Defining polarised neutron beams in high-precision experiments with PERC

• Applicant: Professor Dr. Erwin Jericha
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 237612194

This project is part of the overall PERC project and consists of the aim to define the polarised neutron beam inside this instrument for the investigation of the neutron beta decay. The term definition comprises in this context the transfer of the neutron from the polariser into the decay volume including the possibility of inverting the orientation of the beam polarisation, and in the process to preserve the assumed high degree of polarisation as well as the decoupling of the neutrons from the decay volume and their absorption in a beam stop that produces a radiation background and an amount of secondary particles as low as possible and allows for the determination of the current neutron flux and the transmitted degree of polarisation. Additionally, this proposal includes the continuation of a development for the spectral and temporal forming of polarised neutron pulses by means of neutron spin resonance in spatially varying magnetic fields which is now referred to as the MONOPOL project. A neutron beam may be defined in its spectral and temporal structure conventionally with a velocity selector and a beam chopper – the alternative concept of MONOPOL, which is in its initial development phase, could represent an attractive addition to the experimental opportunities which exceeds the capabilities of the standard solution by decoupling the time and energy resolution for the neutron beam. Like the measurements with PERC depend on a high and well defined degree of neutron polarisation, this is also a basic requirement for the spin resonator. Therefore it is essential to design a guiding which is capable to preserve this high polarisation of the neutron beam from the polariser into the decay volume. This is particularly important since the polarisation vectors at production and later in the decay volume are perpendicular whereby the transition of the related magnetic fields needs to receive special consideration. Additionally, it is required for experiments with PERC to reverse the initial neutron polarisation for which we will define an appropriate broad-band spin flipper and optimise its position in the beam guidance where several options are available. At the end of the decay volume, the neutron beam must be caught without producing unwanted events by scattered neutrons or created gamma radiation and secondary particles in the subsequent detectors and spectrometers. At the same time the measurement of the transmitted neutron polarisation and intensity must be made possible at the end of the neutron flight path to enable normalisation of the experimentally obtained decay data on these quantities. The first applicant was nominated “Time and Project Manager” for PERC already in the first phase of the project and represents the Vienna group during procurement, manufacturing, quality control and installation of the PERC magnet system.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1491: Precision Experiments in Particle- and Astrophysics with Cold and Ultracold Neutrons
• International Connection: Austria
• Participating Person: Professor Dr. Hartmut Abele