H. Deschamps

Identification of backgrounds in the EDELWEISS-I dark matter search experiment

Abstract This paper presents our interpretation and understanding of the different backgrounds in the EDELWEISS-I data sets. We analyze in detail the several populations observed, which include gammas, alphas, neutrons, thermal sensor events and surface events, and try to combine all data sets to provide a coherent picture of the nature and localization of the background sources. In light of this interpretation, we draw conclusions regarding the background suppression scheme for the EDELWEISS-II phase.

Fast photon detection for particle identification with COMPASS RICH-1

Particle identification at high rates is an important challenge for many current and future high-energy physics experiments. The upgrade of the COMPASS RICH-1 detector requires a new technique for Cherenkov photon detection at count rates of several

Pattern recognition and PID for COMPASS RICH-1

10^6

The fast readout system for the MAPMTs of COMPASS RICH-1

per channel in the central detector region, and a read-out system allowing for trigger rates of up to 100 kHz. To cope with these requirements, the photon detectors in the central region have been replaced with the detection system described in this paper. In the peripheral regions, the existing multi-wire proportional chambers with CsI photocathode are now read out via a new system employing APV pre-amplifiers and flash ADC chips. The new detection system consists of multi-anode photomultiplier tubes (MAPMT) and fast read-out electronics based on the MAD4 discriminator and the F1-TDC chip. The RICH-1 is in operation in its upgraded version for the 2006 CERN SPS run. We present the photon detection design, constructive aspects and the first Cherenkov light in the detector.

Fast photon detection for the COMPASS RICH detector

Abstract A package for pattern recognition and PID by COMPASS RICH-1 has been developed and used for the analysis of COMPASS data collected in the years 2002–2004, and 2006–2007 with the upgraded RICH-1 photon detectors. It has allowed the full characterization of the detector in the starting version and in the upgraded one as well as the PID for physics results. We report about the package structure and algorithms, and the detector characterization and PID results.

A highly integrated low-cost readout system for the COMPASS RICH-1 detector

A fast readout system for the upgrade of the COMPASS RICH detector has been developed and successfully used for data taking in 2006 and 2007. The new readout system for the multi-anode PMTs in the central part of the photon detector of the RICH is based on the high-sensitivity MAD4 preamplifier-discriminator and the dead-time free F1-TDC chip characterized by high-resolution. The readout electronics has been designed taking into account the high photon flux in the central part of the detector and the requirement to run at high trigger rates of up to 100 kHz with negligible dead-time. The system is designed as a very compact setup and is mounted directly behind the multi-anode photomultipliers. The data are digitized on the front-end boards and transferred via optical links to the readout system. The readout electronics system is described in detail together with its measured performances.

Towards a Background-Free ββ-Decay Experiment Using the EDELWEISS Cryogenic Ge Detectors

Particle identification at high rates is a central aspect of many present and future experiments in high-energy particle physics. The COMPASS experiment at the SPS accelerator at CERN uses a large scale Ring Imaging CHerenkov detector (RICH) to identify pions, kaons and protons in a wide momentum range. For the data taking in 2006, the COMPASS RICH has been upgraded in the central photon detection area (25% of the surface) with a new technology to detect Cherenkov photons at very high count rates of several 10 6 s −1 per channel and a new dead-time free read-out system, which allows trigger rates up to 100 kHz. The Cherenkov photons are detected by an array of 576 visible and ultra-violet sensitive multi-anode photomultipliers with 16 channels each. Lens telescopes of fused silica lenses have been designed and built to focus the Cherenkov photons onto the individual photomultipliers. The read-out electronics of the PMTs is based on the MAD4 amplifier-discriminator chip and the dead-time free high resolution F1-TDC. The 120 ps time resolution of the digital card guarantees negligible background from uncorrelated physical events. In the outer part of the detector, where the particle rates are lower, the present multi-wire proportional chambers (MWPC) with Cesium Iodide photo-cathodes have been upgraded with a new read-out electronic system based on the APV preamplifier and shaper ASIC with analog pipeline and sampling ADCs. The project was fully designed and implemented in the period November 2004 until May 2006. The upgraded detector showed an excellent performance during the 2006 data taking: the number of detected Cherenkov photons per ring was increased from 14 to above 60 at saturation. The time resolution was improved from about 3 microseconds to about one nanosecond which allows an excellent suppression of the background photons from uncorrelated events.

LATEST RESULTS OF THE EDELWEISS EXPERIMENT

Particle identification at high multiplicities is a key feature of the COMPASS experiment at CERNs SPS. Hadrons up to 50 GeV/c are identified by a RICH detector with a large horizontal and vertical acceptance of plusmn250 mrad and plusmn180 mrad, respectively. The central region of the photon detector is equipped with multi-anode photomultiplier tubes, the remaining 75% of the total active area are covered by MWPCs with Csl photocathodes. In order to improve the performance of the detector at very high beam intensities, more than 62000 channels of a new analog readout system of the MWPCs, based on the APV25 chip, were developed and installed in 2006. The new system features good single photon detection efficiency due to its low noise, negligible dead time at trigger rates up to 50 kHz, and low cost. In addition, sampling of the MWPC signal allows us to measure the signal time with a resolution of about 30 ns or better. The architecture of the new readout system as well as the performance results of the RICH-1 detector in the outer region during 2006 COMPASS run will be discussed.

Read-out electronics for fast photon detection with COMPASS RICH-1

The present generation of double-beta experiments is limited by two main backgrounds: surface alpha interactions and Compton interactions from high-energy gamma-ray lines. Using the detector developments realized for the EDELWEISS Dark Matter experiment, we propose a strategy to eliminate completely the alpha radioactivity background and to reduce by nearly two orders of magnitude the Compton background. This would lead to a nearly background-free experiment, and an effective neutrino mass sensitivity of 15 meV achieved in three years with a one-ton array of ionisation-heat 76Ge detectors. In a first stage, the existence of the double-beta 0 -υ Heidelberg candidate could be tested in a few years in the EDELWEISS-II cryostat.

Design and construction of the fast photon detection system for COMPASS RICH-1

The EDELWEISS experiment is a direct detection Dark Matter Search, under the form of WIMPs. It uses heat and ionization Ge cryogenic detectors. We present the latest results obtained by the experiment with three new 320g bolometers. At present, EDELWEISS I is the most sensitive experiment for all WIMP masses compatible with accelerator constraints (Mwimp>30 GeV/c^2). We also briefly describe the status of the second stage EDELWEISS II involving initially 10 kg of detectors aiming a gain of two orders of magnitude in sensitivity.