50 research outputs found
Jets in QCD matter: Monte Carlo approaches
Monte Carlo approaches are a powerful tool in collider physics as they allow
to make theory-data comparison on complex multi-particle observables, otherwise
difficult for perturbative calculations. In heavy-ion collisions, there is a
multitude of Monte Carlo approaches that try to address jet quenching
phenomena, name given to the collection of medium-induced modifications that
high momentum particles and jets undergo when traversing the hot and dense
medium that is produced in such collisions. These models are being continuous
developed alongside the theoretical efforts to understand and accurately
describe experimental results provided by both RHIC and the LHC. In this
manuscript, it is given a general overview about the fundamental building
blocks that these tools have to address to describe jets in heavy-ion
collisions. It follows a comparison on the latest results provided by some of
the jet quenching Monte Carlo models to jet and intra-jet observables. A final
personal outlook is presented at the end of the manuscript.Comment: Hard Probes Proceeding
Recent progress on the understanding of the medium-induced jet evolution and energy loss in pQCD
Motivated by the striking modifications of jets observed both at RHIC and the
LHC, significant progress towards the understanding of jet dynamics within QGP
has occurred over the last few years. In this talk, I review the recent
theoretical developments in the study of medium-induced jet evolution and
energy loss within a perturbative framework. The main mechanisms of energy loss
and broadening will be firstly addressed with focus on leading particle
calculations beyond the eikonal approximation. Then, I will provide an overview
of the modifications of the interference pattern between the different parton
emitters that build up the parton shower when propagating through an extended
coloured medium. I will show that the interplay between color
coherence/decoherence that arises from such effects is the main mechanism for
the modification of the jet core angular structure. Finally, I discuss the
possibility of a probabilistic picture of the parton shower evolution in the
limit of a very dense or infinite medium.Comment: XIIth Quark Confinement and the Hadron Spectrum Proceeding
An analysis of the influence of background subtraction and quenching on jet observables in heavy-ion collisions
Subtraction of the large background in reconstruction is a key ingredient in
jet studies in high-energy heavy-ion collisions at RHIC and the LHC. Here we
address the question to which extent the most commonly used subtraction
techniques are able to eliminate the effects of the background on the most
commonly discussed observables at present: single inclusive jet distributions,
dijet asymmetry and azimuthal distributions. We consider two different
background subtraction methods, an area-based one implemented through the
FastJet pack- age and a pedestal subtraction method, that resemble the ones
used by the experimental collaborations at the LHC. We also analyze different
ways of defining the optimal parame- ters in the second method. We use a toy
model that easily allows variations of the background characteristics: average
background level and fluctuations and azimuthal structure, but cross- checks
are also done with a Monte Carlo simulator. Furthermore, we consider the
influence of quenching using Q-PYTHIA on the dijet observables with the
different background subtrac- tion methods and, additionally, we examine the
missing momentum of particles. The average background level and fluctuations
affect both single inclusive spectra and dijet asymmetries, although
differently for different subtraction setups. A large azimuthal modulation of
the background has a visible effect on the azimuthal dijet distributions.
Quenching, as imple- mented in Q-PYTHIA, substantially affects the dijet
asymmetry but little the azimuthal dijet distributions. Besides, the missing
momentum characteristics observed in the experiment are qualitatively
reproduced by Q-PYTHIA.Comment: 29 pages, 43 figures Accepted by JHE
Sub-jet structure as a discriminating quenching probe
In this work, we propose a new class of jet substructure observables which,
unlike fragmentation functions, are largely insensitive to the poorly known
physics of hadronization. We show that sub-jet structures provide us with a
large discriminating power between different jet quenching Monte Carlo
implementations.Comment: 4 pages, 3 figures, Quarks Matter conference 201
Energy loss and (de)coherence effects beyond eikonal approximation
The parton branching process is known to be modified in the presence of a
medium. Colour decoherence processes are known to determine the process of
energy loss when the density of the medium is large enough to break the
correlations between partons emitted from the same parent. In order to improve
existing calculations that consider eikonal trajectories for both the emitter
and the hardest emitted parton, we provide in this work, the calculation of all
finite energy corrections for the gluon radiation off a quark in a QCD medium
that exist in the small angle approximation and for static scattering centres.
Using the path integral formalism, all particles are allowed to undergo
Brownian motion in the transverse plane and the offspring allowed to carry an
arbitrary fraction of the initial energy. The result is a general expression
that contains both coherence and decoherence regimes that are controlled by the
density of the medium and by the amount of broadening that each parton acquires
independently.Comment: 4 pages, to appear in the proceedings of the Quark Matter 2014
conferenc
Novel subjet observables for jet quenching in heavy-ion collisions
Using a novel observable that relies on the momentum difference of the two
most energetic subjets within a jet we study the internal
structure of high-energy jets simulated by several Monte Carlo event generators
that implement the partonic energy-loss in a dense partonic medium. Based on
inclusive jet and di-jet production we demonstrate that is an
effective tool to discriminate between different models of jet modifications
over a broad kinematic range. The new quantity, while preserving the colinear
and infrared safety of modern jet algorithms, it is experimentally attractive
because of its inherent resiliance against backgrounds of heavy-ion collisions.Comment: v1: 10 pages. v2: Includes (i) additional discussion about best
discriminant by calculating the RSD (ii) new section about hadronization
effects on the reconstructed subjets; version to be published in European
Physical Journal