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

The production of $K^{*}{\left(892\right)}^{\pm }$ meson resonance is measured at midrapidity ($\left|y\right|<0.5$) in $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02$ TeV using the ALICE detector at the CERN Large Hadron Collider. The resonance is reconstructed via its hadronic decay channel $K^{*}{\left(892\right)}^{\pm }\to K_{\mathrm{S}}^0{\pi }^{\pm }$. The transverse momentum distributions are obtained for various centrality intervals in the $p_{\mathrm{T}}$ range of $0.4\text{−}16 \mathrm{GeV}/c$. Measurements of integrated yields, mean transverse momenta, and particle yield ratios are reported and found to be consistent with previous ALICE measurements for $K^{*}{\left(892\right)}^0$ within uncertainties. The $p_{\mathrm{T}}$-integrated yield ratio $2K^{*}{\left(892\right)}^{\pm }/(K^{+}+K^{-}$) in central $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions shows a significant suppression at a level of $9.3\sigma$ relative to $pp$ collisions. Thermal model calculations result in an overprediction of the particle yield ratio. Although both hadron resonance gas in partial chemical equilibrium (HRG-PCE) and music $+$ smash simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas music $+$ smash simulations tend to overpredict the particle yield ratio. These observations, along with the kinetic freeze-out temperatures extracted from the yields measured for light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which decreases with increasing collision centrality percentile. The $p_{\mathrm{T}}$-differential yield ratios $2K^{*}{\left(892\right)}^{\pm }/(K^{+}+K^{-}$) and $2K^{*}{\left(892\right)}^{\pm }/({\pi }^{+}+{\pi }^{-}$) are presented and compared with measurements in pp collisions at $\sqrt{s}=5.02$ TeV. Both particle ratios are found to be suppressed by up to a factor of five at $p_{\mathrm{T}}<2.0 \mathrm{GeV}/c$ in central $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor ($R_{\mathrm{AA}}$) shows a smooth evolution with centrality and is found to be below unity at $p_{\mathrm{T}}>8 \mathrm{GeV}/c$, 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.

Figure 1

(left panel) Invariant-mass distribution of $K_{\mathrm{S}}^0{\pi }^{\pm }$ pairs in same (black marker) and mixed events (red marker). (right panel) Invariant-mass distribution of $K_{\mathrm{S}}^0{\pi }^{\pm }$ 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 $K^{*\pm }$ as a function of transverse momentum for different centrality intervals.

Figure 3

The $p_{\mathrm{T}}$ distributions of $K^{*\pm }$ meson in various centrality intervals in $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02$ TeV. The statistical and systematic uncertainties are shown as bars and boxes, respectively.

Figure 4

The $p_{\mathrm{T}}$ distributions of $K^{*\pm }$ (blue circles) and $K^{*0}$ (red squares) [39] in $0\%–10\%$ (left) and $40\%–60\%$ (right) centrality intervals in Pb-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV. Statistical and systematic uncertainties are shown by bars and shaded boxes, respectively. The bottom panels show the $K^{*\pm }$ to $K^{*0}$ ratio as a function of $p_{\mathrm{T}}$.

Figure 5

The $\mathrm{d}N/\mathrm{d}y$ (left) and $\langle p_{\mathrm{T}}\rangle$ (right) as a function of system size for $K^{*\pm }$ (solid markers) and $K^{*0}$ (open markers) [39] in $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02$ TeV and $\sqrt{s_{NN}}=2.76$ TeV [77]. 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 $p_{\mathrm{T}}$-integrated particle yield ratios $K^{*\pm }/K, K^{*0}/K$, and $\varphi /K$ measured at midrapidity ($\left|y\right|<0.5$) in $pp$ and $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02$ TeV as a function of ${\langle \mathrm{d}{N}_{\mathrm{ch}}/\mathrm{d}\eta \rangle }_{\left|\eta \right|<0.5}^{1/3}$. For $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions, $K^{*0}/K$ and $\varphi /K$ data points are taken from Ref. [39] and for $pp$ collisions $K^{*\pm }/K$ is taken from Ref. [69]. The results of the Gamma canonical statistical model calculation [79] for $K^{*0}/K$, in addition to predictions from the HRG-PCE model [59], as well as music with and without afterburner [75] 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 $K^{*0}$ and $\varphi$ mesons are slightly shifted for visibility.

Figure 7

The $p_{\mathrm{T}}$-differential particle yield ratios (a) $K^{*\pm }/K$ and (b) $K^{*\pm }/\pi$ in $pp$ (black markers) and $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02$ TeV for $0\%–10\%$ (red marker) and $60\%–80\%$ (blue markers) centrality intervals. The bottom panels (c) and (d) show the ratios of $\mathrm{Pb}\text{−}\mathrm{Pb}$ to $pp$ results, compared with $0\%–10\% K^{*0}$ results [39]. 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 [39, 40, 57], and the right panel shows the $R_{\mathrm{AA}}$ of $K^{*\pm }$ for different centrality intervals both as a function of $p_{\mathrm{T}}$ in $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions at $\sqrt{{\mathit{s}}_{NN}}=5.02$ TeV. Statistical (systematic) uncertainties are shown by bars (shaded boxes). The shaded bands around unity represents the normalization uncertainty on $R_{\mathrm{AA}}$.