Systematic study of charged-pion and kaon femtoscopy in Au + Au collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV

We present a systematic study of charged-pion and kaon interferometry in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{\mathit{NN}}}}=200$ GeV. The kaon mean source radii are found to be larger than pion radii in the outward and longitudinal directions for the same transverse mass; this difference increases for more central collisions. The azimuthal-angle dependence of the radii was measured with respect to the second-order event plane and similar oscillations of the source radii were found for pions and kaons. Hydrodynamic models qualitatively describe the similar oscillations of the mean source radii for pions and kaons, but they do not fully describe the transverse-mass dependence of the oscillations.

Figure 1

The layout of PHENIX detectors in the 2007 run configuration. The top figure shows the central arm detectors viewed along the beam axis. The bottom figure shows the side view of the global detectors and muon arm detectors.

Figure 2

Correlation functions of negative pions and charged kaons for 0%–10% centrality (a)–(c), where positive and negative kaons are combined. Open boxes show the systematic uncertainties. Solid and dashed lines show the fit functions and the extracted radii values are shown in the figure.

Figure 3

Extracted HBT parameters of charged pions and kaons as a function of $m_T$ for the centralities indicated, where open boxes show the systematic uncertainties. Results of charged pions from STAR [37] are compared. Calculations from the hydrokinetic model (HKM) [38] and viscous-hydrodynamic model (Bozek) [39] are also shown.

Figure 4

Ratio of $R_{\mathrm{o}}$ and $R_{\mathrm{s}}$ for charged pions and kaons as a function of $m_T$. Calculations from the hydrokinetic model (HKM) [38] and viscous-hydrodynamic model (Bozek) [39] are also shown.

Figure 5

HBT radii of charged pions and kaons as a function of $k_T$, where open boxes show the systematic uncertainties.

Figure 6

Comparison of HBT radii between positive and negative kaons pairs in central and peripheral collisions, where open boxes show the systematic uncertainties.

Figure 7

Correlation functions of charged kaons in 20%–60% centrality (a)–(c), where positive and negative kaons are combined. The correlation functions along $q_{\mathrm{s}}$ and $q_{\mathrm{o}}$ directions are averaged out between positive and negative $q$. Lines show the fit functions and the extracted radii values are shown in the figure.

Figure 8

Squared HBT radii of charged kaon pairs as a function of azimuthal pair angle $\varphi$ with respect to ${\mathrm{\Psi }}_2$ for two centrality bins, where $k_T$ is integrated over 0.3–1.5 GeV/$c$. The open symbols at $\varphi -{\mathrm{\Psi }}_2=\pi$ are the same data as that at $\varphi -{\mathrm{\Psi }}_2=0$. Open boxes show systematic uncertainties and the solid lines are the fitting functions given by Eq. (13).

Figure 9

Squared HBT radii of charged-pion pairs as a function of azimuthal pair angle $\varphi$ with respect to ${\mathrm{\Psi }}_2$ for six $k_T$ bins and two centrality bins [(a)–(d) for 0%–20% and (e)–(h) for 20%–60%], where open symbols at $\varphi -{\mathrm{\Psi }}_2=\pi$ are the same data as those at $\varphi -{\mathrm{\Psi }}_2=0$. Open boxes show systematic uncertainties and solid lines show the fit functions by Eq. (13).

Figure 10

The BW model fits (Fit A) to the $p_T$ spectra (a), elliptic flow of $\pi , K, p$ (d), and HBT radii of $\pi$ (b),(c),(e),(f). The solid lines show the fit functions.

Figure 11

The zeroth-order Fourier coefficient of HBT radii of charged pions as a function of $m_T$ and BW model calculations for both pions (dashed line) and kaons (solid line), where the BW model parameters shown in Fit A of Table 3 were used.

Figure 12

Oscillation amplitudes relative to the average for four different combinations of the azimuthal-dependent HBT radii as a function of $m_T$ for charged pions and kaons. Open boxes show systematic uncertainties. Calculations from the BW model with parameters of Fit A shown in Table 3 are shown for comparison.

Figure 13

Oscillation amplitudes relative to the average for four different combinations of the azimuthal-dependent HBT radii as a function of $m_T$ for charged pions. Open boxes show systematic uncertainties. Calculations from the $3+1$-D viscous-hydrodynamic model [39] are shown for comparison.