Abstract
We report the measurement of a new observable of jet quenching in central Pb-Pb collisions at \( \sqrt{s_{\mathrm{NN}}}=2.76 \) TeV, based on the semi-inclusive rate of charged jets recoiling from a high transverse momentum (high-p T) charged hadron trigger. Jets are measured using collinear-safe jet reconstruction with infrared cutoff for jet constituents of 0.15 GeV, 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 < p chT,jet < 100 GeV. Reference distributions for pp collisions at \( \sqrt{s}=2.76 \) TeV are calculated using Monte Carlo and NLO pQCD methods, which are validated by comparing with measurements in pp collisions at \( \sqrt{s}=7 \) 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 radians 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.

Article PDF
Similar content being viewed by others
References
A. Majumder and M. Van Leeuwen, The theory and phenomenology of perturbative QCD based jet quenching, Prog. Part. Nucl. Phys. A 66 (2011) 41 [arXiv:1002.2206] [INSPIRE].
JET collaboration, K.M. Burke et al., Extracting the jet transport coefficient from jet quenching in high-energy heavy-ion collisions, Phys. Rev. C 90 (2014) 014909 [arXiv:1312.5003] [INSPIRE].
F. D’Eramo, M. Lekaveckas, H. Liu and K. Rajagopal, Momentum broadening in weakly coupled quark-gluon plasma (with a view to finding the quasiparticles within liquid quark-gluon plasma), JHEP 05 (2013) 031 [arXiv:1211.1922] [INSPIRE].
PHENIX collaboration, K. Adcox et al., Suppression of hadrons with large transverse momentum in central Au+Au collisions at \( \sqrt{s_{N\;N}}= 130\hbox{-} GeV \), Phys. Rev. Lett. 88 (2002) 022301 [nucl-ex/0109003] [INSPIRE].
PHENIX collaboration, A. Adare et al., Neutral pion production with respect to centrality and reaction plane in Au+Au collisions at \( \sqrt{s_{N\;N}}=200 \) GeV, Phys. Rev. C 87 (2013) 034911 [arXiv:1208.2254] [INSPIRE].
PHENIX collaboration, A. Adare et al., Trends in yield and azimuthal shape modification in dihadron correlations in relativistic heavy ion collisions, Phys. Rev. Lett. 104 (2010) 252301 [arXiv:1002.1077] [INSPIRE].
STAR collaboration, C. Adler et al., Centrality dependence of high p T hadron suppression in Au+Au collisions at