. Early efforts suggested that viscous diffusion broadens the rapidity dependence of transverse momentum correlations [2]. That work stimulated an experimental analysis by STAR [3]. We attack this new data along two fronts. First, we compute STAR's fluctuation observable using the NeXSPheRIO code, which combines fluctuating initial conditions from a string fragmentation model with deterministic viscosity-free hydrodynamic evolution. We find that NeXSPheRIO produces a longitudinal narrowing, in contrast to the data. Second, we study the hydrodynamic evolution using second order causal viscous hydrodynamics including Langevin noise. We obtain a deterministic evolution equation for the transverse momentum density correlation function. We use the latest theoretical equations of state and transport coefficients to compute STAR's observable. The results are in excellent accord with the measured broadening. In addition, we predict features of the distribution that can distinguish 2nd and 1st order diffusion. \\[4pt] [1] J. Kapusta, B. Mueller, M. Stephanov, arXiv:1112.6405 [nucl-th].\\[0pt] [2] S. Gavin and M. Abdel-Aziz, Phys. Rev. Lett. 97, 162302 (2006)\\[0pt] [3] H. Agakishiev et al., STAR, STAR, Phys. Lett. B704 [Preview Abstract] |
Saturday, October 27, 2012 9:18AM - 9:30AM |
NB.00003: Using Data to Determine the Initial Conditions in Heavy Ion Collisions Ron Soltz, Irakli Garishvili, Betty Abelev We have developed a framework, the Comprehensive Heavy Ion Model Evaluation Reporting Algorithm (CHIMERA) to determine the optimal model and initial conditions of heavy ion collisions by comparing to data from a variety of observables. We have used this framework to study simple participant and binary collisions scaling in the presence of pre-equilibrium flow in the context of the VH2 2D+1 viscous hydrodynamic model with UrQMD afterburner for data from RHIC. We have also used this framework to explore the significance of variations in the equation of state. We have recently begun to apply this framework to a new hydro-solver tools known as CHOMBO, which incorporates adaptive mesh refinement techniques that are well suited to the study of initial state fluctuations. We will review results from using CHIMERA with VH2, and discuss future plans for using CHOMBO to study initial state fluctuations. [Preview Abstract] |
Saturday, October 27, 2012 9:30AM - 9:42AM |
NB.00004: Measurement of $R_{d+Au}$ at Low $x$ in $\sqrt{s}$=200 GeV d+Au and p+p collisions Kenneth Sedgwick Nuclear modification factor measurements in d+Au collisions ($R_{d+Au}$) at large rapidities and low x can be used to determine the suppression effects of nuclear shadowing and gluon saturation. These measurements lead to a better understanding of the initial conditions of heavy ion collisions and, in particular, can be used to investigate the possible existence of a Colored Glass Condensate (CGC). At transverse momenta greater than 2 GeV/$c$, photons from neutral pion decay cannot be independently resolved by the high rapidity 3 $<$ $\eta$ $<$ 4 Muon Piston Calorimeter (MPC) detector at PHENIX. Therefore, to obtain a measurement of neutral pion production at high $p_T$ and high rapidity it is necessary to examine decay products that appear in the detector as a single cluster. This talk will discuss the present status of the analysis for d+Au and p+p collisions at $\sqrt{s}$=200 GeV. [Preview Abstract] |
Saturday, October 27, 2012 9:42AM - 9:54AM |
NB.00005: Forward di-hadron correlation study at STAR Xuan Li Quarks and Gluons, known generically as partons, are the current known fundamental constituents of the proton. The gluon density increases as the longitudinal momentum faction (x) of the gluon decreases, but it cannot increase without bound and saturation is expected at a certain low x value. The dynamics of quarks and gluons at low x is an open question. Studies of correlations between pairs of particles emitted in the forward direction at STAR aim to probe the small-x gluons in protons and in denser nuclear targets like gold. Suppression of back-to-back forward $\pi^{0}$ - forward $\pi^{0}$ azimuthal correlations which is consistent with Color Glass Condensate (CGC) prediction has been observed in central d+Au collisions at STAR. By studying the rapidity dependence of the forward triggered di-hadron correlations in p+p and d+Au collisions at $\sqrt{s}=200GeV$, we aim to address the question of how sharp the transition is in going from a dilute parton gas to the dense parton state. STAR has nearly continuous electromagnetic calorimeter coverage in pseudo-rapidity $-1<\eta<4$ range. The forward $\pi^{0}$+near-forward jet-like cluster azimuthal correlations suggests a smooth transition. Newer results extend previous studies to a low $p_{t}$ region. [Preview Abstract] |
Saturday, October 27, 2012 9:54AM - 10:06AM |
NB.00006: Exploring cold nuclear matter effects in d+Au collisions with high-pT reconstructed jets at PHENIX Dennis Perepelitsa Deuteron-nucleus (d+A) collisions can be used to investigate cold nuclear matter effects on hard-scattered partons and serve as an important baseline for heavy-ion collisions. In particular, d+A collisions at different centrality selections can probe the impact parameter dependence of nuclear parton distribution functions, initial state energy loss and final state parton interactions in the cold nucleus. Jet reconstruction can better determine the initial parton kinematics and recent improvements in analysis techniques allow the exploration of these effects over a wide p$_{T}$ range. We present the latest jet reconstruction measurements performed with the PHENIX detector at RHIC in deuteron-gold (d+Au) collisions at 200 GeV using the Gaussian filter and anti-k$_{T}$ algorithms and discuss the possible implications on descriptions of cold nuclear matter. [Preview Abstract] |
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