Exposure-background duality in the searches of neutrinoless double beta decay

Abstract

Tremendous efforts are required to scale the summit of observing neutrinoless double beta decay (0νββ). This article quantitatively explores the interplay between exposure (target mass×data taking time) and background levels in 0νββ experiments. In particular, background reduction can substantially alleviate the necessity of unrealistic large exposure as the normal mass hierarchy (NH) is probed. The nondegenerate (ND)-NH can be covered with an exposure of O(100) ton-year, which is only an order of magnitude larger than those planned for next-generation projects - provided that the background could be reduced by O(10-6) relative to the current best levels. It follows that background suppression will be playing increasingly important and investment-effective, if not determining, roles in future 0νββ experiments with sensitivity goals of approaching and covering ND-NH.