Status of the GERDA Phase II upgrade

The GERDA experiment is designed to search for neutrinoless double beta (0νββ) decay of ⁷⁶Ge. In Phase I of the experiment a background index of 10⁻² cts/(keV·kg·yr) was reached. A lower limit on the half-life of the 0νββ decay of ⁷⁶Ge was set to 2.1·10²⁵ yr (at 90% C.L.). The aim of Phase II is to reach a sensitivity of the half-life of about 10²⁶ yr. To increase the exposure thirty new Broad Energy Germanium (BEGe) detectors have been produced. These detectors are distinct for their improved energy resolution and enhanced pulse shape discrimination of signal from background events. Further background reduction will be reached by a light instrumentation to read out argon scintillation light. In April 2015 the light instrumentation together with eight BEGe detectors has been successfully deployed in the GERDA cryostat. In a commissioning run it was shown that two of the major background components, external γ-rays from ²¹⁴Bi and ²⁰⁸Tl decays, were suppressed up to two orders of magnitude. We are confident to reach a background index of 10⁻³ cts/(keV·kg·yr) which is the design goal for GERDA Phase II.