Investigations of Jet Quenching in Peripheral Pb+Pb Collisions at 5.02 TeV with ATLAS*

The quark-gluon plasma (QGP) is an exotic state of matter consisting of deconfined quarks and gluons which is produced in collisions of heavy ions at relativistic energies. With the ATLAS detector at the Large Hadron Collider, we seek to further characterize one of the most important signatures of QGP formation, known as jet quenching. Specifically, we address the question of where jet quenching begins in the spectrum of various collision systems. A recent ATLAS study shows a lack of jet quenching in p+Pb collisions, suggesting that a study of jet quenching in peripheral Pb+Pb collisions (in which only a few of the incoming nucleons participate) will be a useful tool in answering this question. This study reports jet-triggered hadron yields – an observable sensitive to jet quenching – as a function of event centrality in Pb+Pb collisions. The data selected consists of hadrons correlated with high-p_T, anti-k_T R = 0.4 jets from 5.02 TeV Pb+Pb collisions. To select peripheral events in an unbiased way, we utilize the ATLAS Zero-Degree Calorimeters to define event centrality. Finally, we compare these yields with those in 5.02 TeV pp collisions, in which no jet quenching is observed.