Calibration sources for proton spectroscopy in neutron decay

• Applicant: Dr. Torsten Soldner
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 237559329

Protons from neutron decay have a maximum energy of 751 eV only. Proton spectroscopy therefore requires a very good knowledge of the electrostatic potentials along the full proton trajectory, from the position of the neutron decay to the detector. For example, the attempted accuracy of the aSPECT retardation spectrometer of 0.3% for the electron-antineutrino correlation coefficient a requires knowledge of the electrostatic potentials of decay volume and analyzing plane at the level of 7 mV. For proton spectroscopy with PERC, these potentials have to be known at similar accuracy, all along the neutron guide inside the PERC spectrometer. Characterization of the spectrometers by protons from the decay is limited because of the broad energy distribution of the protons. Monoenergetic sources are required. Furthermore, detector commissioning in the spectrometers would profit enormously from a proton source in the energy range between 0 and 800 eV. The availability of such a source would allow detector and spectrometer development independent on reactor operation and make this work much more efficient. We propose to develop two monoenergetic sources of positive particles for these purposes. A proton source with small energy width will allow spectrometer characterization and detector commissioning without neutrons and will be used for the off-line development of secondary proton spectrometers for PERC. A source of moderated positrons will provide a monoenergetic positron beam with an excellent energy width of below 100 meV, only limited by the thermal broadening. Furthermore, this source will provide a well-defined angular distribution of the positron beam. Compared to electrons, the potentials in the spectrometer do not need to be changed for positrons. The source is very compact and can be installed inside a spectrometer. Both proposed sources are complementary: The proton source has probably a larger energy width and is less flexible in use but is indispensable to characterize the detectors and those spectrometer properties that depend on the ratio mass/charge. The source of moderated positrons with its excellent energy width and stability is ideally suited to characterize the electrostatic potential distribution, the transmission function, and the stability of the spectrometer. The sources shall be optimized for the retardation spectrometer aSPECT and tested with this spectrometer. Before connecting the proton source to aSPECT it will be used to characterize the proton detectors of PERKEO-III. After finishing the measurements with aSPECT, the sources are available for characterizing PERC and its secondary proton spectrometers.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1491: Precision Experiments in Particle- and Astrophysics with Cold and Ultracold Neutrons
• International Connection: France