Direct measurement of neutrons induced in lead by cosmic muons at a shallow underground site

Neutron production in lead by cosmic muons has been studied with a Gadolinium doped liquid scintillator detector. The detector was installed next to the Muon-Induced Neutron Indirect Detection EXperiment (MINIDEX), permanently located in the T\"ubingen shallow underground laboratory where the mean muon energy is approximately 7 GeV. The MINIDEX plastic scintillators were used to tag muons; the neutrons were detected through neutron capture and neutron-induced nuclear recoil signals in the liquid scintillator detector. Results on the rates of observed neutron captures and nuclear recoils are presented and compared to predictions from GEANT4-9.6 and GEANT4-10.3. The predicted rates are significantly too low for both versions of GEANT4. For neutron capture events, the observation exceeds the predictions by factors of $1.65\,\pm\,0.02\,\textrm{(stat.)}\,\pm\,0.07\,\textrm{(syst.)}$ and $2.58\,\pm\,0.03\,\textrm{(stat.)}\,\pm\,0.11\,\textrm{(syst.)}$ for GEANT4-9.6 and GEANT4-10.3, respectively. For neutron nuclear recoil events, which require neutron energies above approximately 5 MeV, the factors are even larger, $2.22\,\pm\,0.05\,\textrm{(stat.)}\,\pm\,0.25\,\textrm{(syst.)}$ and $3.76\,\pm\,0.09\,\textrm{(stat.)}\,\pm\,0.41\,\textrm{(syst.)}$, respectively. Also presented is the first statistically significant measurement of the spectrum of neutrons induced by cosmic muons in lead between 5 and 40 MeV. It was obtained by unfolding the nuclear recoil spectrum. The observed neutron spectrum is harder than predicted by GEANT4. An investigation of the distribution of the time difference between muon tags and nuclear recoil signals confirms the validity of the unfolding procedure and shows that GEANT4 cannot properly describe the time distribution of nuclear recoil events. In general, the description of the data is worse for GEANT4-10.3 than for GEANT4-9.6.Comment: 29 pages, 22 figures, 4 table

Modeling of GERDA Phase II data

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 technological challenge of GERDA is to operate in a "background-free" regime in the region of interest (ROI) after analysis cuts for the full 100$\,$kg$\cdot$yr target exposure of the experiment. A careful modeling and decomposition of the full-range energy spectrum is essential to predict the shape and composition of events in the ROI around $Q_{\beta\beta}$ for the $0\nu\beta\beta$ search, to extract a precise measurement of the half-life of the double-beta decay mode with neutrinos ($2\nu\beta\beta$) and in order to identify the location of residual impurities. The latter will permit future experiments to build strategies in order to further lower the background and achieve even better sensitivities. In this article the background decomposition prior to analysis cuts is presented for GERDA Phase II. The background model fit yields a flat spectrum in the ROI with a background index (BI) of $16.04^{+0.78}_{-0.85} \cdot 10^{-3}\,$cts/(kg$\cdot$keV$\cdot$yr) for the enriched BEGe data set and $14.68^{+0.47}_{-0.52} \cdot 10^{-3}\,$cts/(kg$\cdot$keV$\cdot$yr) for the enriched coaxial data set. These values are similar to the one of Gerda Phase I despite a much larger number of detectors and hence radioactive hardware components

Modeling of GERDA Phase II data

The GERmanium Detector Array (Gerda) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double-beta (0νββ) decay of 76Ge. The technological challenge of Gerda is to operate in a “background-free” regime in the region of interest (ROI) after analysis cuts for the full 100 kg·yr target exposure of the experiment. A careful modeling and decomposition of the full-range energy spectrum is essential to predict the shape and composition of events in the ROI around Qββ for the 0νββ search, to extract a precise measurement of the half-life of the double-beta decay mode with neutrinos (2νββ) and in order to identify the location of residual impurities. The latter will permit future experiments to build strategies in order to further lower the background and achieve even better sensitivities. In this article the background decomposition prior to analysis cuts is presented for Gerda Phase II. The background model fit yields a flat spectrum in the ROI with a background index (BI) of 16.04+0.78−0.85⋅10−3 cts/(keV·kg·yr) for the enriched BEGe data set and 14.68+0.47−0.52⋅10−3 cts/(keV·kg·yr) for the enriched coaxial data set. These values are similar to the one of Phase I despite a much larger number of detectors and hence radioactive hardware components

The GERDA Neutrinoless-Double-Beta decay experiment

Neutrinoless double beta (0$\nu\beta\beta$)-decay is a key process to gain understanding of the nature of neutrinos. The GErmanium Detector Array (GERDA) is designed to search for 0$\nu\beta\beta$-decay of the isotope $^{76}$Ge. Germanium crystals enriched in $^{76}$Ge, acting as source and detector simultaneously, will be submerged directly into an ultra pure cooling medium that also serves as a radiation shield. This concept will allow for a reduction of the background by up to two orders of magnitudes with respect to earlier experiments. The experiment is currently being installed in hall A of the underground laboratory of the LNGS, INFN in Italy. Data taking is expected to start in 2009

MADMAX: A new Dark Matter Axion Search using a dielectric Haloscope

Axions are an intriguing dark matter candidate, emerging from the Peccei-Quinn solution to the strong CP problem. Current experimental searches for axion dark matter focus on axion masses below 40$\mu$eV. However, if the Peccei-Quinn symmetry is restored after inflation the axion mass is predicted to be in the 100\,$\mu$eV range. A new project based on axion-photon conversion at the transition between different dielectric media is presented. The axion-photon conversion could be enhanced by a factor $\sim 10^5$ over a single mirror by using $\sim 80$ layers of dielectrics. Within a 10 T magnetic field this could be enough to detect $\sim 100$\,$\mu$eV axions with HEMT linear amplifiers. The proposed design for an experiment is discussed. Results from noise, transmissivity and reflectivity measurements in a prototype setup are presented. The expected sensitivity is shown

MADMAX: A new Dark Matter Axion Search using a dielectric Haloscope

Axions are an intriguing dark matter candidate, emerging from the Peccei-Quinn solution to the strong CP problem. Current experimental searches for axion dark matter focus on axion masses below 40$\mu$eV. However, if the Peccei-Quinn symmetry is restored after inflation the axion mass is predicted to be in the 100\,$\mu$eV range. A new project based on axion-photon conversion at the transition between different dielectric media is presented. The axion-photon conversion could be enhanced by a factor $\sim 10^5$ over a single mirror by using $\sim 80$ layers of dielectrics. Within a 10 T magnetic field this could be enough to detect $\sim 100$\,$\mu$eV axions with HEMT linear amplifiers. The proposed design for an experiment is discussed. Results from noise, transmissivity and reflectivity measurements in a prototype setup are presented. The expected sensitivity is shown

MADMAX: A new road to axion dark matter detection

The axion is a hypothetical low-mass boson predicted by the Peccei-Quinn mechanism solving the strong CP problem. It is naturally also a cold dark matter candidate if its mass is below ∼1 meV, thus simultaneously solving two major problems of nature. All existing experimental efforts to detect QCD axions focus on a range of axion masses below ∼25 μeV. The mass range above ∼40 μeV, predicted by modern models in which the Peccei-Quinn symmetry was restored after inflation, could not be explored so far. The MADMAX project is designed to be sensitive for axions with masses (40–400) μeV. The experimental design is based on the idea of enhanced axion-photon conversion in a system with several layers with alternating dielectric constants. The concept and the proposed design of the MADMAX experiment are discussed. Measurements taken with a prototype test setup are discussed. The prospects for reaching sensitivity enough to cover the parameter space predicted for QCD dark matter axions with mass in the range around 100 μeV is presented