Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session Y14: Properties of Bulk Matter at RHIC |
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Sponsoring Units: DNP Chair: Derek Teaney, SUNY Stony Brook Room: Washington 4 |
Tuesday, February 16, 2010 1:30PM - 1:42PM |
Y14.00001: Two particle $\Delta\eta-\Delta\phi$ correlations in Au+Au Collisions at $\sqrt{S_{NN}}=200 GeV$ in the PHENIX experiment Chin-Hao Chen We present the measurement of two dimensional inclusive photon - charged hadron two particle correlations in the PHENIX experiment. Jet-like correlations are modified in central Au+Au collisions, compared to p+p, in both the trigger and opposing jet. The trigger jet is elongated in pseudo-rapidity (the ``ridge''), while the opposing jet shows a double peak structure (``head'' and ``shoulder''). We decompose the structures by fitting the $\Delta\eta$ and $\Delta\phi$ correlations to disentangle contributions from the medium, the punch-through jet, and trigger jet. The trigger and opposing jet fragment spectra are compared to each other and to the ridge. The spectra of both ridge and shoulder are softer than that from hard scattering, but harder than the inclusive hadrons. The momentum flow between jet and medium is investigated using this decomposition technique. [Preview Abstract] |
Tuesday, February 16, 2010 1:42PM - 1:54PM |
Y14.00002: Tri-hadron correlation measurements of jet-like emissions in Au + Au collisions at $\sqrt s = 200 GeV$ with the PHENIX detector Nuggehalli Ajitanand Charged hadron correlation measurements provide an important probe for the hot and dense matter created in RHIC collisions.In a recent experiment, the PHENIX collaboration has measured three particle correlation functions using a novel technique that approximates the lead-jet axis with the direction of a high transverse momentum hadron. The observed correlation patterns indicate away-side jet modification compatible with the collective excitations of a shock wave leading to conical flow. The inferred Mach angle for this conical flow, gives a direct probe of the equation of state of the low viscosity fluid produced in central and mid-central Au+Au collisions. [Preview Abstract] |
Tuesday, February 16, 2010 1:54PM - 2:06PM |
Y14.00003: Estimates for the transport coefficients of the quark gluon plasma produce in Au+Au collisions at RHIC Roy Lacey There is now compelling evidence that the quark gluon plasma (QGP) is produced in a rapid crossover phase transition in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC). However, the properties of the QGP still require more detailed study. I will present state-of-the-art scaling techniques which provide important constraints for estimates of the sound speed ($c_s$), mean free path ($\lambda$), viscosity ($\eta/s$) and stopping power ($\hat{q}$). I will also discuss their implication for the coupling strength of the plasma. [Preview Abstract] |
Tuesday, February 16, 2010 2:06PM - 2:18PM |
Y14.00004: Quark Coalescence with Quark Number Conservation and the Effect on Quark-Hadron Scaling Ziwei Lin We incorporate unitarity to quark coalescence by describing its time evolution (Z.W. Lin, arXiv:0901.3737). Our general results reproduce the previous quark coalescence model for hard quarks, which have small coalescence probabilities. However, the relations for soft partons (the bulk) are totally different. If we consider the formations of light meson $M$, charm meson $D$ and $J/\psi$, the general results give $f^{soft}_M(\vec p) \propto f_{q0}(\vec p/2)$ and $f^{soft}_D(\vec p_D) \propto f_{c0}(\vec p_c)$. These two linear relations are the result of quark number conservation for light quarks and charm quarks, respectively. They also lead to $v^{soft}_{2,M}(p_{\perp}) \approx v_{2,q}(p_{\perp}/2)$ and $v^{soft}_{2,D}(p_{\perp D}) \approx v_{2,c}(p_{\perp c})$ for elliptic flows. The weaker scaling comes from the fact that, as coalescence progresses in time, the remaining soft quarks have smaller and smaller $v_2$, leading to a smaller overall hadron $v_2$. We also obtain $v^{soft}_{2,\psi}(p_{\perp}) \approx v_{2,c}(p_{\perp}/2) -a v_{2,q}(p_{\perp q})$ with $a>0$. An interesting scenario is that soft $J/\psi$ can have a negative $v_2$ even if charm quarks have no $v_2$. This can be understood in the following picture. As coalescence progresses in time, some charm quarks will coalesce with co-moving light quarks to form $D$ mesons. Because light quarks have a positive $v_2$, those charm quarks forming $D$ mesons also have a positive $v_2$. Given that charm quarks have zero $v_2$ overall, the charm quarks available for $J/\psi$ production will have a negative $v_2$, leading to a negative $J/\psi$ elliptic flow. [Preview Abstract] |
Tuesday, February 16, 2010 2:18PM - 2:30PM |
Y14.00005: Study of the Number of Quark Scaling of $v_2$ at High Transverse Momentum Na Li The number of quark (NCQ) scaling in the anisotropy parameter $v_2$, for almost all measured hadrons at transverse momentum region up to $p_T$ about 5GeV/c, has been observed in high-energy nuclear collisions at RHIC. The scaling results imply the formation of the de-confined matter with partonic collectivity in the collisions. In this talk, we report systematic studies of $v_2$ at midrapidity for $\pi$, p, $K_s^0$ and $\Lambda$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV using the STAR detector. The FTPC detectors, which sit at large rapidity, were used for the determination of the event plane. Comparing to previous results, a high statistics data set is used in the analysis. We find that in the high transverse momentum region, $p_T \ge$ 6GeV/c ($(m_T-m)/n_q>1.5$ GeV/$c$), the NCQ in $v_2$ is breaking down. A comparison to models suggests this is mainly caused by an increase in particles coming from hard process at high $p_T$. [Preview Abstract] |
Tuesday, February 16, 2010 2:30PM - 2:42PM |
Y14.00006: Estimation of viscosity based on transverse momentum correlations Monika Sharma The heavy ion program at RHIC created a paradigm shift in the exploration of strongly interacting hot and dense matter. An important milestone achieved is the discovery of the formation of strongly interacting matter which seemingly flows like a perfect liquid at temperatures on the scale of T $\simeq$ 2 $\times 10^{12}$ K [1]. As a next step, we consider measurements of transport coefficients such as kinematic, shear or bulk viscosity? Many calculations based on event anisotropy measurements indicate that the shear viscosity to the entropy density ratio ($\eta/s$) of the fluid formed at RHIC is significantly below that of all known fluids including the superfluid ${}^4He$ [2]. Precise determination of $\eta/s$ ratio is currently a subject of extensive study. We present an alternative technique for the determination of medium viscosity proposed by Gavin and Aziz [3]. Preliminary results of measurements of the evolution of the transverse momentum correlation function with collision centrality of Au + Au interactions at $\sqrt{s_{NN}} = 200$ GeV will be shown. We present results on differential version of the correlation measure and describe its use for the experimental determination of $\eta/s$.\\[4pt] [1] J. Adams {\it et al.,} [STAR Collaboration], Nucl. Phys. A {\bf 757} (2005) 102.\\[0pt] [2] R. A. Lacey {\it et al.,} Phys. Rev. Lett. {\bf98} (2007) 092301.\\[0pt] [3] S. Gavin and M. Abdel-Aziz, Phys. Rev. Lett. {\bf97} (2006) 162302. [Preview Abstract] |
Tuesday, February 16, 2010 2:42PM - 2:54PM |
Y14.00007: The Sound of the Little Bang Agnes Mocsy, Paul Sorensen, Alexander Doig The matter created in collisions at Brookhaven's Relativistic Heavy Ion Collider is as hot and dense as the Universe was one microsecond after the Big Bang. For this reason the collisions are sometimes called ``little bangs.'' The matter created in the little bangs at Brookhaven Lab has been found to contain interesting acoustic signatures. We Fourier transform momentum correlation measurements into a frequency spectrum and then scale the frequencies to be audible to the human ear. We therefore are able to present an acoustic picture of the collisions. Our analysis of the frequency spectrum from momentum correlations is analogous to the analysis of the Cosmic Microwave Background. [Preview Abstract] |
Tuesday, February 16, 2010 2:54PM - 3:06PM |
Y14.00008: Modeling of Momentum Correlations in Heavy Ion Collisions Claude Pruneau, Monika Sharma Measurements of transverse momentum ($p_t$) correlations and fluctuations in heavy ion collisions (HIC) are of interest because they provide information on the collision dynamics not readily available from number correlations. For instance, $p_t$ fluctuations are expected to diverge for a system near its tri-critical point [1]. Integral momentum correlations may also be used to estimate the shear viscosity of the quark gluon plasma produced in HIC [2]. Integral correlations measured over large fractions of the particle phase space average out several dynamical contributions and as such may be difficult to interpret. It is thus of interest to seek extensions of integral correlation variables that may provide more detailed information about the collision dynamics. We introduce a variety of differential momentum correlations and discuss their basic properties in the light of simple toy models. We also present theoretical predictions based on the PYTHIA, HIJING, AMPT, and EPOS models. Finally, we discuss the interplay of various dynamical effects that may play a role in the determination of the shear viscosity based on the broadening of momentum correlations measured as function of collision centrality. [1] L. Stodolsky, Phys. Rev. Lett. {\bf 75} (1995) 1044. [2] S. Gavin and M. A. Aziz, Phys. Rev. Lett. {\bf 97} (2006) 162302. [Preview Abstract] |
Tuesday, February 16, 2010 3:06PM - 3:18PM |
Y14.00009: Cluster model and two-particle pseudorapidity and azimuthal correlations in $p+p$ and $A+A$ collisions Laurence Tarini Cluster models have had consistent success in explaining correlations among final state particles in hadronic multiparticle production [1]. In this talk two-particle correlations are presented for simulated $p+p$ and $A+A$ collisions based on the picture of particle production via cluster decay. The modification of correlations due to radial flow of clusters is also studied. Features are found to be similar to those observed experimentally.\\[4pt] [1] B. Alver {\it et al}., (PHOBOS Collaboration), Phys. Rev. C {\bf 75}, 05493 (2007); R. E. Ansorge {\it et al}., (UA5 Collaboration), Z. Phys. C {\bf 37}, 191 (1988); L. Fo\`{a}, Phys. Rep. {\bf 22}, 1 (1975). [Preview Abstract] |
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