Calculating quenching weights

We calculate the probability (``quenching weight'') that a hard parton radiates an additional energy fraction ΔE due to scattering in spatially extended QCD matter. This study is based on an exact treatment of a finite in-medium path length; it includes the case of a dynamically expanding medium, and it extends to the angular dependence of the medium-induced gluon radiation pattern. All calculations are done in the multiple soft scattering approximation [Baier-Dokshitzer-Mueller-Peign\'e-Schiff-Zakharov (BDMPSZ) formalism] and in the single hard scattering approximation $[N=1$ opacity approximation]. By comparison, we establish a simple relation between the transport coefficient, Debye screening mass and opacity, for which both approximations lead to comparable results. Together with this paper, a CPU-inexpensive numerical subroutine for calculating quenching weights is provided electronically. To illustrate its applications, we discuss the suppression of hadronic transverse momentum spectra in nucleus-nucleus collisions. Remarkably, the kinematic constraint resulting from finite in-medium path lengths reduces significantly the p_⊥ dependence of the nuclear modification factor, thus leading to consistency with the data measured at the BNL Relativistic Heavy Ion Collider.