The AMS-02 RICH Imager Prototype - In-Beam Tests with 20 GeV/c per Nucleon Ions -

A prototype of the AMS Cherenkov imager (RICH) has been tested at CERN by means of a low intensity 20 GeV/c per nucleon ion beam obtained by fragmentation of a primary beam of Pb ions. Data have been collected with a single beam setting, over the range of nuclear charges 2<Z<~45 in various beam conditions and using different radiators. The charge Z and velocity beta resolutions have been measured.Comment: 4 pages, contribution to the ICRC 200

The AMS-RICH velocity and charge reconstruction

The AMS detector, to be installed on the International Space Station, includes a Ring Imaging Cerenkov detector with two different radiators, silica aerogel (n=1.05) and sodium fluoride (n=1.334). This detector is designed to provide very precise measurements of velocity and electric charge in a wide range of cosmic nuclei energies and atomic numbers. The detector geometry, in particular the presence of a reflector for acceptance purposes, leads to complex Cerenkov patterns detected in a pixelized photomultiplier matrix. The results of different reconstruction methods applied to test beam data as well as to simulated samples are presented. To ensure nominal performances throughout the flight, several detector parameters have to be carefully monitored. The algorithms developed to fulfill these requirements are presented. The velocity and charge measurements provided by the RICH detector endow the AMS spectrometer with precise particle identification capabilities in a wide energy range. The expected performances on light isotope separation are discussed.Comment: Contribution to the ICRC07, Merida, Mexico (2007); Presenter: F. Bara

The RICH detector of the AMS-02 experiment: status and physics prospects

The Alpha Magnetic Spectrometer (AMS), whose final version AMS-02 is to be installed on the International Space Station (ISS) for at least 3 years, is a detector designed to measure charged cosmic ray spectra with energies up to the TeV region and with high energy photon detection capability up to a few hundred GeV. It is equipped with several subsystems, one of which is a proximity focusing RICH detector with a dual radiator (aerogel+NaF) that provides reliable measurements for particle velocity and charge. The assembly and testing of the AMS RICH is currently being finished and the full AMS detector is expected to be ready by the end of 2008. The RICH detector of AMS-02 is presented. Physics prospects are briefly discussed.Comment: 5 pages. Contribution to the 10th ICATPP Conference on Astroparticle, Particle, Space Physics, Detectors and Medical Physics Applications (Como 2007). Presenter: Rui Pereir

The Ring Imaging Cherenkov detector (RICH) of the AMS experiment

The Alpha Magnetic Spectrometer (AMS) experiment to be installed on the International Space Station (ISS) will be equipped with a proximity focusing Ring Imaging Cherenkov (RICH) detector for measuring the electric charge and velocity of the charged cosmic particles. A RICH prototype consisting of 96 photomultiplier units, including a piece of the conical reflector, was built and its performance evaluated with ion beam data. Preliminary results of the in-beam tests performed with ion fragments resulting from collisions of a 158 GeV/c/nuc primary beam of Indium ions (CERN SPS) on a Pb target are reported. The collected data included tests to the final front-end electronics and to different aerogel radiators. Cherenkov rings for a large range of charged nuclei and with reflected photons were observed. The data analysis confirms the design goals. Charge separation up to Fe and velocity resolution of the order of 0.1% for singly charged particles are obtained.Comment: 29th International Conference on Cosmic Rays (Pune, India

A search for low-mass WIMPs with EDELWEISS-II heat-and-ionization detectors

We report on a search for low-energy (E < 20 keV) WIMP-induced nuclear recoils using data collected in 2009 - 2010 by EDELWEISS from four germanium detectors equipped with thermal sensors and an electrode design (ID) which allows to efficiently reject several sources of background. The data indicate no evidence for an exponential distribution of low-energy nuclear recoils that could be attributed to WIMP elastic scattering after an exposure of 113 kg.d. For WIMPs of mass 10 GeV, the observation of one event in the WIMP search region results in a 90% CL limit of 1.0x10^-5 pb on the spin-independent WIMP-nucleon scattering cross-section, which constrains the parameter space associated with the findings reported by the CoGeNT, DAMA and CRESST experiments.Comment: PRD rapid communication accepte

Final results of the EDELWEISS-II WIMP search using a 4-kg array of cryogenic germanium detectors with interleaved electrodes

The EDELWEISS-II collaboration has completed a direct search for WIMP dark matter with an array of ten 400-g cryogenic germanium detectors in operation at the Laboratoire Souterrain de Modane. The combined use of thermal phonon sensors and charge collection electrodes with an interleaved geometry enables the efficient rejection of gamma-induced radioactivity as well as near-surface interactions. A total effective exposure of 384 kg.d has been achieved, mostly coming from fourteen months of continuous operation. Five nuclear recoil candidates are observed above 20 keV, while the estimated background is 3.0 events. The result is interpreted in terms of limits on the cross-section of spin-independent interactions of WIMPs and nucleons. A cross-section of 4.4x10^-8 pb is excluded at 90%CL for a WIMP mass of 85 GeV. New constraints are also set on models where the WIMP-nucleon scattering is inelastic.Comment: 23 pages, 5 figures; matches published versio

Background studies for the EDELWEISS dark matter experiment

The EDELWEISS-II collaboration has completed a direct search for WIMP dark matter using cryogenic Ge detectors (400 g each) and 384 kg$\times$days of effective exposure. A cross-section of $4.4 \times 10^{-8}$ pb is excluded at 90% C.L. for a WIMP mass of 85 GeV. The next phase, EDELWEISS-III, aims to probe spin-independent WIMP-nucleon cross-sections down to a few $\times10^{-9}$ pb. We present here the study of gamma and neutron background coming from radioactive decays in the set-up and shielding materials. We have carried out Monte Carlo simulations for the completed EDELWEISS-II setup with GEANT4 and normalised the expected background rates to the measured radioactivity levels (or their upper limits) of all materials and components. The expected gamma-ray event rate in EDELWEISS-II at 20-200 keV agrees with the observed rate of 82 events/kg/day within the uncertainties in the measured concentrations. The calculated neutron rate from radioactivity of 1.0-3.1 events (90% C.L.) at 20-200 keV in the EDELWEISS-II data together with the expected upper limit on the misidentified gamma-ray events ($\le0.9$), surface betas ($\le0.3$), and muon-induced neutrons ($\le0.7$), do not contradict 5 observed events in nuclear recoil band. We have then extended the simulation framework to the EDELWEISS-III configuration with 800 g crystals, better material purity and additional neutron shielding inside the cryostat. The gamma-ray and neutron backgrounds in 24 kg fiducial mass of EDELWEISS-III have been calculated as 14-44 events/kg/day and 0.7-1.4 events per year, respectively. The results of the background studies performed in the present work have helped to select better purity components and improve shielding in EDELWEISS-III to further reduce the expected rate of background events in the next phase of the experiment.Comment: 15 pages, 9 figures, to be published in Astroparticle Physic