Publications (22)16.03 Total impact
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ABSTRACT: We have measured the moment $A_{LU}^{\sin\phi}$ corresponding to the polarized electron beamspin asymmetry in SIDIS. $A_{LU}^{\sin\phi}$ is a twist3 quantity providing information about quarkgluon correlations. Data were taken with the CLAS Spectrometer at Jefferson Lab using a 5.498 GeV longitudinally polarized electron beam and an unpolarized liquid hydrogen target. All three pion channels ($\pi^+$, $\pi^0$ and $\pi^$) were measured simultaneously over a large range of kinematics within the virtuality range $Q^2 \approx$ 1.04.5 GeV$^2$. The observable was measured with good statistical precision over a large range of $z$, $P_T$, $x_B$, and $Q^{2}$, which permits comparison with several reaction models. The discussed measurements provide an upgrade in statistics over previous measurements, and serve as the first evidence for the negative sign of the $\pi^{}$ $\sin\phi$ moment.  [Show abstract] [Hide abstract]
ABSTRACT: We report the first observation of the line shape of the $\Lambda(1405)$ from electroproduction, and show that it is not a simple BreitWigner resonance. Electroproduction of $K^+ \Lambda(1405)$ off the proton was studied by using data from CLAS at Jefferson Lab in the range $1.0<Q^2<3.0$ (GeV/c)$^2$. The analysis utilized the decay channels $\Sigma^+ \pi^$ of the $\Lambda(1405)$ and $p \pi^0$ of the $\Sigma^+$. Neither the standard (PDG) resonance parameters, nor free parameters fitting to a single BreitWigner resonance represent the line shape. In our fits, the line shape corresponds approximately to predictions of a twopole mesonbaryon picture of the $\Lambda(1405)$, with a lower mass pole near 1368 MeV/c$^2$ and a higher mass pole near 1423 MeV/c$^2$. Furthermore, with increasing photon virtuality the mass distribution shifts toward the higher mass pole.  [Show abstract] [Hide abstract]
ABSTRACT: Exclusive $\pi^0$ electroproduction at a beam energy of 5.75 GeV has been measured with the Jefferson Lab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in $Q^2$, $x_B$, $t$, and $\phi_\pi$, in the $Q^2$ range from 1.0 to 4.6 GeV$^2$,\ $t$ up to 2 GeV$^2$, and $x_B$ from 0.1 to 0.58. Structure functions $\sigma_T +\epsilon \sigma_L, \sigma_{TT}$ and $\sigma_{LT}$ were extracted as functions of $t$ for each of 17 combinations of $Q^2$ and $x_B$. The data were compared directly with two handbagbased calculations including both longitudinal and transversity GPDs. Inclusion of only longitudinal GPDs very strongly underestimates $\sigma_T +\epsilon \sigma_L$ and fails to account for $\sigma_{TT}$ and $\sigma_{LT}$, while inclusion of transversity GPDs brings the calculations into substantially better agreement with the data. There is very strong sensitivity to the relative contributions of nucleon helicity flip and helicity nonflip processes. The results confirm that exclusive $\pi^0$ electroproduction offers direct experimental access to the transversity GPDs. 
Article: Measurement of the Nucleon Structure Function F2 in the Nuclear Medium and Evaluation of its Moments
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ABSTRACT: We report on the measurement of inclusive electron scattering off a carbon target performed with CLAS at Jefferson Laboratory. A combination of three different beam energies 1.161, 2.261 and 4.461 GeV allowed us to reach an invariant mass of the finalstate hadronic system W~2.4 GeV with fourmomentum transfers Q2 ranging from 0.2 to 5 GeV2. These data, together with previous measurements of the inclusive electron scattering off proton and deuteron, which cover a similar continuous twodimensional region of Q2 and Bjorken variable x, permit the study of nuclear modifications of the nucleon structure. By using these, as well as other world data, we evaluated the F2 structure function and its moments. Using an OPEbased twist expansion, we studied the Q2evolution of the moments, obtaining a separation of the leadingtwist and the total highertwist terms. The carbontodeuteron ratio of the leadingtwist contributions to the F2 moments exhibits the well known EMC effect, compatible with that discovered previously in xspace. The total highertwist term in the carbon nucleus appears, although with large systematic uncertainites, to be smaller with respect to the deuteron case for n<7, suggesting partial parton deconfinement in nuclear matter. We speculate that the spatial extension of the nucleon is changed when it is immersed in the nuclear medium. Comment: 37 pages, 15 figures  [Show abstract] [Hide abstract]
ABSTRACT: The photoproduction of vector mesons on various nuclei has been studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory. The vector mesons, $\rho$, $\omega$, and $\phi$, are observed via their decay to $e^+e^$, in order to reduce the effects of final state interactions in the nucleus. Of particular interest are possible inmedium effects on the properties of the $\rho$ meson. The $\rho$ spectral function is extracted from the data on various nuclei, carbon, iron, and titanium, and compared to the spectrum from liquid deuterium, which is relatively free of nuclear effects. We observe no significant mass shift for the $\rho$ meson; however, there is some widening of the resonance in titanium and iron, which is consistent with expected collisional broadening. Comment: 8 pages, 4 figures  [Show abstract] [Hide abstract]
ABSTRACT: Experimental data on the F2 structure functions of the proton and deuteron, including recent results from CLAS at Jefferson Lab, have been used to construct their n<=12 moments. A comprehensive analysis of the moments in terms of the operator product expansion has been performed to separate the moments into leading and higher twist contributions. Particular attention was paid to the issue of nuclear corrections in the deuteron, when extracting the neutron moments from data. The difference between the proton and neutron moments was compared directly with lattice QCD simulations. Combining leading twist moments of the neutron and proton we found the d/u ratio at x>1 approaching 0, although the precision of the data did not allow to exclude the 1/5 value. The higher twist components of the proton and neutron moments suggest that multiparton correlations are isospin independent.  [Show abstract] [Hide abstract]
ABSTRACT: The experimental data on F 2 structure functions of the proton and deuteron were used to construct their moments. In particular, recent measurements performed with CLAS detector at Jefferson Lab allowed to extend our knowledge of structure functions in the large‐x region. The phenomenological analysis of these experimental moments in terms of the Operator Product Expansion permitted to separate the leading and higher twist contributions. Applying nuclear corrections to extracted deuteron moments we obtained the contribution of the neutron. Combining leading twist moments of the neutron and proton we found d/u ratio at x → 1 approaching 0, although 1/5 value could not be excluded. The twist expansion analysis suggests that the contamination of higher twists influences the extraction of the d/u ratio at x → 1 even at Q 2‐scale as large as 12 (GeV/c)2.  [Show abstract] [Hide abstract]
ABSTRACT: Single spin azimuthal asymmetries ALT′ were measured at Jefferson Lab using 2.2 and 4.4 GeV longitudinally polarised electrons incident on 4He and 12C targets in the CLAS detector. ALT′ is related to the imaginary part of the longitudinaltransverse interference and in quasifree nucleon knockout it provides an unambiguous signature for final state interactions (FSI). Experimental values of ALT′ were found to be below 5%, typically ALT′⩽3% for data with good statistical precision. Optical model in eikonal approximation (OMEA) and relativistic multiplescattering Glauber approximation (RMSGA) calculations are shown to be consistent with the measured asymmetries. 
Article: The spin program with CLAS at JLab
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ABSTRACT: We report on the status of an extensive program to study the scattering of longitudinally polarized electrons from longitudinally polarized NH3 and ND3 targets using the CLAS detector at JLab. The data span a range inQ 2 from 0.05–4.5 (GeV/c)2 and a range inW, the γ* N invariant mass, up to about 3 GeV. With the excellent particle identification available with the CLA, both inclusive and exclusive scattering can be studied. The experimental techniques are reviewed and some preliminary results are presented. This paper focuses on extraction of the spin structure functiongg 1 for the proton and the deuteron. 
Article: Measurement of beamspin asymmetries for π+ electroproduction above the baryon resonance region
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ABSTRACT: We report the first evidence for a nonzero beamspin azimuthal asymmetry in the electroproduction of positive pions in the deepinelastic kinematic region. Data for the reaction ep>e'pi+X have been obtained using a polarized electron beam of 4.3 GeV with the CEBAF Large Acceptance Spectrometer at the Thomas Jefferson National Accelerator Facility. The amplitude of the sin phi modulation increases with the momentum of the pion relative to the virtual photon, z. In the range z=0.5 0.8 the average amplitude is 0.038±0.005±0.003 for a missing mass MX>1.1 GeV and 0.037±0.007±0.004 for MX>1.4 GeV.  [Show abstract] [Hide abstract]
ABSTRACT: Twoproton correlations at small relative momentum q were studied in the eA(3He, 4He, C, Fe)> e'ppX reaction at E_0 = 4.46 GeV using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small q was found to be in accordance with theoretical expectation. Emission region sizes were extracted and proved to be dependent on A and proton momentum. The size of the twoproton emission region on the lightest possible nucleus, He, was measured for the first time. Comment: 14 pages, 2 figures  [Show abstract] [Hide abstract]
ABSTRACT: Asymmetries for inclusive scattering of 2.6 and 4.3 GeV polarized electrons on polarized protons were measured. These asymmetries were used to extract the structure function g1(x,Q2) for Q2 from 0.15 to 1.64 GeV2. The first moment Τ1 depended strongly on Q2, with its sign changing near Q2=0.3 GeV2. 







Publication Stats
130  Citations  
16.03  Total Impact Points  
Top Journals
Institutions

2005

The University of Edinburgh
 School of Physics and Astronomy
Edinburgh, Scotland, United Kingdom


2004

University of Virginia
 Department of Physics
Charlottesville, Virginia, United States 
Christopher Newport University
НьюпортНьюс, Virginia, United States
