GraXe, graphene and xenon for neutrinoless double beta decay searches

Abstract

We propose a new detector concept, GraXe (to be pronounced as grace), to search for neutrinoless double beta decay in 136XE. GraXe combines a popular detection medium in rare-event searches, liquid xenon, with a new, background-free material, graphene.In our baseline design of GraXe, a sphere made of graphene-coatedtitanium mesh and filled with liquid xenon (LXe) enriched in the136XE isotope is immersed in a large volume of natural LXe instrumentedwith photodetectors. Liquid xenon is an excellent scintillator,reasonably transparent to its own light. Graphene is transparent overa large frequency range, and impermeable to the xenon. Event positioncould be deduced from the light pattern detected in thephotosensors. External backgrounds would be shielded by the buffer ofnatural LXe, leaving the ultra-radiopure internal volume virtuallyfree of background.Industrial graphene can be manufactured at a competitive cost toproduce the sphere. Enriching xenon in the isotope 136XE is easy andrelatively cheap, and there is already near one ton of enriched xenonavailable in the world (currently being used by the EXO, KamLAND-Zenand NEXT experiments). All the cryogenic know-how is readily availablefrom the numerous experiments using liquid xenon. An experiment usingthe GraXe concept appears realistic and affordable in a short timescale, and its physics potential is enormous.