Two-pion femtoscopic correlations in Be+Be collisions at √sNN = 16.84 GeV measured by the NA61/SHINE at CERN

Abstract

This paper reports measurements of two-pion femtoscopic correlations in Be+Be collisions at a beam momentum of 150A GeV/c (energy available in the center-of-mass system for nucleon pair √sNN = 16.84 GeV) by the NA61/SHINEexperiment at the CERN SPS accelerator. The obtained momentum space correlation functions can be well described by a Lévy distributed source model. The transverse mass dependence of the Lévy source parameters is presented, and their possible theoretical interpretations are discussed. The results show that the Lévy exponent α is approximately constant as a function of mT , and far from both the Gaussian case of α = 2 or the conjectured value at the critical endpoint, α = 0.5. The radius scale parameter R shows a slight decrease in mT , which can be explained as a signature of transverse flow. Finally, an approximately constant trend of the intercept parameter λ as a function of mTwas observed, similar to previous NA44 S + Pb results (obtained with a Gaussian approximation, but unlike RHIC results).