Publications (2)0 Total impact
ABSTRACT: . The annihilation channels pp!! 0 , !j, !j 0 were studied with the Crystal Barrel detector at LEAR at p-momenta of 600, 1200, and 1940 MeV=c. In most cases angular distributions were measured which allowed a complete J P -analysis using the helicity formalism. The contribution of all relevant initial states could be determined. The maximal contributing angular momenta are dependent on the p-momentum and range up to J = 5. 1 Introduction This paper reports on the measurement of selected twobody pp-annihilation channels performed with the Crystal Barrel (CB) detector at LEAR at p-momenta of 600, 1200 and 1940 MeV=c. The aims of the measurements were 2-fold: (1) Determine the angular momenta in the pp-system, which contribute to the annihilation process with increasing p-momenta. This information is vital for the analysis of 3-or more body annihilation pro- ? This work is part of the PhD. thesis of K. Beuchert ?? Now at University of Freiburg, Freiburg,Germany ??? Universi...
ABSTRACT: . In a joint effort the CERES/NA45 and TAPS collaborations have measured low-mass electron pairs in p--Be and p--Au collisions at 450 GeV/c at the CERN SPS. In the range covered up to ß 1.5 GeV/c 2 the mass spectra from p--Be and p--Au collisions are well explained by electron pairs from decays of neutral mesons. For p--Au our result is new. For p--Be, the simultaneously measured electron pairs and photons served as a direct measure of the j Dalitz decay contribution to the inclusive pair spectrum in which instrumental uncertainties are highly reduced. We confirm the earlier finding of HELIOS-1 with significantly reduced systematic uncertainties of 23% in the mass range below 450 MeV/c 2 , and of 28% in the mass range above 750 MeV/c 2 at 90% confidence limit. Any unconventional source of electron pairs is limited by these error margins as the percentage fraction of the hadronic contribution. 1 Introduction The investigation of low-mass lepton pair production (m pair ! 1 GeV/c ...