Transverse momentum and rapidity dependence of Hanbury-Brown–Twiss correlations in Au+Au collisions at $\sqrt{s_{\mathit{NN}}}=$ 62.4 and 200 GeV

Two-particle correlations of identical charged pion pairs from Au+Au collisions at $\sqrt{s_{\mathit{NN}}}=62.4$ and 200 GeV were measured by the PHOBOS experiment at BNL Relativistic Heavy Ion Collider (RHIC). Data for the 15% most central events were analyzed with Bertsch-Pratt and Yano-Koonin-Podgoretskii parametrizations using pairs with rapidities of $0.4<y_{\pi \pi }<1.3$ and transverse momenta $0.1<k_T<1.4$ GeV/c. The Bertsch-Pratt radii $R_o$ and $R_{\ell }$ decrease as a function of pair transverse momentum. $R_o$ and $R_s$ are independent of collision energy, while $R_{\ell }$ shows a slight increase. The source rapidity $y_{\mathrm{YKP}}$ scales roughly with the pair rapidity $y_{\pi \pi }$, indicating strong dynamical correlations.

Figure 1

Distribution of the truncated average energy loss $\langle \mathit{dE}/\mathit{dx}\rangle$ as a function of reconstructed particle momentum. The region between the solid black lines corresponds to the $\pm 3\sigma$ cut used to select pions for this analysis.

Figure 2

Bertsch-Pratt parameters $R_o,R_s,R_{\ell }$ and the ratio $R_o/R_s$ for ${\pi }^{-}{\pi }^{-}$ pairs at $\sqrt{s_{\mathit{NN}}}=200$ GeV (left panel) and 62.4 GeV (right panel) as a function of $\langle k_T\rangle$. For comparison, data from STAR [30] (open stars) and PHENIX [31] (open crosses) are presented at 200 GeV. PHOBOS systematic errors (90% C.L.) are shown as boxes; systematic errors from STAR and PHENIX are not shown.

Figure 3

Bertsch-Pratt parameters $\lambda ,R_s,R_o$, and $R_{\ell }$ as a function of $\sqrt{s_{\mathit{NN}}}$ for ${\pi }^{-}{\pi }^{-}$ pairs. The presented data are near midrapidity and represent comparable $k_T$ bins from each experiment [11, 12, 27, 29, 30, 31, 32, 33, 34, 35]. PHOBOS data are represented by solid circles. Systematic errors are not shown.

Figure 4

Dependence of the source rapidity $y_{\mathrm{YKP}}$ vs the pair rapidity $y_{\pi \pi }$ for PHOBOS at 200 GeV (circles), PHOBOS at 62.4 GeV (triangles), and NA49 (negatively charged hadrons) at 17.2 GeV [38] (squares).