Speaker
Description
Collisions of small systems show signatures suggestive of collective flow associated with QGP formation in heavy-ion collisions. Jet quenching is also a consequence of QGP formation, but no significant evidence of it in small systems has been found to date. Measuring or constraining the magnitude of jet quenching in small systems is essential to determine the limits of QGP formation. The ALICE collaboration presents a broad search for jet quenching in high multiplicity (HM) pp collisions at $\sqrt{s} = 13$ TeV, based on several observables: the semi-inclusive acoplanarity distribution of jets recoiling from a high-$p_{\text{T}}$ hadron (h+jet); di-hadron correlations; and intra-jet measurements. Marked broadening of the h+jet acoplanarity distribution is observed in HM compared to minimum-bias (MB) events, which could arise from jet quenching. Both data and PYTHIA simulations suggest that this broadening arises from a generic bias of the HM selection towards multi-jet final states. In contrast, the di-hadron correlations between low-momentum particles exhibit azimuthal narrowing in HM relative to MB events, which are described by PYTHIA simulations and might arise from a similar HM bias. We also report the average charged-particle multiplicity and jet fragmentation functions in HM and MB-selected populations, whose differences are qualitatively described by PYTHIA. We discuss the implications of these results for the understanding of collective effects and jet quenching in small systems.
| Category | Experiment |
|---|---|
| Collaboration (if applicable) | ALICE |
