HERA-B

  

Figure 6: Schematic of the HERA-B detector at DESY.

To guarantee the observation of standard model CP violation in B decays (after folding in the detector efficiencies), interactions at the HERA-B detector have to occur approximately 4 times for every one of the 10 MHz bunch crossings of the HERA machine. The HERA-B experiment is essentially a fixed target experiment with a wire target in the beam halo [8]. A schematic of the HERA-B spectrometer is shown in fig. 6. It has a single dipole momentum spectrometer situated 4.5 m downstream of the target. Directly downstream of the target wires, but before the magnet, there is a silicon vertex detector of length of $\sim 2{\rm \ m}.$ The main tracking system uses a variety of technologies dependent on the distance away from the beam (Si-strips, microstrip gas counters and honeycomb-drift chambers at ever increasing radii from the beam.) This is followed by a ring imaging Cerenkov (RICH) detector to tag the charged kaon and a transition radiation detector to improve electron identification. There are additional large tracking chambers immediately behind the RICH and in front of the calorimeter. The electromagnetic calorimetry is designed to use Lead/Scintillator and Tungsten/Scintillator. This is followed by a conventional muon system with four chamber layers at various depths in the absorber. The muon chambers are essential for the triggering of HERA-B when the $J/\psi$ decays to two muons.