Measurement of jet suppression in central Pb-Pb collisions at \(\sqrt{s_{\rm NN}}\) = 2.76 TeV

Abstract

The transverse momentum \(p_{\rm T}\) spectrum and nuclear modification factor \(R_{\rm AA}\) of reconstructed jets in 0-10% and 10-30% central Pb-Pb collisions at \(\sqrt{s_{\rm NN}}=2.76\) TeV were measured. Jets were reconstructed from charged and neutral particles, utilizing the ALICE tracking detectors and Electromagnetic Calorimeter (EMCal), with the anti-\)._{\rm T}\) jet algorithm with a resolution parameter of R=0.2. The jet \(p_{\rm T}\) spectra are reported in the pseudorapidity interval of \(|{\eta}_{\rm jet}|<0.5\) for \(40<p_{\rm T,jet}<120\) GeV/\).\) in 0-10% and for \(30<p_{\rm T,jet}<100\) GeV/\).\) in 10-30% collisions. Reconstructed jets were required to contain a leading charged particle with \(p_{\rm T}>5\) GeV/\).\) to suppress jets constructed from the combinatorial background in Pb-Pb collisions. The effect of the leading charged particle requirement has been studied in both pp and Pb-Pb collisions and has been shown to have negligible effects on the \(R_{\rm AA}\) within the uncertainties of the measurement. The nuclear modification factor is obtained by dividing the jet spectrum measured in Pb-Pb by that in pp collisions scaled by the number of independent nucleon-nucleon collisions estimated using a Glauber model. \(R_{\rm AA}\) is found to be \(0.28\pm0.04\) in 0-10% and \(0.35\pm0.04\) in 10-30% collisions, independent of \(p_{\rm T,jet}\) within the uncertainties of the measurement. The observed suppression is in fair agreement with expectations from two model calculations with different approaches to jet quenching.