Study of inclusive Λ0 production cross sections in P-P and P-nucleus collisions at 12 GeV

The inclusive cross sections for the reaction P+A→Λ0+X at 12-GeV beam energy have been measured for five kinds of nuclear targets (Be, C, CH2, Cu and W) at production angles of 3.50, 5.00, 6.50, 8.00 and 9.50. In terms of Feynman's x sub(F) and the transverse momentum p sub(T) of Λ0, the kinematic range is 0.2<x sub(F)<1.0 and 0.3<p sub(T)<2.0 GeV/c. The Λ0's are identified by a kinematic fitting to their predominant decay mode Λ0→pπ-; the decay pions and protons are detected with a double magnetic spectrometer. The data from the carbon and polyethylene targets are used to derive the corresponding hydrogen cross section. The cross sections off hydrogens and other nuclei are measured in the same detector system, so that detailed comparison between the A=1 data and the higher-A data is possible without any systematics. The target dependence of cross sections is studied in the framework of the power law and the constituent quark model. The power law fits the nuclear data well. However, the A=1 cross sections extrapolated according to the power law do not reproduce the hydrogen data in our kinematic region; a discrepancy of a factor of 2 is observed between them. The p sub(T)-distribution and x sub(F)-distribution of cross sections are analyzed, and results are compared with bubble chamber data and higher-energy counter experiments (CERN ISR and FNAL). The hydrogen cross sections are integrated over p sub(T) and are compared with results from bubble chamber experiments. Our hydrogen data are in good agreement with CERN 12-GeV bubble chamber data, but are smaller than higher-energy data, indicating that the Λ0 production at 12 GeV has not yet reached to the scaling limit. The result of the triple Regge analysis is compared with CERN 19-GeV bubble chamber and FNAL 300-GeV experiments. Our trajectory is in good agreement with that obtained at FNAL, but is smaller by a factor of 2 than that obtained at CERN. (author)