Intermediate vector boson cross sections at the CERN super proton synchrotron collider and the number of neutrino types

We present updated results from the UA1 experiment on cross sections times leptonic branching ratios for intermediate vector bosons produced in proton-antiproton collisions at a centre-of-mass energy of 0.630 TeV. We find that σ·B(W→lβn)=0.63±0.04±0.10 nb and σ·B(Z⁰→l⁺l^-=0.071 ±0.011 nb where l denotes an average of electron and muon channels. An average over all data (electron and muon channels at 0.546 and 0.630 TeV) gives a ratio of R≡σ·(W→lν)/σ·B(Z⁰ →l⁺l^-) = 9.1^+1.7_-1.2. Using current theoretical predictions for this quantity, limits are extracted on the number of light neutrino types. Combining UA1 and UA2 data and imposing the bound N_ν≥3 we find that N_ν≤5.9 at 90% CL. Constraints on the mass of the top quark are also discussed.