Multiplicity dependence of (multi)strange hadrons in oxygen-oxygen collisions at $\sqrt{s_{\mathrm{NN}}}~=~7$ TeV using EPOS4 and AMPT

TL;DR

This work addresses whether Quark-Gluon Plasma–like collectivity and strangeness enhancement extend to small systems by predicting observables for $ m O+ m O$ collisions at $ obreak\sqrt{s_{\mathrm{NN}}}=7$ TeV using two approaches: EPOS4, which incorporates full viscous hydrodynamics with a QGP phase, and AMPT, a transport model with preformed partonic interactions. It provides predictions for $p_T$ spectra, rapidity densities $dN/dy$, and $p_T$-dependent and integrated strange-hadron-to-pion ratios for $(K^0_S, \Lambda, \Xi, \phi, \Omega)$, highlighting how core–corona dynamics and hadronization schemes affect strangeness production and flow signals. The key findings are that EPOS4 exhibits stronger radial flow and larger strangeness yields than AMPT, though neither model fully reproduces all trends seen in larger systems; both predict a final-state multiplicity overlap with $p+p$, $p+Pb$, and $Pb+Pb$, and reveal centrality-dependent patterns in strange-hadron production that are most pronounced at intermediate $p_T$. The study emphasizes that upcoming O+O data will constrain model parameters and clarify the onset of collectivity and hadronization mechanisms in small-system collisions.

Abstract

It is anticipated that the Large Hadron Collider (LHC) will collect data from oxygen-oxygen ($O+O$) collisions at a center-of-mass energy of $\sqrt{s_{\mathrm{NN}}}$ = 7 TeV to explore the effects observed in high multiplicity proton-proton ($p+p$) and proton-lead ($p+pb$) collisions that closely related to lead-lead ($Pb+Pb$) collisions. These effects include azimuthal asymmetries in particle production, as well as variations in the abundances and momentum distributions across different hadron species, which are indicative of collective particle production mechanisms induced by the interactions in the presence of a QGP. The upcoming data on $O+O$ collisions at the LHC are expected to constrain the model parameters and refine our understanding of theoretical models. In this work, the predicted transverse momentum ($p_T$) spectra, rapidity density distributions ($dN/dy$), particle yield ratios, and $p_T$-differential ratios of (multi)strange hadrons produced in $O+O$ collisions at $\sqrt{s_{\mathrm{NN}}}$ = 7 TeV using AMPT and EPOS4 models are presented. AMPT focuses on preformed hadronic interactions, while EPOS4 incorporates a QGP phase. Stronger radial flow in EPOS4 as compared to AMPT is also observed. AMPT incorporates some flow effects, but the implementation of full hydrodynamic flow in EPOS4 appears to be significantly more effective in reproducing the existing experimental data. Both models predict the final state multiplicity overlap with $p+p$, $p+pb$, and $Pb+Pb$ collisions.

Figures (6)

• Figure 1: (Color online) $p_{\rm T}$-spectra of (multi)strange hadrons ($\mathrm{K}^{0}_{\mathrm S}$, $\Lambda$, $\Xi$, $\phi$ and $\Omega$) from EPOS4 (left) and AMPT (right) in $\rm O+O$ collisions at $\sqrt{s_{\mathrm{NN}}}~=~7$ TeV for most central (0--5%) and most peripheral (60--80%) centrality classes. 0--5% $p_{\rm T}$ spectra for (multi)strange hadrons are scaled by a factor of $10$ for better visualization. In the right-side figure, solid lines represent AMPT-SM, while dotted lines represent AMPT-Def.
• Figure 2: (Color online) Multiplicity dependence of the particle yield $\mathrm{d}N/\mathrm{d}y$ of strange hadrons ($\mathrm{K}^{0}_{\mathrm S}$, $\Lambda$, $\Xi$, $\phi$, and $\Omega$) in $\rm O+O$ collisions at $\sqrt{s_{\mathrm{NN}}}~=~7$ TeV using AMPT-Def, AMPT-SM and EPOS4. Solid lines are used for EPOS4, whereas the dotted and dashed lines represent AMPT-Def and AMPT-SM, respectively.
• Figure 3: (Color online) $p_{\rm T}$-integrated yield ratios of $\mathrm{K}^{0}_{\mathrm S}$, $\Lambda$, $\Xi$, $\phi$, and $\Omega$ to pions ($\pi^+ + \pi^-$) as a function of $\langle\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\xspace\rangle$ in $\rm O+O$ collisions at $\sqrt{s_{\mathrm{NN}}}~=~7$ TeV using AMPT-Def, AMPT-SM and EPOS4. Solid lines are used for EPOS4, whereas the dotted and dashed lines represent the AMPT-Def and AMPT-SM models, respectively. The values are compared to the published results from $\rm p+p$, $\rm p+Pb$, and $\rm Pb+Pb$ collisions 54549505152.
• Figure 4: (Color online) $p_{\rm T}$-differential $K/\pi$ and $\Lambda/\pi$ ratios in most central (0--5%) and the most peripheral (60--80%) $\rm O+O$ collisions at $\sqrt{s_{\mathrm{NN}}}~=~7$ TeV using EPOS4 (top) and AMPT (bottom). Different colors are used to represent different models across various centrality classes.
• Figure 5: (Color online) $p_{\rm T}$-differential $\phi/\pi$ and $\Xi/\pi$ ratios in most central (0--5%) and the most peripheral (60--80%) $\rm O+O$ collisions at $\sqrt{s_{\mathrm{NN}}}~=~7$ TeV using EPOS4 (top) and AMPT (bottom). Different colors are used to represent different models across various centrality classes.