Nuclear Modification Factor of High Momentum Jets in PbPb Collisions

Abstract

According to quantum chromodynamics (QCD), the release of quarks and gluons creates a new form of matter, the quark gluon plasma (QGP), expected to occur in relativistic heavy-ion collisions at high energies. The structure and dynamics of the QGP can be studied using partonic interactions at large momentum transfers. This was studied at the Relativistic Heavy Ion Collider starting in 2002 utilizing AuAu collisions at 200 GeV center-of-mass. In this analysis, fully reconstructed jets in pp and PbPb collisions at 2.76 TeV center-of-mass energy are analyzed with the CMS detector at the Large Hadron Collider (LHC) in CERN. The ratio of inclusive reconstructed jet transverse momenta spectra of PbPb collisions to that of proton+proton (pp) collisions is defined as jets nuclear modification factor (R_AA) and it is studied to quantify the medium modification within transverse momenta above 100GeV/c. Jet R_AA results are compared for three different unfolding methods: Bayesian Unfolding, bin-by-bin Unfolding and Generalized Singular Value Decomposition (GSVD) Unfolding, as well as corrections performed with pp data smearing. A jet R_AA of approximately 0.5 is observed in the most central collisions and close to unity in the most peripheral collisions without a strong indication of the transverse momenta (p_T) dependence. A suppression of high p_T jets is observed in central PbPb collisions in comparison to peripheral collisions. This is consistent with the observation of jet quenching.