Eur. Phys. J. C (2024) 84: 940
https://doi.org/10.1140/epjc/s10052-024-13020-0

Regular Article - Experimental Physics

Searches for new physics below twice the electron mass with GERDA

¹ INFN Laboratori Nazionali del Gran Sasso, Assergi, Italy
² INFN Laboratori Nazionali del Gran Sasso and Gran Sasso Science Institute, Assergi, Italy
³ INFN Laboratori Nazionali del Gran Sasso and Università degli Studi dell’Aquila, L’Aquila, Italy
⁴ INFN Laboratori Nazionali del Sud, Catania, Italy
⁵ Institute of Physics, Jagiellonian University, Cracow, Poland
⁶ Institut für Kern- und Teilchenphysik, Technische Universität Dresden, Dresden, Germany
⁷ Joint Institute for Nuclear Research, Dubna, Russia
⁸ European Commission, JRC-Geel, Geel, Belgium
⁹ Max-Planck-Institut für Kernphysik, Heidelberg, Germany
¹⁰ Department of Physics and Astronomy, University College London, London, UK
¹¹ INFN Milano Bicocca, Milan, Italy
¹² Dipartimento di Fisica, Università degli Studi di Milano and INFN Milano, Milan, Italy
¹³ Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, Russia
¹⁴ Institute for Theoretical and Experimental Physics, NRC “Kurchatov Institute”, Moscow, Russia
¹⁵ National Research Centre “Kurchatov Institute”, Moscow, Russia
¹⁶ Max-Planck-Institut für Physik, Munich, Germany
¹⁷ Physik Department, Technische Universität München, Munich, Germany
¹⁸ Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Padua, Italy
¹⁹ INFN Padova, Padua, Italy
²⁰ Physikalisches Institut, Eberhard Karls Universität Tübingen, Tübingen, Germany
²¹ Physik-Institut, Universität Zürich, Zürich, Switzerland
²² NRNU MEPhI, Moscow, Russia
²³ Duke University, Durham, NC, USA
²⁴ Moscow Inst. of Physics and Technology, Dolgoprudny, Russia
²⁵ Semilab Zrt, Budapest, Hungary
²⁶ Dubna State University, Dubna, Russia
²⁷ Nuclear Science Division, Berkeley, USA
²⁸ Max-Planck-Institut für Kernphysik, Heidelberg, Germany

^a gerda-eb@mpi-hd.mpg.de

Received: 26 March 2024
Accepted: 11 June 2024
Published online: 18 September 2024

Abstract

A search for full energy depositions from bosonic keV-scale dark matter candidates of masses between 65 and 1021 keV has been performed with data collected during Phase II of the GERmanium Detector Array (Gerda) experiment. Our analysis includes direct dark matter absorption as well as dark Compton scattering. With a total exposure of 105.5 kg years, no evidence for a signal above the background has been observed. The resulting exclusion limits deduced with either Bayesian or Frequentist statistics are the most stringent direct constraints in the major part of the 140–1021 keV mass range. As an example, at a mass of 150 keV the dimensionless coupling of dark photons and axion-like particles to electrons has been constrained to ${\alpha }^{\prime }/\alpha <8.7\times {10}^{-24}$ and $g_{\text{ae}}<3.3\times {10}^{-12}$ at 90% credible interval (CI), respectively. Additionally, a search for peak-like signals from beyond the Standard Model decays of nucleons and electrons is performed. We find for the inclusive decay of a single neutron in $_{}^{76}$Ge a lower lifetime limit of ${\tau }_{\text{n}}>1.5\times {10}^{24}$ years and for a proton ${\tau }_{\text{p}}>1.3\times {10}^{24}$ years at 90% CI. For the electron decay $e^{\text{-}}\to {\nu }_{\text{e}}\gamma$ a lower limit of ${\tau }_{\text{e}}>5.4\times {10}^{25}$ years at 90% CI has been determined.