Search results for "COMPASS experiment"
showing 10 items of 25 documents
Highlights from the COMPASS experiment at CERN. Hadron spectroscopy and excitations
2016
The COMPASS experiment at the CERN-SPS studies the spectrum and the structure of hadrons by scattering high energy hadrons and polarised muons off various fixed targets. Recent results for the hadron programme comprise highlights from different topics. A selective overview is given and, among others, the following results are discussed. The precise determination of the pion polarisability, a long standing puzzle that has been solved now, is presented as well as measurements of radiative widths. The observation of a new narrow axial-vector state, the $a_1(1420)$, as well as deeper insights into the exotic $1^{-+}$-wave, which is under study since decades by several experiments, are discussed…
Aging measurements with the gas electron multiplier (GEM)
2001
Abstract Continuing previous aging measurements with detectors based on the Gas Electron Multiplier (GEM), we investigated a 31×31 cm 2 triple-GEM detector, as used in the small area tracking of the COMPASS experiment at CERN. With a detector identical to those installed in the experiment, long-term high-rate exposures to 8.9 keV X-ray radiation were performed to study its aging properties. In standard operation conditions, with Ar/CO2 (70:30) gas filling and operated at an effective gain of 8.5×103, no change in gain and energy resolution is observed after collecting a total charge of 7 mC / mm 2 , corresponding to seven years of normal operation. This observation confirms previous results…
Construction, test and commissioning of the triple-gem tracking detector for compass
2002
The Small Area Tracking system of the COMPASS experiment at CERN includes a set of 20 large area, fast position-sensitive Gas Electron Multiplier (GEM) detectors, designed to reliably operate in the harsh radiation environment of the experiment. We describe in detail the design, choice of materials, assembly procedures and quality controls used to manufacture the devices. The test procedure in the laboratory, the performance in test beams and in the initial commissioning phase in the experiment are presented and discussed.
The COMPASS experiment at CERN
1998
Abstract The recently approved COMPASS experiment attempts a measurement of the gluon polarization around η ⋍ 0.1 with a precision of δ(Δ g / g ) ⋍ 0.1. The experiment uses open charm muo-production and large PT hadron pairs to tag the photon-gluon fusion process. COMPASS will also cover a rich spin-physics program in polarized DIS.
New measurements of at COMPASS
2007
One of the main goals of the COMPASS experiment at CERN is the determination of the gluon polarisation in the nucleon, Δ G / G . It is determined from spin asymmetries in the scattering of polarised muons at 160 GeV/c on a polarised LiD target. The gluon polarisation is accessed by the selection of photon-gluon fusion events. Such events are tagged either with a charmed meson or a hadron pair with high transverse momenta in the final state. The selection of charmed mesons is based on the reconstruction of decayed D ⋆ and D 0 mesons in the COMPASS spectrometer. For the high- p T hadron pairs two independent analyses are performed in the kinematic regimes of DIS ( Q 2 > 1 ( GeV / c ) 2 ) and …
The COMPASS trigger system for muon scattering
2005
Abstract The trigger system of the COMPASS experiment at the CERN polarized muon beam is presented. It detects muon scattering events on (polarized) nucleons with a relative energy loss exceeding a selectable value y min independent of the four-momentum transfer. The requirement of a minimum energy deposit in a hadron calorimeter rejects background events like scattering on electrons, elastic and quasi-elastic radiative events as well as events from beam halo tracks. The trigger system which can be considered as a tagger for quasi-real photon events is now, along with larger trigger hodoscope system for deep inelastic scattering events, in regular use for the measurement of the gluon polari…
Read-out electronics for fast photon detection with COMPASS RICH-1
2008
A new read-out electronics system has been developed for the fast photon detection of the central region of the COMPASS RICH-1. The project is based on multi-anode photomultipliers read out by the high-sensitivity MAD4 preamplifier-discriminator and the dead-time free F1 TDC chip characterised by high time resolution. The system has been designed taking into account the high photon flux in the central region of the detector and the high rate requirement of the COMPASS experiment. The system is described in detail together with the measured performances. The new electronics system has been installed and used for the 2006 data taking; it entirely fulfils the expected performances.
Spin asymmetry A1d and the spin-dependent structure function g1d of the deuteron at low values of x and Q2
2007
Abstract We present a precise measurement of the deuteron longitudinal spin asymmetry A 1 d and of the deuteron spin-dependent structure function g 1 d at Q 2 1 ( GeV / c ) 2 and 4 × 10 −5 x 2.5 × 10 −2 based on the data collected by the COMPASS experiment at CERN during the years 2002 and 2003. The statistical precision is tenfold better than that of the previous measurement in this region. The measured A 1 d and g 1 d are found to be consistent with zero in the whole range of x.
A highly integrated low-cost readout system for the COMPASS RICH-1 detector
2007
Particle identification at high multiplicities is a key feature of the COMPASS experiment at CERN's SPS. Hadrons up to 50 GeV/c are identified by a RICH detector with a large horizontal and vertical acceptance of plusmn250 mrad and plusmn180 mrad, respectively. The central region of the photon detector is equipped with multi-anode photomultiplier tubes, the remaining 75% of the total active area are covered by MWPCs with Csl photocathodes. In order to improve the performance of the detector at very high beam intensities, more than 62000 channels of a new analog readout system of the MWPCs, based on the APV25 chip, were developed and installed in 2006. The new system features good single pho…
Leading order determination of the gluon polarisation from DIS events with high-pThadron pairs
2013
We present a determination of the gluon polarisation Delta g/g in the nucleon, based on the longitudinal double-spin asymmetry of DIS events with Q(2) > 1 (GeV/c)(2) including a pair of large transverse-momentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam scattering off a polarised (LiD)-Li-6 target. The gluon polarisation is evaluated by a Neural Network approach for three intervals of the gluon momentum fraction x(g) covering the range 0.04 < x(g) < 0.27. The values obtained at leading order in QCD do not show any significant dependence on x(g). Their average is Delta g/g = 0.125 +/- 0.060 (stat.) +/- 0.063 (sy…