QCD jets in a hot and dense medium: A study of shower formation time and collision kernels

With the use of , a model which considers evolving QCD jets against a fluid dynamical background, it is shown that the introduction of formation time to the parton shower after the initial hard scattering is essential for a simultaneous description of charged hadron and jet <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi>R</a:mi><a:mrow><a:mi>A</a:mi><a:mi>A</a:mi></a:mrow></a:msub></a:math>. This inclusion also improves jet shape ratios at small angle and jet fragmentation function ratios of leading charged hadrons. The framework is then aimed at a study of the leading-order, next-to-leading-order, and nonperturbative collision kernels. Sizable differences in the modification of jet substructure observables, i.e., jet shape and fragmentation functions, are observed. Such differences are caused by the difference in the radiation rates of relatively soft gluons that survive in the evolution in medium.