The role of electron scattering from registration detector in the “Troitsk nu-mass” MAC-E type spectrometer

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 832; pp. 15 - 20
• Main Authors: Grigorieva, P.V., Nozik, A.A., Pantuev, V.S., Skasyrskaya, A.K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-10-2016
• Subjects: Electron scattering; MAC-E filter; Neutrino mass; MAC-E filter; Electron scattering; Neutrino mass
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2016.06.058

There is a proposal to search for a sterile neutrino in a few keV mass range by the “Troitsk nu-mass” facility. In order to estimate sterile neutrino mixing one needs to make precision spectrum measurements well below the endpoint using the existing electrostatic spectrometer with a magnetic adiabatic collimation, or MAC-E filter. The expected signature will be a kink in the electron energy spectrum in tritium beta-decay. In this paper we consider the systematic effect of electron backscattering on the detector used in the spectrometer. For this purpose we provide a set of Monte-Carlo simulation results of electron backscattering on a silicon detector with a thin golden window with realistic electric and magnetic fields in the spectrometer. We have found that the probability of such an effect reaches up to 20–30%. The scattered electron could be reflected backwards to the detector by electrostatic field or by magnetic mirror. There is also a few percent probability to escape from the spectrometer through its entrance. A time delay between the scattering on the detector and the return of the reflected electron can reach a couple of microseconds in the Troitsk spectrometer. Such estimations are critical for the planning upgrades of the detector and the registration electronics. All considered effects are relevant to any MAC-E type spectrometer with solid detector.