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Register a new userLPM-Effect in Monte Carlo Models of Radiative Energy Loss
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Extending the use of Monte Carlo (MC) event generators to jets in nuclear collisions requires a probabilistic implementation of the non-abelian LPM effect. We demonstrate that a local, probabilistic MC implementation based on the concept of formation times can account fully for the LPM-effect. The main features of the analytically known eikonal and collinear approximation can be reproduced, but we show how going beyond this approximation can lead to qualitatively different results.
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Monte Carlo (MC) simulations are the standard tool for describing jet-like multi-particle final states. To apply them to the simulation of medium-modified jets in heavy ion collisions, a probabilistic implementation of medium-induced quantum interference effects is needed. Here, we analyze in detail how the quantum interference effects included in the BDMPS-Z formalism of medium-induced gluon radiation can be implemented in a quantitatively controlled, local probabilistic parton cascade. The resulting MC algorithm is formulated in terms of elastic and inelastic mean free paths, and it is by construction insensitive to the IR and UV divergences of the total elastic and inelastic cross sections that serve as its basic building blocks in the incoherent limit. Interference effects are implemented by reweighting gluon production histories as a function of the number of scattering centers that act within the gluon formation time. Unlike existing implementations based on gluon formation time, we find generic arguments for why a quantitative implementation of quantum interference cannot amount to a mere dead-time requirement for subsequent gluon production. We validate the proposed MC algorithm by comparing MC simulations with parametric dependencies and analytical results of the BDMPS-Z formalism. In particular, we show that the MC algorithm interpolates correctly between analytically known limiting cases for totally coherent and incoherent gluon production, and that it accounts quantitatively for the medium-induced gluon energy distribution and the resulting average parton energy loss. We also verify that the MC algorithm implements the transverse momentum broadening of the BDMPS-Z formalism. We finally discuss why the proposed MC algorithm provides a suitable starting point for going beyond the approximations of the BDMPS-Z formalism.
For high precision measurements of K decays, the presence of radiated photons cannot be neglected. The Monte Carlo simulations must include the radiative corrections in order to compute the correct event counting and efficiency calculations. In this paper we briefly describe a method for simulating such decays.
We compute the in-medium energy loss probability distribution of two neighboring subjets at leading order, in the large-$N_c$ approximation. Our result exhibits a gradual onset of color decoherence of the system and accounts for two expected limiting cases. When the angular separation is smaller than the characteristic angle for medium-induced radiation, the two-pronged substructure lose energy coherently as a single color charge, namely that of the parent parton. At large angular separation the two subjets lose energy independently. Our result is a first step towards quantifying effects of energy loss as a result of the fluctuation of the multi-parton jet substructure and therefore goes beyond the standard approach to jet quenching based on single parton energy loss. We briefly discuss applications to jet observables in heavy-ion collisions.
The theory and numerical modelling of radiation processes and radiative transfer play a key role in astrophysics: they provide the link between the physical properties of an object and the radiation it emits. In the modern era of increasingly high-quality observational data and sophisticated physical theories, development and exploitation of a variety of approaches to the modelling of radiative transfer is needed. In this article, we focus on one remarkably versatile approach: Monte Carlo Radiative Transfer (MCRT). We describe the principles behind this approach, and highlight the relative ease with which they can (and have) been implemented for application to a range of astrophysical problems. All MCRT methods have in common a need to consider the adverse consequences of Monte Carlo noise in simulation results. We overview a range of methods used to suppress this noise and comment on their relative merits for a variety of applications. We conclude with a brief review of specific applications for which MCRT methods are currently popular and comment on the prospects for future developments.
In this contribution the new event generation framework SHERPA will be presented, which aims at a full simulation of events at current and future high-energy experiments. Some first results exemplify its capabilities.
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