Probing jet hadrochemistry modification with measurements of $\mathbfπ$, K, and p in jets and the underlying event in pp and Pb--Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV

TL;DR

This work probes how the quark–gluon plasma modifies the hadrochemical composition inside jets by measuring $\pi$, $K$, and $p$ yields in jets and the underlying event at $\sqrt{s_{NN}}=5.02$ TeV in pp and Pb–Pb collisions with ALICE PID. It introduces a detailed method to subtract the underlying event and to smear the pp reference to Pb–Pb conditions, enabling a direct comparison of jet hadrochemistry across collision systems. The results show that jet-associated $K/\pi$ and $p/\pi$ ratios are smaller than inclusive values in jets, while Pb–Pb jets show hints of enhanced low-$p_T$ pions and enhanced intermediate-$p_T$ baryons and strange hadrons, hinting at medium-induced modifications of jet fragmentation and wake dynamics. These findings are in qualitative agreement with theoretical predictions and motivate unfolding, extended PID reach, centrality dependence, and radial studies to disentangle jet fragmentation from wake‑driven effects.

Abstract

Measurements of jet substructure observables in heavy-ion (HI) collisions provide powerful constraints on the microscopic mechanisms of interactions between energetic partons and the quark--gluon plasma (QGP). Although there has been remarkable progress in measuring inclusive jet substructure, a complete understanding of identified particle production inside jets (jet hadrochemistry) and its modification in HI collisions remains elusive. Jet quenching models predict that the jet hadrochemical composition is modified in the QGP, arising from both jet-medium interactions and altered particle production in the jet wake. Measurements of jet hadrochemistry can help discriminate between proposed jet-medium interaction mechanisms. Enabled by the excellent particle identification (PID) capabilities of ALICE, we present the first measurements of $π$, K, and p ratios within jets and the underlying event as a function of particle transverse momentum in pp and Pb--Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV. These measurements provide insight into soft particle production mechanisms and helps distinguish various jet quenching effects.

Figures (3)

• Figure 1: Top: The $\pi$ spectra for inclusive, jet+UE, UE, and jet signal in pp collisions. Bottom: The K/$\pi$ (left) and p/$\pi$ (right) particle ratios in jets and inclusive particles in pp collisions.
• Figure 2: The $\pi$ (top left), K (top right), and p (bottom) spectra in 0$-$10% Pb--Pb and smeared pp jets.
• Figure 3: The K/$\pi$ (left) and p/$\pi$ (right) particle ratios in 0$-$10% Pb--Pb and smeared pp jets.