41 research outputs found

    Observation of exclusive DVCS in polarized electron beam asymmetry measurements

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    We report the first results of the beam spin asymmetry measured in the reaction e + p -> e + p + gamma at a beam energy of 4.25 GeV. A large asymmetry with a sin(phi) modulation is observed, as predicted for the interference term of Deeply Virtual Compton Scattering and the Bethe-Heitler process. The amplitude of this modulation is alpha = 0.202 +/- 0.028. In leading-order and leading-twist pQCD, the alpha is directly proportional to the imaginary part of the DVCS amplitude.Comment: 6 pages, 5 figure

    Complete measurement of three-body photodisintegration of 3He for photon energies between 0.35 and 1.55 GeV

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    The three-body photodisintegration of 3He has been measured with the CLAS detector at Jefferson Lab, using tagged photons of energies between 0.35 GeV and 1.55 GeV. The large acceptance of the spectrometer allowed us for the first time to cover a wide momentum and angular range for the two outgoing protons. Three kinematic regions dominated by either two- or three-body contributions have been distinguished and analyzed. The measured cross sections have been compared with results of a theoretical model, which, in certain kinematic ranges, have been found to be in reasonable agreement with the data.Comment: 22 pages, 25 eps figures, 2 tables, submitted to PRC. Modifications: removed 2 figures, improvements on others, a few minor modifications to the tex

    A Kinematically Complete Measurement of the Proton Structure Function F2 in the Resonance Region and Evaluation of Its Moments

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    We measured the inclusive electron-proton cross section in the nucleon resonance region (W < 2.5 GeV) at momentum transfers Q**2 below 4.5 (GeV/c)**2 with the CLAS detector. The large acceptance of CLAS allowed for the first time the measurement of the cross section in a large, contiguous two-dimensional range of Q**2 and x, making it possible to perform an integration of the data at fixed Q**2 over the whole significant x-interval. From these data we extracted the structure function F2 and, by including other world data, we studied the Q**2 evolution of its moments, Mn(Q**2), in order to estimate higher twist contributions. The small statistical and systematic uncertainties of the CLAS data allow a precise extraction of the higher twists and demand significant improvements in theoretical predictions for a meaningful comparison with new experimental results.Comment: revtex4 18 pp., 12 figure

    eta-prime photoproduction on the proton for photon energies from 1.527 to 2.227 GeV

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    Differential cross sections for the reaction gamma p -> eta-prime p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here possess much greater accuracy than previous measurements. Analyses of these data indicate for the first time the coupling of the etaprime N channel to both the S_11(1535) and P_11(1710) resonances, known to couple strongly to the eta N channel in photoproduction on the proton, and the importance of j=3/2 resonances in the process.Comment: 6 pages, 3 figure

    Measurement of the Deuteron Structure Function F2 in the Resonance Region and Evaluation of Its Moments

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    Inclusive electron scattering off the deuteron has been measured to extract the deuteron structure function F2 with the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. The measurement covers the entire resonance region from the quasi-elastic peak up to the invariant mass of the final-state hadronic system W~2.7 GeV with four-momentum transfers Q2 from 0.4 to 6 (GeV/c)^2. These data are complementary to previous measurements of the proton structure function F2 and cover a similar two-dimensional region of Q2 and Bjorken variable x. Determination of the deuteron F2 over a large x interval including the quasi-elastic peak as a function of Q2, together with the other world data, permit a direct evaluation of the structure function moments for the first time. By fitting the Q2 evolution of these moments with an OPE-based twist expansion we have obtained a separation of the leading twist and higher twist terms. The observed Q2 behaviour of the higher twist contribution suggests a partial cancellation of different higher twists entering into the expansion with opposite signs. This cancellation, found also in the proton moments, is a manifestation of the "duality" phenomenon in the F2 structure function

    Tensor Polarization of the phi meson Photoproduced at High t

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    As part of a measurement of the cross section of ϕ\phi meson photoproduction to high momentum transfer, we measured the polar angular decay distribution of the outgoing K+K^+ in the channel ϕK+K\phi \to K^+K^- in the ϕ\phi center-of-mass frame (the helicity frame). We find that s-channel helicity conservation (SCHC) holds in the kinematical range where tt-channel exchange dominates (up to t2.5-t \sim 2.5 GeV2^2 for EγE_{\gamma}=3.6 GeV). Above this momentum, uu-channel production of a ϕ\phi meson dominates and induces a violation of SCHC. The deduced value of the ϕNN\phi NN coupling constant lies in the upper range of previously reported values.Comment: 6 pages; 5 figure

    Exclusive ρ0\rho^0 meson electroproduction from hydrogen at CLAS

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    The longitudinal and transverse components of the cross section for the epepρ0e p\to e^\prime p \rho^0 reaction were measured in Hall B at Jefferson Laboratory using the CLAS detector. The data were taken with a 4.247 GeV electron beam and were analyzed in a range of xBx_B from 0.2 to 0.6 and of Q2Q^2 from 1.5 to 3.0 GeV2^2. The data are compared to a Regge model based on effective hadronic degrees of freedom and to a calculation based on Generalized Parton Distributions. It is found that the transverse part of the cross section is well described by the former approach while the longitudinal part can be reproduced by the latter.Comment: 6 pages, 4 figure

    Measurement of the xx- and Q2Q^2-Dependence of the Asymmetry A1A_1 on the Nucleon

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    We report results for the virtual photon asymmetry A1A_1 on the nucleon from new Jefferson Lab measurements. The experiment, which used the CEBAF Large Acceptance Spectrometer and longitudinally polarized proton (15^{15}NH3_3) and deuteron (15^{15}ND3_3) targets, collected data with a longitudinally polarized electron beam at energies between 1.6 GeV and 5.7 GeV. In the present paper, we concentrate on our results for A1(x,Q2)A_1(x,Q^2) and the related ratio g1/F1(x,Q2)g_1/F_1(x,Q^2) in the resonance and the deep inelastic regions for our lowest and highest beam energies, covering a range in momentum transfer Q2Q^2 from 0.05 to 5.0 GeV2^2 and in final-state invariant mass WW up to about 3 GeV. Our data show detailed structure in the resonance region, which leads to a strong Q2Q^2--dependence of A1(x,Q2)A_1(x,Q^2) for WW below 2 GeV. At higher WW, a smooth approach to the scaling limit, established by earlier experiments, can be seen, but A1(x,Q2)A_1(x,Q^2) is not strictly Q2Q^2--independent. We add significantly to the world data set at high xx, up to x=0.6x = 0.6. Our data exceed the SU(6)-symmetric quark model expectation for both the proton and the deuteron while being consistent with a negative dd-quark polarization up to our highest xx. This data setshould improve next-to-leading order (NLO) pQCD fits of the parton polarization distributions.Comment: 7 pages LaTeX, 5 figure

    Beam Spin Asymmetries in DVCS with CLAS at 4 .8 GeV

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    We report measurements of the beam spin asymmetry in Deeply Virtual Compton Scattering (DVCS) at an electron beam energy of 4.8 GeV using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The DVCS beam spin asymmetry has been measured in a wide range of kinematics, 1(GeV/c)2^2 <Q2<2.8<Q^2<2.8(GeV/c)2^2, 0.12<xB<0.480.12<x_B<0.48, and 0.1 (GeV/c)2^2 <t<0.8<-t<0.8(GeV/c)2^2, using the reaction \pEpX. The number of H(e,eγp)(e,e^{\prime}\gamma p) and H(e,eπ0p)(e,e^{\prime}\pi^0 p) events are separated in each (Q2,xB,t)(Q^2,x_B,t) bin by a fit to the line shape of the H(e,ep)X(e,e^{\prime}p)X Mx2M_x^2 distribution. The validity of the method was studied in detail using experimental and simulated data. It was shown, that with the achieved missing mass squared resolution and the available statistics, the separation of DVCS-BH and π0\pi^0 events can reliably be done with less than 5% uncertainty. The Q2Q^2- and tt-dependences of the sinϕ\sin\phi moments of the asymmetry are extracted and compared with theoretical calculations
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