Jet Observables of Parton Energy Loss in High-Energy Nuclear Collisions

While strong attenuation of single particle production and particle correlations has provided convincing evidence for large parton energy loss in the QGP, its application to jet tomography has inherent limitations due to the inclusive nature of the measurements. Generalization of this suppression to full jet observables leads to an unbiased, more differential and thus powerful approach to determining the characteristics of the hot QCD medium created in high-energy nuclear collisions. In this article we report on recent theoretical progress in calculating jet shapes and the related jet cross sections in the presence of QGP-induced parton energy loss. (i) A theoretical model of intra-jet energy flow in heavy-ion collisions is discussed. (ii) Realistic numerical simulations demonstrate the nuclear modification factor $R_{AA}(p_T)$ evolves continuously with the jet cone size $R^{\max}$ or the acceptance cut $\omega_{\min}$ - a novel feature of jet quenching. The anticipated broadening of jets is subtle and most readily manifested in the periphery of the cone for smaller cone radii.Comment: Proceedings for Quark Matter 2009, updated version with minor correction

Vector boson tagged jets and jet substructure

In these proceedings, we report on recent results related to vector boson-tagged jet production in heavy ion collisions and the related modification of jet substructure, such as jet shapes and jet momentum sharing distributions. $Z^0$-tagging and $\gamma$-tagging of jets provides new opportunities to study parton shower formation and propagation in the quark-gluon plasma and has been argued to provide tight constrains on the energy loss of reconstructed jets. We present theoretical predictions for isolated photon-tagged and electroweak boson-tagged jet production in Pb+Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV at the LHC, addressing the modification of their transverse momentum and transverse momentum imbalance distributions. Comparison to recent ATLAS and CMS experimental measurements is performed that can shed light on the medium-induced radiative corrections and energy dissipation due to collisional processes of predominantly quark-initiated jets. The modification of parton splitting functions in the QGP further implies that the substructure of jets in heavy ion collisions may differ significantly from the corresponding substructure in proton-proton collisions. Two such observables and the implication of tagging on their evaluation is also discussed.Comment: Proceedings of the XLVII International Symposium on Multiparticle Dynamics; 9 pages, 9 eps figure

The conical flow from quenched jets in sQGP

Starting with a reminder of what is strongly coupled Quark-Gluon Plasma (sQGP), we proceed to recent advances in jet quenching and heavy quark diffusion, with a brief summary of various results based on AdS/CFT correspondence. The conical flow is a hydrodynamical phenomenon created by energy and entropy deposited by high energy jets propagating in matter, similar in nature to well known sonic boom from the supersonic planes. After a brief review, we discuss excitations of two hydro modes -- sound and ``diffuson'' -- which can be excited in this way. We also study expanding matter case, with a variable sped of sound, and use adiabatic invariants to show that the parameter $v/T$ ($v$ velocity in the wave, $T$ temperature) is increasing, up to a factor 3, during expansion. At the end we discuss recent results of the Princeton group which derived conical flow from AdS/CFT.Comment: 17 pages, a talk at Hard Probes 06, Monterey July 200

High-p_T Tomography of d+Au and Au+Au at SPS, RHIC, and LHC

The interplay of nuclear effects on the p_T > 2 GeV inclusive hadron spectra in d+Au and Au+Au reactions at root(s) = 17, 200, 5500 GeV is compared to leading order perturbative QCD calculations for elementary p+p (p-bar+p) collisions. The competition between nuclear shadowing, Cronin effect, and jet energy loss due to medium-induced gluon radiation is predicted to lead to a striking energy dependence of the nuclear suppression/enhancement pattern in A+A reactions. We show that future d+Au data can used to disentangle the initial and final state effects.Comment: Final version to appear in Phys. Rev. Lett. Preliminary PHENIX and STAR data included in Fig. 3. Pages - 4, figures - 3. Uses bbox.st

Anomalous Anti-proton to Negative Pion Ratio as Revealed by Jet Quenching at RHIC

We study the apparent discrepancy between the standard PQCD predictions for the meson and baryon ratios and multiplicities at moderate high $p_{T} > 2$ GeV and recent experimental measurements in $Au+Au$ collisions at $\sqrt{s}_{NN}=130$ GeV at the Relativistic Heavy Ion Collider (RHIC). We show that the differences, most pronounced in central collisions, can be explained by a strong non-perturbative baryon Junction component, which dominates the currently accessible experimental $p_{T}$ window and the non-abelian energy loss of fast partons propagating through hot and dense medium. The recently introduced two component hybrid model, which combines a quenched jet PQCD calculation in the Gyulassy-Levai-Vitev (GLV) formalism and a phenomenological "soft" part, is further elaborated to take into account the full 3D expansion in the pre-hadronization phase and include particle flavor dependent "soft" inverse slopes as suggested by the baryon Junction picture. We show that such approach can resolve what seems to be a factor of $\simeq 2$ difference in the moderate high $p_{T}$ suppression of $\pi^0$ and $h^-$ as recently reported by the PHENIX collaboration. The observed quenching of the high $p_{T}$ particle spectra and the large $\bar{p}/\pi^-$ and $p/\pi^+$ ratios as a function of $p_{T}$ are found to be consistent with a creation of a deconfined phase and non-abelian energy loss of fast partons in a plasma of initial gluon rapidity density $dN^g/dy \sim 1000$.Comment: 5 pages, uses revtex and bbox.sty, INPC 2001 conference proceeding