Lambda hyperon production and polarization in collisions of p(3.5 GeV)_s16Nb

Abstract

Results on _s13_s17923_s19 hyperon production are reported for collisions of p(3.5 GeV) _s16 Nb, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. The transverse mass distributions in rapidity bins are well described by Boltzmann shapes with a maximum inverse slope parameter of about 90MeV at a rapidity of y=1.0, i.e. slightly below the center-of-mass rapidity for nucleon-nucleon collisions, ycm=1.12. The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The _s13_s17923_s19 phase-space distribution is compared with results of other experiments and with predictions of two transport approaches which are available publicly. None of the present versions of the employed models is able to fully reproduce the experimental distributions, i.e. in absolute yield and in shape. Presumably, this finding results from an insufficient modelling in the transport models of the elementary processes being relevant for _s13_s17923_s19 production, rescattering and absorption. The present high-statistics data allow for a genuine two-dimensional investigation as a function of phase space of the self-analyzing _s13_s17923_s19 polarization in the weak decay _s13_s17923_s19_s13_s178594_s19p_s13_s17960_s19_s13_s178722_s19. Finite negative values of the polarization in the order of 5_s13_s178722_s1920% are observed over the entire phase space studied. The absolute value of the polarization increases almost linearly with increasing transverse momentum for pt>300MeV/c and increases with decreasing rapidity for y