https://doi.org/10.1140/epjc/s10052-014-2764-z
Regular Article - Experimental Physics
The background in the 
experiment Gerda
1
INFN Laboratori Nazionali del Gran Sasso, LNGS, Assergi, Italy
2
Institute of Physics, Jagiellonian University, Cracow, Poland
3
Institut für Kern- und Teilchenphysik, Technische Universität Dresden, Dresden, Germany
4
Joint Institute for Nuclear Research, Dubna, Russia
5
Institute for Reference Materials and Measurements, Geel, Belgium
6
Max Planck Institut für Kernphysik, Heidelberg, Germany
7
Dipartimento di Fisica, Università Milano Bicocca, Milan, Italy
8
INFN Milano Bicocca, Milan, Italy
9
Dipartimento di Fisica, Università degli Studi di Milano e INFN Milano, Milan, Italy
10
Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, Russia
11
Institute for Theoretical and Experimental Physics, Moscow, Russia
12
National Research Centre “Kurchatov Institute”, Moscow, Russia
13
Max-Planck-Institut für Physik, München, Germany
14
Physik Department and Excellence Cluster Universe, Technische Universität München, München, Germany
15
Dipartimento di Fisica e Astronomia dell‘Università di Padova, Padua, Italy
16
INFN Padova, Padua, Italy
17
Physikalisches Institut, Eberhard Karls Universität Tübingen, Tübingen, Germany
18
Physik Institut der Universität Zürich, Zurich, Switzerland
* e-mail: bela.majorovits@mpp.mpg.de
Received:
21
June
2013
Accepted:
2
December
2013
Published online:
4
April
2014
The GERmanium Detector Array (Gerda) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double beta () decay of 
Ge. The signature of the signal is a monoenergetic peak at 2039 keV, the 
value of the decay. To avoid bias in the signal search, the present analysis does not consider all those events, that fall in a 40 keV wide region centered around . The main parameters needed for the analysis are described. A background model was developed to describe the observed energy spectrum. The model contains several contributions, that are expected on the basis of material screening or that are established by the observation of characteristic structures in the energy spectrum. The model predicts a flat energy spectrum for the blinding window around with a background index ranging from 17.6 to 23.8 
cts/(keV kg yr). A part of the data not considered before has been used to test if the predictions of the background model are consistent. The observed number of events in this energy region is consistent with the background model. The background at is dominated by close sources, mainly due to 
K, 
Bi, 
Th, 
Co and 
emitting isotopes from the 
Ra decay chain. The individual fractions depend on the assumed locations of the contaminants. It is shown, that after removal of the known 
peaks, the energy spectrum can be fitted in an energy range of 200 keV around with a constant background. This gives a background index consistent with the full model and uncertainties of the same size.
© SIF and Springer-Verlag Berlin Heidelberg, 2014
