The COMPASS experiment at CERN is investigating the nucleon spin structure in polarised deep inelastic muon scattering, mainly the gluon polarisation
δ
G
G
.
The recoil proton polarization has been measured in the p(e-->,e'p-->)pi(0) reaction in parallel kinematics around W = 1232 MeV, Q2 = 0.121 (GeV/c)2, and epsilon = 0.718 using the polarized cw ...electron beam of the Mainz Microtron. All three proton polarization components, Px/P(e) = (-11.4+/-1.3+/-1.4)%, P(y) = (-43.1+/-1.3+/-2.2)%, and P(z)/P(e) = (56.2+/-1.5+/-2.6)%, could be measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio, CMR = (-6.4+/-0.7(stat)+/-0.8(syst))%, was determined from Px in the framework of the Mainz Unitary Isobar Model. The consistency among the reduced polarizations and the extraction of the ratio of longitudinal-to-transverse response is discussed.
The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semi-inclusive deep inelastic scattering using a 160 GeV mu + beam and a ...transversely polarised NH3 target. The Sivers asymmetry of the proton has been extracted in the Bjorken x range 0.003 0.03 . The asymmetry is different from zero and positive also in the low x region, where sea-quarks dominate. The kinematic dependence of the asymmetry has also been investigated and results are given for various intervals of hadron and virtual photon fractional energy. In contrast to the case of the Collins asymmetry, the results on the Sivers asymmetry suggest a strong dependence on the four-momentum transfer to the nucleon, in agreement with the most recent calculations.
The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semi-inclusive deep inelastic scattering using a 160 GeV mu + beam and a ...transversely polarised NH3 target. The Collins asymmetry of the proton was extracted in the Bjorken x range 0.003 < x < 0.7 . These new precise measurements confirm previous measurements from the COMPASS and HERMES Collaborations, which exhibit a definite effect in the valence quark region. The asymmetries for negative and positive hadrons are similar in magnitude and opposite in sign. They are compatible with model calculations in which the u-quark transversity is opposite in sign and somewhat larger than the d-quark transversity distribution function. The asymmetry is extracted as a function of Bjorken x, the relative hadron energy z and the hadron transverse momentum p T h . The high statistics and quality of the data also allow for more detailed investigations of the dependence on the kinematic variables. These studies confirm the leading-twist nature of the Collins asymmetry.
The COMPASS experiment at CERN Albrecht, E.; Alexeev, G.D.; Anosov, V.A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2007, Letnik:
577, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The COMPASS experiment makes use of the CERN SPS high-intensity muon and hadron beams for the investigation of the nucleon spin structure and the spectroscopy of hadrons. One or more outgoing ...particles are detected in coincidence with the incoming muon or hadron. A large polarised target inside a superconducting solenoid is used for the measurements with the muon beam. Outgoing particles are detected by a two-stage, large angle and large momentum range spectrometer. The setup is built using several types of tracking detectors, according to the expected incident rate, required space resolution and the solid angle to be covered. Particle identification is achieved using a RICH counter and both hadron and electromagnetic calorimeters. The setup has been successfully operated from 2002 onwards using a muon beam. Data with a hadron beam were also collected in 2004. This article describes the main features and performances of the spectrometer in 2004; a short summary of the 2006 upgrade is also given.
New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised
6LiD target are presented. The data ...were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160
GeV
/
c
. Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with naive expectations and with existing model calculations.
First measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarized 6LiD target are presented. The data were taken ...in 2002 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. The Collins asymmetry turns out to be compatible with zero, as does the measured Sivers asymmetry within the present statistical errors.
The focal plane proton-polarimeter for the 3-spectrometer setup at MAMI Pospischil, Th; Bartsch, P.; Baumann, D. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2002, Letnik:
483, Številka:
3
Journal Article
Recenzirano
Odprti dostop
For
(
e
→
,
e′
p
→
)
experiments the 3-spectrometer setup of the A1 collaboration at MAMI has been supplemented by a focal plane proton-polarimeter. To this end, a carbon analyzer of variable ...thickness and two double-planes of horizontal drift chambers have been added to the standard detector system of Spectrometer A. Due to the spin precession in the spectrometer magnets, all three polarization components at the target can be measured simultaneously. The performance of the polarimeter has been studied using elastic
p(
e
→
,
e′
p
→
)
scattering.
We present a determination of the gluon polarisation Δg/g in the nucleon, based on the longitudinal double-spin asymmetry of DIS events with Q2>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 LiD6 target. The gluon polarisation is evaluated by a Neural Network approach for three intervals of the gluon momentum fraction xg covering the range 0.04<xg<0.27. The values obtained at leading order in QCD do not show any significant dependence on xg. Their average is Δg/g=0.125±0.060 (stat.)±0.063 (syst.) at average xg=0.09 and a scale of μ2=3 (GeV/c)2.
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 (syst.) at average x(g) = 0.09 and a scale of mu(2) = 3 (GeV/c)(2).
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