Results from the HERA-B Experiment
 
HERA-B is a fixed target experiment at the 920 GeV HERA
proton beam at DESY. Thin wires of different materials
are inserted into the proton beam halo and give rise to
deep-inelastic proton-nucleus collisions. A di-lepton trigger
selects events containing J/\psi decays.
 
The HERA-B detector was completed in the beginning of the
year 2000. The running time until September 2000 when the HERA
upgrade program began was used  to commission the detector
and first level trigger. During the commissioning several million
minimum bias triggers as well as 16 million di-lepton triggers,
both in the electron and in the muon channel, have been recorded.
We would like to report on results from the following analysis:
 
- J/Psi production in proton-nucleus collisions:
  The shapes of the differential cross sections for inclusive J/Psi
  production at sqrts(s)=41.6 GeV are measured in the range of
  -0.275<xF<0.075 and 0<pt<3.75~GeV/c.
  This is the highest energy measurement of the J/Psi production from
  nuclear targets and the only measurement accessing the negative xF
  region. Signals of 3000 and 1000 events were obtained with
  targets of carbon and titanium, respectively. The shape of the
  differential cross section can be parameterized in terms of <pt>
  and c where dsigma/dxf ~ (1-|xF|)^c. The parameters <pt>
  and c are reported and compared other measurements and theoretical
  predictions.
 
- Chi_c production in proton-nucleus collisions:
  We present the measurement of the fraction $R_{\chi_c}$ of  $J/\psi$
  events produced
  via radiative decays of $\chi_{c1}$ and $\chi_{c2}$. The fraction
  $R_{\chi_c}$  is of interest for the
  study of the production mechanism of charmonium states in hadronic
  collisions.

- Measurement of the \b\bar{b} production cross section in proton-nucleus
  collisions:
  For the measurement of the \bbar\ production in proton-nucleus
  interactions HERA-B uses inclusive B->J/Psi+X decays.  The B event
  selection consists first of a J/Psi decay search followed by a cut on
  the separation between J/Psi decay vertex and the primary vertex of
  the proton-nucleon interaction. The analysis exploits the excellent
  resolution of the HERA-B silicon vertex detector.  To minimize
  systematic errors related to the detector and trigger efficiencies and
  to remove the dependence on the luminosity determination, the \bbar\
  production is measured relative to the prompt \jpsi\ production cross
  section.
 
  The number of reconstructed B->J/Psi+X candidates in the year 2000
  sample is small ($O(10)$) reflecting the low efficiency of the
  not-fully commissioned detector and trigger but nevertheless affords a
  cross section estimate comparable in precision to the existing
  measurements at similar beam energies.