First observation of deuteron-Λ correlations at RHIC

Abstract

Precise experimental information on hyperon-nucleon interactions is scarce but of paramount importance to our understanding of the inner structure of compact stars. In this letter, we report the first experimental results of correlation functions between deuterons (d) and Λ hyperons in Au+Au collisions at \sqrt{s_{NN} = 3.0 GeV measured by the STAR experiment at RHIC. A clear enhancement at small relative momenta has been observed in the correlation function. Through a Bayesian inference analysis, the source size parameters as a function of collision centrality and the spin- dependent strong interaction parameters (scattering length f0 and effective range d0) are extracted using the Lednický-Lyuboshitz formalism. The derived doublet spin state parameters (f0, d0) lead to a novel method to precisely determine Λ separation energy for the weakly bounded hypertriton ^{3}_{Λ}H.

Figures (4)

• Figure 1: (Left) Selection of deuterons by TPC $z$ (vertical axis) at different momentum ($p$). TPC is used when $p<3$ GeV/$c$, and TOF information additionally constrains the selection to remove protons when $p>3$ GeV/$c$. (Right) The $p-\pi^-$ invariant mass distribution for the reconstructed $\Lambda$ candidates vs. $p_{T}$. Red curves show the selection cuts.
• Figure 2: $d$-$\Lambda$correlation function ($C(k^*)$) shown as a function of relative momentum ($k^*$) at different centralities. Statistical and systematical uncertainties are shown with bars and boxes, respectively. Solid red lines are curves from the constrained fits with the LL approach (from 0 to 100 MeV/c). The combined $\chi^2/ndf$ for the three centralities is 83.4/53. Blue and orange dashed lines show the contribution from the D-state and Q-state, respectively. The dashed purple line shows the SMASH+LL model SMASH:2016zqfSteinheimer:2012tb. See text for details.
• Figure 3: The extracted final state interaction parameters, scattering length ($f_0$) and effective range ($d_0$), for $d$-$\Lambda$interaction shown as contours of the probability distribution for both doublet (D) (blue) and quartet (Q) (orange) spin states. The unconstrained fit results are shown in panel (a) and panel (b) for Q state and D state, respectively. The constrained fit results for both states are shown in panel (c). The purple triangles show the different model calculationsCobis:1996ruHammer:2001ngAlexander:1968acuRijken:2010zzbHaidenbauer:2013oca, the forbidden region is shaded.
• Figure 4: $\Lambda$ separation energy of $^{3}_{\Lambda}{\mathrm{H}}$ ($B_{\Lambda}$). The upper panel shows the probability distribution of the $\Lambda$ separation energy of $^{3}_{\Lambda}{\mathrm{H}}$ from $d$-$\Lambda$correlation. The corresponding radius is shown along the top. The middle panel shows our measured $B_{\Lambda}$ at 95% Confidence Level (CL). Previous world-wide data Chen:2023melJuric:1973zqKeyes:1970ckGajewski:1967rujBohm:1968qkcSTAR:2019wjmALICE:2022sco are presented in the lower panel, with their weighted average of 0.19 $\pm$ 0.06 MeV illustrated by a shaded band.