$K^{*0}$ production in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, and 39 GeV from the RHIC beam energy scan

We report the measurement of $K^{*0}$ meson at midrapidity ($\left|y\right|<$ 1.0) in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, and 39 GeV collected by the STAR experiment during the Relativistic Heavy Ion Collider (RHIC) beam energy scan program. The transverse momentum spectra, yield, and average transverse momentum of $K^{*0}$ are presented as functions of collision centrality and beam energy. The $K^{*0}/K$ yield ratios are presented for different collision centrality intervals and beam energies. The $K^{*0}/K$ ratio in heavy-ion collisions are observed to be smaller than that in small-system collisions ($e+e$ and $p+p$). The $K^{*0}/K$ ratio follows a similar centrality dependence to that observed in previous RHIC and Large Hadron Collider measurements. The data favor the scenario of the dominance of hadronic rescattering over regeneration for $K^{*0}$ production in the hadronic phase of the medium.

Figure 1

The track-rotation combinatorial background subtracted $K\pi$ invariant mass distribution for the 1.2 $<p_T<1.6\mathrm{GeV}/c$ (14.5 and 39 GeV). The data are fitted with a Breit-Wigner function plus a first-order polynomial [as given in Eq. (3)] by the solid line. The dashed line represents the residual background only. The uncertainties on the data points are statistical only and shown by bars.

Figure 2

The detector efficiency $\times$ acceptance in reconstructing the $K^{*0}$ at various collision centralities in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, and 39 GeV. The statistical uncertainties are within the marker size.

Figure 3

$K^{*0}$ transverse momentum ($p_T$) spectra at midrapidity ($\left|y\right|<1$) for various collision centrality intervals in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, and 39 GeV. The solid and dashed lines indicate the Tsallis fit to the data and its extrapolation to the unmeasured low $p_T$ region. The statistical and systematic uncertainties are within the marker size.

Figure 4

Midrapidity yield of $K^{*0}$ as a function of average number of participating nucleons in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, and 39 GeV. The vertical bars and open boxes respectively denote the statistical and systematic uncertainties.

Figure 5

Midrapidity yield per average number of participating nucleons for $K^{*0}, K^{\pm }, p$, and $\overline{p}$ as a function of $\langle N_{\mathrm{part}}\rangle$ from $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, and 39 GeV. The vertical bars and open boxes denote the statistical and systematic uncertainties, respectively.

Figure 6

The mean transverse momentum of $K^{*0}$ as a function of $\langle N_{\mathrm{part}}\rangle$ in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, and 39 GeV. The vertical bars and open boxes respectively denote the statistical and systematic uncertainties.

Figure 7

The average transverse momentum of $\pi , K, p$ [34, 37], and $K^{*0}$ as a function of average number of participating nucleons in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, and 39 GeV. The vertical bars and boxes denote the statistical and systematic uncertainties, respectively.

Figure 8

$K^{*0}/K$ ratio at midrapidity as a function of average number of participating nucleons in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV. The vertical bars and open boxes respectively denote the statistical and systematic uncertainties. The results are compared with previously published STAR [12, 14] measurements.

Figure 9

$K^{*0}/K$ ratio at midrapidity as a function of ${\langle d{N}_{\mathrm{ch}}/dy\rangle }^{1/3}$ in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, and 39 GeV. The vertical bars and open boxes respectively denote the statistical and systematic uncertainties. The results are compared with previously published STAR [12, 14] and ALICE [18, 19, 20, 24] measurements.

Figure 10

Comparison of $K^{*0}/K$ and $\varphi /K$ [43] ratio at midrapidity as a function of average number of participating nucleons in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}$ = 7.7–39 GeV. The vertical bars and boxes respectively denote the statistical and systematic uncertainties. The dashed lines are used to guide the eyes.

Figure 11

The beam energy dependence of $K^{*0}/K$ ratio in $e+e$ [44, 45, 46, 47], $p+p$ [12, 48, 49, 50], $d+\mathrm{Au}$ [13], $p+\mathrm{Au}$ [51, 52], and most-central $\mathrm{C}+\mathrm{C}, \mathrm{Si}+\mathrm{Si}$ [16], $\mathrm{Au}+\mathrm{Au}$ [12, 14], and $\mathrm{Pb}+\mathrm{Pb}$ [18, 19, 20] collisions. For $e+e$ and $p+p$ collisions, the bars denote the quadratic sum of statistical and systematic uncertainties. For $p+A$ and $A+A$ data, the bars denote the statistical uncertainties and the boxes denote the systematic uncertainties.

Figure 12

The lower limit on the time difference ($\mathrm{\Delta }t$) between the chemical and kinetic freeze-out as a function of average number of participating nucleons ($\langle N_{\mathrm{part}}\rangle$). The results are compared with previous STAR [12, 14] and ALICE [18, 19, 20] measurements. The bars denote combined statistical and systematic uncertainties which is propagated from the uncertainties in $K^{*0}/K$ ratio.