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Register a new userGeometrical aspects of jet quenching in JEWEL
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Korinna C. Zapp
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In this publication the performance of the Monte Carlo event generator JEWEL in non-central heavy-ion collisions is investigated. JEWEL is a consistent perturbative framework for jet evolution in the presence of a dense medium. It yields a satisfactory description of a variety of jet observables in central collisions at the LHC, although so far with a simplistic model of the medium. Here, it is demonstrated that also jet measurements in non-central collisions, and in particular the dependence of the jet suppression on the angle relative to the reaction plane, are reproduced by the same model.
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A study of several observables characterising fragment distributions of medium-modified parton showers using the JEWEL and Q-PYTHIA models is presented, with emphasis on the relation between the different observables.
Processes in which a jet recoils against an electroweak boson complement studies of jet quenching in heavy ion collisions at the LHC. As the boson does not interact strongly it escapes the dense medium unmodified and thus provides a more direct access to the hard scattering kinematics than can be obtained in di-jet events. First measurements of jet modification in these processes are now available from the LHC experiments and will improve greatly with better statistics in the future. We present an extension of JEWEL to boson-jet processes. JEWEL is a dynamical framework for jet evolution in a dense background based on perturbative QCD, that is in agreement with a large variety of jet observables. We also obtain a good description of the CMS and ATLAS data for y+jet and Z+jet processes at 2.76 TeV and 5.02 TeV.
In the last 30 years, the physics of jet quenching has gone from an early stage of a pure theoretical idea to initial theoretical calculations, experimental verification and now a powerful diagnostic tool for studying properties of the quark-gluon plasma (QGP) in high-energy heavy-ion collisions. I will describe my collaboration with Miklos Gyulassy in this exciting area of high-energy nuclear physics in the past 30 years on this special occasion of his 70th birthday and discuss what is ahead of us in jet tomographic study of QGP in heavy-ion collisions.
Based on a pQCD inspired dynamical model of jet-medium interactions, Jewel, we have studied possible modifications to inclusive jet yields and a set of jet shape observables, namely, the fragmentation functions and radial momentum distributions when jets propagate through a deconfined partonic medium created in collisions of heavy nuclei at Large Hadron Collider (LHC) energies. Jets are reconstructed with anti-k T algorithm in the pseudorapidity range $|eta_{rm jet} | < 2.1$ for resolution parameter R= 0.2, 0.3 and 0.4. For background subtraction, a Jewel-compatible 4-Momenta subtraction technique (4MomSub) have been used. The modification of inclusive jet-yields in Pb-Pb collisions relative to proton-proton interactions, quantified by $R^{rm jet}_{AA}$, are seen to be in reasonable agreement with ALICE, ATLAS and CMS data over a broad transverse momentum range. Jewel is able to capture the qualitative features of the modifications to the fragmentation functions and radial momentum distributions in data but not always quantitatively. This quantitative discrepancy may be related to the simplified treatment of recoil partons in the background model and partly due to background subtraction procedure itself. Nevertheless, observed modification of jet shape variables in Jewel corroborates the fact that in-medium fragmentation is harder and more collimated than the fragmentation in vacuum. We further observe that these modifications depend on the transverse momentum of jets and it seems that medium resolves the core structure of low momentum jets below 100 GeV/c at LHC energies.
QCD monopoles are magnetically charged quasiparticles whose Bose-Einstein condensation (BEC) at $T<T_c$ creates electric confinement and flux tubes. The magnetic scenario of QCD proposes that scattering on the non-condensed component of the monopole ensemble at $T>T_c$ is responsible for the unusual kinetic properties of QGP. In this paper, we study the contribution of the monopoles to jet quenching phenomenon, using the BDMPS framework and hydrodynamic backgrounds. In the lowest order for cross sections, we calculate the nuclear modification factor, $R_text{AA},$ and azimuthal anisotropy, $v_2$, of jets, as well as the dijet asymmetry, $A_j$, and compare those to the available data. We find relatively good agreement with experiment when using realistic hydrodynamic backgrounds. In addition, we find that event-by-event fluctuations are not necessary to reproduce $R_text{AA}$ and $v_2$ data, but play a role in $A_j$. Since the monopole-induced effects are maximal at $Tapprox T_c$, we predict that their role should be significantly larger, relative to quarks and gluons, at lower RHIC energies.
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