Measurement of jet quenching with semi-inclusive hadron-jet distributions in central Pb–Pb collisions at √sNN = 2.76 TeV

Adam, J. and Adamova, D. and Aggarwal, M. M. and Rinella, G. A. and Agnello, M. and Barnaföldi, Gergely Gábor and Bencédi, Gyula and Berényi, Dániel and Boldizsár, László and Dénes, Ervin and Hamar, Gergő and Kiss, Gábor and Varga-Kőfaragó, Mónika and Lévai, Péter and Lowe, Andrew John and Oláh, László and Pochybova, Sona and Varga, Dezső (2015) Measurement of jet quenching with semi-inclusive hadron-jet distributions in central Pb–Pb collisions at √sNN = 2.76 TeV. JOURNAL OF HIGH ENERGY PHYSICS, 2015 (9). ISSN 1126-6708

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Abstract

We report the measurement of a new observable of jet quenching in central Pb–Pb collisions at √sNN = 2.76 TeV, based on the semi-inclusive rate of charged jets recoiling from a high transverse mo- mentum (high-pT) charged hadron trigger. Jets are measured using collinear-safe jet reconstruction with infrared cutoff for jet constituents of 0.15 GeV/c, for jet resolution parameters R = 0.2, 0.4 and 0.5. Underlying event background is corrected at the event-ensemble level, without imposing bias on the jet population. Recoil jet spectra are reported in the range 20 < pch T,jet < 100 GeV/c. Reference distributions for pp collisions at √s = 2.76 TeV are calculated using Monte Carlo and NLO pQCD methods, which are validated by comparing with measurements in pp collisions at √s = 7 TeV. The recoil jet yield in central Pb–Pb collisions is found to be suppressed relative to that in pp collisions. No significant medium-induced broadening of the intra-jet energy profile is observed within 0.5 radi- ans relative to the recoil jet axis. The angular distribution of the recoil jet yield relative to the trigger axis is found to be similar in central Pb–Pb and pp collisions, with no significant medium-induced acoplanarity observed. Large-angle jet deflection, which may provide a direct probe of the nature of the quasi-particles in hot QCD matter, is explored.

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