Correlations and flavors in jets in ALICE

TL;DR

This paper presents measurements of hadron composition in jets from proton-proton, p-Pb, and Pb-Pb collisions at the LHC, revealing that jet fragmentation does not explain baryon enhancement and showing suppression of recoil jets in Pb-Pb without intra-jet broadening.

Contribution

It provides the first data on particle type dependent jet fragmentation at the LHC and introduces a bias-free method to measure recoil jet suppression in heavy-ion collisions.

Findings

Jet fragmentation does not contribute to baryon anomaly.

Recoil jet yield is suppressed in central Pb-Pb collisions.

No intra-jet broadening observed even with large jet resolution parameter.

Abstract

We report on the measurement of hadron composition in charged jets in pp at $\sqrt{s}=7$ TeV and show the first data on particle type dependent jet fragmentation at the LHC. Further, we present $(\Lambda+\bar{\Lambda})/2$K$^{0}_{\mathrm{S}}$ ratios measured in charged jets in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV and in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV. While the ratio of the inclusive $p_{\mathrm{T}}$ spectra of $\Lambda$ and K$^{0}_{\mathrm{S}}$ exhibits centrality dependent enhancement both in Pb-Pb and p-Pb system, the $(\Lambda+\bar{\Lambda})/2$K$^{0}_{\mathrm{S}}$ ratio measured in charged jets reveals that jet fragmentation does not contribute to the observed baryon anomaly. Finally, we discuss the measurement of semi-inclusive $p_{\mathrm{T}}$ spectra of charged jets that recoil from a high-$p_{\mathrm{T}}$ hadron trigger in Pb-Pb and pp collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV and $\sqrt{s} = 7$ TeV, respectively. The jet yield uncorrelated with the trigger hadron is removed at the event-ensemble level without introducing a bias on the jet population which is therefore infrared and collinear safe. The recoil jet yield in central Pb-Pb is found to be suppressed w.r.t. that from pp PYTHIA reference. On the other hand, there is no sign of intra-jet broadening even for anti-$k_{\mathrm{T}}$ jets with a resolution parameter as large as $R=0.5$.