Exploring hadronic rescattering effects on resonance productions in pp and p-Pb collisions with PYTHIA8

TL;DR

The paper addresses whether late-stage hadronic interactions modify resonance production in small systems by employing PYTHIA8 with Angantyr to switch hadronic rescattering on/off (with/without inelastic scattering) and examining resonance-to-stable-particle yield ratios for $\rho(770)^0$, $K^{*}(892)^0$, and $\phi(1020)$ across $p_{\rm T}$ and multiplicity. It introduces double ratios to isolate the rescattering contribution and extracts a lower limit on the hadronic-phase lifetime $\tau$ from the integrated yields using $[R_{yield}]_{kinetic} = [R_{yield}]_{chemical} \times e^{-\tau/\tau_{res}}$, with $\tau_{res}$ corresponding to each resonance. The results show strong low-$p_{\rm T}$ suppression for short-lived resonances when rescattering is on, a multiplicity-dependent suppression pattern that is similar in pp and p--Pb, and a hierarchy $\tau$ increasing with resonance lifetime, larger in p--Pb than in pp. These findings extend resonance-based probes of the hadronic phase to small systems and provide a quantitative lower bound on hadronic-phase duration, informing models of late-stage dynamics and their system-size dependence.

Abstract

In relativistic heavy-ion collisions, the quark-gluon plasma is created, and as the medium cools down, the system transitions into a hadronic phase. While such interactions are well established for large systems, such as Pb-Pb collisions, their relevance in smaller collision systems remains unclear. Consequently, hadronic interactions during the hadronic phase are studied in pp collisions at $\sqrt{s}=13$ TeV and p-Pb collisions at $\sqrt{s_{\rm{NN}}}=5.02$ TeV with the PYTHIA8 event generator. The interaction is studied via the yield ratios between resonances and stable particles with similar quark contents, which are obtained as a function of transverse momentum ($p_{\rm{T}}$) using $\mathrm{ρ(770)^0}$, $\mathrm{K^*(892)^0}$, and $\mathrm{φ(1020)}$ mesons and their stable particles, $\mathrm{π^\pm}$ and $\mathrm{K^\pm}$ at midrapidity ($|\rm{y}|<0.5$). Yield ratios are calculated in five multiplicity classes for pp and six for p-Pb collisions, using the 60-100% multiplicity class in pp as a reference. Although rescattering leads to stronger suppression at low $p_{\rm{T}} < 2$ GeV/$c$, a visible suppression remains even when rescattering is turned off. To isolate the rescattering effect, double ratios between the rescattering on and off configurations are obtained. These are then integrated in the full $p_{\rm{T}}$ range ($0<p_{\rm{T}}<6.0$ GeV/$c$). The normalized double ratios show a decreasing trend with increasing multiplicity, independent of the collision system. The lower limit of the hadronic phase lifetimes extracted in the integrated-$p_{\rm{T}}$ region increases with multiplicity in both systems, but with a notable discrepancy between pp and p-Pb collisions.

Figures (10)

• Figure 1: The invariant mass distribution for $\rho(770)^0$ (left), $\mathrm{K^{*}(892)^{0}}$ (middle), and $\phi(1020)$ mesons (right) in multiplicity 0--5% in $2.0<p_\mathrm{T}<2.5$ GeV/$c$ before (top) and after (bottom) the background subtraction, when the rescattering option is off. In the bottom panels, fit results with signal and background functions are also presented.
• Figure 2: Mean values extracted from fit functions as a function of $p_\mathrm{T}$ in p--Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV for the 0--5% (top) and 60--100% (bottom) multiplicity classes. Results are shown for $\rho(770)^0$ (left), $\mathrm{K^{*}(892)^{0}}$ (middle), and $\phi(1020)$ (right) mesons. The PDG reference values are indicated by dashed lines.
• Figure 3: Width values extracted from fit functions as a function of $p_\mathrm{T}$ in p--Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV for the 0--5% (top) and 60--100% (bottom) multiplicity classes. Results are shown for $\rho(770)^0$ (left), $\mathrm{K^{*}(892)^{0}}$ (middle), and $\phi(1020)$ (right) mesons. The PDG reference values are indicated by dashed lines.
• Figure 4: Comparison of $p_\mathrm{T}$ spectra for the three configurations—hadronic rescattering on with inelastic scattering on, hadronic rescattering on with inelastic scattering off, and hadronic rescattering off—for stable particles (top) and resonances (bottom) in the 0--5% and 60--100% multiplicity classes. The lower panels show the ratios of spectra with hadronic rescattering on to those with rescattering off.
• Figure 5: The particle yield ratios between resonances and stable particles as a function of $p_\mathrm{T}$ in 0--5% and 60--100% multiplicity classes in pp collisions $\sqrt{s}=13$, which top figure represents hadronic rescattering off, middle figure for hadronic rescattering on with inelastic collision off, and the bottom figure for hadronic rescattering on with inelastic collision on. In each figure, the ratios of different multiplicity classes to the 60--100% multiplicity class are shown.