Abstract
In ultra relativistic heavy-ion collisions at the Large Hadron Collider (LHC), conditions are met to produce a hot, dense and strongly interacting medium known as the Quark Gluon Plasma (QGP). Quarks and gluons from incoming nuclei collide to produce partons at high momenta early in the collisions. By fragmenting into collimated sprays of hadrons, these partons form 'jets'. The outgoing partons scatter and interact with the medium, leading to a manifestation of medium modifications of jets in the final state, known as jet quenching. Within the framework of perturbative QCD, jet production is well understood in pp collisions. We use jets measured in pp interactions as a baseline reference for comparing to heavy-ion collision systems to detect and study jet quenching. The jet quenching mechanism can be studied through the angular correlations of jets with charged hadrons and is examined in transverse momentum (pT) bins of the jets, pT bins of the associated hadrons, and as a function of collision centrality. A robust and precise background subtraction method is used in this analysis to remove the complex, flow dominated, heavy-ion background. The analysis of angular correlations for different orientations of the jet relative to the event plane allows for the study of the path-length dependence of medium modifications to jets. The event plane dependence of azimuthal angular correlations of charged hadrons with respect to the axis of an R=0.2 reconstructed full (charged + neutral) jet in Pb–Pb collisions at sNN=2.76 TeV in ALICE is presented. Results are compared for three angular bins of the jet relative to the event plane in mid-peripheral events. The yields relative to the event plane are presented and then quantified through yield ratio calculations. The results show no significant path-length dependence on the medium modifications.
Highlights
Jets are formed from hard-scattered partons created early in the collision, prior to the formation of the Quark Gluon Plasma (QGP), making them ideal probes to study the properties of the QGP
The results show no significant path-length dependence on the medium modifications
Jets are formed from hard-scattered partons created early in the collision, prior to the formation of the QGP, making them ideal probes to study the properties of the QGP
Summary
Jets are formed from hard-scattered partons created early in the collision, prior to the formation of the QGP, making them ideal probes to study the properties of the QGP. The hard-scattered partons are modified in the presence of a medium through additional scatterings (collisional energy loss) or mediuminduced gluon radiation (radiative energy loss), both of which depend on the path-length traversed through the medium. These partonic modifications are observed at both RHIC and LHC energies via the suppression of high-momentum particles [1, 2, 3, 4, 5, 6, 7] and by the suppression of high-momentum di-hadron correlations [8, 9, 10, 11]. The goal is to answer the question: can we experimentally distinguish between the effects of path-length dependence and the enhancement of vacuum-like fluctuations [12]?
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