Constraints on jet quenching in p–Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV measured by the event-activity dependence of semi-inclusive hadron-jet distributions

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5.02 TeV
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We report the measurement of the semi-inclusive distribution of charged-particle jets recoiling from a high-pT trigger hadron, for centrality-selected p–Pb collisions at $\sqrt{s}_{NN} = 5.02$ TeV. This coincidence observable has been used to measure jet quenching in Pb–Pb collisions at the LHC. The analysis applies a data-driven statistical approach to correct the complex uncorrelated jet background, including multi-partonic interactions. The semi-inclusive observable corresponds to the ratio of inclusivecross sections, $\sigma_{h+jet} /\sigma_{trig}$, and measurement of the centrality-dependent recoil yield in p–Pb collisions therefore does not require knowledge of $T_{pPb}$, thereby avoiding the need for geometric modeling. Jets are reconstructed using the anti-kT algorithm, and recoil jet distributions are reported for $15 < p_{T,jet}^{ch} < 50$ GeV/c, for R = 0.2 and 0.4. We compare the trigger-normalized recoil jet yield for different p–Pb centrality classes, providing new constraints on the magnitude of jet quenching in small systems at the LHC. For jets with R = 0.4 and $15 < p_{T,jet}^{ch} < 50$ GeV/c, at the 95% statistical confidence level the average medium-induced out-of-cone energy transport for events with high event activity is less than (0.8 ± 0.3 syst ) GeV/c.