Search for Quasiparticle Scattering in the Quark-Gluon Plasma with Jet Splittings in pp and Pb-Pb Collisions at sNN =5.02 TeV

Abstract

The ALICE Collaboration reports measurements of the large relative transverse momentum ( k T ) component of jet substructure in p p and Pb-Pb collisions at center-of-mass energy per nucleon pair s NN = 5.02 TeV . Enhancement in the yield of such large- k T emissions in head-on Pb-Pb collisions is predicted to arise from partonic scattering with quasiparticles of the quark-gluon plasma. The analysis utilizes charged-particle jets reconstructed by the anti- k T algorithm with resolution parameter R = 0.2 in the transverse-momentum interval 60 p T , ch , jet 80 GeV / c . The soft drop and dynamical grooming algorithms are used to identify high transverse momentum splittings in the jet shower. Comparison of measurements in Pb-Pb and p p collisions shows medium-induced narrowing, corresponding to yield suppression of high- k T splittings, in contrast to the expectation of yield enhancement due to quasiparticle scattering. The measurements are compared to theoretical model calculations incorporating jet modification due to jet-medium interactions (“jet quenching”), both with and without quasiparticle scattering effects. These measurements provide new insight into the underlying mechanisms and theoretical modeling of jet quenching.