Y. Giomataris

Micromegas, a multipurpose gaseous detector

In this paper the advantages of a new gaseous detector. Micromegas, are described. Some of its properties are given and the consequences are out-lined in a series of experiments related to charged particle localization, neutron imaging, gamma or X-ray imaging.

Study of sparking in Micromegas chambers

Abstract The discharge properties of Micromegas detector are studied in detail. Tests have demonstrated that the origin of discharges in hadron beams is mainly associated with nuclear interactions of the incident particle with the gas of the detector. Use of low average Z gas mixtures diminishes the spark rate. The streamer discharge model of Raether has been proved to be valid for this detector. A detector polarization which minimizes the spark energy is proposed. Gas and geometry factors improving the discharge limit are discussed.

Some studies of the applications of CsI photocathodes in gaseous detectors

Abstract Cesium-iodide photocathodes have been investigated in combination with gaseous detectors. The quantum efficiency of a semi-transparent CsI photocathode has been measured in the UV range and found to be 10% at 140 nm. We report experimental results obtained with such photocathodes coupled to BaF2 and KMgF3 scintillators and read out by parallel-plate gaseous detectors.

A trigger for beauty

The possibility of B-meson experiments, in a fixed-target high-energy proton machine (Tevatron) is discussed. Compared to a B-meson factory experiment, it can produce 105 BBs per hour, using 108 protons per second, but it suffers from high background and needs high selectivity to cope with the million times higher interaction rate. To overcome these difficulties a technique called the “optical trigger for beauty” is proposed, based on the detection of Cherenkov photons produced in a 2 mm thick LiF crystal, through a fast photodetector. Its virtue is that it is opaque to minimum-bias events originating in a small target, but sensitive to the high impact parameter B-meson decay charged particles from a secondary vertex. Calculations and first simulations results give a good efficiency for B-meson detection. A multistep trigger, combining the “optical trigger” and a tracking detector, allows significant selection and a consequent enrichment of the data sample. Taking into account its fast response (∼ 1 ns), the above considerations can be extended to other hadronic machines, especially those with high-rate environments such as the LHC or SSC.

New generation of Cherenkov counters

Abstract Experimental results with a parallel plate avalanche chamber (PPAC) having a CsI photocathode and pad array readout are reported. High gains in excess of 105 have been obtained with He gas at atmospheric pressure and traces of CH4 or CF4 quencher. Such light gas mixtures extend the transparency for the Cherenkov light to the extreme UV region and allow detector operation with very low sensitivity to the ionization produced by minimum ionizing particles. A hadron blind detector (HBD) is discussed which exploits the broad photon energy bandwidth (≈ 10 eV) and the high Cherenkov threshold (pπ = 15 GeV). This fast detector, since it has a good spatial resolution, can be used at the future Large Hadron Collider (LHC) or the Superconductivity Super Collider (SSC) either as an efficient electron tagger, rejecting hadrons faking electrons in the calorimeter, or as a pretracker giving fast electron and high-energy muon signature and momentum estimation. Other potential applications in the domain of Cherenkov light detection are also discussed.

Experimental study of an impact-parameter optical discriminator

Abstract An optical discriminator, sensitive to the impact parameter has been tested in a particle beam. The device is based on the detection of Cherenkov light produced and trapped in a thin spherical crystal shell viewed by a fast photodetector. The detector is only sensitive to charged particles with a nonzero impact parameter relative to the centre of the crystal sphere. A prototype using a LiF crystal has been tested and the experimental results are in agreement with expectations. We outline the foreseen developments in order to use such a detector for a fast selection of B events in fixed-target experiments at proton accelerators. We also discuss the use of the detector as presently conceived for the fast selection of strange particles.

Performance of MICROMEGAS with preamplification at high intensity hadron beams

We present systematic studies of efficiency-rate characteristics of the MICROMEGAS detector in high-intensity hadron beams. The discharge probability has been studied as a function of the gain for several gas mixtures. Using a full tracking system of several MICROMEGAS chambers we measured simultaneously the gain, the efficiency, the spatial resolution and the sparking probability. We are discussing the various issues, with single and double amplification, for the use of this detector in future high-rate hadron accelerators.

Results of a first beam test of hadron blind trackers

Abstract We describe the experimental results of a new type of electron tracker, called Hadron Blind Detector or HBD. An HBD prototype was tested with gas mixtures of CF4 with He or Ne and a parallel plate avalanche chamber having a CsI photocathode of eight pads. Beam tests confirm the large Cherenkov light bandwidth in the EUV region that can be obtained with such gas mixtures. It results in a large quality factor of about 500 cm−1 which allows HBD operation with a much shorter radiator thickness than conventional Cherenkov counters. Full electron efficiency was obtained, while pions were rejected up to momenta of 9 GeV/c. HBD is unique in measuring electron trajectories near the vertex, vetoing Dalitz pairs, and providing trigger on electrons among heavy hadron background. We discuss the use of such detectors for lepton identification and detection in high energy physics experiments and especially in heavy ion colliders.

RD30 - study of an optical trigger proposed for a beauty search in fixed target mode at the LHC

Abstract The optical discriminator is based on the detection of Cherenkov light produced and trapped in a thin, spherical, crystal shell. It is only sensitive to charged particles with a non-zero impact parameter relative to the centre of the crystal sphere. The properties of this device, the results of tests in a particle beam and the expected performance in a fast selection of B events in fixed target experiments are reported.

The optical trigger for beauty research, recent developments and perspectives

An optical detector sensitive to impact parameter has been tested in a particle beam. The device is based on the detection of Cerenkov light produced and trapped in a thin spherical crystal shell viewed by a fast photodetector. The detector is only sensitive to charged particles with a non‐zero impact parameter relative to the center of the crystal sphere. A prototype using a LiF 3 mm thick crystal has been tested and the experimental results are in agreement with the expectations. We discuss applications of this detector for fast selection of B‐events in fixed target experiments at proton accelerators. A program of technical development has started, aiming at a high efficiency in B‐meson pairs and a rejection factor of 100 against unwanted minimum bias events. We also present a modified collider configuration, the Asymmetric Tilted Collider, to optimize the sensitivity and the efficiency of a B‐meson experiment.