Measurement of ΛΛ spin correlations in the SELEX experiment

Abstract

Abstract. We study HBT interferometry of ΛΛ pairs produced in Σ − A interactions using a ΛΛ spin composition measurement with data taken by SELEX, which accumulated data during the 1996-97 fixed target run at Fermilab. While the spin composition of a ΛΛ pair in the range of four-momentum difference of a pair Q < 1.5 GeV was found to be consistent with the suppression of spin state one, for Q > 1.5 GeV it was found to be consistent with statistical spin mixture. For the ΛΛ system the spin one fraction was found to be consistent with the expectation for a statistical spin mixture. We also estimated the dimension of the ΛΛ production region. IntroductionHBT correlations of pairs of identical particles are sensitive to the size of the emission source. These correlations were found to originate from two-particle wave function properties: according to the Bose-Einstein (BE) statistics, production of identical bosons is enhanced and according to the Fermi-Dirac (FD) statistics, production of identical fermions is suppressed.Currently data on Λ hyperons correlations is limited to the following experiments: ALEPH [1], OPAL [2], DELPHI 1 [3] in handronic Z 0 decays produced in e + e − annihilation at LEP, NA49 [4] in P b ions collisions and EXCHARM [5] in nC interactions.In this paper we report preliminary results on a study of ΛΛ spin composition using events obtained on Σ − beam in the SELEX experiment. An estimation of the size of the ΛΛ particle production region is presented. We compare our results to those obtained with the correlation function technique [6,7] and with world results.