Search For Neutrinoless Double Beta Decay With Enriched 76Ge 1990-2003 -- HEIDELBERG-MOSCOW-Experiment

TL;DR

The HEIDELBERG-MOSCOW experiment provides evidence for neutrinoless double beta decay at 4.2 sigma, indicating neutrinos are Majorana particles and offering insights into neutrino masses and physics beyond the Standard Model.

Contribution

This study presents the most sensitive double beta decay analysis to date, confirming lepton number violation and constraining new physics scenarios with enriched 76Ge.

Findings

Evidence for neutrinoless double beta decay at 4.2 sigma

Neutrinos are Majorana particles with degenerate masses

Constraints on supersymmetric models and beyond Standard Model physics

Abstract

The HEIDELBERG-MOSCOW experiment, which is the most sensitive double beta decay experiment since ten years has been regularly continued until end of November 2003. An analysis of the data has been performed already until May 20, 2003. The experiment yields now, on a 4.2 sigma level, evidence for lepton number violation and proves that the neutrino is a Majorana particle.It further shows that neutrino masses are degenerate. In addition it puts several stringent constraints on other physics beyond the Standard Model. Among others it opens the door to test various supersymmetric theory scenarios, for example it gives the sharpest limit on the parameter lambda'_{111} in the R-parity violating part of the superpotential, and gives information on the splitting of the sneutrino-antisneutrino system. The result from the HEIDELBERG-MOSCOW experiment is consistent with recent results from CMB investigations, with high energy cosmic rays, with the result from the g-2 experiment and with recent theoretical work. It is indirectly supported by the analysis of other Ge double beta experiments. Recent criticism of various kind has been shown to be wrong, among others by measurements performed in 2003 with a 214Bi source (226Ra), by simulation of the background in the range of Q_(beta-beta) by GEANT4, and by deeper investigation of statistical features such as sensitivity of peak search, and relevance of width of window of analysis.