194 research outputs found

    YaJEM - a Monte Carlo code for in-medium shower evolution

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    High transverse momentum (P_T) QCD scattering processes are regarded as a valuable tool to study the medium produced in heavy-ion collisions, as due to uncertainty arguments their cross section should be calculable independent of medium properties whereas the medium then modifies only the final state partons emerging from a hard vertex. With the heavy-ion physics program at the CERN LHC imminent, the attention of high P_T physics in heavy ion collisions is shifting from the observation of hard single hadrons to fully reconstructed jets. However, the presence of a background medium at low P_T complicates jet-finding as compared to p-p collisions. Monte-Carlo (MC) codes designed to simulate the evolution of parton showers evolving into hadron jets are valuable tools to understand the complicated interplay between the medium modification of the jet and the bias introduced by a specific jet-finding scheme. However, such codes also use a set of approximations which needs to be tested against the better understood single high P_T hadron observables. In this paper, I review the ideas underlying the MC code YaJEM (Yet another Jet Energy-loss Model) and present some of the results obtained with the code.Comment: Talk given at the workshop 'Jets in Proton-Proton and Heavy-Ion Collisions', Prague, Czech Republic, 12-14 Aug 201

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

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    We study the apparent discrepancy between the standard PQCD predictions for the meson and baryon ratios and multiplicities at moderate high pT>2p_{T} > 2 GeV and recent experimental measurements in Au+AuAu+Au collisions at sNN=130\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 pTp_{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 2\simeq 2 difference in the moderate high pTp_{T} suppression of π0\pi^0 and hh^- as recently reported by the PHENIX collaboration. The observed quenching of the high pTp_{T} particle spectra and the large pˉ/π\bar{p}/\pi^- and p/π+p/\pi^+ ratios as a function of pTp_{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 dNg/dy1000dN^g/dy \sim 1000.Comment: 5 pages, uses revtex and bbox.sty, INPC 2001 conference proceeding

    Tagged jets and jet reconstruction as a probe of QGP induced partonic energy loss

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    Recent experimental advances at the Relativistic Heavy Ion Collider (RHIC) and the large center-of-mass energies available to the heavy-ion program at the Large Hadron Collider (LHC) will enable strongly interacting matter at high temperatures and densities, that is, the quark-gluon plasma (QGP), to be probed in unprecedented ways. Among these exciting new probes are fully-reconstructed inclusive jets and the away-side hadron showers associated with a weakly or electromagnetically interacting boson, or, tagged jets. Full jet reconstruction provides an experimental window into the mechanisms of quark and gluon dynamics in the QGP which is not accessible via leading particles and leading particle correlations. Theoretical advances in this growing field can help resolve some of the most controversial points in heavy ion physics today. I here discuss the power of jets to reveal the spectrum of induced radiation, thereby shedding light on the applicability of the commonly used energy loss formalisms and present results on the production and subsequent suppression of high energy jets tagged with Z bosons in relativistic heavy-ion collisions at RHIC and LHC energies using the Gyulassy-Levai-Vitev (GLV) parton energy loss approach.Comment: Proceedings for the Jets in Proton-Proton and Heavy-Ion Collisions Workshop held in Prague this August. 5 pages and 4 figure

    The Z^0-tagged jet event asymmetry in heavy-ion collisions at the CERN Large Hadron Collider

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    Tagged jet measurements provide a promising experimental channel to quantify the similarities and differences in the mechanisms of jet production in proton-proton and nucleus-nucleus collisions. We present the first calculation of the transverse momentum asymmetry of Z^0/gamma^*-tagged jet events in sqrt{s}=2.76$ TeV reactions at the LHC. Our results combine the O(G_F\alpha_s^2) perturbative cross sections with the radiative and collisional processes that modify parton showers in the presence of dense QCD matter. We find that a strong asymmetry is generated in central lead-lead reactions that has little sensitivity to the fluctuations of the underlying soft hadronic background. We present theoretical model predictions for its shape and magnitude.Comment: 4 pages, 4 figures, as published in PR

    Formation and decay of hadronic resonances in the QGP

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    Hadronic resonances can play a pivotal role in providing experimental evidence for partial chiral symmetry restoration in the deconfined quark-gluon phase produced at RHIC. Their lifetimes, which are comparable to the lifetime of the partonic plasma phase, make them an invaluable tool to study medium modifications to the resonant state due to the chiral transition. In this paper we show that the heavier, but still abundant, light and strange quark resonances K*, phi, Delta and Lambda* have large probability to be produced well within the plasma phase due to their short formation times. We demonstrate that, under particular kinematic conditions, these resonances can be formed and will decay inside the partonic state, but still carry sufficient momentum to not interact strongly with the hadronic medium after the QCD phase transition. Thus, K*, phi, Delta and Lambda* should exhibit the characteristic property modifications which can be attributed to chiral symmetry restoration, such as mass shifts, width broadening or branching ratio modifications.Comment: 8 pages, 7 figure

    Non-Abelian Bremsstrahlung and Azimuthal Asymmetries in High Energy p+A Reactions

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    We apply the GLV reaction operator solution to the Vitev-Gunion-Bertsch (VGB) boundary conditions to compute the all-order in nuclear opacity non-abelian gluon bremsstrahlung of event-by-event fluctuating beam jets in nuclear collisions. We evaluate analytically azimuthal Fourier moments of single gluon, vnM{1}v_n^M\{1\}, and even number 22\ell gluon, vnM{2}v_n^M\{2\ell\} inclusive distributions in high energy p+A reactions as a function of harmonic nn, %independent target recoil cluster number, MM, and gluon number, 22\ell, at RHIC and LHC. Multiple resolved clusters of recoiling target beam jets together with the projectile beam jet form Color Scintillation Antenna (CSA) arrays that lead to characteristic boost non-invariant trapezoidal rapidity distributions in asymmetric B+AB+A nuclear collisions. The scaling of intrinsically azimuthally anisotropic and long range in η\eta nature of the non-abelian \br leads to vnv_n moments that are similar to results from hydrodynamic models, but due entirely to non-abelian wave interference phenomena sourced by the fluctuating CSA. Our analytic non-flow solutions are similar to recent numerical saturation model predictions but differ by predicting a simple power-law hierarchy of both even and odd vnv_n without invoking kTk_T factorization. A test of CSA mechanism is the predicted nearly linear η\eta rapidity dependence of the vn(kT,η)v_n(k_T,\eta). Non-abelian beam jet \br may thus provide a simple analytic solution to Beam Energy Scan (BES) puzzle of the near s\sqrt{s} independence of vn(pT)v_n(p_T) moments observed down to 10 AGeV where large xx valence quark beam jets dominate inelastic dynamics. Recoil \br from multiple independent CSA clusters could also provide a partial explanation for the unexpected similarity of vnv_n in p(D)+Ap(D)+A and non-central A+AA+A at same dN/dηdN/d\eta multiplicity as observed at RHIC and LHC.Comment: 16 pages, 10 figure