Light-Flavour Resonance Production in High-Energy Heavy-Ion Collisions: An Experimental Review

TL;DR

This review consolidates experimental measurements of light-flavour resonances across pp, pA, and AA collisions from SPS to the LHC, highlighting how short lifetimes and hadronic interactions encode the hadronic phase's duration and dynamics. It emphasizes the competition between rescattering and regeneration, the separation of chemical and kinetic freeze-out via HRG-PCE fits, and the role of resonance yields, spectra, and flow as chronometers and tracers of collectivity. Spin alignment and ultra-peripheral collisions emerge as complementary probes of local spin dynamics and vacuum baselines, while prospects in charm-resonance studies promise to extend these insights into the heavy-flavour sector. Together, these observables constrain the space–time evolution, hadronization mechanisms, and chiral-transition signatures of strongly interacting matter in high-energy nuclear collisions.

Abstract

Resonances provide sensitivity to the late-stage dynamics of heavy-ion collisions, as their lifetimes are comparable to the duration of the hadronic phase. This review summarizes state-of-the-art measurements of light-flavour mesonic and baryonic resonances, including $ρ$(770), $K^{\star}$(892), $φ$(1020), $Δ$(1232), $Λ^{\star}$(1520), $Σ^{\star}$(1385) and $Ξ^\star$(1530), in pp, p-A and A-A collisions at SPS, RHIC and the LHC. Systematic trends in yields, mass and width modifications, transverse-momentum spectra, nuclear modification factors, and particle ratios reveal the interplay of re-scattering and regeneration, medium-induced suppression, and the development of collective dynamics with increasing system size and multiplicity. Anisotropic flow results confirm the coupling of resonances to the expanding medium, while recent vector-meson spin-alignment measurements offer fresh insights into hadronization mechanisms and local fields. Ultra-peripheral collisions provide vacuum-like baselines for isolating in-medium effects. Emerging opportunities for charm-resonance studies in upcoming high-luminosity experiments are also outlined.Together, these advances demonstrate the important role of resonance measurements in constraining the space-time evolution of strongly interacting matter.

Figures (42)

• Figure 2.1: Invariant mass distributions for $K^{*0}$ and $\phi$ mesons in p--Pb collisions at $\sqrt{s_{\rm{NN}}} = 8.16$ TeV ALICE:2021rpa. Panels (a, b): same-event distributions (black) overlaid with normalized mixed-event backgrounds (red). Panels (c, d): background-subtracted spectra fitted with a Breit--Wigner (for $K^{*0}$) and a Voigtian function (for $\phi$), respectively. The residual background is described by a second-order polynomial.
• Figure 2.2: Invariant mass distributions for $\Lambda\pi^{+}$ and $\Xi^{\mp}\pi^{\pm}$ in p--Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ TeV ALICE:2017pgw. Upper panels: same-event spectra with overlaid mixed-event backgrounds. Lower panels: background-subtracted signals fitted with Voigtian (for $\Sigma^{*+}$) and Breit--Wigner (for $\Xi^{*0}$) functions plus a second-order polynomial.
• Figure 2.3: Mass as function $p_{\rm T}$, at midrapidity for various resonance particles across different collision systems and energies STAR:2004bghSTAR:2008twtALICE:2014jbqSTAR:2010avo.
• Figure 2.4: Transverse momentum dependence of resonance widths at midrapidity across different systems and energies STAR:2004bghSTAR:2008twtALICE:2014jbqSTAR:2010avo.
• Figure 2.5: $p_{\rm T}$-integrated yield ($\mathrm{d}N/\mathrm{d}y$) as a function of the charged-particle multiplicity density at midrapidity for various resonance species in different collision systems and energies ALICE:2017banALICE:2021ptzALICE:2019etbALICE:2016sakALICE:2021rpaALICE:2023egxALICE:2017pgwALICE:2022zucALICE:2018ewoALICE:2020lamALICE:2023edrALICE:2021_xexe.