B. Majorovits

Max Planck Institute for Physics, München, Bavaria, Germany

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Publications (92)212.5 Total impact

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    ABSTRACT: Two neutrino double beta decay of ${}^{76}\mathrm{Ge}$ to excited states of ${}^{76}\mathrm{Se}$ has been studied using data from Phase I of the GERDA experiment. An array composed of up to 14 germanium detectors including detectors that have been isotopically enriched in ${}^{76}\mathrm{Ge}$ was deployed in liquid argon. The analysis of various possible transitions to excited final states is based on coincidence events between pairs of detectors where a de-excitation γ ray is detected in one detector and the two electrons in the other. No signal has been observed and an event counting profile likelihood analysis has been used to determine Frequentist 90% C.L. bounds for three transitions: ${0}_{{\rm{g}}.{\rm{s}}.}^{+}-{2}_{1}^{+}:$ ${T}_{1/2}^{2\nu }$ $\;\gt \;1.6\times {10}^{23}$ yr, ${0}_{{\rm{g}}.{\rm{s}}.}^{+}-{0}_{1}^{+}:$ ${T}_{1/2}^{2\nu }$ $\;\gt \;3.7\times {10}^{23}$ yr and ${0}_{{\rm{g}}.{\rm{s}}.}^{+}-{2}_{2}^{+}:$ ${T}_{1/2}^{2\nu }$ $\;\gt \;2.3\times {10}^{23}$ yr. These bounds are more than two orders of magnitude larger than those reported previously. Bayesian 90% credibility bounds were extracted and used to exclude several models for the ${0}_{{\rm{g}}.{\rm{s}}.}^{+}-{0}_{1}^{+}$ transition.
    Full-text · Article · Sep 2015 · Journal of Physics G Nuclear Physics
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    ABSTRACT: A pulse-shape discrimination method based on artificial neural networks was applied to pulses simulated for different background, signal and signal-like interactions inside a germanium detector. The simulated pulses were used to investigate variations of efficiencies as a function of used training set. It is verified that neural networks are well-suited to identify background pulses in true-coaxial high-purity germanium detectors. The systematic uncertainty on the signal recognition efficiency derived using signal-like evaluation samples from calibration measurements is estimated to be 5 %. This uncertainty is due to differences between signal and calibration samples.
    Preview · Article · Jul 2015 · European Physical Journal C
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    ABSTRACT: Two neutrino double beta decay of $^{76}$Ge to excited states of $^{76}$Se has been studied using data from Phase I of the GERDA experiment. An array composed of up to 14 germanium detectors including detectors that have been isotopically enriched in $^{76}$Ge was deployed in liquid argon. The analysis of various possible transitions to excited final states is based on coincidence events between pairs of detectors where a de-excitation $\gamma$ ray is detected in one detector and the two electrons in the other. No signal has been observed and an event counting profile likelihood analysis has been used to determine Frequentist 90\,\% C.L. bounds for three transitions: ${0^+_{\rm g.s.}-2^+_1}$: $T^{2\nu}_{1/2}>$1.6$\cdot10^{23}$ yr, ${0^+_{\rm g.s.}-0^+_1}$: $T^{2\nu}_{1/2}>$3.7$\cdot10^{23}$ yr and ${0^+_{\rm g.s.}-2^+_2}$: $T^{2\nu}_{1/2}>$2.3$\cdot10^{23}$ yr. These bounds are more than two orders of magnitude larger than those reported previously. Bayesian 90\,\% credibility bounds were extracted and used to exclude several models for the ${0^+_{\rm g.s.}-0^+_1}$ transition.
    Full-text · Article · Jun 2015 · Journal of Physics G Nuclear and Particle Physics
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    I Abt · B Majorovits · C Keller · D Mei · G Wang · W Wei
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    ABSTRACT: The 2nd workshop on Germanium (Ge) detectors and technology was held at the University of South Dakota on September 14-17th 2014, with more than 113 participants from 8 countries, 22 institutions, 15 national laboratories, and 8 companies. The participants represented the following big projects: (1) GERDA and Majorana for the search of neutrinoless double-beta decay (0νββ); (2) SuperCDMS, EDELWEISS, CDEX, and CoGeNT for search of dark matter; (3) TEXONO for sub-keV neutrino physics; (4) AGATA and GRETINA for gamma tracking; (5) AARM and others for low background radiation counting; (5) as well as PNNL and LBNL for applications of Ge detectors in homeland security. All participants have expressed a strong desire on having better understanding of Ge detector performance and advancing Ge technology for large-scale applications.
    Preview · Article · May 2015 · Journal of Physics Conference Series
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    C Gooch · L Garbini · I Abt · O Schulz · M Palermo · B Majorovits · H-Y Liao · X Liu · H Seitz
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    ABSTRACT: The GeDetgroup at the Max Planck Institute for Physics in Munich, Germany, operates a number of test stands in order to conduct research on novel germanium detectors. The test stands are of a unique design and construction that provide the ability to probe the properties of new detector types. The GALATEA test stand was especially designed for surface scans, specifically a-induced surface events, a problem faced in low background experiments due to unavoidable surface contamination of detectors. A special 19-fold segmented coaxial prototype detector has already been investigated inside GALATEA with an a-source. A top surface scan provided insight into the physics underneath the passivation layer. Detector segmentation provides a direct path towards background identification and characterisation. With this in mind, a 4-fold segmentation scheme was implemented on a broad-energy point-contact detector and is being investigated inside the groups K1 test stand. A cryogenic test-stand where detectors can be submerged directly in liquid nitrogen or argon is also available. The goal is to establish segmentation as a viable option to reduce background in future large scale experiments.
    Preview · Article · May 2015 · Journal of Physics Conference Series
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    ABSTRACT: An optimized digital shaping filter has been developed for the GERDA experiment which searches for neutrinoless double beta decay in 76Ge. The GERDA Phase I energy calibration data have been reprocessed and an average improvement of 0.3 keV in energy resolution (FWHM) at the 76Ge Q value for 0\nu\beta\beta decay is obtained. This is possible thanks to the enhanced low-frequency noise rejection of this Zero Area Cusp (ZAC) signal shaping fillter.
    Full-text · Article · Feb 2015 · European Physical Journal C
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    ABSTRACT: The GERmanium Detector Array (GERDA) at the Gran Sasso Underground Laboratory (LNGS) searches for the neutrinoless double beta decay (0{\nu}{\beta}{\beta}) of $^{76}$Ge. Germanium detectors made of material with an enriched $^{76}$Ge fraction act simultaneously as sources and detectors for this decay. During Phase I of the experiment mainly refurbished semi-coaxial Ge detectors from former experiments were used. For the upcoming Phase II, 30 new $^{76}$Ge enriched detectors of broad energy germanium (BEGe)-type were produced. A subgroup of these detectors has already been deployed in GERDA during Phase I. The present paper reviews the complete production chain of these BEGe detectors including isotopic enrichment, purification, crystal growth and diode production. The efforts in optimizing the mass yield and in minimizing the exposure of the $^{76}$Ge enriched germanium to cosmic radiation during processing are described. Furthermore, characterization measurements in vacuum cryostats of the first subgroup of seven BEGe detectors and their long-term behavior in liquid argon are discussed. The detector performance fulfills the requirements needed for the physics goals of GERDA Phase~II.
    Full-text · Article · Feb 2015 · European Physical Journal C
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    ABSTRACT: A search for neutrinoless $\beta\beta$ decay processes accompanied with Majoron emission has been performed using data collected during Phase I of the GERmanium Detector Array (GERDA) experiment at the Laboratori Nazionali del Gran Sasso of INFN (Italy). Processes with spectral indices n = 1, 2, 3, 7 were searched for. No signals were found and lower limits of the order of 10$^{23}$ yr on their half-lives were derived, yielding substantially improved results compared to previous experiments with $^{76}$Ge. A new result for the half-life of the neutrino-accompanied $\beta\beta$ decay of $^{76}$Ge with significantly reduced uncertainties is also given, resulting in $T^{2\nu}_{1/2} = (1.926 \pm 0.095)\cdot10^{21}$ yr.
    Full-text · Article · Jan 2015
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    ABSTRACT: A search for neutrinoless ββ decay processes accompanied with Majoron emission has been performed using data collected during Phase I of the GERmanium Detector Array (Gerda) experiment at the Laboratori Nazionali del Gran Sasso of INFN (Italy). Processes with spectral indices n = 1, 2, 3, 7 were searched for. No signals were found and lower limits of the order of 1023 yr on their half-lives were derived, yielding substantially improved results compared to previous experiments with 76Ge. A new result for the half-life of the neutrino-accompanied ββ decay of 76Ge with significantly reduced uncertainties is also given, resulting in T2ν1/2=(1.926± 0.095) · 1021 yr.
    Full-text · Article · Jan 2015
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    ABSTRACT: A pulse-shape discrimination method based on artificial neural networks was applied to pulses simulated for different background, signal and signal-like interactions inside a germanium detector. The simulated pulses were used to investigate the systematic uncertainties of the method. It is verified that neural networks are well-suited to identify background pulses in true-coaxial high-purity germanium detectors. The systematic uncertainty on the signal recognition efficiency derived using signal-like samples from calibration measurements is estimated to be 5\%. This uncertainty is due to differences between signal and calibration samples.
    Preview · Article · Dec 2014
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    ABSTRACT: GALATEA is a test facility designed to investigate bulk and surface effects in high purity germanium detectors. A vacuum tank houses an infrared screened volume with a cooled detector inside. A system of three stages allows an almost complete scan of the detector. The main feature of GALATEA is that there is no material between source and detector. This allows the usage of alpha and beta sources as well as of a laser beam to study surface effects. A 19-fold segmented true-coaxial germanium detector was used for commissioning.
    Full-text · Article · Sep 2014 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: The GERmanium Detector Array (Gerda) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double beta ( 0νββ ) decay of 76 Ge. The signature of the signal is a monoenergetic peak at 2039 keV, the Qββ 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 Qββ . The main parameters needed for the 0νββ 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 Qββ with a background index ranging from 17.6 to 23.8 × 10−3 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 Qββ is dominated by close sources, mainly due to 42 K, 214 Bi, 228 Th, 60 Co and α emitting isotopes from the 226 Ra decay chain. The individual fractions depend on the assumed locations of the contaminants. It is shown, that after removal of the known γ peaks, the energy spectrum can be fitted in an energy range of 200 keV around Qββ with a constant background. This gives a background index consistent with the full model and uncertainties of the same size.
    Full-text · Article · Apr 2014 · European Physical Journal C
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    ABSTRACT: The GERmanium Detector Array (Gerda) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double beta (\(0\nu \beta \beta \)) decay of \(^{76}\)Ge. The signature of the signal is a monoenergetic peak at 2039 keV, the \(Q_{\beta \beta }\) 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 \(Q_{\beta \beta }\). The main parameters needed for the \(0\nu \beta \beta \) 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 \(Q_{\beta \beta }\) with a background index ranging from 17.6 to 23.8 \(\times \) \(10^{-3}\) 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 \(Q_{\beta \beta }\) is dominated by close sources, mainly due to \(^{42}\)K, \(^{214}\)Bi, \(^{228}\)Th, \(^{60}\)Co and \(\alpha \) emitting isotopes from the \(^{226}\)Ra decay chain. The individual fractions depend on the assumed locations of the contaminants. It is shown, that after removal of the known \(\gamma \) peaks, the energy spectrum can be fitted in an energy range of 200 keV around \(Q_{\beta \beta }\) with a constant background. This gives a background index consistent with the full model and uncertainties of the same size.
    Full-text · Article · Apr 2014 · European Physical Journal C
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    Full-text · Article · Apr 2014 · European Physical Journal C
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    ABSTRACT: The Gerda experiment located at the Laboratori Nazionali del Gran Sasso of INFN searches for neutrinoless double beta (0νββ) decay of 76Ge 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 76Ge 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 γ rays from 208Tl decays as well as two-neutrino double beta (2νββ) decays of 76Ge are used as proxies for 0νββ decay. For BEGe detectors the chosen selection is based on a single pulse shape parameter. It accepts 0.92±0.02 of signal-like events while about 80 % of the background events at Q ββ =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 0νββ decay. It retains 90 % of DEP events and rejects about half of the events around Q ββ . The 2νββ events have an efficiency of 0.85±0.02 and the one for 0νββ 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 2νββ decays.
    Full-text · Article · Oct 2013 · European Physical Journal C
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    ABSTRACT: Neutrinoless double beta decay is a process that violates lepton number conservation. It is predicted to occur in extensions of the standard model of particle physics. This Letter reports the results from phase I of the Germanium Detector Array (GERDA) experiment at the Gran Sasso Laboratory (Italy) searching for neutrinoless double beta decay of the isotope ^{76}Ge. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kg yr. A blind analysis is performed. The background index is about 1×10^{-2} counts/(keV kg yr) after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of ^{76}Ge, T_{1/2}^{0ν}>2.1×10^{25} yr (90% C.L.). The combination with the results from the previous experiments with ^{76}Ge yields T_{1/2}^{0ν}>3.0×10^{25} yr (90% C.L.).
    Full-text · Article · Sep 2013 · Physical Review Letters
  • I. Abt · A. Caldwell · B. Dönmez · S. Irlbeck · B. Majorovits · O. Volynets
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    ABSTRACT: Segmented high-purity germanium detectors have been developed for a variety of experiments. The segmentation is used to augment the excellent energy resolution of such a device with spatial information to disentangle event topologies. Several performance aspects of true-coaxial segmented detectors are presented, especially the effects due to the crystallographic axes and the problem of events close to the surfaces of the detector. A test stand and Monte Carlo tools developed to study such effects are introduced. The simulation tools can also be used to design novel detectors, such as segmented point-contact detectors. A particular design is presented and discussed.
    No preview · Article · Aug 2013 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: Neutrinoless double beta decay is a process that violates lepton number conservation. It is predicted to occur in extensions of the Standard Model of particle physics. This Letter reports the results from Phase I of the GERmanium Detector Array (GERDA) experiment at the Gran Sasso Laboratory (Italy) searching for neutrinoless double beta decay of the isotope 76Ge. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kgyr. A blind analysis is performed. The background index is about 1.10^{-2} cts/(keV kg yr) after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of 76Ge, T_1/2 > 2.1 10^{25} yr (90% C.L.). The combination with the results from the previous experiments with 76Ge yields T_1/2 > 3.0 10^{25} yr (90% C.L.).
    Full-text · Article · Jul 2013
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    ABSTRACT: The GERmanium Detector Array (GERDA) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double beta decay of 76Ge. The signature of the signal is a monoenergetic peak at 2039 keV, the Q-value of the decay, Q_bb. 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 Q_bb. The main parameters needed for the neutrinoless double beta decay 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 Q_bb with a background index ranging from 17.6 to 23.8*10^{-3} counts/(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 Q-bb is dominated by close sources, mainly due to 42K, 214Bi, 228Th, 60Co and alpha emitting isotopes from the 226Ra decay chain. The individual fractions depend on the assumed locations of the contaminants. It is shown, that after removal of the known gamma peaks, the energy spectrum can be fitted in an energy range of 200 kev around Q_bb with a constant background. This gives a background index consistent with the full model and uncertainties of the same size.
    Full-text · Article · Jun 2013
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    ABSTRACT: Low background experiments place stringent constraints on amount of radioactive impurities in the materials used for their assembly. Often these are in conflict with the constraints placed on the materials by their roles in the experiment. This is especially true for certain electronic components. A high value, high voltage capacitor for use in low background experiments has been developed from specially selected radiopure materials. Electroformed copper foils are separated by polyethylene napthalate (PEN) foils and supported within a PTFE teflon spiral coil tube. The electrical performance as well as radiopurity are scrutinized here. With some minor modifications to tune the performance for the application, this capacitor can be well suited for a variety of applications in low background experiments. Here the use of the capacitor for high voltage (HV) decoupling in the operation of high purity germanium (HPGe) detectors is demonstrated.
    Full-text · Article · May 2013 · European Physical Journal C

Publication Stats

2k Citations
212.50 Total Impact Points

Institutions

  • 2007-2015
    • Max Planck Institute for Physics
      München, Bavaria, Germany
  • 2013
    • Technische Universität München
      München, Bavaria, Germany
  • 2004-2010
    • University of Oxford
      • Department of Physics
      Oxford, England, United Kingdom
  • 1998-2002
    • Max Planck Institute for Nuclear Physics
      Heidelburg, Baden-Württemberg, Germany