arXiv subjects

H. Simgen

Publications and source records attributed to H. Simgen.

70 records · Page 4Linked to original sources

arXiv2013

Measurement of geo-neutrinos from 1353 days of Borexino

We present a measurement of the geo--neutrino signal obtained from 1353 days of data with the Borexino detector at Laboratori Nazionali del Gran Sasso in Italy. With a fiducial exposure of (3.69 $\pm$ 0.16) $\times$ $10^{31}$ proton $\times$ year after all selection cuts and background subtraction, we detected (14.3 $\pm$ 4.4) geo-neutrino events assuming a fixed chondritic mass Th/U ratio of 3.9. This corresponds to a geo-neutrino signal $S_{geo}$ = (38.8 $\pm$ 12.0) TNU with just a 6 $\times$ $10^{-6}$ probability for a null geo-neutrino measurement. With U and Th left as free parameters in the fit, the relative signals are $S_{\mathrm{Th}}$ = (10.6 $\pm$ 12.7) TNU and $S_\mathrm{U}$ = (26.5 $\pm$ 19.5) TNU. Borexino data alone are compatible with a mantle geo--neutrino signal of (15.4 $\pm$ 12.3) TNU, while a combined analysis with the KamLAND data allows to extract a mantle signal of (14.1 $\pm$ 8.1) TNU. Our measurement of a reactor anti--neutrino signal $S_{react}$ = 84.5$^{+19.3}_{-18.9}$ TNU is in agreement with expectations in the presence of neutrino oscillations.

hep-ex↗

arXiv2013

Dark Matter Results from 225 Live Days of XENON100 Data

We report on a search for particle dark matter with the XENON100 experiment, operated at the Laboratori Nazionali del Gran Sasso (LNGS) for 13 months during 2011 and 2012. XENON100 features an ultra-low electromagnetic background of (5.3 \pm 0.6) \times 10^-3 events (kg day keVee)^-1 in the energy region of interest. A blind analysis of 224.6 live days \times 34 kg exposure has yielded no evidence for dark matter interactions. The two candidate events observed in the pre-defined nuclear recoil energy range of 6.6-30.5 keVnr are consistent with the background expectation of (1.0 \pm 0.2) events. A Profile Likelihood analysis using a 6.6-43.3 keVnr energy range sets the most stringent limit on the spin-independent elastic WIMP-nucleon scattering cross section for WIMP masses above 8 GeV/c^2, with a minimum of 2 \times 10^-45 cm^2 at 55 GeV/c^2 and 90% confidence level.

astro-ph.CO↗

arXiv2013

Study of the electromagnetic background in the XENON100 experiment

The XENON100 experiment, located at the Laboratori Nazionali del Gran Sasso (LNGS), aims to directly detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs) via their elastic scattering off xenon nuclei. We present a comprehensive study of the predicted electronic recoil background coming from radioactive decays inside the detector and shield materials, and intrinsic contamination. Based on GEANT4 Monte Carlo simulations using a detailed geometry together with the measured radioactivity of all detector components, we predict an electronic recoil background in the WIMP-search energy range (0-100 keV) in the 30 kg fiducial mass of less than 10e-2 events/(kg-day-keV), consistent with the experiment's design goal. The predicted background spectrum is in very good agreement with the data taken during the commissioning of the detector, in Fall 2009.

astro-ph.IM↗

arXiv2013

Limits on spin-dependent WIMP-nucleon cross sections from 225 live days of XENON100 data

We present new experimental constraints on the elastic, spin-dependent WIMP-nucleon cross section using recent data from the XENON100 experiment, operated in the Laboratori Nazionali del Gran Sasso in Italy. An analysis of 224.6 live days x 34 kg of exposure acquired during 2011 and 2012 revealed no excess signal due to axial-vector WIMP interactions with 129-Xe and 131-Xe nuclei. This leads to the most stringent upper limits on WIMP-neutron cross sections for WIMP masses above 6 GeV, with a minimum cross section of 3.5 x 10^{-40} cm^2 at a WIMP mass of 45 GeV, at 90% confidence level.

astro-ph.CO↗

arXiv2012

Measurement of the half-life of the two-neutrino double beta decay of Ge-76 with the Gerda experiment

The primary goal of the GERmanium Detector Array (Gerda) experiment at the Laboratori Nazionali del Gran Sasso of INFN is the search for the neutrinoless double beta decay of Ge-76. High-purity germanium detectors made from material enriched in Ge-76 are operated directly immersed in liquid argon, allowing for a substantial reduction of the background with respect to predecessor experiments. The first 5.04 kg yr of data collected in Phase I of the experiment have been analyzed to measure the half-life of the neutrino-accompanied double beta decay of Ge-76. The observed spectrum in the energy range between 600 and 1800 keV is dominated by the double beta decay of Ge-76. The half-life extracted from Gerda data is T(1/2) = (1.84 +0.14 -0.10) 10^{21} yr.

nucl-ex↗

arXiv2012

Borexino calibrations: Hardware, Methods, and Results

Borexino was the first experiment to detect solar neutrinos in real-time in the sub-MeV region. In order to achieve high precision in the determination of neutrino rates, the detector design includes an internal and an external calibration system. This paper describes both calibration systems and the calibration campaigns that were carried out in the period between 2008 and 2011. We discuss some of the results and show that the calibration procedures preserved the radiopurity of the scintillator. The calibrations provided a detailed understanding of the detector response and led to a significant reduction of the systematic uncertainties in the Borexino measurements.

physics.ins-det↗

arXiv2012

Cosmic-muon flux and annual modulation in Borexino at 3800 m water-equivalent depth

We have measured the muon flux at the underground Gran Sasso National Laboratory (3800 m w.e.) to be (3.41 \pm 0.01) \times 10-4m-2s-1 using four years of Borexino data. A modulation of this signal is observed with a period of (366\pm3) days and a relative amplitude of (1.29 \pm 0.07)%. The measured phase is (179 \pm 6) days, corresponding to a maximum on the 28th of June. Using the most complete atmospheric data models available, muon rate fluctuations are shown to be positively correlated with atmospheric temperature, with an effective coefficient αT = 0.93 \pm 0.04. This result represents the most precise study of the muon flux modulation for this site and is in good agreement with expectations.

hep-ex↗

arXiv2012

The distributed Slow Control System of the XENON100 Experiment

The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, was designed to search for evidence of dark matter interactions inside a volume of liquid xenon using a dual-phase time projection chamber. This paper describes the Slow Control System (SCS) of the experiment with emphasis on the distributed architecture as well as on its modular and expandable nature. The system software was designed according to the rules of Object-Oriented Programming and coded in Java, thus promoting code reusability and maximum flexibility during commissioning of the experiment. The SCS has been continuously monitoring the XENON100 detector since mid 2008, remotely recording hundreds of parameters on a few dozen instruments in real time, and setting emergency alarms for the most important variables.

astro-ph.IM↗

arXiv2012

Comment on "On the subtleties of searching for dark matter with liquid xenon detectors"

In a recent manuscript (arXiv:1208.5046) Peter Sorensen claims that XENON100's upper limits on spin-independent WIMP-nucleon cross sections for WIMP masses below 10 GeV "may be understated by one order of magnitude or more". Having performed a similar, though more detailed analysis prior to the submission of our new result (arXiv:1207.5988), we do not confirm these findings. We point out the rationale for not considering the described effect in our final analysis and list several potential problems with his study.

astro-ph.CO↗

arXiv2012

Solar neutrino physics with Borexino I

Borexino is a large-volume liquid scintillator detector installed in the underground halls of the Laboratori Nazionali del Gran Sasso in Italy. After several years of construction, data taking started in May 2007. The Borexino phase I ended after about three years of data taking. Borexino provided the first real time measurement of the $^{7}$Be solar neutrino interaction rate with accuracy better than 5% and confirmed the absence of its day-night asymmetry with 1.4% precision. This latter Borexino results alone rejects the LOW region of solar neutrino oscillation parameters at more than 8.5 $σ$ C.L. Combined with the other solar neutrino data, Borexino measurements isolate the MSW-LMA solution of neutrino oscillations without assuming CPT invariance in the neutrino sector. Borexino has also directly observed solar neutrinos in the 1.0-1.5 MeV energy range, leading to the first direct evidence of the $pep$ solar neutrino signal and the strongest constraint of the CNO solar neutrino flux up to date. Borexino provided the measurement of the solar $^{8}$B neutrino rate with 3 MeV energy threshold.

hep-ex↗

arXiv2011

Implications on Inelastic Dark Matter from 100 Live Days of XENON100 Data

The XENON100 experiment has recently completed a dark matter run with 100.9 live-days of data, taken from January to June 2010. Events in a 48kg fiducial volume in the energy range between 8.4 and 44.6 keVnr have been analyzed. A total of three events have been found in the predefined signal region, compatible with the background prediction of (1.8 \pm 0.6) events. Based on this analysis we present limits on the WIMP-nucleon cross section for inelastic dark matter. With the present data we are able to rule out the explanation for the observed DAMA/LIBRA modulation as being due to inelastic dark matter scattering off iodine at a 90% confidence level.

astro-ph.CO↗

arXiv2011

Dark Matter Results from 100 Live Days of XENON100 Data

We present results from the direct search for dark matter with the XENON100 detector, installed underground at the Laboratori Nazionali del Gran Sasso of INFN, Italy. XENON100 is a two-phase time projection chamber with a 62 kg liquid xenon target. Interaction vertex reconstruction in three dimensions with millimeter precision allows to select only the innermost 48 kg as ultra-low background fiducial target. In 100.9 live days of data, acquired between January and June 2010, no evidence for dark matter is found. Three candidate events were observed in a pre-defined signal region with an expected background of 1.8 +/- 0.6 events. This leads to the most stringent limit on dark matter interactions today, excluding spin-independent elastic WIMP-nucleon scattering cross-sections above 7.0x10^-45 cm^2 for a WIMP mass of 50 GeV/c^2 at 90% confidence level.

astro-ph.CO↗

arXiv2011

Muon and Cosmogenic Neutron Detection in Borexino

Borexino, a liquid scintillator detector at LNGS, is designed for the detection of neutrinos and antineutrinos from the Sun, supernovae, nuclear reactors, and the Earth. The feeble nature of these signals requires a strong suppression of backgrounds below a few MeV. Very low intrinsic radiogenic contamination of all detector components needs to be accompanied by the efficient identification of muons and of muon-induced backgrounds. Muons produce unstable nuclei by spallation processes along their trajectory through the detector whose decays can mimic the expected signals; for isotopes with half-lives longer than a few seconds, the dead time induced by a muon-related veto becomes unacceptably long, unless its application can be restricted to a sub-volume along the muon track. Consequently, not only the identification of muons with very high efficiency but also a precise reconstruction of their tracks is of primary importance for the physics program of the experiment. The Borexino inner detector is surrounded by an outer water-Cherenkov detector that plays a fundamental role in accomplishing this task. The detector design principles and their implementation are described. The strategies adopted to identify muons are reviewed and their efficiency is evaluated. The overall muon veto efficiency is found to be 99.992% or better. Ad-hoc track reconstruction algorithms developed are presented. Their performance is tested against muon events of known direction such as those from the CNGS neutrino beam, test tracks available from a dedicated External Muon Tracker and cosmic muons whose angular distribution reflects the local overburden profile. The achieved angular resolution is 3-5 deg and the lateral resolution is 35-50 cm, depending on the impact parameter of the crossing muon. The methods implemented to efficiently tag cosmogenic neutrons are also presented.

physics.ins-det↗

arXiv2008

Highly sensitive gamma-spectrometers of GERDA for material screening: Part I

The GERDA experiment aims to search for the neutrinoless double beta-decay of 76Ge and possibly for other rare processes. The sensitivity of the first phase is envisioned to be more than one order of magnitude better than in previous neutrinoless double beta-decay experiments. This implies that materials with ultra-low radioactive contamination need to be used for the construction of the detector and its shielding. Therefore the requirements on material screening include high-sensitivity low-background detection techniques and long measurement times. In this article, an overview of material-screening laboratories available to the GERDA collaboration is given, with emphasis on the gamma-spectrometry. Additionally, results of an intercomparison of the evaluation accuracy in these laboratories are presented.

physics.ins-det↗

arXiv2008

Highly Sensitive Gamma-Spectrometers of GERDA for Material Screening: Part 2

The previous article about material screening for GERDA points out the importance of strict material screening and selection for radioimpurities as a key to meet the aspired background levels of the GERDA experiment. This is directly done using low-level gamma-spectroscopy. In order to provide sufficient selective power in the mBq/kg range and below, the employed gamma-spectrometers themselves have to meet strict material requirements, and make use of an elaborate shielding system. This article gives an account of the setup of two such spectrometers. Corrado is located in a depth of 15 m w.e. at the MPI-K in Heidelberg (Germany), GeMPI III is situated at the Gran-Sasso underground laboratory at 3500 m w.e. (Italy). The latter one aims at detecting sample activities of the order ~0.01 mBq/kg, which is the current state-of-the-art level. The applied techniques to meet the respective needs are discussed and demonstrated by experimental results.

physics.ins-det↗

arXiv2004

A New 76Ge Double Beta Decay Experiment at LNGS

This Letter of Intent has been submitted to the Scientific Committee of the INFN Laboratori Nazionali del Gran Sasso (LNGS) in March 2004. It describes a novel facility at the LNGS to study the double beta decay of 76Ge using an (optionally active) cryogenic fluid shield. The setup will allow to scrutinize with high significance on a short time scale the current evidence for neutrinoless double beta decay of 76Ge using the existing 76Ge diodes from the previous Heidelberg-Moscow and IGEX experiments. An increase in the lifetime limit can be achieved by adding more enriched detectors, remaining thereby background-free up to a few 100 kg-years of exposure.

hep-ex↗