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Title: Recent Physics Results with the COMPASS Experiment

Abstract

The COMPASS experiment has obtained first physics results in the field of polarized distribution functions for quarks and gluons using muon scattering off polarized deuterons. The analysis using open charm production and pairs of high pT hadrons is presented. We also have used a transversely polarized target to address transverse information for quarks inside the nucleon. In addition, a pilot run with incoming pions taken late 2004 will give first information on the pion polarizabilities and hadron resonances. The physics prospects from this run as well as from future data taking in this field are also outlined.

Authors:
 [1]
  1. Technische Universitaet Muenchen, Physik Department E18, James-Franck Strasse, D-85478 Garching (Germany)
Publication Date:
OSTI Identifier:
20798066
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 814; Journal Issue: 1; Conference: 11. international conference on hadron spectroscopy, Rio de Janeiro (Brazil), 21-26 Aug 2005; Other Information: DOI: 10.1063/1.2176479; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; DEUTERONS; DISTRIBUTION FUNCTIONS; GLUONS; INFORMATION; MULTIPARTICLE SPECTROMETERS; MUON REACTIONS; MUONS; NUCLEONS; PARTICLE INTERACTIONS; PIONS; POLARIZABILITY; POLARIZATION; POLARIZED TARGETS; QUARKS; RESONANCE PARTICLES; SCATTERING; TRANSVERSE MOMENTUM

Citation Formats

Paul, Stephan. Recent Physics Results with the COMPASS Experiment. United States: N. p., 2006. Web. doi:10.1063/1.2176479.
Paul, Stephan. Recent Physics Results with the COMPASS Experiment. United States. doi:10.1063/1.2176479.
Paul, Stephan. Sat . "Recent Physics Results with the COMPASS Experiment". United States. doi:10.1063/1.2176479.
@article{osti_20798066,
title = {Recent Physics Results with the COMPASS Experiment},
author = {Paul, Stephan},
abstractNote = {The COMPASS experiment has obtained first physics results in the field of polarized distribution functions for quarks and gluons using muon scattering off polarized deuterons. The analysis using open charm production and pairs of high pT hadrons is presented. We also have used a transversely polarized target to address transverse information for quarks inside the nucleon. In addition, a pilot run with incoming pions taken late 2004 will give first information on the pion polarizabilities and hadron resonances. The physics prospects from this run as well as from future data taking in this field are also outlined.},
doi = {10.1063/1.2176479},
journal = {AIP Conference Proceedings},
number = 1,
volume = 814,
place = {United States},
year = {Sat Feb 11 00:00:00 EST 2006},
month = {Sat Feb 11 00:00:00 EST 2006}
}
  • The investigation of transverse spin and transverse momentum dependent effects in deep inelastic scattering of muons off nucleons is one of the key physics programs of the COMPASS collaboration at CERN. We have investigated the effects from the data obtained with a polarized proton target. In order to access the transversity distribution function, following channels have been analyzed: The azimuthal distribution of single hadrons, the azimuthal dependence of the plane containing hadron pairs, and the measurement of the transverse polarization of lambda hyperons in the final state. The Sivers distribution function which is one of the transverse momentum dependent functionsmore » has been investigated also from the azimuthal distribution of single hadrons. Azimuthal asymmetries in unpolarized deep inelastic scattering give important information on the inner structure of the nucleon to access the so-far unmeasured Boer-Mulders function. We have measured these asymmetries using spin-averaged {sup 6}L{sub i}D.« less
  • The study of the spin dependent structure functions of the deuteron is part of a broad physics program addressed by the COMPASS collaboration at CERN. The longitudinal spin asymmetry A{sub 1}{sup d} is evaluated from data on inelastic scattering of longitudinally polarised muons off a large 6LiD polarised target. Recent results on g{sub 1}{sup d} both for low and high Q2 are presented. The obtained values for the first moment {gamma}{sub 1}{sup d} and the flavor-singlet axial current a0 are also shown.
  • The spin structure of the nucleon is studied in the COMPASS experiment at CERN/SPS, from the collisions of 160 GeV polarized muon beam with a {sup 6}LiD target. The data collected from 2002 to 2006 provide an accurate measurement of longitudinal double spin cross-section asymmetries. The latest results on the gluon polarization, accessed from two independent analyses of photon-gluon fusion selected events, are presented. The study of the open-charm production allows to extract the gluon polarization (in LO QCD) from the measurement of the asymmetry, the value obtained being {delta}g/g -0.49{+-}0.27(stat){+-}0.11(syst), at an average x{sub g} 0.11{sub -0.05}{sup +0.11} andmore » a scale <{mu}{sup 2}> = 13(GeV/c){sup 2}. An alternative and independent way to study the gluon polarization, by studying the high transverse momentum hadron pairs produced, leads to a value {delta}g/g 0.08{+-}0.10(stat){+-}0.05(syst), at x{sub g}{sup a{nu}} 0.082{sub -0.027}{sup +0.041} and <{mu}{sup 2}> = 3(GeV/c){sup 2}.« less
  • A sample of recent results in muon scattering measurements from the COMPASS experiment at CERN will be reviewed. These include high energy processes with longitudinally polarised proton and deuteron targets. High energy polarised measurements provide important constraints for studying the nucleon spin structure and thus permit to test the applicability of the theoretical framework of factorisation theorems and perturbative QCD. Specifically, latest results on longitudinal quark polarisation, quark helicity densities and gluon polarisation will be reviewed.
  • The COMPASS Collaboration has accumulated the world’s highest statistics on the reaction π{sup −} p → π{sup +}π{sup −}π{sup −} p at 190 GeV/c. The results, presented in Section 1, show that a new state J{sup PC} = 1{sup ++} state never reported before, the a{sub 1}(1420), decaying to f{sub 0}(980)π followed by f{sub 0}(980) → ππ. In addition, the Collaboration reports an exotic J{sup PC} = 1{sup −+} state, the π{sub 1}(1600), which cannot be a quarkonium. Both states are likely to be a tetra-quark, i.e. qq{sup ¯}+qq{sup ¯} or a gluonic hybrid, a qq{sup ¯} object with anmore » excited gluon inside it. Section 2 is devoted to a brief discussion of the central production of resonances, which is being investigated by both COMPASS and ALICE collaborations. However, the results are not yet released, so it is limited to a broad discussion of the central production, with emphasis on different analyses dictated by differences in the experimental setup.« less