Measurement of the Upsilon Production Cross Section in 920 GeV Fixed-Target Proton-Nucleus Collisions

B Collaboration, I. Abt

The proton-nucleon cross section ratio $R=Br({\rm Y}\to l^{+}{l}^{-})d\sigma ({\rm Y})/dy{|}_{y=0}/\sigma (J/\psi )$ has been measured with the HERA-B spectrometer in fixed-target proton-nucleus collisions at 92…