Mainz 2026 – scientific programme

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A: Fachverband Atomphysik

A 44: Precision Spectroscopy of Atoms and Ions VI (joint session A/Q)

A 44.2: Talk

Friday, March 6, 2026, 14:45–15:00, N 3

Atomic Hydrogen beam formation and cryogenic pre-cooling for Project 8 — •Aya El Boustani and Sebastian Böser for the Project 8 collaboration — Institute of Physics, Johannes Gutenberg University of Mainz, Germany

The Project 8 experiment aims to determine the absolute neutrino mass using Cyclotron Radiation Emission Spectroscopy (CRES) to measure radiation from tritium beta-decay electrons near the spectrum's endpoint, where the neutrino mass effect is most significant. Achieving sensitivity requires an atomic tritium source with well-characterized beam properties. At JGU Mainz, molecular hydrogen serves as a tritium analog and is dissociated in a tungsten capillary heated to 2200 K. The dissociated gas undergoes multi-stage cooling to 8 K, enabling atom trapping while minimizing recombination.

In this study, theoretical modeling and gas-flow simulations investigate the hot source and the first cooling stage. The tungsten capillary is modeled with axial temperature gradients, dissociation kinetics, and pressure profiles; the predicted flux and beam properties are benchmarked against Direct Simulation Monte Carlo results from the SPARTA code for low-density gas flows. In the pre-cooling stage, the atomic hydrogen beam passes through a bent, cold tube (Accommodator), whose geometry and gas*surface interaction parameters are studied with SPARTA to quantify beam capture, cooling, and recombination. These results guide the design and prototyping of an improved pre-cooling stage, being prepared for testing as part of a future atomic tritium source for Project 8.

Keywords: Atomic Tritium; Cryogenic systems; Cold atoms; Dissociation; Neutrino mass