83 research outputs found
Jet physics in heavy-ion collisions
Jets are expected to play a prominent role in the ongoing efforts to
characterize the hot and dense QCD medium created in ultrarelativistic heavy
ion collisions. The success of this program depends crucially on the existence
of a full theoretical account of the dynamical effects of the medium on the
jets that develop within it. By focussing on the discussion of the essential
ingredients underlying such a theoretical formulation, we aim to set the
appropriate context in which current and future developments can be understood.Comment: 36 pages, 5 figures, few minor corrections, references added. Final
version published in IJMP
Jet coherence in QCD media: the antenna radiation spectrum
We study the radiation of a highly energetic partonic antenna in a colored
state traversing a dense QCD medium. Resumming multiple scatterings of all
involved constituents with the medium we derive the general gluon spectrum
which encompasses both longitudinal color coherence between scattering centers
in the medium, responsible for the well known Landau-Pomeranchuk-Migdal (LPM)
effect, and transverse color coherence between partons inside a jet, leading,
in vacuum, to angular ordering of the parton shower. We discuss shortly the
onset of transverse decoherence which is reached in opaque media. In this
regime, the spectrum consists of independent radiation off the antenna
constituents.Comment: 15 pages, 2 figures, paper shortened and partly rewritten, references
added, results unchange
Jet thermalization in QCD kinetic theory
We perform numerical studies in QCD kinetic theory to investigate the energy
and angular profiles of a high energy parton - as a proxy for a jet produced
heavy ion collisions - passing through a Quark-Gluon Plasma (QGP). We find that
the fast parton loses energy to the plasma mainly via a radiative turbulent
gluon cascade that transport energy locally from the jet down to the
temperature scale where dissipation takes place. In this first stage, the
angular structure of the turbulent cascade is found to be relatively
collimated. However, when the lost energy reaches the plasma temperature is it
rapidly transported to large angles w.r.t. the jet axis and thermalizes. We
investigate the contribution of the soft jet constituents to the total jet
energy. We show that for jet opening angles of about 0.3 rad or smaller the
effect is negligible. Conversely, larger opening angles become more and more
sensitive to the thermal component of the jet and thus to medium response. Our
result showcase the importance of the jet cone size in mitigating or enhancing
the details of dissipation in jet quenching observables.Comment: 41 pages, 11 figures
Stopping in central Pb + Pb collisions at SPS energies and beyond
We investigate stopping and baryon transport in central relativistic Pb + Pb
and Au + Au collisions. At energies reached at the CERN Super Proton
Synchrotron [sqrt(s_NN) = 6.3-17.3 GeV] and at RHIC (62.4 GeV), we determine
the fragmentation-peak positions from the data. The resulting linear growth of
the peak positions with beam rapidity is in agreement with our results from a
QCD-based approach that accounts for gluon saturation. No discontinuities in
the net-proton fragmentation peak positions occur in the expected transition
region from partons to hadrons at 6-10 GeV.Comment: 5 pages, 3 figures, 1 table. Figures updated, table shortened, 1
reference adde
Mass effect and coherence in medium-induced QCD radiation off a antenna
The medium-induced one-gluon radiation spectrum off a massive quark-antiquark
() antenna traversing a colored QCD medium is calculated in this
contribution. The gluon spectrum off the antenna computed at first order in the
opacity expansion is collinear finite but infrared divergent, which is
different from the result obtained from an independent emitter which is both
infrared and collinear finite. The interference between emitters dominates the
soft gluon radiation when the antenna opening angle is small and the emitted
gluon is soft, whereas the antenna behaves like a superposition of independent
emitters when the opening angle is large and the radiated gluon is hard. As a
phenomenological consequence, we investigate the energy lost by the projectiles
due to the radiation. In general, the size of the mass effects is similar in
both cases.Comment: 4 pages, 1 figure, Proceedings of Quark Matter 2011, Annecy, Franc
Antiangular Ordering of Gluon Radiation in QCD Media
We investigate angular and energy distributions of medium-induced gluon
emission off a quark-antiquark antenna in the framework of perturbative QCD as
an attempt toward understanding, from first principles, jet evolution inside
the quark-gluon plasma. In-medium color coherence between emitters, neglected
in all previous calculations, leads to a novel mechanism of soft-gluon
radiation. The structure of the corresponding spectrum, in contrast with known
medium-induced radiation, retains some properties of the vacuum case; in
particular, it exhibits a soft divergency. However, as opposed to the vacuum,
the collinear singularity is regulated by the pair opening angle, leading to a
strict angular separation between vacuum and medium-induced radiation, denoted
as antiangular ordering. We comment on the possible consequences of this new
contribution for jet observables in heavy-ion collisions.Comment: 4 pages, 2 figures; v2. a number of minor improvements, figures
updated, accepted for publication in PR
Monte Carlo Tools for Jet Quenching
A thorough understanding of jet quenching on the basis of multi-particle
final states and jet observables requires new theoretical tools. This talk
summarises the status and propects of the theoretical description of jet
quenching in terms of Monte Carlo generators.Comment: proceedings of the 22nd International Conference on
Ultra-Relativistic Nucleus Nucleus Collisions (Quark Matter 2011
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