Eur. Phys. J. Plus (2015) 130: 139
https://doi.org/10.1140/epjp/i2015-15139-8

Regular Article

Double-beta decay with majoron emission in GERDA Phase I

Dipartimento di Fisica e Astronomia dell’Università di Padova and INFN Padova, Padova, Italy

^* e-mail: sabine.hemmer@pd.infn.it

Received: 4 June 2015
Accepted: 25 June 2015
Published online: 21 July 2015

Abstract

Neutrinoless double-beta decay with emission of one or two majorons (0νββχ(χ)) is predicted by several beyond-Standard-Model theories. This article reviews the results of a search for 0νββχ(χ) of ⁷⁶Ge using data from the Germanium Detector Array (GERDA) experiment, located underground at the INFN Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The analysis comprised data with an exposure of 20.3 kg·yr from the first phase of the experiment. No indication of contributions to the observed energy spectra was detected for any of the majoron models. The lower limit on the half-life for the ordinary majoron model (spectral index n = 1 was determined to be T _1/2 ^0νβ > 4.2 · 10²³ yr (90% quantile). This limit and the limits derived for the other majoron modes constitute the most stringent limits on 0νββχ(χ) decay of ⁷⁶Ge measured to date.