K$^{*}$(892)$^{\pm}$ resonance production in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV

The production of K$^*$(892)$^\pm$ meson resonance is measured at midrapidity ($|y|<~0.5$) in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV using the ALICE detector at the LHC. The resonance is reconstructed via its hadronic decay channel K$^*$(892)$^\pm \rightarrow \rm{K^0_S \pi^\pm}$. The transverse momentum distributions are obtained for various centrality intervals in the $p_{\rm T}$ range of 0.4-16 GeV/$c$. The reported measurements of integrated yields, mean transverse momenta, and particle yield ratios are consistent with previous ALICE measurements for K$^*$(892)$^0$. The $p_{\rm T}$-integrated yield ratio 2K$^*$(892)$^\pm$/($\rm{K^+ + K^-}$) in central Pb-Pb collisions shows a significant suppression (9.3$\sigma$) relative to pp collisions. Thermal model calculations overpredict the particle yield ratio. Although both simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas MUSIC+SMASH tends to overpredict them. These observations, along with the kinetic freeze-out temperatures extracted from the yields of light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which increases towards central collisions. The $p_{\rm T}$-differential yield ratios 2K$^*$(892)$^\pm$/($\rm{K^+ + K^-}$) and 2K$^*$(892)$^\pm$/($\rm{\pi^+ + \pi^-}$) are suppressed by up to a factor of five at $p_{\rm T}<~2$ GeV/$c$ in central Pb-Pb collisions compared to pp collisions at $\sqrt{s} =$ 5.02 TeV. Both particle ratios and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor shows a smooth evolution with centrality and is below unity at $p_{\rm T}>8$ GeV/$c$, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium.


Physical Review C 109 (2024) 044902
HEP Data
e-Print: arXiv:2308.16119 | PDF | inSPIRE
Figure group

Figure 1

(Left panel): Invariant mass distribution of ${\rm K^0_S}\pi^\pm$ pairs in same (black marker) and mixed events (red marker). (Right panel): Invariant mass distribution of ${\rm K^0_S}\pi^\pm$ pairs after the subtraction of normalized mixed-event background distribution. The solid red curve is the fit function defined by Eq. 2, with the dotted blue line describing the residual background distribution given by Eq. 3.

Figure 2

The acceptance times efficiency correction for ${\rm K}^{*\pm}$ as a function of transverse momentum for different centrality intervals.

Figure 3

The $\pt$ distributions of ${\rm K}^{*\pm}$ meson in various centrality intervals in Pb$-$Pb collisions at $\snn$ = 5.02 TeV. The statistical and systematic uncertainties are shown as bars and boxes, respectively.

Figure 4

The $\pt$ distributions of ${\rm K}^{*\pm}$ (blue circles) and ${\rm K}^{*0}$ (red squares)  in 0$-$10$\%$ (left) and 40$-$60$\%$ (right) centrality intervals in Pb--Pb collisions at $\snn$ = 5.02 TeV. Statistical and systematic uncertainties are shown by bars and shaded boxes, respectively. The bottom panels show the ${\rm K}^{*\pm}$ to ${\rm K}^{*0}$ ratio as a function of $\pt$.

Figure 5

The d$N$/d$y$ (left) and $\langle \pt \rangle$ (right) as a function of system size for ${\rm K}^{*\pm}$ (closed marker) and ${\rm K}^{*0}$ (open markers)  in Pb$-$Pb collisions at $\snn$ = 5.02 TeV and $\snn$ = 2.76 TeV . Comparison with predictions of MUSIC hydrodynamic model with and without the hadronic phase afterburner (SMASH) are presented by solid and dashed lines, respectively. Statistical (systematic) uncertainties are shown by bars (boxes).

Figure 6

The $\pt$-integrated particle yield ratios ${\rm K}^{*\pm}$/K, ${\rm K}^{*0}$/K and $\phi$/K measured at midrapidity ($|y| <$ 0.5) in pp and Pb$-$Pb collisions at $\snn$ = 5.02 TeV as a function of $\langle $d$N_{\mathrm{ch}}/$d$\eta \rangle^{1/3}_{|\eta|<0.5}$. For Pb$-$Pb collisions, ${\rm K}^{*0}$/K and $\phi$/K data points are taken from Ref. [39] and for pp collisions ${\rm K}^{*\pm}$/K is taken from Ref. [69]. The results of the Gamma canonical statistical model calculation  for ${\rm K}^{*0}$/K, in addition to predictions from the HRG-PCE model , as well as MUSIC with and without afterburner  are shown. Statistical uncertainties are shown by bars, total systematic uncertainties by open boxes, and the multiplicity-uncorrelated systematic uncertainty by the shaded boxes. The two highest multiplicity data points for ${\rm K}^{*0}$ and $\phi$ mesons are slightly shifted for visibility.

Figure 7

The $\pt$-differential particle yield ratios ${\rm K}^{*\pm}$/K (a) and ${\rm K}^{*\pm}$/$\pi$ (b) in pp (black marker) and Pb$-$Pb collisions at $\snn$ = 5.02 TeV for 0$-$10$\%$ (red marker) and 60$-$80$\%$ (blue marker) centrality intervals. The bottom panels (c) and (d) show the ratios of Pb$-$Pb to pp results, compared with 0$-$10$\%$ ${\rm K}^{*0}$ results . Statistical uncertainties are shown by bars and systematic uncertainties by boxes. The statistical and systematic uncertainties on the data points are obtained by propagating the statistical and total systematic uncertainties of the measurements.

Figure 8

Left panel shows the $R_{\mathrm{AA}}$ comparison of various light-flavored hadrons , and the right panel shows the $R_{\mathrm{AA}}$ of ${\rm K}^{*\pm}$ for different centrality intervals both as a function of $\pt$ in Pb$-$Pb collisions at $\snn$ = 5.02 TeV. Statistical (systematic) uncertainties are shown by bars (shaded boxes). The shaded bands around unity reprsents the normalisation uncertainty on $R_{\mathrm{AA}}$.