A. Brez

THE MICRO-GAP CHAMBER

Abstract The micro-gap chamber (MGC), a new type of position sensitive proportional gas counter, is introduced. The device is built using microelectronics technology. In this detector the separation between the electrodes collecting the avalanche charge (the anode-cathode gap) is only a few microns. The time it takes to collect the positive ions is therefore very short ( ≈ 10 ns). The speed of the device now equals that of solid state detectors but it is more than three orders of magnitude higher than in standard proportional counters and one order of magnitude higher than in the recently introduced microstrip gas chamber (MSGC). As a result, the rate capability is extremely high (> 9×10 6 c /mm 2 s). The amplifying electric field around the thin anode microstrip extends over a small volume but is very intense (270 kV/mm). It provides a gas gain of 2.5 × 10 3 at 400 V with 14% (FWHM) energy resolution at 5.4 keV. The anode pitch is 100 μm and the readout is intrinsically two-dimensional. Because there is practically no insulating material in view, charging was not observed even at the highest rate. This device seems very well suited for instrumentation of the tracking system at the new hadron colliders (LHC/SSC) as well as in many other fields of research.

A microstrip gas avalanche chamber with two-dimensional readout

A microstrip gas avalanche chamber with a 200 μm anode pitch has been built and successfully tested in our laboratory. A gas gain of 104 and an energy resolution of 18% (FWHM) at 6 keV have been measured using a gas mixture of argon-CO2 at atmospheric pressure. A preliminary measurement of the positional sensitivity indicates that a spatial resolution of 50 μm can be obtained.

First results on proton extraction from the CERN SPS with a bent crystal

Abstract The feasibility of extracting protons from the halo of a high energy beam by means of a bent silicon crystal has been investigated. Protons diffusing from a GeV beam circulating in the SPS at CERN have been extracted at an angle of 8.5 mrad. Efficiencies of abour 10 percent, orders of magnitude higher than the values achieved previously, have been measured. The present results are promising in view of beam extraction from future multi-TeV proton accelerators.

The WELL detector

Abstract We introduce the WELL detector, a new type of position-sensitive gas proportional counter produced using advanced Printed Circuit Board (PCB) technology. The WELL is based on a thin kapton foil, copper-clad on both sides. Charge amplifying micro-wells are etched into the first metal and kapton layers. These end on a micro-strip pattern which is defined on the second metal plane. The array of micro-strips is used for read-out to obtain 1-D positional information. First results from our systematic assessment of this device are reported.

A microstrip gas chamber with true two-dimensional and pixel readout

A true two-dimensional μstrip gas chamber has been constructed and successfully tested. This new detector has an effective substrate thickness of less than 2 μm. An ion implanted oxide layer of 1.8 μm thickness provides the necessary insulation between the front and back plane and permits collection on the back electrodes of a large fraction of the induced charge. The back electrode signal is used to measure the coordinate along the anode strips (X-Y readout) or to provide true space points (pixel readout). Very good imaging capabilities have been obtained in both cases. A flux of 107 particles/mm2 s has been measured without significant gain loss. No charging effect has been observed after three days continuously running at a flux of 104 particles/mm2 s, while a 15% gain loss, probably due to ageing effects, has been measured after collection on the strips of a charge corresponding to the more than six years of running at the design luminosity of LHC, at 50 cm from the beam axis.

The micro-groove detector

We introduce the Micro-Groove Detector (MGD), a new type of two-dimensional position-sensitive gas proportional counter produced using advanced Printed Circuit Board (PCB) technology. The MGD is based on a thin kapton foil, clad with gold-plated copper on both sides. An array of micro-strips at a typical pitch of 200 lm is defined on the top metal layer. Using as a protection mask the metal left after the patterning, charge amplifying micro-grooves are etched into the kapton layer. These end on a second micro-strip pattern defined on the bottom metal plane. The two arrays of micro-strips can have an arbitrary relative orientation and so can be used for read-out to obtain 2-D positional information. First results from our systematic assessment of this device are reported: gas gain ’15 000, rate capability above 106 mm~2 s~1, energy resolution 22% at 5.4 keV, no significant charging or aging e⁄ects up to 5 mC/cm and full primary charge collection eƒciency even at high drift fields. ( 1999 Published by Elsevier Science B.V. All rights reserved.

Results from the first use of microstrip gas chambers in a high-energy physics experiment

Abstract The first use of microstrip gas chambers in a high-energy physics experiment is described. The forward magnetic spectrometer of NA12 (GAMS) experiment at CERN-SPS has been equipped with 8 planes of microstrip gas chambers for a total of 1100 low-noise analog channels. The detectors have been exposed for 100 days to a high flux proton beam. A 0.2% momentum resolution at 450 GeV/c, a rate capability higher than 5 × 105/s−1mm−2 and a 9 ns time resolution have been measured.

Production of G(1590) in 300 GeV central

Abstract Significant production of G(1590), a scalar glueball candidate, is observed in a study of η pairs produced in π−N central collisions at 300 GeV/ c .

\pi^-

We have observed very high gains (up to 7000) from GEMs with ‘standard’ parameters (kapton thickness 50 lm, pitch 120 lm, copper hole diameter 65 lm, kapton hole diameter 30 lm). This was achieved using GEMs coupled to a simple array of copper read-out strips. From the measurements of the current on all the electrodes, we conclude that the high observed gains are fully attributable to electron multiplication in the holes of the mesh, and not to electronics related e⁄ects as had been previously suggested. Furthermore, we report that this large gain may only be fully exploited when the field in the second GEM gap is high. The e⁄ect on the gain of coupling a GEM to another charge amplifying device was investigated using a GEM—PMGC combination. ( 1998 Elsevier Science B.V. All rights reserved.

N collisions

Abstract The effective mass spectrum of π0 pairs produced in pp central collisions (pp → pfπ0π0ps) at 450 GeV/c, s = 29 GeV , below 1 GeV differs from that observed in peripheral charge exchange reactions. In particular, there is a large number of events between ππ-threshold and 1 GeV, that interfere with f0(980) destructively. The possible existence of a broad S-wave state is suggested.