Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session BB: Mini-Symposium on Heavy Flavor and Hard Probes in the Quark Gluon Plasma I |
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Chair: Saskia Mioduszewski, Texas A&M University Room: Kona 4 |
Wednesday, October 14, 2009 7:00PM - 7:30PM |
BB.00001: Latest results from jet measurements Invited Speaker: A first stage in understanding the phenomenon of jet quenching in the hot and dense nuclear matter has been successfully reached at RHIC through measurements of inclusive hadron suppression and di-hadron azimuthal correlations. A significant step forward in this field is being obtained by full jet reconstruction in heavy-ion collisions, that in principle should give access to the energy of the hard scattering independent of the presence of the medium and should enable the study of jet quenching at the partonic level. Due to the intrinsic difficulties of such a measurement in the high multiplicity environment, this is an innovative analysis and the first results of full jet reconstruction were obtained only over the last year thanks to the recently developed jet-finding techniques. We discuss the current methods to treat the large background, which is the main critical aspect that makes full jet reconstruction a challenge at RHIC. New measurements directed to address the mechanisms of partonic energy loss in hot QCD matter are presented. These measurements include the ratio of inclusive jet cross sections in Au+Au and p+p and the comparison of jet fragmentation functions in Au+Au and p+p. [Preview Abstract] |
Wednesday, October 14, 2009 7:30PM - 7:45PM |
BB.00002: Direct jet reconstruction in $p + p$ and $\mathrm{Cu} + \mathrm{Cu}$ collisions with the PHENIX detector Yue Shi Lai Full jet measurements in heavy ion collision can elucidate the mechanisms responsible for in-medium parton energy loss and the response of the medium to the passage of a high-energy parton. However, at RHIC energies jets are difficult to measure in the presence of an large underlying background of soft hadrons. Jet reconstruction in such an environment requires an algorithm that is robust in the presence of such a background and efficiently suppresses fake jets resulting from possibly correlated fluctuations in that background. Efficient rejection of fake jets is especially important at RHIC energies due to the low rate for production of real jets at moderate to high $p_T$. We developed the Gaussian filter based jet reconstruction algorithm with a corresponding a fake rejection strategy, which is designed to be applicable both $p + p$ and heavy ion collisions. It both preserves the cone-like behavior found in many hadronic jet algorithms~[1], while providing an acceptable fake rate in a background environment up to the central $\mathrm {Au} + \mathrm{Au}$ collision at RHIC energies. We present results of its application in both $p + p$ and $\mathrm{Cu} + \mathrm{Cu}$ collisions using data from the PHENIX detector, including jet spectra, jet--jet angular correlation, and the nuclear modification factor. We discuss the comparison and implication for models, and further outline our future program for jet physics using the PHENIX detector. [1] Y.-S.~Lai and B.A.~Cole, arXiv:0806.1499 (2008). [Preview Abstract] |
Wednesday, October 14, 2009 7:45PM - 8:00PM |
BB.00003: Jet studies in STAR via di-jet (2+1) correlations in d+Au and Au+Au Hua Pei We report a correlation work for Au+Au and d+Au collisions at $\sqrt{s}=$ 200GeV from STAR experiment at RHIC. This correlation is defined as a three-particle technique called ``2+1'', by using a di-jet trigger of two back-to-back high-pT particles including both charged hadrons and high-energy photons. This analysis explores the relative distributions of soft hadrons with the two triggers. The trigger $p_T$ ranges are varied to control the relative strength of jet modification. In contrast to those di-hadron correlations with a single high- pT trigger, the associated hadron distributions in our ``2+1'' analysis reveal no modification in either $\Delta\phi$ or $\Delta\eta$ from d+Au to central Au+Au collisions. The present results indicate that di-jet triggered correlations select those jets that undergo no interactions or energy-loss with the medium created in collisions. The associated yields and trigger rates for such di-jets are studied as a function of $N_{part}$ to provide additional insights into medium properties. [Preview Abstract] |
Wednesday, October 14, 2009 8:00PM - 8:15PM |
BB.00004: Jet modifications in conditionally triggered di-hadron correlations at $\sqrt{s_{NN}}=200$ GeV in Au+Au at RHIC-PHENIX Eric Vazquez A hot dense medium exceeding the critical energy density for the formation of a partonic state of matter is created in Au+Au collisions at RHIC. This dense matter is extremely opaque to high energy partons and therefore leads to strong modifications of di-jets traversing the medium. These modifications are typically studied by comparing the di-hadron azimuthal correlation functions in Au+Au collisions to those in p+p collisions. However, di-hadron correlations measured in events triggered on a single hadron are subject to a surface bias due to the larger probability of a high-$p_T$ parton emerging with little or no energy loss from production points near the surface of the medium. This effect can be reduced, and in fact controlled, by studying events in which the production of two high-$p_T$ hadrons at large azimuthal separation is required. We present results of such an analysis performed in p+p and Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. [Preview Abstract] |
Wednesday, October 14, 2009 8:15PM - 8:30PM |
BB.00005: Infinite Matter Calculation of Jet Energy-Loss with the Parton Cascade Model Steffen Bass Parton Cascade Models, which describe the full time-evolution of a system of quarks and gluons using pQCD interactions are ideally suited for the description of jet production, including the emission, evolution and energy-loss of the full parton shower in a hot and dense QCD medium. However, before applying the PCM to the off-equilibrium dynamics of the early stage of an ultra-relativistic heavy-ion collision, it is important to validate these calculations against analytically calculable test cases. In this talk, I shall present results of PCM calculations for parton energy loss in infinite matter and compare them to some analytically accessible test cases. [Preview Abstract] |
Wednesday, October 14, 2009 8:30PM - 8:45PM |
BB.00006: High $p_T$ hadron production and its quantitative constraint to model parameters Takao Sakaguchi Hot and dense matter created in relativistic heavy ion collisions is found to be opaque according to the degree of suppression of high $p_T$ hadrons, which are considered to carry the major fraction of the momentum of hard scattered partons. The nuclear modification factors ($R_{AA}$) of $\pi^0$ from the latest PHENIX publication\footnote{Phys.Rev.Lett. {\bf 101}, 232301(2008)} are found to be constant, meaning that the energy loss of partons is constant fractional. The phenomena have stimulated theoretical field, and deduced many models, but the quantitative discussion had not been realized until recently because of large uncertainty on both experimental and theoretical work. The PHENIX experiment has recently succeeded to constrain parameters of models by quantitatively comparing models and data. Such comparison became possible by properly taking systematic and statistical errors into account. In this presentation, an attempt to constrain model parameters using the latest high $p_T$ hadron spectra with most statistics available from PHENIX Run7 data will be shown, and the characteristics of the matter produced obtained in the study will be discussed. [Preview Abstract] |
Wednesday, October 14, 2009 8:45PM - 9:00PM |
BB.00007: Neutral pion production with respect to the reaction plane in $\sqrt{s_{NN}}=200$~GeV Au+Au collisions at PHENIX Yoki Aramaki It has been observed that the yield of neutral pion at high transverse momentum ($p_{T}>6$~GeV/$c$) region is strongly suppressed in central Au+Au collisions at Relativistic Heavy Ion Collider (RHIC), compared to the one expected from $p+p$ collisions. This suppression is interpreted as a consequence of an energy loss of hard scattered partons in the medium (jet quenching), which results in a decrease of the yield at a given $p_{T}$. Many calculations of parton energy loss predict the quantity of energy loss is proportional to square of the path length. Therefore measuring the quantity of the energy loss for each path length will be able to strongly constrain these calculations. A new reaction plane detector was installed in the PHENIX detector in RHIC 2007 run, and the reaction plane can be determined about 2 times better than before. Furthermore the integrated luminosity in RHIC 2007 run achieved 813~${\mu}b^{-1}$ and this is about 4 times larger than the previous run. With these improvements both the nuclear modification factor as a function of reaction plane can be measured and the respective average pathlength estimated with about a factor of 4 smaller errors than in the published RHIC 2004 data [1].\\[4pt] [1] PHENIX Collaboration: A~Adare, \textit{et al.} arXiv:0903.4886v1 [Preview Abstract] |
Wednesday, October 14, 2009 9:00PM - 9:15PM |
BB.00008: Reaction plane dependence of inclusive photon-hadron $\Delta \phi$-$\Delta \eta$ correlation in Au+Au $\sqrt{s_{NN}}$=200 GeV collisions at RHIC-PHENIX Takahito Todoroki Quark Gluon Plasma (QGP) is the phase composed of de-confined quarks and gluons of which interaction is described by QCD, and is formed by relativistic heavy ion collision. In QGP medium, back-to-back jet arises as a consequence of hard parton-parton scattering. In the process of the propagation of back-to-back partons, the effects of the parton-medium interactions should depend on the path length the parton travel through the matter, which is determined by the initial scattering point and the direction of the momentum vector. Furthermore, away side wide azimuthal angle correlation (possible Mach cone) and near side wide eta correlation (ridge) have been seen with respect to the trigger particle. In order to understand these phenomena, 2-dimensional analysis of $\Delta \phi$-$\Delta \eta$ is useful especially with centrality and reaction plane dependence. In this presentation, we show the current analysis status of inclusive photon-hadron $\Delta \phi$-$\Delta \eta$ correlation as a function of the centrality and the trigger photon angle from reaction plane. [Preview Abstract] |
Wednesday, October 14, 2009 9:15PM - 9:30PM |
BB.00009: Are direct photons suppressed in PHENIX at high $p_T$ in relativistic heavy ion collisions? Gabor David Preliminary results from PHENIX on direct photon production in 200GeV Au+Au collisions indicated that while at moderate $p_T$ (4-14GeV/$c$) the nuclear modification factor $R_{AA}^{\gamma}$ for photons is unity, at higher $p_T$ it may be significantly smaller and possibly, similar to the well-established hadron suppression (jet quenching) level. Since $R_{AA}^{\gamma}$ has been derived using $p$+$p$ data measured in the same experiment, such suppression may have both trivial reasons (the difference in charge squared sum of quarks in proton and neutron that enters in the hard photon production rate in case of Au+Au) and/or be the consequence of new phenomena. The initial parton distributions themselves may be changed, which should be manifested already in $d$+Au collisions. Furthermore, the presence of the hot, dense medium in Au+Au collisions may either enhance (by collinear parton-photon ``conversion'') or reduce the yield of high $p_T$ photons. Based upon the latest $\sqrt{s}=200$GeV $d$+Au and Au+Au photon data from PHENIX we will investigate if direct photons are suppressed at high $p_T$ and if so, what the physics implications may be. [Preview Abstract] |
Wednesday, October 14, 2009 9:30PM - 9:45PM |
BB.00010: Fragmentation photons in p+p collisions at 200GeV with PHENIX Ali Hanks Direct photons produced in relativistic heavy ion collisions are often viewed as insensitive to the final state effects leading to jet quenching, and are thus considered powerful penetrating probes. However, there is a contribution to direct photon production that is sensitive to jet quenching in the QGP. pQCD predict that up to 30\% of direct photons are produced through parton fragmentation. In A+A this contribution is expected to be modified due to stimulated photon emission as the parton propagates through the medium. Detection of these photons would provide a direct observation of the energy loss of jets in the medium. Measurements of fragmentation photon properties in p+p serve both as an important test for pQCD descriptions and as a baseline for A+A. A natural way of selecting fragmentation photons is with intra jet correlations of photons and high-pT hadrons. This method also allows for further study of the jet properties of fragmentation photons such as p$_{out}$, the component of the photon pT perpendicular to the trigger hadron, providing further constraint on the details of parton fragmentation. We present results from p+p data and discuss the potential for measurements in d+Au and Au+Au collisions. [Preview Abstract] |
Wednesday, October 14, 2009 9:45PM - 10:00PM |
BB.00011: First High $p_T$ Physics Prospects with the Photon Spectrometer at ALICE Kenta Shigaki Suppression of high $p_T$ hadrons, or so-called jet quenching, provided the first strong signature of hot and dense partonic matter created in heavy ion collisions at RHIC\@. The suppression patterns have been measured for $\pi^0$ up to $\sim 20$~GeV/$c$, and also for various particles with a hope of systematic investigation of energy loss of quarks in the deconfined matter. At the ALICE experiment at LHC, starting its physics operation in the fall of 2009, the high $p_T$ suppression is expected to be an even more powerful tool to investigate and quantitatively understand energy loss of quarks. LHC will provide high production rates of particles up to much higher $p_T$ regions than RHIC does, and the high performance photon spectrometer, PHOS, of ALICE will allow identification of particles decaying into multiple photons up to very high $p_T$. Any dependence on quark flavors of energy loss and/or a possible difference between pseudo-scalar and vector mesons will be studied in details. Feasibility and prospects of high $p_T$ measurements with the PHOS detector, especially in the first $p+p$ and Pb+Pb running in 2009-2010, will be discussed. [Preview Abstract] |
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