Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session HF: Relativistic Heavy Ions |
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Chair: Steffen Bass, Duke University Room: Simmons Ballroom 4 |
Saturday, October 25, 2008 2:00PM - 2:12PM |
HF.00001: HBT correlations of charged pion pairs in {\boldmath $\sqrt{s}$ = 200 GeV $p$+$p$} collisions at RHIC-PHENIX Andrew Glenn Femtoscopic methods, such as those exploiting the Hanbury-Brown Twiss effect, have long been used to provide space-time information about the bulk medium formed in heavy ion collisions, but these techniques are capable of having a broader impact in understanding this data. Arguably, the most important effects observed at RHIC are the strong modification of jets by the produced Quark Gluon Plasma and conversely, the feedback of the jet into the medium. The first experimental step for using HBT techniques to study these is the benchmark measurement for $p$+$p$ collisions, where kinematic correlations require careful consideration. Comparisons of correlations from minimum bias data to those from the region of a triggered jet are of particular importance. The status of the first HBT analysis for pions from $\sqrt{s}$ = 200 GeV $p$+$p$ collisions measured by the PHENIX collaboration will be presented. [Preview Abstract] |
Saturday, October 25, 2008 2:12PM - 2:24PM |
HF.00002: Pseudorapidity and p$_{t}$ dependence of identified-particle azimuthal flow for $\sqrt{s_{NN}}=200~\rm GeV$ Au+Au and Cu+Cu collisions Victoria Zhukova The observation of a strong azimuthal flow signature at RHIC suggests rapid system equilibration leading to an almost perfect fluid state. The longitudinal extent of the flow behavior depends on the formation dynamics for this state and can be studied by measuring the pseudorapidity dependence of the second Fourier component (v$_{2}$) of the azimuthal angular distribution. We report on a measurement of identified-particle v$_{2}$ as a function of p$_{t}$ (0.5-2.0 GeV/c), centrality (0-50$\%$), and pseudorapidity ($0\leq\eta<3.2$) for $\sqrt{s_{NN}} = 200~\rm GeV$ Au+Au and Cu+Cu collisions. The results are obtained using the BRAHMS spectrometers for particle identification ($\pi$, K, p) and the BRAHMS global detectors to determine the corresponding reaction-plane angles. Preliminary results for the Au+Au system have been reported earlier. Here we compare the final Au+Au results to new results obtained for the Cu+Cu system. [Preview Abstract] |
Saturday, October 25, 2008 2:24PM - 2:36PM |
HF.00003: Yields and elliptic flow of $d(\overline{d})$ and $^{3}He(\overline{^{3}He})$ in Au+Au collisions at $\sqrt{s_{NN}} = 200\ GeV$ Jianhang Zhou, Jack Engelage, Haidong Liu, Zhangbu Xu We present the transverse momentum ($p_{T}$) spectra and the
coalescence parameters
$B_{2}$ (related to collisional volume) for $d$, $\overline{d}$
($1 |
Saturday, October 25, 2008 2:36PM - 2:48PM |
HF.00004: Baryon resonance yields after QGP hadronization Inga Kuznetsova, Johann Rafelski Yields of baryon resonances which have been studied at RHIC, considering their decay (e.g. $\Delta(1232) \to N+\pi $ , $\Sigma(1385) \to \Lambda +\pi$), are studied in the framework of a kinetic master equations. The detailed balance requirement implied that they can be also produced by back-reaction. Particularly interesting is the case of entropy rich QGP fast hadronization leading to initial above chemical equilibrium yields of hadrons. In this case the resonance yield in a rapidly expanding system does not always develop towards global chemical equilibrium. We find that a significant additional hadron resonance yields can be produced by the back-reaction of the over-abundance of the decay products of resonances. A more complex situation arises for a relatively narrow resonance such as $\Lambda(1520)$, which can be in part seen as a stable state, which is depopulated to increase the heavier resonance yield. We find that a suppression of yield of such resonances, as compared to statistical hadronization model is possible. The pattern of deviation of hadron resonance yields from expectations based on statistical hadronization model are another characteristic signature for a fast hadronization of entropy rich QGP. The total yields of the ground state baryons used in analysis of data (such as $N$, $\Lambda$) are not affected. [Preview Abstract] |
Saturday, October 25, 2008 2:48PM - 3:00PM |
HF.00005: Dielectron Continuum in p+p Collisions at $\sqrt s =200GeV$measured by the PHENIX Experiment at RHIC Jason Kamin Color neutral probes, such as e$^{+}$e$^{-}$ pairs, do not interact with the hot, dense medium created in RHIC collisions. Therefore, they are effective tools for investigating the full time evolution and dynamics of this new state of matter. The intermediate mass region of the dielectron continuum (1$<$m$<$3 GeV/c$^{2})$ is dominated by semi-leptonic charm decays and allows a measurement of medium modifications of charm correlations. The PHENIX experiment has measured the dielectron continuum in both p+p and heavy-ion collisions at $\sqrt {s_{NN} } =200GeV$. The p+p data from the 2005 RHIC run allowed a measurement of the charm cross section as well as providing a tantalizing glimpse of the bottom cross section. The increased luminosity of the 2006 RHIC run along with a higher electron trigger threshold provides increased statistics for the measurement of the dielectron continuum, particularly in the higher mass region (m$>$1 GeV/c$^{2})$. This enables an analysis of additional dependencies, such as the p$_{T}$ and azimuthal correlations, of e$^{+}$e$^{-}$ pairs originating from heavy flavor decays. Such a study can illuminate the production mechanism for heavy flavor and can provide a crucial benchmark to test pQCD while also providing a baseline for future heavy-ion runs. The status of the p+p analysis from the 2006 RHIC run will be discussed. [Preview Abstract] |
Saturday, October 25, 2008 3:00PM - 3:12PM |
HF.00006: Low mass lepton pair production at large transverse momentum Jianwei Qiu, Zhongbo Kang, Werner Vogelsang PHENIX collaboration has recently measured the transverse momentum distribution of lepton pair production at RHIC with the pair's invariant mass as low as 120 $< Q <$ 300 MeV. We will show that the distribution of low mass lepton pair production at large transverse momentum $Q_T \gg Q$ can be systematically calculated in terms of the perturbative QCD factorization approach. All factorized short-distance parotnic hard parts are evaluated at a distance scale $\sim 1/Q_T$, while all long-distance non-perturbative physics are factorized into the universal parton-to-lepton pair fragmentation functions. We introduce a model for the input lepton pair fragmentation functions at a scale $\mu\sim$ 1 GeV, which are then evolved perturbatively to scales relevant at RHIC. Using the evolved fragmentation functions, we calculate the transverse momentum distributions of low mass lepton pair production in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions. We demonstrate that the transverse momentum distribution of low mass lepton pairs is extremely sensitive to the shape of gluon distribution. [Preview Abstract] |
Saturday, October 25, 2008 3:12PM - 3:24PM |
HF.00007: Centrality Dependent Studies of Identified Particle Spectra at RHIC Selemon Bekele We present preliminary results from the BRAHMS experiment on
identified particle spectra and ratios at $y \sim 0$ and $y
\sim 3$ as a function of centrality for 200 GeV/NN Cu+Cu
collisions. By comparing the Cu+Cu data with earlier results
for the Au+Au and d+Au systems, it is possible to study how the
heavy-ion reaction dynamics for a given number of participants
depends on the overall system size. Particle yields, $ |
Saturday, October 25, 2008 3:24PM - 3:36PM |
HF.00008: Coulomb Corrections and Ion Finite Size Effects in $\mu$ Pair Production at RHIC and LHC Anthony Baltz A higher order QED calculation of the ultraperipheral heavy ion cross section for $\mu^+ \mu^-$ pair production at RHIC and LHC is carried out. The so-called ``Coulomb corrections'' lead to an even greater percentage decrease of $\mu^+ \mu^-$ production from perturbation theory than the corresponding decrease for $e^+ e^-$ pair production. Unlike the $e^+ e^-$ case, the finite charge distribution of the ions (form factor) and the necessary subtraction of impact parameters with matter overlap are significant effects in calculating an observable ultraperipheral $\mu^+ \mu^-$ total cross section. [Preview Abstract] |
Saturday, October 25, 2008 3:36PM - 3:48PM |
HF.00009: Parity Violation in Strong Interactions Dhevan Gangadharan Recent theoretical findings suggest parity violation of the strong interaction. This may be seen in heavy-ion collisions through the separation of charged particles relative to the reaction plane of the colliding nuclei. Charged particle separation in heavy-ion collisions is by definition P-odd and is theoretically a consequence of a ``topological charge'' changing transition of the vacuum structure via instantons/sphalerons in the colliding region. Recent experimental results from the STAR detector at RHIC using charged particle correlations will be presented. [Preview Abstract] |
Saturday, October 25, 2008 3:48PM - 4:00PM |
HF.00010: Jet energy loss in a dynamical QCD medium Magdalena Djordjevic We calculate, to first order in the number of scattering centers, the energy loss of a heavy quark traveling through a finite size QCD medium consisting of dynamical constituents. Our results suggest a simple general mapping between energy loss expressions for static and dynamical QCD media. Numerically, we show that the result for a dynamical medium is significantly larger compared to a medium consisting of randomly distributed static scattering centers. Therefore, an accurate description of jet suppression in RHIC and LHC experiments must correctly account for the dynamics of the medium's constituents. Finally, we show that finite size effects induce a non-linear path length dependence of the energy loss, which effectively reproduces the effects of destructive Landau-Pomeranchuk-Migdal interference in the ultrarelativistic limit. [Preview Abstract] |
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