Monte Carlo tools for jet quenching Zapp, Korinna
Journal of physics. G, Nuclear and particle physics,
12/2011, Letnik:
38, Številka:
12
Journal Article, Conference Proceeding
A Monte Carlo model for ‘jet quenching’ Zapp, Korinna; Ingelman, Gunnar; Rathsman, Johan ...
European physical journal. C, Particles and fields,
04/2009, Letnik:
60, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We have developed the Monte Carlo simulation program
Jewel
1.0 (Jet Evolution With Energy Loss), which interfaces a perturbative final-state parton shower with medium effects occurring in ...ultra-relativistic heavy-ion collisions. This is done by comparing for each jet fragment the probability of further perturbative splitting with the density-dependent probability of scattering with the medium. A simple hadronisation mechanism is included. In the absence of medium effects, we validate
Jewel
against a set of benchmark jet measurements. For elastic interactions with the medium, we characterise not only the medium-induced modification of the jet, but also the jet-induced modification of the medium. Our main physical result is the observation that collisional and radiative medium modifications lead to characteristic differences in the jet fragmentation pattern, which persist above a soft background cut. We argue that this should allow one to disentangle collisional and radiative parton energy loss mechanisms by measuring the
n
-jet fraction or a class of jet shape observables.
Jewel is a fully dynamical event generator for jet evolution in a dense QCD medium, which has been validated for multiple jet and jet-like observables. Jet constituents (partons) undergo collisions ...with thermal partons from the medium, leading to both elastic and radiative energy loss. The recoiling medium scattering centers carry away energy and momentum from the jet. Keeping track of these recoils is essential for the description of intra-jet observables. Since the thermal component of the recoils is part of the soft background activity, comparison with data on jet observables requires the implementation of a background subtraction procedure. We will show two independent procedures through which background subtraction can be performed and discuss the impact of the medium recoil on jet shape observables and jet-background correlations. Keeping track of the medium recoil significantly improves the Jewel description of jet shape measurements.
Jet quenching is one of the major discoveries of the heavy-ion program at Rhic. While there is a wealth of data from Rhic that will soon be supplemented with measurements at the Lhc, on the ...theoretical side the situation is less clear. A thorough understanding of jet quenching is, however, beneficial, as it is expected that medium-induced modifications of jets allow one to characterise properties of the QCD matter produced in heavy ion collisions. This talk aims at summarising the main ideas and concepts of the currently available Monte Carlo models for jet quenching.
In hadronization models with colour recombination, partons are allowed to regroup into colour singlet structures that are different from those determined by the perturbative parton shower. This aims ...at modeling the possibility that soft interactions of partons with the underlying event can change colour connections. If such an effect is at play in proton-proton collisions, it may be expected to be enhanced in proton-nucleus collisions due to the higher colour charge density in the underlying event. Here, we provide a qualitative argument that colour recombination effects could lead to a multiplicity dependent hardening of single inclusive hadron spectra that dies out very weakly (∝1/p⊥) with increasing transverse momentum. We present results of a (conservative) model implementation in the cluster hadronization model of the SHERPA event generator. In this model, we find that colour recombination effects harden indeed the single inclusive hadron spectra without affecting the jet spectra, but that this effect does not depend significantly on underlying event activity. We explain this model feature and we argue why, in general, data on proton-nucleus collisions can help to constrain hadronization models used in proton-proton event generators.
Jet quenching in heavy ion collisions and in particular the sub-structure of quenched jets are promising tools for investigating the microscopic processes underlying jet quenching and the background ...medium's response to energy and momentum depositions. A quantitative understanding of the data can, however, be complicated by the presence of initial state radiation in reconstructed jets. Using an extended version of JEWEL the effect of initial state radiation on different jet observables is studied in proton-proton and heavy ion collisions. It is shown that, depending on the observable and the jet radius, the initial state contributions can be sizable. Some general insights into when sizable effects can be expected also emerges.
Triple gauge boson hadroproduction, in particular the production of three W-bosons at the LHC, is considered at next-to leading order accuracy in QCD. The NLO matrix elements are combined with parton ...showers. Multijet merging is invoked such that NLO matrix elements with one additional jet are also included. The studies here incorporate both the signal and all relevant backgrounds for V H production with the subsequent decay of the Higgs boson into W– or τ–- pairs. They have been performed using SHERPA+OPENLOOPS in combination with COLLIER.
The non-Abelian Landau-Pomeranschuk-Migdal (LPM) effect arises from the quantum interference between spatially separated, inelastic radiation processes in matter. A consistent probabilistic ...implementation of this LPM effect is a prerequisite for extending the use of Monte Carlo (MC) event generators to the simulation of jetlike multiparticle final states in nuclear collisions. Here, we propose a local MC algorithm, which is based solely on relating the LPM effect to the probabilistic concept of formation time for virtual quanta. This accounts probabilistically for the characteristic L{sup 2} dependence of average parton energy loss and the characteristic 1/sq root(omega) modification of the non-Abelian LPM effect. Additional kinematic constraints are found to modify these L{sup 2} and omega dependencies characteristically in accordance with analytical estimates.
We look at thermalization and isotropization processes in the newly introduced AMY QCD kinetic theory parton cascade ALPACA. For thermalization, we consider the case of overoccupied initial ...conditions, and study the time evolution of the distribution as it relaxes to thermal equilibrium. We find that the system thermalizes as expected compared to known analytical results. For anisotropic systems, we take a first look at the qualitative behaviour of isotropization for Color Glass Condensate-like initial conditions in a homogeneous box with periodic boundary conditions.
Understanding how momentum anisotropies arise in small collision systems is important for a quantitative understanding of collectivity in terms of QCD dynamics in small and large collision systems. ...In this letter we present results for small collision systems from the newly developed parton cascade ALPACA, which faithfully encodes the AMY effective kinetic theory. ALPACA reproduces quantitatively previously know results from a calculation in the single-hit approximation for small values of the coupling. We discuss in detail how such a comparison is to be carried out. Particularly at larger coupling a generic differences between the two approaches becomes apparent, namely that in parton cascades particles interact over a finite distance while in direct integrations of the Boltzmann equation the interactions are local. This leads to quantitative differences in the extracted values for the elliptic flow coefficient, but also raises questions of a much more fundamental nature that are worth exploring in the future.
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