STAR focus: ΛΛ Correlation Function in Au+Au collisions at √sNN = 200 GeV

The STAR Collaboration published in Physical Review Letters, Phys. Rev. Lett. 114, 022301 (2015), the first high statistics measurement of ΛΛ correlation function in Au+Au collisions at √sNN = 200 GeV and it is also highlighted as PRL editors' suggestion. This research pioneered the venue of using RHIC as a hyperon factory to investigate hyperon-hyperon interactions. The STAR measurement can provide precious data for the understanding of hyperon-hyperon interaction which is an important input to various baryon-baryon interaction potential model as well as for the study of equation of state for neutron stars. The ΛΛ interaction is also closely related to the existence of the H dibaryon, one of the most searched for exotic hadrons in nuclear collisions.

Left Fig. The combined ΛΛ and anti-Λ anti-Λ correlation function for 0-80% centrality Au+Au collisions at √sNN = 200 GeV. Curves correspond to fits using the Lednicky and Lyuboshitz analytical model with and without a residual correlation term. The dotted line corresponds to Fermi statistics with a source size of 3.13 fm. The shaded band corresponds to the systematic error.

The Lednicky and Lyuboshitz analytical model is used to fit the experimental correlation function and the resulting parameters suggest that the strength of the ΛΛ interaction is weak. The measured ΛΛ correlation shows deviation from unity as well as the free correlation expected from Fermi statistics. The correlation measurement also allowed extraction of an upper limit for possible production of the H dibaryon in Au+Au collisions at 200 GeV which is significantly lower than theoretical predictions based on coalescence calculations.

Posted Jan. 28, 2015

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