Sudakov suppression of jets in QCD media

We compute modifications to the jet spectrum in the presence of a dense medium. We show that in the large-$N_c$ approximation and at leading logarithmic accuracy the jet nuclear modification factor factorizes into a quenching factor associated to the total jet color charge and a Sudakov suppression factor which accounts for the energy loss of jet substructure fluctuations. This factor, called the jet collimator, implements the fact that subjets, that are not resolved by the medium, lose energy coherently as a single color charge, whereas resolved large angle fluctuations suffer more quenching. For comparison, we show that neglecting color coherence results in a stronger suppression of the jet nuclear modification factor.

Figure 1

The phase-space of higher-order corrections to the jet inclusive spectrum in the presence of radiative energy loss. We have incorporated lines denoting $t_{\mathrm{f}}=L$, $t_{\mathrm{f}}=t_{\mathrm{d}}$ and $t_{\mathrm{d}}=L$ (implying $\theta ={\theta }_c$) and all related scales. The shaded region describes the ordering $t_{\mathrm{f}}<t_{\mathrm{d}}<L$.

Figure 2

The quark jet suppression factor calculated using the quenching weight alone (solid line) and additionally supplemented by the Sudakov suppression with and without coherence effects, see text for further details.