Eur. Phys. J. A (2005) 23: 135-146
https://doi.org/10.1140/epja/i2004-10057-1

The neutron decay retardation spectrometer aSPECT: Electromagnetic design and systematic effects

¹ Institut für Physik, Universität Mainz, D-55099, Mainz, Germany
² Theory Department, Research Institute for Nuclear and Particle Physics, P.O. Box 49, H-1525, Budapest 114, Hungary
³ Institut für Kernphysik, Forschungszentrum Karlsruhe, Pf. 3640, D-76021, Karlsruhe, Germany
⁴ Department of Physics and Astronomy, University of Sussex, BN1 9QH, Falmer, Brighton, UK
⁵ Physik-Department E18, Technische Universität München, D-85748, Garching, Germany

Received: 2 February 2004
Accepted: 30 July 2004
Published online: 23 November 2004

Abstract

The apparatus described here, aSPECT, will be used for a measurement of the neutrino-electron angular correlation coefficient a in the decay of free neutrons. The idea of the aSPECT spectrometer is to measure the integrated proton energy spectrum very accurately using an energy filter by electrostatic retardation and magnetic adiabatic collimation. The main ideas of the spectrometer are presented, followed by an explanation of the adiabatic transmission function. Details of the superconducting coil and of the electrode system are given, as well as a discussion of the most important systematic effects: magnetic field and electrostatic potential inhomogeneities, deviation from adiabatic motion, scattering in the residual gas, background, Doppler effect, edge effect, and detector efficiency. Using this spectrometer, the parameter a is planned to be measured with an absolute experimental uncertainty of δa ≈ 3 ^. 10^-4, from which the axial vector to vector coupling constant ratio λ can be determined with an accuracy of δλ ≈ 0.001.