Abstract
Meson factories are powerful drivers of diverse physics programmes. With beam powers already in the MW-regime attention has to be turned to target and beam line design to further significantly increase surface muon rates available for experiments. For this reason we have explored the possibility of using a neutron spallation target as a source of surface muons by performing detailed Geant4 simulations with pion production cross sections based on a parametrization of existing data. While the spallation target outperforms standard targets in the backward direction by more than a factor 7 it is not more efficient than standard targets viewed under 90{\deg}. Not surprisingly, the geometry of the target plays a large role in the generation of surface muons. Through careful optimization, a gain in surface muon rate of between 30 - 60% over the standard "box-like" target used at the Paul Scherrer Institute could be achieved by employing a rotated slab target. An additional 10% gain could also be possible by utilizing novel target materials such as, e.g., boron carbide.
Highlights
The development of powerful proton drivers in the 1970s enabled a broad experimental program centered around the various secondary particles produced at dedicated target stations
With beam powers already in the MW-regime attention has to be turned to target and beam line design to further significantly increase surface muon rates available for experiments. For this reason we have explored the possibility of using a neutron spallation target as a source of surface muons by performing detailed GEANT4 simulations with pion production cross sections based on a parametrization of existing data
With the combined capture and transport efficiencies of traditional beam lines being of Oð1%Þ there is certainly a large potential for improvement and first beam lines with larger acceptances have been constructed [9,10]
Summary
The development of powerful proton drivers in the 1970s enabled a broad experimental program centered around the various secondary particles produced at dedicated target stations. Typical experiments make use of the beneficial properties of so-called surface muons [4] These are copiously produced low-energy muons that can be stopped in extremely thin targets (∼160 mg=cm). Corresponding to a maximum depth of less than 1 mm in graphite and following a p3.5 power law [4] Muons above this momentum are present in the beam but are suppressed by typically 2 orders of magnitude in this momentum region. These “cloud muons” originate from pion decay in flight in and around the production target and can have both charge signs, unlike surface muons which are only positively charged. V and VI, where we explore the possibilities of enhancing the surface muon production by optimizing the shape and material of the standard target
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