We discuss recent applications of the partonic pQCD based cascade model BAMPS with focus on heavy-ion phenomeneology in hard and soft momentum range. The nuclear modification factor as well as ...elliptic flow are calculated in BAMPS for RHIC end LHC energies. These observables are also discussed within the same framework for charm and bottom quarks. Contributing to the recent jet-quenching investigations we present first preliminary results on application of jet reconstruction algorithms in BAMPS. Finally, collective effects induced by jets are investigated: we demonstrate the development of Mach cones in ideal matter as well in the highly viscous regime.
The phenomenon of jet quenching provides essential information about the properties of hot and dense matter created in ultra-relativistic heavy-ion collisions. Recent results from experiments at the ...Large Hadron Collider (LHC) show evidence for an unexpectedly similar suppression of both light and heavy flavor jets. Furthermore, the role of radiative energy loss of heavy quarks is still under active discussion within the theoretical community. By employing the parton cascade Boltzmann Approach to Multi-Parton Scatterings (BAMPS), which numerically solves the 3+1D Boltzmann equation both for light and heavy flavor partons, we calculate the nuclear modification factor of inclusive and b-tagged reconstructed jets in 0-10% central \(\sqrt{s_{\rm LHC}}\) = 2.76 ATeV Pb+Pb collisions. Based on perturbative QCD cross sections we find a suppression of both light and heavy flavor jets. While the inclusive jets are slightly too strong suppressed within BAMPS in comparison with data, both elastic+radiative and only elastic interactions lead to a realistic b-tagged jet suppression. To further investigate light and heavy flavor energy loss we predict the R dependence of inclusive and b-tagged jet suppression. Furthermore, we propose the medium modification of b-tagged jet shapes as an observable for discriminating between different heavy quark energy loss scenarios.
We compare a perturbative QCD-based jet-energy loss model to the measured data of the pion nuclear modification factor and the high-pT elliptic flow at RHIC and LHC energies. This jet-energy loss ...model (BBMG) is currently coupled to state-of-the-art hydrodynamic descriptions. We report on a model extension to medium backgrounds generated by the parton cascade BAMPS. In addition, we study the impact of realistic medium transverse flow fields and a jet-medium coupling which includes the effects of the jet energy, the temperature of the bulk medium, and non-equilibrium effects close to the phase transition. By contrasting the two different background models, we point out that the description of the high-pT elliptic flow for a non-fluctuating medium requires to include such a jet-medium coupling and the transverse flow fields. While the results for both medium backgrounds show a remarkable similarity, there is an impact of the background medium and the background flow on the high-pT elliptic flow.
The measured data on the nuclear modification factor for pions and reconstructed jets as well as on the high-pT elliptic flow at RHIC and LHC energies are compared to results from a linear pQCD and a ...highly non-linear hybrid AdS holographic model of jet-energy loss. We find that the high-pT ellitic flow requires to include realistic medium transverse flow fields and a jet-medium coupling including the effects of the energy of the jet, the temperature of the bulk medium, and non-equilibrium effects close to the phase transition. We extend our jet-energy loss model that is coupled to state-of-the-art hydrodynamic prescriptions to backgrounds generated by the parton cascade BAMPS. We demonstrate that the results for the hydrodynamic and the parton-cascade backgrounds show a remarkable similarity. Unfortunately, the results for both the pion and a parton-jet nuclear modification factor are insensitive to the jet-path dependence of the models considered.
We discuss the implementation of leading-order photon production in nonequilibrium partonic transport simulations. In this framework photons are produced by microscopic scatterings, where we include ...the exact matrix elements of Compton scattering, quark-antiquark annihilation, and bremsstrahlung processes. We show how the hard-thermal loop inspired screening of propagators has to be modified such that the microscopic production rate agrees well with the analytically known resummed leading-order rate. We model the complete quark-gluon plasma phase of heavy-ion collisions by using the partonic transport approach called the Boltzmann approach to multiparton scatterings (BAMPS), which solves the ultrarelativistic Boltzmann equation with Monte Carlo methods. We show photon spectra and elliptic flow of photons from BAMPS and discuss nonequilibrium effects. Due to the slow quark chemical equilibration in BAMPS, the yield is lower than the results from other groups; in turn we see a strong effect from scatterings of energetic jet-like partons with the medium. This nonequilibrium photon production can dominate the thermal emission, such that the spectra are harder and the photonic elliptic flow of the quark-gluon plasma becomes negative.
Experimental data measured in sqrt(s)=2.76 TeV Pb+Pb collisions at the LHC show a significant enhancement of events with an unbalanced pair of reconstructed jet momenta in comparison with p+p ...collisions. This enhancement of momentum imbalance is supposed to be caused by the different momentum loss of the initial back-to-back di-partons by scatterings within the created dense medium. For investigating the underlying partonic momentum loss we employ the on-shell transport model BAMPS (Boltzmann Approach for Multi-Parton Scattering) for full heavy-ion collisions, which numerically solves the 3+1D Boltzmann equation based on 2->2 as well as inelastic 2<->3 scattering processes, together with PYTHIA initial state conditions for the parton showers. Due to the employed test-particle approach jet reconstruction within BAMPS events is not trivial. We introduce a method that nevertheless allows the microscopic simulation of the full evolution of the shower particles, recoiled medium particles, and the underlying bulk medium in one common microscopic framework. With this method it is possible to investigate the role of the medium recoil for the momentum imbalance A_J while using well-established background subtraction algorithms. Due to the available particle information in configuration as well as momentum space within BAMPS, it is additionally possible to reproduce the entire evolution of the reconstructed jets within the medium. With this information we investigate the sensitivity of the jet momentum loss from the difference in the partonic in-medium path lengths.
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As a new observable for heavy flavor correlations the momentum imbalance \(A_D\) of D mesons is proposed. It is defined analogously to the jet momentum imbalance \(A_J\) of fully reconstructed jets. ...However, since D mesons are flavor tagged particles, no jet reconstruction is necessary. \(A_D\) quantifies the influence of the medium created in heavy-ion collisions on correlated charm pairs. We present results with the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS), which describes well the nuclear modification factor and elliptic flow of all heavy flavor particles at RHIC and LHC. The \(A_D\) distribution in heavy-ion collisions at LHC is shifted to larger values of \(A_D\) compared to proton-proton collisions. We argue that this shift is due to medium effects and can be explained partially by a path length imbalance of charm pairs and partially by momentum fluctuations in the initial charm pair distribution.
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