Cryogenic source of atomic tritium for neutrino-mass measurements and precision spectroscopy

TL;DR

This paper proposes a cryogenic atomic tritium source for high-precision spectroscopy and neutrino-mass measurements, utilizing solid T2 dissociation, buffer-gas cooling, and magnetic trapping to achieve high fluxes at sub-Kelvin energies.

Contribution

It introduces a novel method for producing a high-flux, low-energy atomic tritium source suitable for advanced spectroscopic and neutrino experiments, combining recent dissociation and cooling techniques.

Findings

Achieves atomic tritium fluxes >1e15 atoms/sec at 100 mK.

Enables Doppler-free 1S-2S spectroscopy for high-precision measurements.

Facilitates next-generation neutrino mass experiments with reduced molecular broadening.

Abstract

We propose a concept for a cryogenic source of atomic tritium at sub-Kelvin temperatures and energies suitable for magnetic trapping. The source is based on the dissociation of solid molecular T2 films below 1 K by electrons from a pulsed RF discharge, a technique recently demonstrated for atomic hydrogen, combined with buffer-gas cooling and magnetic confinement. We analyze the key processes limiting the source performance, adsorption, spin exchange and recombination, and show that atomic tritium fluxes exceeding 1e15 1/s at kinetic energies of 100 mK can be achieved at the entrance to the magnetic trap. Such a source would enable Doppler-free two-photon 1S-2S spectroscopy in atomic tritium for high-precision measurements of the triton charge radius, providing a crucial benchmark for bound-state QED and improving the comparison between electronic, muonic, and scattering determinations of nuclear sizes in light systems. Beyond spectroscopy, an atomic tritium source avoids molecular final state broadening in the beta decay and is therefore necessary for next generation neutrino mass measurements; combined with detector technologies such as sub-eV resolution quantum sensors or cyclotron radiation emission spectroscopy, it enables an order of magnitude improvement compared to the current best experimental limit. Additionally, the source can be used to generate a beam of low field seeking deuterium atoms for loading magnetic traps, an important benchmark before trapping tritium atoms, which is useful for precision spectroscopy.