Transverse-momentum spectra of strange particles produced in Pb + Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV in the chemical nonequilibrium model

We analyze the transverse-momentum spectra of strange hadrons produced in Pb + Pb collisions at the collision energy $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV for different centrality bins. Our approach combines the concept of chemical nonequilibrium with the single-freeze-out scenario. The two ideas are realized in the framework of the Cracow model, whose thermodynamic parameters have been established in earlier studies of the ratios of hadron multiplicities. The geometric parameters of the model are obtained from the fit to the spectra of pions and kaons, only. Using these parameters, we obtain an excellent description of the spectra of protons and the $K_S^0,K^{*}{\left(892\right)}^0$, and $\varphi \left(1020\right)$ mesons. A satisfactory description is obtained for the $\Lambda ,\Xi$, and $\Omega$ hyperons.

Figure 1

Temperature $T$ shown as a function of centrality for the chemical nonequilibrium model (solid red [gray] line). The results from Ref. [34] are denoted as PLPR.

Figure 2

The parameters ${\gamma }_q$ (a) and ${\gamma }_s$ (b) as functions of centrality for the chemical nonequilibrium model.

Figure 3

Geometric parameters (a) and the volume per unit rapidity (b) for both the chemical nonequilibrium and chemical equilibrium models.

Figure 4

Upper panels: Transverse-momentum spectra of pions (left), kaons (middle), and protons (right) in different centrality classes. The data [23] are shown by the open symbols. The calculations in the nonequilibrium version of the Cracow model are indicated by the lines. Lower panels: The ratios of the experimental and theoretical $p_T$ spectra in the most central $(c$ = 0–5%), semiperipheral $(c$ = 30–40%), and ultraperipheral $(c$ = 80–90%) collisions for pions, kaons, and protons.

Figure 5

Same as Fig. 4 but in the equilibrium Cracow model.

Figure 6

The centrality dependance of the ${\chi }^2$ calculated for the joint fit of the $p_T$ spectra of pions and kaons.

Figure 7

Transverse-momentum spectra of $K_S^0$ (left), $K^{*}{\left(892\right)}^0$ (middle), and $\varphi \left(1020\right)$ (right) in different centrality classes. The data [65, 66] are shown by the open symbols. The calculations in the nonequilibrium Cracow model are indicated by the lines.

Figure 8

The same as in Fig. 7 but for $\Lambda$ [65], $\Xi$, and $\Omega$ [67].