Unveiling hadronic resonance dynamics at LHC energies: insights from EPOS4

Abstract

Hadronic resonances, with lifetimes of a few fm/\textit{c}, are key tools for studying the hadronic phase in high-energy collisions. This work investigates resonance production in pp collisions at $\sqrt{s} = 13.6$ TeV and in Pb$-$Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.36$ TeV using the EPOS4 model, which can switch the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) ON and OFF, enabling the study of final-state hadronic interactions. We focus on hadronic resonances and the production of non-strange and strange hadrons, addressing effects like rescattering, regeneration, baryon-to-meson production, and strangeness enhancement, using transverse momentum ($p_\textrm{T}$) spectra and particle ratios. Rescattering and strangeness effects are important at low $p_\rm{T}$, while baryon-to-meson ratios dominate at intermediate $p_\rm{T}$. A strong mass-dependent radial flow is observed in the most central Pb$-$Pb collisions. The average $p_\rm{T}$, scaled with reduced hadron mass (mass divided by valence quarks), shows a deviation from linearity for short-lived resonances. By analyzing the yield ratios of short-lived resonances to stable hadrons in pp and Pb$-$Pb collisions, we estimate the time duration ($τ$) of the hadronic phase as a function of average charged multiplicity. The results show that $τ$ increases with multiplicity and system size, with a nonzero value in high-multiplicity pp collisions. Proton (p), strange ($\rmΛ$), and multi-strange ($\rmΞ$, $\rmΩ$) baryon production in central Pb$-$Pb collisions is influenced by strangeness enhancement and baryon-antibaryon annihilation. Comparing with LHC measurements offers insights into the dynamics of the hadronic phase.

Figures (13)

• Figure 1: Upper panel: The $p_{\rm T}$ spectra of $\rm {K}^{\rm{* 0}}$ and $\phi$ resonances in the midrapidity region for central (0--10%) and peripheral (60--80%) Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.36 TeemV with EPOS4 in UrQMD ON and UrQMD OFF tunes. The solid lines represent measurements with UrQMD ON while dotted lines represent measurements with UrQMD OFF. Lower panel: The $p_{\rm T}$-differential yield ratios of $\rm {K}^{\rm{* 0}}$ and $\phi$ for UrQMD ON to UrQMD OFF tunes. The bands represent the statistical uncertainties in the measurements.
• Figure 2: Upper panel: The $p_{\rm T}$ spectra of $\rm {K}^{\rm{* 0}}$ and $\phi$ resonances in the midrapidity region for high multiplciity (0--1%) and low multiplciity (70--100%) in pp collisions at $\sqrt{s}$ = 13.6 TeemV with EPOS4 in UrQMD ON and UrQMD OFF tunes. The solid lines represent measurements with UrQMD ON while dotted lines represent measurements with UrQMD OFF. Lower panel: The $p_{\rm T}$-differential yield ratios of $\rm {K}^{\rm{* 0}}$ and $\phi$ for UrQMD ON to UrQMD OFF tunes. The bands represent the statistical uncertainties in the measurements.
• Figure 3: The comparison of $p_{\rm T}$-differential spectra of hadronic resonances with UrQMD to the spectra without UrQMD in central (0-10%) Pb--Pb collisions with EPOS4. The bands in the measurements represent the statistical uncertainty.
• Figure 4: Upper panel: The $p_{\rm T}$-differential ratios $\rm{K^{*0}/K}$ (left) and $\rm{\phi/K}$ (right) in the central (0--10%) and peripheral (60--80%) Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.36 TeemV and also in the high multiplicity (0-1%) pp collisions at $\sqrt{s}$ = 13.6 TeemV with UrQMD. Lower panel: The comparison of $p_{\rm T}$-differential ratios in the central and peripheral Pb--Pb collisions to the high multiplicity pp collisions. The bands in the measurements represent statistical uncertainty.
• Figure 5: The comparison of $p_{\rm T}$-differential ratios $\rho^{0}/\pi$, $\rm{K^{*0}/K}$, $\rm{\phi/K}$, $\rm{\Delta^{++}/p}$, $\rm{\Lambda^{*}/\Lambda}$, $\rm{\Xi^{*0}/\Xi^{-}}$ and $\rm{\Sigma^{*\pm}/\Lambda}$ in the central (0--10%, left) and peripheral (60--80%, right) Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.36 TeemV to the high multiplicity (0-1%) pp collisions at $\sqrt{s}$ = 13.6 TeemV with UrQMD. The bands in the measurements represent statistical uncertainty.