Background Studies

The flux of neutrinos is estimated to be 1.0 × 10¹¹ neutrinos per spill, with an energy spectrum ranging from 2 GeV to about 350 GeV. A large statistic sample of neutrino interactions with the detector material was simulated, corresponding to the amount of neutrino interactions expected in five years of SHiP operation. Neutrino interactions were found to mainly take place in the muon magnetic spectrometer of the tau neutrino detector, in the entrance window of the vacuum vessel and in its surrounding walls. The probability that neutrinos interact with the residual gas inside the decay volume is negligible if the vacuum pressure is set to 10⁻⁶ bar. A deeper analysis showed that many of these background events can be rejected by using of the surround veto tagger andrequiring that the reconstructed candidate points back to the primary target. This would allow to relax the requirements on the vacuum pressure.
The topology of the products of neutrino interactions is such that relatively loose selection cuts allow efficient rejection. Our group is taking care for the investigation of the neutrino background level in 5 years.