No Arabic abstract
New Micromegas (Micro-mesh gaseous detectors) are being developed in view of the future physics projects planned by the COMPASS collaboration at CERN. Several major upgrades compared to present detectors are being studied: detectors standing five times higher luminosity with hadron beams, detection of beam particles (flux up to a few hundred of kHz/mm^{2}, 10 times larger than for the present Micromegas detectors) with pixelized read-out in the central part, light and integrated electronics, and improved robustness. Two solutions of reduction of discharge impact have been studied, with Micromegas detectors using resistive layers and using an additional GEM foil. Performance of such detectors has also been measured. A large size prototypes with nominal active area and pixelized read-out has been produced and installed at COMPASS in 2010. In 2011 prototypes featuring an additional GEM foil, as well as an resistive prototype, are installed at COMPASS and preliminary results from those detectors presented very good performance. We present here the project and report on its status, in particular the performance of large size prototypes with an additional GEM foil.
New Micromegas (Micro-mesh gaseous detectors) are being developed in view of the future physics projects planned by the COMPASS collaboration at CERN. Several major upgrades compared to present detectors are being studied: detectors standing five times higher luminosity with hadron beams, detection of beam particles (flux up to a few hundred of kHz/mm^2, 10 times larger than for the present detectors) with pixelized read-out in the central part, light and integrated electronics, and improved robustness. Studies were done with the present detectors moved in the beam, and two first pixelized prototypes are being tested with muon and hadron beams in real conditions at COMPASS. We present here this new project and report on two series of tests, with old detectors moved into the beam and with pixelized prototypes operated in real data taking condition with both muon and hadron beams.
The current state of the art in fast timing resolution for existing experiments is of the order of 100 ps on the time of arrival of both charged particles and electromagnetic showers. Current R&D on charged particle timing is approaching the level of 10 ps but is not primarily directed at sustained performance at high rates and under high radiation (as would be needed for HL-LHC pileup mitigation). We demonstrate a Micromegas based solution to reach this level of performance. The Micromegas acts as a photomultiplier coupled to a Cerenkov-radiator front window, which produces sufficient UV photons to convert the ~100 ps single-photoelectron jitter into a timing response of the order of 10-20 ps per incident charged particle. A prototype has been built in order to demonstrate this performance. The first laboratory tests with a pico-second laser have shown a time resolution of the order of 27 ps for ~50 primary photoelectrons, using a bulk Micromegas readout.
A low background Micromegas detector has been operating in the CAST experiment at CERN for the search of solar axions during the first phase of the experiment (2002-2004). The detector, made out of low radioactivity materials, operated efficiently and achieved a very low level of background rejection (5 x 10^-5 counts/keV/cm^2/s) without shielding.
The NA61 Experiment at CERN SPS is a large acceptance hadron spectrometer, aimed to studying of hadron-hadron, hadron-nucleus, and nucleus-nucleus interactions in a fixed target environment. The present paper discusses the construction and performance of the Low Momentum Particle Detector (LMPD), a small time projection chamber unit which has been added to the NA61 setup in 2012. The LMPD considerably extends the detector acceptance towards the backward region, surrounding the target in hadron-nucleus interactions. The LMPD features simultaneous range and ionization measurements, which allows for particle identification and momentum measurement in the 0.1-0.25 GeV/c momentum range for protons. The possibility of Z=1 particle identification in this range is directly demonstrated.
The MicroMegas technology was selected by the ATLAS experiment at CERN to be adopted for the Small Wheel upgrade of the Muon Spectrometer, dedicated to precision tracking, in order to meet the requirements of the upcoming luminosity upgrade of the Large Hadron Collider. A large surface of the forward regions of the Muon Spectrometer will be equipped with 8 layers of MicroMegas modules forming a total active area of $1200,m^{2}$. The New Small Wheel is scheduled to be installed in the forward region of $1.3<vert eta vert <2.7$ of the ATLAS detector during the second long shutdown of the Large Hadron Collider. The New Small Wheel will have to operate in a high background radiation environment, while reconstructing muon tracks as well as furnishing information for the Level-1 trigger. The project requires fully efficient MicroMegas chambers with spatial resolution down to $100,{mu}m$, a rate capability up to about $15,kHz/cm^{2}$ and operation in a moderate (highly inhomogeneous) magnetic field up to $B=0.3,T$. The required tracking is linked to the intrinsic spatial resolution in combination with the demanding mechanical accuracy. An overview of the design, construction and assembly procedures of the MicroMegas modules will be reported.