Abstract
The SHiP experiment is designed to search for very weakly interacting particles beyond the Standard Model which are produced in a 400 GeV/c proton beam dump at the CERN SPS. An essential task for the experiment is to keep the Standard Model background level to less than 0.1 event after 2× 1020 protons on target. In the beam dump, around 1011 muons will be produced per second. The muon rate in the spectrometer has to be reduced by at least four orders of magnitude to avoid muon-induced combinatorial background. A novel active muon shield is used to magnetically deflect the muons out of the acceptance of the spectrometer. This paper describes the basic principle of such a shield, its optimization and its performance.
Highlights
The SHiP experiment is designed to search for very weakly interacting particles beyond the Standard Model which are produced in a 400 GeV/c proton beam dump at the CERN SPS
This paper describes the basic principle of such a shield, its optimization and its performance
To test the basic principle of the muon shielding concept described in section 2 and optimize its layout, a fast program was written which traces the muons through the magnets
Summary
The principle of the magnet based shielding is shown in 2-D in figure 2. The first part of the shield should be long enough, i.e. providing sufficient ∫ Bdl, to separate both muon polarities to either side of the z-axis. For a 350 GeV/c muon, taking into account the pT distribution at its production point, this requires a ∼ 18 m long magnet with a field in the iron of 1.8 T. Lower momentum muons, which traverse the return field of this magnet, will be bent back in the direction of the spectrometer as is shown in figure 2 for a 50 GeV/c muon. To shield the spectrometer from these muons, an additional magnet is added with opposite polarity field close to the z-axis, and the lower momentum muons will be swept out again. Shows that an air gap as small as 2 cm between the two field polarities can be used without distorting the 1.8 T field in the iron
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