Status Report of the GERDA Phase II Startup

TL;DR

The GERDA Phase II experiment aims to detect neutrinoless double beta decay in germanium with enhanced sensitivity and background suppression, building on Phase I achievements and implementing new veto technologies.

Contribution

This paper reports on the upgrade, goals, and initial results of GERDA Phase II, including new detector and veto systems for improved sensitivity.

Findings

Achieved a background index of about 10^{-3} cts/(keV·kg·yr)

Upgraded to a 35 kg enriched germanium detector array

Aimed for a half-life sensitivity > 10^{26} years in 3 years

Abstract

The GERmanium Detector Array GERDA experiment, located at the Laboratori Nazionali del Gran Sasso (LNGS) of INFN, searches for $0\nu\beta\beta$ of $^{76}$Ge. Germanium diodes enriched to $\sim 86~\%$ in the double beta emitter $^{76}$Ge ($^{enr}$Ge) are exposed being both source and detectors of $0\nu\beta\beta$ decay. Neutrinoless double beta decay is considered a powerful probe to address still open issues in the neutrino sector of the (beyond) Standard Model of particle Physics. Since 2013, just after the completion of the first part of its experimental program (Phase I), the GERDA setup has been upgraded to perform its next step in the $0\nu\beta\beta$ searches (Phase II). Phase II aims to reach a sensitivity to the $0\nu\beta\beta$ decay half-life larger than $10^{26}~$yr in about 3 years of physics data taking. This exposing a detector mass of about $35~$kg of $^{enr}$Ge and with a background index of about $10^{-3}~$cts/(keV$\cdot$kg$\cdot$yr). One of the main new implementations is the liquid argon scintillation light read-out, to veto those events that only partially deposit their energy both in Ge and in the surrounding LAr. In this paper the GERDA Phase II expected goals, the upgrade work and few selected features from the 2015 commissioning and 2016 calibration runs will be presented. The main Phase I achievements will be also reviewed.