B. Schwingenheuer

Status and prospects of searches for neutrinoless double beta decay

The simultaneous beta decay of two neutrons in a nucleus without the emission of neutrinos (called neutrinoless double beta decay) is a lepton number violating process which is not allowed in the Standard Model of particle physics. More than a dozen experiments using different candidate isotopes and a variety of detection techniques are searching for this decay. Some (EXO-200, Kamland-Zen, and GERDA) started to take data recently. EXO and Kamland-Zen have reported first limits of the half life for 136Xe. After a decade of little progress in this field, these results start to scrutinize the claim from part of the Heidelberg–Moscow collaboration to have observed this decay. The sensitivities of the different proposals are reviewed.

Performance of the HERA-B vertex detector system

Abstract The Vertex Detector System (VDS) of the HERA-B experiment is a forward microvertex detector integrated into the HERA proton storage ring at DESY. Double-sided silicon microstrip detectors mounted in Roman pots are operated at typically 1 cm distance from the beam in a LHC-like high radiation environment. This paper presents results from the commissioning of the VDS that show its performance to meet the specifications.

HEROICA: an underground facility for the fast screening of germanium detectors

HEROICA (Hades Experimental Research Of Intrinsic Crystal Appliances) is an infrastructure to characterize germanium detectors and has been designed and constructed at the HADES Underground Research Laboratory, located in Mol (Belgium). Thanks to the 223 m overburden of clay and sand, the muon flux is lowered by four orders of magnitude. This natural shield minimizes the exposure of radio-pure germanium material to cosmic radiation resulting in a significant suppression of cosmogenic activation in the germanium detectors. The project has been strongly motivated by a special production of germanium detectors for the GERDA experiment. GERDA, currently collecting data at the Laboratori Nazionali del Gran Sasso of INFN, is searching for the neutrinoless double beta decay of 76Ge. In the near future, GERDA will increase its mass and sensitivity by adding new Broad Energy Germanium (BEGe) detectors. The production of the BEGe detectors is done at Canberra in Olen (Belgium), located about 30 km from the underground test site. Therefore, HADES is used both for storage of the crystals over night, during diode production, and for the characterization measurements. A full quality control chain has been setup and tested on the first seven prototype detectors delivered by the manufacturer at the beginning of 2012. The screening capabilities demonstrate that the installed setup fulfills a fast and complete set of measurements on the diodes and it can be seen as a general test facility for the fast screening of high purity germanium detectors. The results are of major importance for a future massive production and characterization chain of germanium diodes foreseen for a possible next generation 1-tonne double beta decay experiment with 76Ge.

First experience and results from the HERA-B vertex detector system

The HERA-B collaboration is building a detector to realize the ambitious goal of observing CP violation in decays of neutral B-mesons. A central element of the apparatus is the silicon vertex detector used to selectively trigger on these decays in a high charged particle multiplicity background environment and to reconstruct secondary vertices from such decays with high precision. The vertex detector, the supporting infrastructure and first results using prototype detectors are described. Results include imaging of the proton interaction region on the HERA-B target, hit distributions in the detector planes, and alignment of the detectors with each other and the target. ( 1998 Elsevier Science B.V. All rights reserved.

Status of the HERA-B vertex detector

Abstract The HERA-B experiment is a forward magnetic spectrometer with good particle identification for hadrons and leptons designed to study violation of CP symmetry in the neutral B meson system. The silicon vertex detector operates in a high-rate environment similar to the ones expected at LHC. In this paper we report on our R&D on strip detector design, frontend ASICs, mechanical and thermal engineering, low-mass RF shielding of the HERA proton beam and on the status of our reconstruction software. First experiences with last years installation are discussed.

Searches for neutrinoless double beta decay

Neutrinoless double beta decay is a lepton number violating process whose observation would also establish that neutrinos are their own anti-particles. There are many experimental efforts with a variety of techniques. Some (EXO, Kamland-Zen, GERDA phase I and CANDLES) started take data in 2011 and EXO has reported the first measurement of the half life for the double beta decay with two neutrinos of 136Xe. The sensitivities of the different proposals are reviewed.

The HERA-B vertex detector system

Abstract The HERA-B experiment is being built to measure CP violation in the B-system using internal targets at the HERA proton storage ring at DESY. This paper presents an overview of its vertex detector which – apart from an additional superlayer – is realized by a system of 20 Roman pots containing seven superlayers of double-sided silicon microstrip detectors that are operated at 10 mm distance from the proton beam in a high-radiation environment.

The First-Level Trigger of the HERA-B experiment: performance and expectations

Abstract HERA-B is a fixed target spectrometer which uses 920 GeV protons incident on various target materials. The experiment is aimed to study various aspects of beauty and charm physics. The detector is designed to operate at high interaction rates with an average of 4–5 interactions per event. The First-Level Trigger (FLT) is required to reduce the input rate by more than two orders of magnitude while keeping high efficiency for beauty and charm channels. The trigger performs online track reconstruction and takes decisions based on particle momenta or pair masses. A pipeline architecture is implemented on about 100 pipelined hardware processors to perform this job. The working principle and first results of the FLT performance based on the data acquired during the run in the year 2000 are described.

Status of the Germanium Detector Array (GERDA) in the search of neutrinoless ββ decays of 76Ge at LNGS

The Germanium Detector Array (GERDA) in the search for neutrinoless ββ decays of 76Ge at LNGS will operate bare germanium diodes enriched in 76Ge in an (optional active) cryogenic fluid shield to investigate neutrinoless ββ decay with a sensitivity of T1/2 > 2 × 1026 yr after an exposure of 100 kg yr. Recent progress includes the installation of the first underground infrastructures at Gran Sasso, the completion of the enrichment of 37.5 kg of germanium material for detector construction, prototyping of low-mass detector support and contacts, and front-end and DAQ electronics, as well as the preparation for construction of the cryogenic vessel and water tank.

Radiation hardness of the HERA-B silicon microstrip detectors

SummaryThis paper presents results of a non-uniform irradiation of a single-sided ac-coupledp-on-n siliconstrip detector integrated ona HERA-B detector module. The fluences received by different areas of the detector wafer ranged from less than2 × 1013 MIP/cm2 to a maximum of 2.7 × 1014 MIP/cm2 which allowed a systematic study of the detector performance both in the originaln-type and type-inverted regime as well as in the transition region. Charge collection efficiency, noise, leakage current and full depletion voltage were determined as a function of strip number,i.e. fluence. Full functionality of the whole detector area has been established.