[en] The COMPASS Experiment at CERN has a broad physics program aimed at the study of nucleon spin structure and hadron spectroscopy. It has an outstanding fixed-target apparatus, mostly commissioned in 2001, presently consisting of a solid 6LiD polarised target and a two stage spectrometer with high resolution tracking, particle identification and calorimetry, capable of standing high event rates. This paper describes the apparatus and its performances during the run of 2002, when 260 TB of polarised muon nucleon scattering data have been collected. First physics signals from the analysis and projections for the expected accuracy of the measurement of the gluon polarisation ΔG/G from photon gluon fusion are presented too

[en] Deployment and development of advanced technologies for accelerators, detectors, electronics and computing is inherent in everyday activity of all research projects and experiments funded by INFN. However, when a part of the research work can be clearly identified as an R D activity aimed at the development of a new technology or procedure for specific, or a more general, application it is worthwhile to cut it off and manage it as an independent self-consistent experiment. For many of them it is also easy to find applications in other research discipline or industry. In this case it is important to verify the potentiality of the technology, customize it and improve it, in collaboration with the end user, for the specific application.

[en] Experiment PS199 at LEAR studied the charge-exchange bar pp→ bar nn reaction and, in particular, its spin structure. Data for the measurement of the depolarization parameter for a polarized target (D_0n0n) and the polarization-transfer parameter from the target to the scattered particle (K_0n0n) have been collected during 1990. The determination of these parameters requires n and bar n polarimetry. Polarimeters are described, and their performances are given. 10 refs., 7 figs

[en] The optical transparency of perfluorocarbons used as Cherenkov media is of prime importance to many Ring Imaging Cherenkov detectors. We will in this paper show that the main photon absorbers in these fluids are hydrocarbons with double or triple bonds. We will moreover discuss a process which can eliminate these pollutants and restore the intrinsic excellent optical transparency of these fluids in the VUV range

[en] The RICH detector of the COMPASS Experiment at CERN SPS is undergoing an important upgrade: the central MWPC-based photon detectors have been replaced with novel Micropattern detectors, to cope with the challenging efficiency and stability requirements of the new COMPASS measurements. The new hybrid MPGD detector consists of two layers of ThickGEMs and a capacitive bulk Micromegas. Photoconversion takes place on the CsI layer deposited onto the first ThickGEM, while position information and signals are read out from the pad-segmented anode via capacitive coupling by analog front-end electronics based on APV25 chips. The paper focuses on the main issues of production, detailed quality assessment technique, and the commissioning status of the first in-experiment MPGD-based photon detectors for RICH application.

[en] A large acceptance gas RICH detector is presently under construction for the spectrometer of the COMPASS Experiment. Its design parameters are presented and the main characteristics of the vessel, the mirrors system, the photon detectors and the front-end electronics are discussed together with some results from prototyping activities

[en] A dedicated Monte Carlo has been built to study the optical properties of the RICH 1 detector presently under construction for the COMPASS experiment at CERN. In this paper we focus on the optimization of the position of the photon detector with respect to the RICH mirror and on the alignment of the mirror elements forming the mirror surface

[en] In this paper we describe the design of the re-configurable front-end boards (BORA boards) for the 82944 channel RICH-1 (Ring Imaging CHerenkov) of the Compass Collaboration (NA58). The front-end electronics controls the sample-and-hold operation after the arrival of an event trigger, acquires the analog voltages from the pre-amp VLSI and converts them into 10 bits at a rate of 20 Ms/s per analog channel. The digitized analogue values are then written into FIFOs. A subsequent operation compares the readings of each and every channel with corresponding programmable thresholds, and transmits those values larger than the threshold, together with the channel number, through an optical fiber to subsequent processing stages of the acquisition system. The overall operation of the board is controlled and supervised by a fast DSP. The availability of local intelligence allows the board to present innovative features such as: to be part of a computer network that connects several similar boards of the detector with a PC. The presence of the DSP allows testing the operability and linearity of the analog channels; and creating engineering frames containing local temperatures and voltages and transmitting the results through the network. The operator can reconfigure the hardware and software of the board by downloading programs from the PC

[en] The set-up of the COMPASS experiment (NA58 at CERN SPS) consists of two spectrometers (a large-angle one followed by a small-angle spectrometer) both equipped with a gas RICH (RICH 1 and RICH 2) for hadron identification. RICH 1 is currently under construction, while RICH 2 will be added at a second stage. RICH 1 design parameters and technological choices are discussed

[en] RICH-1 is a Cherenkov Imaging detector in operation at the COMPASS experiment at CERN SPS since 2001. MWPCs equipped with CsI photocathodes have been used as photon detectors, for the full detection area in the first years of operation, and for 75% of the area after a detector upgrade in 2006. The mean number of detected photons per particle has been extracted from the data collected during six years of COMPASS data taking. An indirect measurement of possible variations of the CsI quantum efficiency versus time is obtained from this analysis