Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session MD: Mini-symposium on Lessons from Leading Particle Jet Energy Loss |
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Chair: Michael Leitch, Los Alamos National Laboratory Room: Sweeny D |
Saturday, November 6, 2010 8:30AM - 9:00AM |
MD.00001: Jet modification in dense matter via leading hadrons Invited Speaker: The state-of-the-art in the study of jet modification in dense matter, at the leading particle level, will be presented. Calculations of the medium modified fragmentation function will be dissected to reveal the various components and inputs. These will be compared and contrasted among the four leading formalisms. [Preview Abstract] |
Saturday, November 6, 2010 9:00AM - 9:12AM |
MD.00002: Event-by-Event Jet Quenching and Higher Fourier Moments of Hard Probes Rainer Fries, Ricardo Rodriguez We investigate the influence of realistic geometries in high energy nuclear collisions, including inhomogeneities and fluctuations, on the extraction of transport coefficients from high momentum probes. We report that jet quenching calculated event-by-event generally leads to less suppression of single inclusive particle production. Over a wide range of momentum this effect can be absorbed in a redefinition of the quenching strength. After this adjustment the experimentally observed centrality dependence of the nuclear modification factor is described very well. We show, for the first time, a systematic study of higher harmonics v$_{n}$ of the hadron spectrum at large momentum, including odd momenta which disappear at midrapidity if fluctuations are neglected. We conclude that a limited spatial tomography of the fireball created in nuclear collisions is feasible despite averaging experimental data over many events. [Preview Abstract] |
Saturday, November 6, 2010 9:12AM - 9:24AM |
MD.00003: Transverse Momentum Broadening and the Jet Quenching Parameter, Redux Francesco D'Eramo, Hong Liu, Krishna Rajagopal We use Soft Collinear Effective Theory (SCET) to analyze the transverse momentum broadening, or diffusion in transverse momentum space, of an energetic parton propagating through quark-gluon plasma. Since we neglect the radiation of gluons from the energetic parton, we can only discuss momentum broadening, not parton energy loss. The interaction responsible for momentum broadening in the absence of radiation is that between the energetic (collinear) parton and the Glauber modes of the gluon fields in the medium. We derive the effective Lagrangian for this interaction, and we show that the probability for picking up transverse momentum $k_{\perp}$ is given by the Fourier transform of the expectation value of two transversely separated light-like path-ordered Wilson lines. This yields a field theoretical definition of the jet quenching parameter $\hat{q}$, and shows that this can be interpreted as a diffusion constant. We close by revisiting the calculation of $\hat{q}$ for the strongly coupled plasma of N=4 SYM theory, showing that previous calculations need some modifications that make them more straightforward and do not change the result. [Preview Abstract] |
Saturday, November 6, 2010 9:24AM - 9:36AM |
MD.00004: How to really measure fragmentation functions with two-particle correlations in p-p and A+A collisions Michael Tannenbaum For the past decade, measurements of semi-inclusive single identified particle spectra and two-particle correlations in p-p and A+A collisions at RHIC have produced a treasure trove of results which indicate a suppression of hard-scattered partons in the medium produced in A+A collisions. It still remains to be determined unambiguously whether the partons emerge from the medium having lost energy (or whether some emerge from well within the medium without having lost energy) then fragment normally outside; whether vacuum fragmentation is modified inside the medium; or whether partons are stopped or absorbed so that only surface emission occurs. One important lesson learned is that the away-side $p_{Ta}$ distribution of particles opposite to a trigger particle (e.g. a $\pi^0$), which is itself the fragment of a jet, does not measure the fragmentation function. The key to measuring the fragmentation function and its possible modification is to know the energy of the original parton which fragments. This can be accomplished by measuring the correlated hadrons opposite to a direct-single $\gamma$ from the reaction $g+q\rightarrow \gamma+q$. Comparison to the $\xi=\ln{1/z}$ representation of fragmentation functions measured in $e^+ +e^-$ collisions, where $z$ is the fragmentation variable, becomes useful for direct-$\gamma-h$ measurements over the full $z$ or $\xi$ range when a semi-log plot is used. Examples will be presented. [Preview Abstract] |
Saturday, November 6, 2010 9:36AM - 9:48AM |
MD.00005: Jet-Hadron Correlations with Respect to the Event Plane Alice Ohlson Partons with high transverse momentum ($p_T$) are produced via hard scatterings in the initial stages of heavy-ion collisions and are therefore promising probes of the quark-gluon plasma (QGP) created in such collisions. The partons fragment into jets of hadrons, which can be reconstructed over the heavy-ion background due to recent advancements in jet-finding algorithms. One of the primary methods used to investigate the propagation and modification of hard-scattered partons through the QGP has been the study of correlations between hadrons and high-$p_T$ particles. It is now possible to use reconstructed jets in these correlation studies. I report on correlations between the jet and event plane in search of a pathlength dependence to parton energy loss or the modification of fragmentation, and investigate the complications that arise when calculating the event plane in the presence of a jet. I also discuss investigations of jet-hadron correlations with a low $p_T$ threshold applied to the associated charged hadrons. At low $p_T$, the anisotropy of the underlying event dominates the measured signal, and so one must correct for this background contribution in order to measure jet properties. The data analyzed were collected by the STAR detector in $\sqrt{s_{NN}}$ = 200 GeV AuAu collisions at the Relativistic Heavy Ion Collider (RHIC). [Preview Abstract] |
Saturday, November 6, 2010 9:48AM - 10:00AM |
MD.00006: Upgrading PHENIX for Deeper Investigation of Partonic Interactions David Morrison PHENIX has reported extensively on partonic interactions in heavy ion collisions, and the current suite of upgrades will greatly improve the ability of the experiment to use heavy flavor in those investigations. In its plan for the coming decade, PHENIX argues for an overhaul of the experiment to greatly increase its acceptance, its $p_T$ reach and discrimination for EM signals, and its capabilities for jet physics, while retaining its high performance data acquisition and triggering abilities. These transformations will enable PHENIX to study many further question regarding the nature of partonic interactions with the medium and the mechanisms of partonic energy loss. [Preview Abstract] |
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