  The proton-nucleon cross section ratio $R=Br(\Upsilon\to l^+l^-)
d\sigma(\Upsilon)/dy|_{y=0} / {\sigma(J/\psi)}$ has been measured with the
HERA-B spectrometer in fixed-target proton-nucleus collisions at 920 GeV proton
beam energy corresponding to a proton-nucleon cms energy of sqrt{s}=41.6 GeV.
  The combined results for the Upsilon decay channels Upsilon $\to e^+e^-$ and
Upsilon $\to\mu^+\mu^-$ yield a ratio $R=(9.0 \pm 2.1) 10^{-6}$. The
corresponding Upsilon production cross section per nucleon at mid-rapidity
(y=0) has been determined to be $Br(\Upsilon\to{}l^+l^-)
{d\sigma(\Upsilon)/dy}|_{y=0}= 4.5 \pm 1.1 $ pb/nucleon.
