Study of χc production using HERA-B data

In this thesis the production of the charmonium states χc1 and χc2 in protonnucleus collisions at a proton-nucleon center-of-mass energy √(s)=41.6 GeV was studied. The data used for the analysis have been taken by the fixed-target experiment HERA-B that uses the HERA proton beam to scatter protons off the nuclei of different wire targets. About 122.103 recorded muonic J/ψ decays, J/ψ→μ+μ-, resulted in almost 10000 reconstructed χc→J/ψγ. The ratio Rχc= sum i=1,2σ(χci)Br(χci→J/ψγ)/σ(J/ψ), which is the ratio of J/ψ from χc decays to all produced J/ψ, was measured in the kinematical range -0.35<xFJ/ψ<0.15 for carbon and tungsten wire targets. The average over both materials yields Rχc=0.190-0.029+0.030. Despite the small separation of the masses of the two χc states, comparable to the detector resolution, the ratio R12=Rχc1/Rχc2 was measured yielding R12=1.30-0.37+0.59 which corresponds to a production cross section ratio (σ(χc1))/(σ(χc2))=0.74-0.22+0.34. By using the known J/ψ production cross section, the χc1 and χc2 production cross sections are calculated to be σ(χc1)=(153±27) nb/nucleon and σ(χc2)=(207±39) nb/nucleon, respectively. All results were obtained under the assumption that both the J/ψ and χc states are produced without polarization. In addition a study of possible deviations of Rχc and R12 due to the polarization of J/ψ and χc was performed. By varying the polarization parameter, λobs, of all produced J/ψ by 2σ around the value measured by HERA-B, and assuming fully polarized χc states, the maximum variations of Rχc and R12 were evaluated. These studies show that Rχc could change up to 21% and R12 from -11% to +16% relative to the values calculated without polarization. (orig.)