A Comprehensive Study of the nTOF Background at CERN

The first experimental measurements performed at the nTOF1,2 facility at CERN have unveiled an important background, 50 to 100 times higher than expected.3 This background has consequences on capture measurements both in terms of accuracy and required beam time. Extensive measurements have been performed in order to better understand the background. However, it was not possible to identify the mechanism responsible for producing it. The present paper describes the work carried out in order to identify the origin of the background, and the following investigation of the possible sources through extensive Monte Carlo simulations. Neutrons generated by negative muon capture have been identified as the dominant background source. Possible remedies have been found and studied in some detail. An extensive experimental program has verified this hypothesis.