Pulse shape discrimination for GERDA Phase I data
Abstract
The GERDA experiment located at the LNGS searches for neutrinoless double beta (0\nu\beta\beta) decay of ^{76}Ge using germanium diodes as source and detector. In Phase I of the experiment eight semi-coaxial and five BEGe type detectors have been deployed. The latter type is used in this field of research for the first time. All detectors are made from material with enriched ^{76}Ge fraction. The experimental sensitivity can be improved by analyzing the pulse shape of the detector signals with the aim to reject background events. This paper documents the algorithms developed before the data of Phase I were unblinded. The double escape peak (DEP) and Compton edge events of 2.615 MeV \gamma\ rays from ^{208}Tl decays as well as 2\nu\beta\beta\ decays of ^{76}Ge are used as proxies for 0\nu\beta\beta\ decay. For BEGe detectors the chosen selection is based on a single pulse shape parameter. It accepts 0.920.02 of signal-like events while about 80% of the background events at Q_{\beta\beta}=2039 keV are rejected. For semi-coaxial detectors three analyses are developed. The one based on an artificial neural network is used for the search of 0\nu\beta\beta\ decay. It retains 90% of DEP events and rejects about half of the events around Q_{\beta\beta}. The 2\nu\beta\beta\ events have an efficiency of 0.85\pm0.02 and the one for 0\nu\beta\beta\ decays is estimated to be 0.90^{+0.05}_{-0.09}. A second analysis uses a likelihood approach trained on Compton edge events. The third approach uses two pulse shape parameters. The latter two methods confirm the classification of the neural network since about 90% of the data events rejected by the neural network are also removed by both of them. In general, the selection efficiency extracted from DEP events agrees well with those determined from Compton edge events or from 2\nu\beta\beta\ decays.
Keywords
Cite
@article{arxiv.1307.2610,
title = {Pulse shape discrimination for GERDA Phase I data},
author = {M. Agostini and M. Allardt and E. Andreotti and A. M. Bakalyarov and M. Balata and I. Barabanov and M. Barnabe Heider and N. Barros and L. Baudis and C. Bauer and N. Becerici-Schmidt and E. Bellotti and S. Belogurov and S. T. Belyaev and G. Benato and A. Bettini and L. Bezrukov and T. Bode and V. Brudanin and R. Brugnera and D. Budjáš and A. Caldwell and C. Cattadori and A. Chernogorov and F. Cossavella and E. V. Demidova and A. Domula and V. Egorov and R. Falkenstein and A. Ferella and K. Freund and N. Frodyma and A. Gangapshev and A. Garfagnini and C. Gotti and P. Grabmayr and V. Gurentsov and K. Gusev and K. K. Guthikonda and W. Hampel and A. Hegai and M. Heisel and S. Hemmer and G. Heusser and W. Hofmann and M. Hult and L. V. Inzhechik and L. Ioannucci and J. Janicskó Csáthy and J. Jochum and M. Junker and T. Kihm and I. V. Kirpichnikov and A. Kirsch and A. Klimenko and K. T. Knöpfle and O. Kochetov and V. N. Kornoukhov and V. V. Kuzminov and M. Laubenstein and A. Lazzaro and V. I. Lebedev and B. Lehnert and H. Y. Liao and M. Lindner and I. Lippi and X. Liu and A. Lubashevskiy and B. Lubsandorzhiev and G. Lutter and C. Macolino and A. A. Machado and B. Majorovits and W. Maneschg and M. Misiaszek and I. Nemchenok and S. Nisi and C. O'Shaughnessy and L. Pandola and K. Pelczar and G. Pessina and A. Pullia and S. Riboldi and N. Rumyantseva and C. Sada and M. Salathe and C. Schmitt and J. Schreiner and O. Schulz and B. Schwingenheuer and S. Schönert and E. Shevchik and M. Shirchenko and H. Simgen and A. Smolnikov and L. Stanco and H. Strecker and M. Tarka and C. A. Ur and A. A. Vasenko and O. Volynets and K. von Sturm and V. Wagner and M. Walter and A. Wegmann and T. Wester and M. Wojcik and E. Yanovich and P. Zavarise and I. Zhitnikov and S. V. Zhukov and D. Zinatulina and K. Zuber and G. Zuzel},
journal= {arXiv preprint arXiv:1307.2610},
year = {2013}
}
Comments
18 pages, 27 figures