Proton-Λ correlations in central Au+Au collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV

We report on $p\text{−}\Lambda ,p\text{−}\overline{\Lambda },\overline{p}\text{−}\Lambda$, and $\overline{p}\text{−}\overline{\Lambda }$ correlation functions constructed in central Au-Au collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV by the STAR experiment at RHIC. The proton and lambda source size is inferred from the $p\text{−}\Lambda$ and $\overline{p}\text{−}\overline{\Lambda }$ correlation functions. It is found to be smaller than the pion source size also measured by the STAR experiment at smaller transverse masses, in agreement with a scenario of a strong universal collective flow. The $p\text{−}\overline{\Lambda }$ and $\overline{p}\text{−}\Lambda$ correlation functions, which are measured for the first time, exhibit a large anticorrelation. Annihilation channels and/or a negative real part of the spin-averaged scattering length must be included in the final-state interactions calculation to reproduce the measured correlation function.

Figure 1

Invariant mass of the selected Λ (a) and $\overline{\Lambda }$ (b) background not substracted with $0.3<p_t<2.0\mathrm{GeV}/c$. The $y$ axis represents the number of candidates used in this analysis.

Figure 2

The purity and momentum-resolution corrected correlation functions $C_{\mathrm{true}}(k^{*})$ for $p\text{−}\Lambda ,\overline{p}\text{−}\overline{\Lambda }$ (a), $\overline{p}\text{−}\Lambda ,p\text{−}\overline{\Lambda }$ (b). Curves correspond to fits done using the Lednický and Lyuboshitz analytical model [12].

Figure 3

($p\text{−}\Lambda )\oplus (\overline{p}\text{−}\overline{\Lambda })$ and $(\overline{p}\text{−}\Lambda )\oplus (p\text{−}\overline{\Lambda })$ combined correlation functions. Correlation functions are corrected for purity and momentum resolution. Curves correspond to fits done using the Lednický and Lyuboshitz analytical model [12].

Figure 4

The combined $(\overline{p}\text{−}\Lambda )\oplus (p\text{−}\overline{\Lambda })$ spin-averaged $s$-wave scattering length compared with the previous measurements for the $p\text{−}\overline{p}$ system [24, 25, 26, 27]. The curves show the one standard deviation contours. Note that for $(\overline{p}\text{−}\Lambda )\oplus (p\text{−}\overline{\Lambda })$ only, one should read $0.1973\times \mathrm{Im}{f}_0$ instead of $\mathrm{Im}{f}_0$ on the x-axis

Figure 5

Pion source size [5] compared with proton and lambda source sizes as a function of the mean transverse mass ($\langle m_t\rangle$). The curve shows the $\langle m_t\rangle {}^{-1/2}$ dependence with an arbitrary normalization.