Micromegas for Imaging Calorimetry

International audienceTwo Micromegas chambers of 1 m2 size and 1 cm2 cell segmentation have recently been built. Designed for Particle-Flow hadron calorimetry, each chamber features ten thousand channels with embedded front-end electronics and three readout thresholds (concept of semi-digital hadron calorimeter or SDHCAL). The chambers have been tested in a muon beam and also exposed to hadron showers inside a steel structure. Excellent performance such as low noise, high efficiency and very uniform spatial response have been measured and will be reported. The measurements will be confronted to the predictions of a Monte Carlo simulation for which a complete digitisation procedure has been established. Finally, prospects towards the use of a Micromegas SDHCAL at a future linear collider will be discussed based on the scalability of current prototypes to larger sizes and on the expected energy resolution and linearity of such a device

RD51, a world-wide collaboration for the development of Micro Pattern Gaseous Detectors

International audienceOriginally introduced to improve the rate capability of traditional wire chambers, Micro Pattern Gaseous Detectors (MPGD) actually demonstrate many more benefits. Be it for medical and industry imaging, collider experiments or more interestingly in the framework of this conference for the search of rare events, they are the subject of constant research and development in several laboratories over the world. The RD51 collaboration has been coordinating this work since April 2008 and is meant to advance the technological development and application of MPGD. The collaboration is presented and emphasis is put on its latest achievements which do make these devices an attractive option for the detection of low energy rare events: the possibility to instrument large area and to detect UV photons

Monte carlo study of the physics performance of a digital hadronic calorimeter

A digital hadronic calorimeter using MICROMEGAS as active elements is a very promising choice for particle physics experiments at future lepton colliders. These experiments will be optimized for application of the particle flow algorithm and therefore require calorimeters with very fine lateral segmentation. A 1 m2 prototype based on MICROMEGAS chambers with 1x1 cm2 readout pads is currently being developed at LAPP. The GEANT4 simulation of the physics performance of a MICROMEGAS calorimeter is presented. The main characteristics, such as energy resolution, linearity and shower profile, have been carefully examined for various passive materials with pions over a wide energy range from 3 to 200 GeV. The emphasis is put on the comparison of the analog and digital readout.Comment: 8 pages, 5 figures, MPGD09 conferenc

A Radiation Imaging Detector Made by Postprocessing a Standard CMOS Chip

An unpackaged microchip is used as the sensing element in a miniaturized gaseous proportional chamber. Thisletter reports on the fabrication and performance of a complete radiation imaging detector based on this principle. Our fabrication schemes are based on wafer-scale and chip-scale postprocessing.\ud Compared to hybrid-assembled gaseous detectors, our microsystem shows superior alignment precision and energy resolution, and offers the capability to unambiguously reconstruct 3-D radiation tracks on the spot.\u

Status of the Micromegas semi-DHCAL

The activities towards the fabrication and test of a 1 m3 semi-digital hadronic calorime- ter are reviewed. The prototype sampling planes would consist of 1 m2 Micromegas chambers with 1 cm2 granularity and embedded 2 bits readout suitable for PFA calorime- try at an ILC detector. The design of the 1 m2 chamber is presented first, followed by an overview of the basic performance of small prototypes. The basic units composing the 1 m2 chamber are 32 \times 48 cm2 boards with integrated electronics and a micro-mesh. Results of character- ization tests of such boards are shown. Micromegas as a proportional detector is well suited for semi-digital hadronic calorimetry. In order to quantify the gain in perfor- mance when using one or more thresholds, simulation studies are being carried out, some of which will be reported in this contribution

Multistage Zeeman deceleration of atomic and molecular oxygen

Multistage Zeeman deceleration is a technique used to reduce the velocity of neutral molecules with a magnetic dipole moment. Here we present a Zeeman decelerator that consists of 100 solenoids and 100 magnetic hexapoles, that is based on a short prototype design presented recently [Phys. Rev. A 95, 043415 (2017)]. The decelerator features a modular design with excellent thermal and vacuum properties, and is robustly operated at a 10 Hz repetition rate. This multistage Zeeman decelerator is particularly optimized to produce molecular beams for applications in crossed beam molecular scattering experiments. We characterize the decelerator using beams of atomic and molecular oxygen. For atomic oxygen, the magnetic fields produced by the solenoids are used to tune the final longitudinal velocity in the 500 - 125 m/s range, while for molecular oxygen the velocity is tunable in the 350 - 150 m/s range. This corresponds to a maximum kinetic energy reduction of 95% and 80% for atomic and molecular oxygen, respectively.Comment: Latest version as accepted by Physical Review

Readout of GEM Detectors Using the Medipix2 CMOS Pixel Chip

We have operated a Medipix2 CMOS readout chip, with amplifying, shaping and charge discriminating front-end electronics integrated on the pixel-level, as a highly segmented direct charge collecting anode in a three-stage gas electron multiplier (Triple-GEM) to detect the ionization from $^{55}$Fe X-rays and electrons from $^{106}$Ru. The device allows to perform moderate energy spectroscopy measurements (20 % FWHM at 5.9 keV $X$-rays) using only digital readout and two discriminator thresholds. Being a truly 2D-detector, it allows to observe individual clusters of minimum ionizing charged particles in $Ar/CO_2$ (70:30) and $He/CO_2$ (70:30) mixtures and to achieve excellent spatial resolution for position reconstruction of primary clusters down to $\sim 50 \mu m$, based on the binary centroid determination method.Comment: 18 pages, 14 pictures. submitted to Nuclear Instruments and Methods in Physics Research

Environmental study of a Micromegas detector

We report on measurements of the basic performance of a Micromegas detector for a digital hadronic calorimeter. Electron collection efficiency, energy resolution and gas gain were measured in various mixtures of Ar and CO2. Also the dependence of the gain on environmental variables (pressure, temperature), gas parameters (flow, mixing ratio) and geometry (amplication gap size) is studied. Eventually, predictions on the impact of these variables on the detection efficiency of thin Micromegas detectors are drawn

Test in a beam of large-area Micromegas chambers for sampling calorimetry

Application of Micromegas for sampling calorimetry puts specific constraints on the design and performance of this gaseous detector. In particular, uniform and linear response, low noise and stability against high ionisation density deposits are prerequisites to achieving good energy resolution. A Micromegas-based hadronic calorimeter was proposed for an application at a future linear collider experiment and three technologically advanced prototypes of 1$\times$1 m$^{2}$ were constructed. Their merits relative to the above-mentioned criteria are discussed on the basis of measurements performed at the CERN SPS test-beam facility