Detection of molecular hydrogen in a neutron beam lifetime experiment

Abstract

One method of determining the free neutron lifetime involves the absolute counting of neutrons and trapped decay protons. In such experiments, a cold neutron beam traverses a segmented proton trap inside a superconducting solenoid while the neutron flux is continuously monitored. Protons that are born within the fiducial volume of the trap are confined radially by the magnetic field and axially by the electrostatic potential supplied by trap electrodes. They are periodically released and counted, and the ratio of the absolute number of neutrons to protons is proportional to the neutron lifetime. Systematic error can be introduced if protons in the trap are lost, gained, or misidentified. The influence of molecular hydrogen interactions is of particular interest because of its ubiquitous presence in ultrahigh vacuum systems. To understand how it could affect the neutron lifetime, measurements were performed on the production and detection of molecular hydrogen in an apparatus used to measure the neutron lifetime. We demonstrate that charge exchange with molecular hydrogen can occur with trapped protons, and we determine the efficiency with which the molecular hydrogen ions in the trap are detected. Finally, we comment on the potential impact on a neutron lifetime experiment using this beam technique. We find that the result of the beam neutron lifetime performed at NIST is unlikely to have been significantly affected by charge exchange with molecular hydrogen.

References in corpus (8)

• Exotic decay channels are not the cause of the neutron lifetime anomaly
• Experimental Search for Neutron to Mirror Neutron Oscillations as an Explanation of the Neutron Lifetime Anomaly
• Precise Measurements of the Decay of Free Neutrons
• Constraints on the Dark Matter Interpretation $n\to \chi +e^{+}{e}^{-}$ of the Neutron Decay Anomaly with the PERKEO II experiment
• Search for explanation of the neutron lifetime anomaly
• Space-based Measurements of Neutron Lifetime: Approaches to Resolving the Neutron Lifetime Anomaly
• Search for a neutron dark decay in ${}^6$He
• Particles in finite volumes and a toy model of decaying neutrons