Calculating the Jet Quenching Parameter

TLDR: It is observed that q can be given a model-independent, nonperturbative, quantum field theoretic definition in terms of the short-distance behavior of a particular lightlike Wilson loop, and a strong-coupling calculation of q is obtained in hot N=4 supersymmetric QCD.

Abstract: Models of medium-induced radiative parton energy loss account for the strong suppression of high-p{sub T} hadron spectra in {radical}(s{sub NN})=200 GeV Au-Au collisions at BNL RHIC in terms of a single 'jet quenching parameter' q-circumflex. We observe that q-circumflex can be given a model-independent, nonperturbative, quantum field theoretic definition in terms of the short-distance behavior of a particular lightlike Wilson loop. We then use the anti-de Sitter/conformal-field-theory correspondence to obtain a strong-coupling calculation of q-circumflex in hot N=4 supersymmetric QCD, finding q-circumflex{sub SYM}=26.69{radical}({alpha}{sub SYM}N{sub c})T{sup 3} in the limit in which both N{sub c} and 4{pi}{alpha}{sub SYM}N{sub c} are large. Thus, at strong coupling q-circumflex is not proportional to the entropy density s, or to some ''number density of scatterers'' since, unlike the number of degrees of freedom, q-circumflex does not grow like N{sub c}{sup 2}.