The CLAS12 Backward Angle Neutron Detector (BAND)

• Published in: arXiv.org 2020-07
• Main Authors: Segarra, E P, Hauenstein, F, Schmidt, A, Beck, A, S May-Tal Beck, Cruz-Torres, R, Denniston, A, Hrnjic, A, Kutz, T, Nambrath, A, Pybus, J R, Pryce, K, Fogler, C, Hartlove, T, Weinstein, L B, Vega, J, Ungerer, M, Hakobyan, H, Brooks, W K, Piasetzky, E, Cohen, E, Duer, M, Korover, I, Barlow, J, Barriga, E, Eugenio, P, Ostrovidov, A, Hen, O
• Format: Article
• Language: English
• Subjects: Charged particles; Momentum; Neutron counters; Neutrons; Scintillation counters
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2004.10339

The Backward Angle Neutron Detector (BAND) of CLAS12 detects neutrons emitted at backward angles of \(155^\circ\) to \(175^\circ\), with momenta between \(200\) and \(600\) MeV/c. It is positioned 3 meters upstream of the target, consists of \(18\) rows and \(5\) layers of \(7.2\) cm by \(7.2\) cm scintillator bars, and read out on both ends by PMTs to measure time and energy deposition in the scintillator layers. Between the target and BAND there is a 2 cm thick lead wall followed by a 2 cm veto layer to suppress gammas and reject charged particles. This paper discusses the component-selection tests and the detector assembly. Timing calibrations (including offsets and time-walk) were performed using a novel pulsed-laser calibration system, resulting in time resolutions better than \(250\) ps (150 ps) for energy depositions above 2 MeVee (5 MeVee). Cosmic rays and a variety of radioactive sources were used to calibration the energy response of the detector. Scintillator bar attenuation lengths were measured. The time resolution results in a neutron momentum reconstruction resolution, \(\delta p/p < 1.5\)\% for neutron momentum \(200\le p\le 600\) MeV/c. Final performance of the BAND with CLAS12 is shown, including electron-neutral particle timing spectra and a discussion of the off-time neutral contamination as a function of energy deposition threshold.