197 research outputs found
YaJEM - a Monte Carlo code for in-medium shower evolution
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
We study the apparent discrepancy between the standard PQCD predictions for
the meson and baryon ratios and multiplicities at moderate high GeV
and recent experimental measurements in collisions at
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 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 difference in the
moderate high suppression of and as recently reported by
the PHENIX collaboration. The observed quenching of the high particle
spectra and the large and ratios as a function of
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 .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
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
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
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
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,
, and even number gluon, inclusive
distributions in high energy p+A reactions as a function of harmonic ,
%independent target recoil cluster number, , and gluon number, , 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 nuclear collisions. The scaling of intrinsically
azimuthally anisotropic and long range in nature of the non-abelian \br
leads to 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 without invoking
factorization. A test of CSA mechanism is the predicted nearly linear
rapidity dependence of the . Non-abelian beam jet \br may thus
provide a simple analytic solution to Beam Energy Scan (BES) puzzle of the near
independence of moments observed down to 10 AGeV where
large 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 in and non-central at same
multiplicity as observed at RHIC and LHC.Comment: 16 pages, 10 figure
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