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

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

In Search of WISPs

Experiments such as MADMAX, IAXO and ALPS II are expanding the search for axions and other weakly interacting ‘slim’ particles that could hail from far above the TeV scale, write Axel Lindner, Béla Majorovits and Andreas Ringwald

Development, Integration, and Test of the MACQU Demo Coil Toward MADMAX Quench Analysis

The MADMAX project aims at detecting axion dark matter in the mass range of 100 μeV. To facilitate axion to photon conversion with detectable rate a superconducting dipole magnet with a large bore is needed. The MADMAX dipole magnet has to generate ~9 T in a 1.35 m aperture over ~1.3 m in length. A key challenge for a magnet made of a cable in-conduit conductor (CICC), operating at 1.8 K with an indirect bath cooling is the quench detection. In order to validate feasibility, a mock-up coil with a quench behavior scalable to MADMAX was designed and produced. This mock-up was used to benchmark numerical simulations of the quench in the THEA code. The paper gives an overview of the technicaldetails of the MACQU test coil. The conductor, the magnet, the busbar and the supporting and cryogenic systems were designed at CEA. The cable was manufactured in China at the Chang Tong INC from WST Nb-Ti strands, the insertion and compaction was achieved in the ASIPP institute with a copper profile from Aurubis. The winding of the coil and the busbar pre-forming were performed at Bilfinger Noell as well as the assembly of the supporting structure and the thermal shield. The magnet was integrated in the JT60 test station at CEA Saclay and extensively tested