Heavy-flavour production in high-energy d-Au and p-Pb collisions

TL;DR

This paper investigates how heavy-flavour particles produced in high-energy small-system collisions are affected by the possible formation of a hot, strongly-interacting medium, revealing modifications consistent with collective medium effects.

Contribution

It provides a detailed analysis of heavy-flavour production in small-system collisions, suggesting medium effects influence heavy-flavour propagation and hadronization, a novel insight in this context.

Findings

Heavy-flavour particles show signs of medium modification in small systems.

Experimental data align with the presence of a hot, collective medium.

Heavy-flavour propagation is affected similarly to light hadrons in these collisions.

Abstract

Soft-hadron measurements in high-energy collisions of small systems like p-Pb and d-Au show peculiar qualitative features (long-range rapidity correlations, flattening of the $p_T$-spectra with increasing hadron mass and centrality, non-vanishing Fourier harmonics in the azimuthal particle distributions) suggestive of the formation of a strongly-interacting medium displaying a collective behaviour, with a hydrodynamic flow as a response to the pressure gradients in the initial conditions. Hard observables (high-$p_T$ jet and hadron spectra) on the other hand, within the current large systematic uncertainties, appear only midly modified with the respect to the benchmark case of minimum-bias p-p collisions. What should one expect for heavy-flavour particles, initially produced in hard processes but tending, in the nucleus-nucleus case, to approach kinetic equilibrium with the rest of the medium? This is the issue we address in the present study, showing how the current experimental findings are compatible with a picture in which the formation of a hot medium even in proton-nucleus collisions modifies the propagation and hadronization of heavy-flavour particles.