Abstract
In addition to the common 3-body decay of the neutron n → pe-ν̅e there should exist an effective 2-body subset with the electron and proton forming a Hydrogen bound state with well defined total momentum, total spin and magnetic quantum numbers. The atomic spectroscopic analysis of this bound system can reveal details about the underlying weak interaction as it mirrors the helicity distributions of all outgoing particles. Thus, it is unique in the information it carries, and an experiment unravelling this information is an analogue to the Goldhaber experiment performed more than 60 years ago. The proposed experiment will search for monoenergetic metastable BoB H atoms with 326 eV kinetic energy, which are generated at the center of a throughgoing beamtube of a high-flux reactor (e.g., at the PIK reactor, Gatchina). Although full spectroscopic information is needed to possibly reveal new physics our first aim is to prove the occurrence of this decay and learn about backgrounds. Key to the detection is the identification of a monoerergtic line of hydrogen atoms occurring at a rate of about 1 s−1 in the environment of many hydrogen atoms, however having a thermal distribution of about room temperature. Two scenarios for velocity (energy) filtering are discussed in this paper. The first builds on an purely electric chopper system, in which metastable hydrogen atoms are quenched to their ground state and thus remain mostly undetectable. This chopper system employs fast switchable Bradbury Nielsen gates. The second method exploits a strongly energy dependent charge exchange process of metastable hydrogen picking up an electron while traversing an argon filled gas cell, turning it into manipulable charged hydrogen. The final detection of hydrogen occurs through multichannel plate (MCP) detector. The paper describes the various methods and gives an outlook on rates and feasibility at the PIK reactor in Gatchina.
Highlights
The neutron decay has for many years been and is subject of intense studies, as it reveals detailed information on the structure of the weak interaction [1]
A new experiment to detect the bound beta neutron decay n → Hνe requires the development of novel methods and technologies
The key requirement is a high rejection of broad band backgrounds from thermal and fast hydrogen atoms of yet unknown magnitude
Summary
The neutron decay has for many years been and is subject of intense studies, as it reveals detailed information on the structure of the weak interaction [1]. If one applies the standard purely left handed V-A interaction (the antineutrino helicity Hνbeing 1) [3, 4], three of the four possible hyperfine spin states are allowed (see Fig. 1) A second detection scenario for bound neutron β-decays is the use of a velocity filter for metastable hydrogen atoms, again using a system of two switchable gates in the beam tube. These gates act on the 2 s state and will quench metastable hydrogen by means of an electric field in the closed mode and leave it untouched in the open mode. The detection of surviving metastable hydrogen atoms can proceed with an argon cell described above or by means of a quenching plate mounted close to a MCP to detect electrons released from the plate in this process
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