Effect of magnetic field on jet transport coefficient $\hat{q}$

Abstract

We report the estimation of jet transport coefficient, $\hat{q}$ for quark- and gluon-initiated jets using a simple quasi-particle model in absence and presence of magnetic field. This model introduces a temperature and magnetic field-dependent degeneracy factor of partons, which is tuned by fitting the entropy density of lattice quantum chromodynamics data. At a finite magnetic field, $\hat{q}$ for quark jets splits into parallel and perpendicular components whose magnetic field dependence comes from two sources: the field-dependent degeneracy factor and the phase space part guided from the shear viscosity to entropy density ratio. Due to the electrically neutral nature of gluons, the estimation of $\hat{q}$ for gluon jets is affected only by the field-dependent degeneracy factor. In presence of a finite magnetic field, we find a significant enhancement in $\hat{q}$ for both quark- and gluon-initiated jets at low temperature, which gradually decreases towards high temperature. We compare the obtained results with the earlier calculations based on the anti-de Sitter/conformal field theory correspondence, and a qualitatively similar trend is observed. The change in $\hat{q}$ in presence of magnetic field is, however, quantitatively different for quark- and gluon-initiated jets. This is an interesting observation which can be explored experimentally to verify the effect of magnetic field on $\hat{q}$.