Neutron bound beta-decay: BOB

Abstract

An experiment to observe the bound beta-decay (BOB) of the free neutron into a hydrogen atom and an electron anti-neutrino is described. The hyperfine spin state population of the monoenergetic hydrogen atom yields the neutrino lefthandedness or possible right-handed admixture as well as possible small scalar and tensor contributions to the weak force. The BOB H(2s) hyperfine states can be separated with a Lamb-Shift Spin Filter. These monoenergetic H(2s) atoms are ionised into H − by charge exchanging within an argon cell. These ions are then separated using an adaptation of a MAC-E Filter. A first experiment is proposed at the FRMII high thermal-neutron flux beam reactor SR6 through-going beam tube, where we will seek to observe this rare neutron decay-mode for the first time and determine the branching ratio. After successful completion, the hyperfine spin state population will be determined, possibly at the ILL high-flux beam reactor through-going beam tube H6-H7, where the thermal neutron flux is a factor of four larger.

Measurement of the occupation number of metastable atoms in the hyperfine-substate β$_3$ in an atomic hydrogen beam

“…The Neutron Bound Beta Decay (BOB) experiment in Munich [2] tries to further investigate the natural decay of neutron. In general, neutrons decay into a proton, an electron and an electron antineutrino.…”

“…Besides the decay into the ground state 1S even a decay into the metastable state 2S (branching ratio 10 −7 ) is possible. Due to momentum and spin preservation there are multiple different spin combinations of the particles involved which are shown in the table below [2]. But only the upper options are allowed, because for the known .…”

Hyperfine-spectroscopy measurement of metastable hydrogen atoms with a Sona-transition unit

“…First indications of oscillations in the occupation numbers have been demonstrated during the PSTP conference in Brookhaven [2]. With a new experiment, the bound beta decay, on the horizon it is necessary to build a detector, which should be able to measure the 𝛽 3 -state, having both spins reversed to the quantization axis [3]. For this reason, a Sona transition unit was proposed by our group to transfer all 𝛽 3 -states into 𝛼 1 -states, that can be measured by a Lamb-Shift polarimeter.…”