2015: LArGe : active background suppression using argon scintillation for the Gerda experiment

The European Physical Journal. C, Particles and Fields, 2015 vol. 75 no. 10

Agostini M., Barnabé-Heider M., Budjáš D., Cattadori C., Gangapshev A., Gusev K., Heisel M., Junker M., Klimenko A., Lubashevskiy A., Pelczar K. , Schönert S., Smolnikov A., Zuzel G.




LArGe is a Gerda low-background test facility to study novel background suppression methods in a low-background environment, for future application in the Gerda experiment. Similar to Gerda, LArGe operates bare germanium detectors submersed into liquid argon (1 m^{3}, 1.4 tons), which in addition is instrumented with photomultipliers to detect argon scintillation light. The scintillation signals are used in anti-coincidence with the germanium detectors to effectively suppress background events that deposit energy in the liquid argon. The background suppression efficiency was studied in combination with a pulse shape discrimination (PSD) technique using a BEGe detector for various sources, which represent characteristic backgrounds to Gerda. Suppression factors of a few times 10^{3} have been achieved. First background data of LArGe with a coaxial HPGe detector (without PSD) yield a background index of (0.12−4.6) \times 10^{−2} cts/(keV kg year) (90 % C.L.), which is at the level of Gerda Phase I. Furthermore, for the first time we monitor the natural ^{42}Ar abundance (parallel to Gerda), and have indication for the 2\nu \beta \beta-decay in natural germanium. These results show the effectivity of an active liquid argon veto in an ultra-low background environment. As a consequence, the implementation of a liquid argon veto in Gerda Phase II is pursued.