M. Slunečka

Detection of single photons with ThickGEM-based counters

The photon detectors based on MPGD (MicroPattern Gaseous Detector) represent the new generation of gaseous photon detectors. We report about an R&D programme dedicated to study both the principles and the engineering aspects of photon detectors based on Thick GEMs (THGEM) electron multipliers coupled to a CsI photoconverting coating. The goal is the development of a gaseous detector of single UV photons, able to stably operate at high gain and high rate, to provide good time resolution and insensitive to magnetic field to be used in the Cherenkov imaging counter RICH-1 of the COMPASS experiment at CERN SPS.

Ion backflow in thick GEM-based detectors of single photons

Photon detectors based on micropattern gas detectors represent a new generation of gaseous photon detectors. In the context of a project to upgrade the gas photon detectors of COMPASS RICH-1, we are performing an R&D programme aimed both to establish the principles and to develop the engineering aspects of photon detectors based on multi-layer arrangements of thick GEMs electron multipliers coupled to a CsI photoconverter. In this context, a reduced rate of the backflow of the positive ions generated in the multiplication process is required to overcome the critical issues related to the bombardment of the CsI photoconverter by ions. Our studies devoted to develop detector architectures able to provide reduced ion backflow rates are reported.

Read-out of scintillating fibres using a weak cross-talk position-sensitive photomultiplier

Abstract Fast and precise readout of scintillating fibres (SciFi) has a great potential for fast tracking and triggering at high-luminosity particle physics experiments. In the framework of the RD-17 experiment at CERN (FAROS) significant milestones in the development of SciFi detectors using position-sensitive photomultipliers have been achieved. Results obtained with a weak cross-talk multi-anode photomultiplier, Philips XP1724, and a parallel readout of the anodes are reported. With 0.5 mm diameter fibres a spatial resolution of about 125 μm and a detection efficiency in excess of 95% have been obtained. The time dispersion of signals from individual photomultiplier channels has been estimated to be about 1 ns. The possibility of digitising the track position in real time by a peak-sensing circuit is studied for the first time

Progresses in the production of large-size THGEM boards

The THicK GEM (THGEM) electron multipliers are derived from the GEM design, by scaling the geometrical parameters and changing the production technology. Small-size (a few cm2) detectors exhibit superb performance, while larger ones exhibit gain response and uniformity limitations. We have studied with a systematic approach several aspects concerning the material (type and thickness of the fibreglass plates) and the production procedure, in particular the cleaning and polishing stages. The net result is the production of large THGEM multipliers reproducing the performance of the small ones. We report in detail about the studies and the results.

The gain in Thick GEM multipliers and its time-evolution

In the context of a project to upgrade the gas photon detectors of COMPASS RICH-1, we have performed an R&D programme aimed to develop photon detectors based on multi-layer arrangements of thick GEM electron multipliers coupled to a CsI photoconverter. For this purpose, thick GEMs have been characterised in detail including the gain performance, its dependance on the geometrical parameters and its time-evolution, a feature exhibited by the gas detectors with open insulator surfaces. The variation due to this evolution drammatically depends on the parameters themselves. In the present article we summarise the outcomes of the studies dedicated to the thick GEM gain and its evolution versus time. We also include a qualitative model which accounts for the peculiar details of the observed thick GEM gain time-evolution.

Status and progress of novel photon detectors based on THGEM and hybrid MPGD architectures

Recent progress in the development of THGEM-based photon detectors confirm the validity of this novel technology. Detectors made of THGEMs, arranged in a three layer architecture, with a CsI coating on the first layer (acting as a reflective photocathode), have been produced and operated in laboratory and during test beam runs: they provide a gain of 105 and a time resolution better than 10 ns. Improvements in the production of THGEMs with 300 ? 300 mm2 active area have recently been introduced leading to a uniform gain response and performance similar to that provided by the small area THGEMs. Promising results have been obtained by combining THGEM and Micromegas technologies to form a hybrid MPGD-based photon detector: the first prototype has proved to stably operate at large gain in a variety of gas mixtures, including pure CH4 and to provide a low ion backflow rate. The RICH-1 detector of the COMPASS Experiment at CERN SPS will be equipped with a set of MPGD-based photon detectors replacing MWPC-based ones.

Spin physics with antiprotons

New possibilities arising from the availability at GSI of antiproton beams, possibly polarised, are discussed. The investigation of the nucleon structure can be boosted by accessing in Drell-Yan processes experimental asymmetries related to cross-sections in which the parton distribution functions (PDF) only appear, without any contribution from fragmentation functions; such processes are not affected by the chiral suppression of the transversity functionh1(x). Spin asymmetries in hyperon production and Single Spin Asymmetries are discussed as well, together with further items like electric and magnetic nucleonic form factors and open charm production. Counting rates estimations are provided for each physical case. The sketch of a possible experimental apparatus is proposed.

MPGD-based counters of single photons developed for COMPASS RICH-1

In fundamental research, gas detectors of single photons are a must in the field of Cherenkov imaging techniques (RICH counters) for particle identification in large momentum ranges and with wide coverage of the phase space domain. These counters, already extensively used, are foreseen in the setups of future experiments in a large variety of fields in nuclear and particle physics. The quest of novel gaseous photon detector is dictated by the fact that the present generation of detectors has unique characteristics concerning operation in magnetic field, low material budget and cost, but it suffers of severe limitations in effective efficiency, rates, life time and stability, discouraging their use in high precision and high rate experiments. We are developing large size THick GEM (THGEM)-based detector of single photons. The RD relevant progress in the engineering aspects, in particular related to the production of large-size THGEMs, where the strict correlation between the local gain-value and the local thickness-value has been demonstrated the operation of a 300 mm × 300 mm2 active area detector at the CERN PS T10 test beam; the introduction of a new hybrid detector architecture offering promising indication, which is formed by a THGEM layer which acts as CsI support and pre-amplification device followed by a MICROMEGAS multiplication stage. The general status of the R&D program and the recent progress are reported

Scintillating fibre detectors using position-sensitive photomultipliers

Scintillating fibre technology has made substantial progress, and has demonstrated great potential for fast tracking and triggering at high luminosity experiments in Particle Physics. This talk presents some recent issues of the RD-17 project at CERN for fast and precise readout of scintillating fibre arrays, as well as for upgrade of position-sensitive photomultipliers. Excellent matching of scintillating fibre and position-sensitive photomultiplier, in particular in time characteristics, allowed to realise high detector performances, typically represented by spatial resolution of ∼ 125 μm as well as time resolution better than 1 ns with detection efficiency greater than 95 %.

Hybrid MPGD-based detectors of single photons for the upgrade of COMPASS RICH-1

A seven year-long R&D programme has been performed and the resulting detector architecture is a hybrid MPGD including two THick GEM (THGEM) multiplication stages followed a MICROMEGAS. The first THGEM board forms the photocathode support: its upper face is CsI coated. The properties of THGEM-based photocathodes have been studied in details. The two THGEM layers act as pre-amplification stages and, thanks to a staggered configuration, namely by the misalignment of the holes of the two THGEMs, the electron shower produced in the pre-amplification phase is distributed onto a larger surface portion of the following MICROMEGAS unit, where the final multiplication takes place: it is so possible to operate at gains as high as 105 and more even in radioactive environments. COMPASS RICH-1 is a large-size Cherenkov imaging counter with gaseous radiator for hadron identification up to 50 GeV/c. The construction of a set of large-size (unit size: 60×60 cm2) gaseous photon detectors based on the hybrid MPGD architecture for the upgrade of COMPASS RICH-1 is ongoing and the upgraded detector will be in operation in 2016. The R&D studies, the engineering aspects and the construction challenges are presented.