Calibration of the ZEUS barrel calorimeter in a test beam and a direct measurement of the J/ψ leptonic branching fraction

The ZEUS detector at the DESY e-p collider HERA has started collecting data. It contains a state-of-the-art fully compensating high resolution Uranium-scintillator calorimeter. The American part of the ZEUS collaboration was responsible for the construction of the 32 modules of the Barrel CALorimeter (BCAL) and the readout electronics for the complete calorimeter. A test beam experiment E790 was set up in a fixed-target beamline at Fermilab to test and calibrate the BCAL modules to 1%. The analysis of the test beam data with different incident beams at different energies showed a 1% tower-to-tower uniformity, studied the inter-module and inter-tower responses, and measured a hadron resolution of 35%/√E(E in GeV), an electromagnetic resolution of 19%/√E. It also demonstrated the equality of the electromagnetic and the hadronic responses and the linearity of the responses of the calorimeter and the readout electronics. The Mark III collaboration has measured the J/ψ leptonic branching fractions using the process ψ (3685) → π+π-J/ψ,J/ψ → l+l-. The results are: B(J/ψ → e+e-) = (5.92 ± 0.15 ± 0.20)% and B(J/ψ → μ+μ-) = (5.90 ± 0.15 ± 0.19)%, where the first error is statistical and the second is systematic. Assuming lepton universality, the leptonic branching fraction of the J/ψ is (5.91 ± 0.11 ± 0.20)%. This result is used to obtain the strong coupling constant αs and the QCD scale factor ΛMS