25,941 research outputs found
Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section
No full textWe report on the first measurement of exclusive single-photon muoproduction on the proton by COMPASS using 160 GeV/c polarised mu(+) and mu(-) beams of the CERN SPS impinging on a liquid hydrogen target. We determine the dependence of the average of the measured mu(+) and mu(-) cross sections for deeply virtual Compton scattering on the squared four-momentum transfer t from the initial to the final proton. The slope B of the t-dependence is fitted with a single exponential function, which yields B = (4.3 +/- 0.6(stat) (+0.1)(-0.3)vertical bar(sys)) (GeV/c)(-2). This result can be converted into a transverse extension of partons in the proton,root(r(perpendicular to)(2)) = (0.58 +/- 0.04(stat) (+0.01)(-0.02)vertical bar(sys) +/- 0.04(model)) fm. For this measurement, the average virtuality of the photon mediating the interaction is = 1.8 (GeV/c)(2) and the average value of the Bjorken variable is = 0.056. (C) 2019 Published by Elsevier B.V
COMPASS Status Report 2010
No full textThis report gives an overview of the setup and the performance of the COMPASS experiment during the 2009 hadron beam run and describes the preparation and startup of the 2010 muon beam run with the polarised target. The status of analysis is presented both for the hadron and muon data with emphasis on the 2008/2009 hadron data
COMPASS-II Proposal: Questions & Answers
No full textThis document presents the answers to the questions on the Compass-II Proposal SPSCP-340 posed by the Referees following the SPSC meeting on 29-30 June, 2010
Generalized Parton Distributions at COMPASS: Present Results and Future Perspectives
No full textUnderstanding the nucleon structure remains one of the key challenges of nuclear physics. The Generalized Parton Distributions (GPDs) grant a new insight for the study of the nucleon structure, as they provide a three-dimensional picture of the nucleon. COMPASS at CERN has a great potential for GPD studies, with its forthcoming measurement of deeply virtual Compton scattering and exclusive meson production off the proton with both and . The current COMPASS GPD program will be discussed, as well as an overview of the investigation on future possible developments. Existing results of exclusive meson production will also be presented
Polarised Drell-Yan measurement in the COMPASS experiment at CERN
No full textThe COMPASS experiment at CERN has been contributing to the description of the nucleon spin structure, namely the transverse momentum dependent parton distribution functions (TMDs), through the Semi-Inclusive Deep Inelastic Scattering (SIDIS) using a muon beam impinging on polarised targets. These TMD functions are also accessible via the transversely polarised Drell-Yan (DY) process, which will be studied in the next COMPASS data taking, starting this Autumn. This process, in which the proton valence region will be explored, will be studied in collisions of a 190 GeV negative pion beam with a transversely polarised ammonia target. The QCD prediction that Sivers TMD change sign when accessed through SIDIS or via DY will be checked by the new COMPASS measurement. Considering one year of data taking, the Sivers azimuthal asymmetry statistical error is expected to be less than 2\%. In addition to the polarised target, other nuclear targets will give the possibility to study unpolarised DY subjects. The experimental setup will be presented, and predictions and expectations will be discussed
Studies of light Mesons at COMPASS
No full textThe COMPASS experiment has taken a large data set with a negative pion beam impinging on a liquid-hydrogen target to study the spectrum of light mesons in diffractive dissociation reactions. The properties of known resonances are studied, and new, possibly spin-exotic states are searched in three-pion final states. A new state at about with quantum numbers is observed in the decay to . The spin-exotic wave is investigated in order to search for the controversial
Hard Exclusive -Meson Production at COMPASS
No full textNew results for the transverse target spin azimuthal asymmetry A_{UT}^{sin(\phi-\phi_S)} for hard exclusive \rho^0-meson production on a transversely polarised ^6LiD and NH_3 target will be presented. The measurement was performed with the COMPASS detector using the 160 GeV/c muon beam of the SPS at CERN. The asymmetry is sensitive to the nucleon helicity-flip generalised parton distribution E, which is related to the orbital angular momentum of quarks in the nucleon
COMPASS Polarized Target for Pion-Induced Drell-Yan Experiment
No full textThe first ever polarized Drell-Yan (DY) measurement is under preparation at COMPASS experiment at CERN. One of the key parts is the low-temperature polarized target. Modifications are required to cope with the intense pion beam that will be used. Solid NH will serve as a transversely-polarized target. Polarization is expected to be up to 90%. Two 55 cm long target cells give the target volume of about 690 cm. The data taking is expected to start on fall 2014 and to continue in 2015 (approximately 180 days). Current status of the target, the modifications and future plans are presented
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