Study of lambda production in Au+Au collisions at 11.5 A·GeVc

Lambda production in central Au+Au collisions at 11.5 A&middot;GeV/c has been studied at forward rapidities (y > 2.2) using the upgraded E877 experimental setup at the AGS. Lambdas are measured via the charged decay channel: &Lambda; &rarr; ppi- and identified from the ppi - invariant mass spectra with the aids of a set of pair cuts. A comprehensive Monte Carlo simulation is made to extensively study the lambda reconstruction. The details of the data analysis for lambda identification are presented. The consistence of data analysis is examined by detailed comparison of the constructed proton and pion spectra with the previous results from the E877 1993 data set. The double differential multiplicities for lambda as a function of collision centrality are presented. Lambda rapidity distribution dN/dy is also studied. A pure thermal model is used to characterize the lambda spectra. The experimental results are compared to the predictions of the RQMD model (v2.3) in its cascade version and in the mode that takes into account the effect of mean-field. We also present the first measurement of the lambda directed flow at the AGS. In spite of limited statistics, a strong positive directed flow for lambda, which is comparable to the amplitude of the proton flow, is observed at forward rapidities (2.8 < y < 3.4) in the semi-central Au+Au collisions. The measured flow amplitude as a function of pt, v 1(pt), is in agreement with the predictions of the RQMD model