G. Niculescu

Measurements of Deuteron Photodisintegration up to 4.0 GeV

The first measurements of the differential cross section for the d(γ,p)n reaction up to 4.0 GeV were performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at Thomas Jefferson Laboratory. We report the cross sections at the proton center-of-mass angles of 36°, 52°, 69°, and 89°. These results are in reasonable agreement with previous measurements at lower energy. The 89° and 69° data show constituent-counting-rule behavior up to 4.0 GeV photon energy. The 52° and 36° data disagree with the counting-rule behavior. The quantum chromodynamics (QCD) model of nuclear reactions involving reduced amplitudes disagrees with the present data.

New Measurements of the European Muon Collaboration Effect in Very Light Nuclei

J. Seely, A. Daniel, D. Gaskell, J. Arrington, ∗ N. Fomin, P. Solvignon, R. Asaturyan, † F. Benmokhtar, W. Boeglin, B. Boillat, P. Bosted, A. Bruell, M.H.S. Bukhari, M.E. Christy, B. Clasie, S. Connell, ‡ M.M. Dalton, D. Day, J. Dunne, D. Dutta, 12 L. El Fassi, R. Ent, H. Fenker, B.W. Filippone, H. Gao, 12 C. Hill, R.J. Holt, T. Horn, 3 E. Hungerford, M.K. Jones, J. Jourdan, N. Kalantarians, C.E. Keppel, D. Kiselev, M. Kotulla, C. Lee, A.F. Lung, S. Malace, D.G. Meekins, T. Mertens, H. Mkrtchyan, T. Navasardyan, G. Niculescu, I. Niculescu, H. Nomura, Y. Okayasu, A.K. Opper, C. Perdrisat, D.H. Potterveld, V. Punjabi, X. Qian, P.E. Reimer, J. Roche, V.M. Rodriguez, O. Rondon, E. Schulte, E. Segbefia, K. Slifer, G.R. Smith, V. Tadevosyan, S. Tajima, L. Tang, G. Testa, R. Trojer, V. Tvaskis, W.F. Vulcan, F.R. Wesselmann, S.A. Wood, J. Wright, L. Yuan, and X. Zheng Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA, USA University of Houston, Houston, TX, USA Thomas Jefferson National Laboratory, Newport News, VA, USA Physics Division, Argonne National Laboratory, Argonne, IL, USA University of Virginia, Charlottesville, VA, USA Yerevan Physics Institute, Armenia University of Maryland, College Park, MD, USA Florida International University, Miami, FL, USA Basel University, Basel, Switzerland Hampton University, Hampton, VA, USA Mississippi State University, Jackson, MS, USA Triangle Universities Nuclear Laboratory, Duke University, Durham, NC, USA Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, CA, USA University of the Witwatersrand, Johannesburg, South Africa James Madison University, Harrisonburg, VA, USA Tohoku University, Sendai, Japan Ohio University, Athens, OH, USA College of William and Mary, Williamsburg, VA, USA Norfolk State University, Norfolk, VA, USA (Dated: October 27, 2009)

New Measurements of High-Momentum Nucleons and Short-Range Structures in Nuclei

We present new measurements of electron scattering from high-momentum nucleons in nuclei. These data allow an improved determination of the strength of two-nucleon correlations for several nuclei, including light nuclei where clustering effects can, for the first time, be examined. The data also include the kinematic region where three-nucleon correlations are expected to dominate.

Inclusive electron - nucleus scattering at large momentum transfer

The response function of nuclei in the quasielastic region at large momentum transfer (q≤10 fm^-1) is measured for a series of nuclei, 4He, 12C, 27Al, 56Fe, and 197Au, up to large values of the Bjorken scaling variables x<2.5.

Semi-Inclusive Charged-Pion Electroproduction off Protons and Deuterons: Cross Sections, Ratios and Access to the Quark-Parton Model at Low Energies

A large set of cross sections for semi-inclusive electroproduction of charged pions (π^±) from both proton and deuteron targets was measured. The data are in the deep-inelastic scattering region with invariant mass squared W^2>4 GeV^2 (up to ≈7 GeV^2) and range in four-momentum transfer squared 2<Q^2<4 (GeV/c)^2, and cover a range in the Bjorken scaling variable 0.2<x<0.6. The fractional energy of the pions spans a range 0.3<z<1, with small transverse momenta with respect to the virtual-photon direction, Pt^(2)_(t)<0.2 (GeV/c)2. The invariant mass that goes undetected, M_x or W′, is in the nucleon resonance region, W′<2 GeV. The new data conclusively show the onset of quark-hadron duality in this process, and the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark→pion production mechanisms. The x, z, and Pt^(2)_(t) dependences of several ratios (the ratios of favored-unfavored fragmentation functions, charged pion ratios, deuteron-hydrogen and aluminum-deuteron ratios for π^+ and π^−) have been studied. The ratios are found to be in good agreement with expectations based upon a high-energy quark-parton model description. We find the azimuthal dependences to be small, as compared to exclusive pion electroproduction, and consistent with theoretical expectations based on tree-level factorization in terms of transverse-momentum-dependent parton distribution and fragmentation functions. In the context of a simple model, the initial transverse momenta of d quarks are found to be slightly smaller than for u quarks, while the transverse momentum width of the favored fragmentation function is about the same as for the unfavored one, and both fragmentation widths are larger than the quark widths.

x and ξ scaling of the nuclear structure function at large x

Inclusive electron scattering data are presented for ^2H, C, Fe, and Au targets at an incident electron energy of 4.045 GeV for a range of momentum transfers from Q^2=1 to 7 (GeV/c)^2. Data were taken at Jefferson Laboratory for low values of energy loss, corresponding to values of Bjorken x ≳ 1. The structure functions do not show scaling in x in this range, where inelastic scattering is not expected to dominate the cross section. The data do show scaling, however, in the Nachtmann variable ξ. This scaling appears to be the result of Bloom- Gilman duality in the nucleon structure function combined with the Fermi motion of the nucleons in the nucleus. The resulting extension of scaling to larger values of ξ opens up the possibility of accessing nuclear structure functions in the high-x region at lower values of Q^2 than previously believed.

Measurement of the EMC Effect in the Deuteron

We have determined the structure function ratio

Electroproduction of kaons on light nuclei

R^d_{\rm EMC}=F_2^d/(F_2^n+F_2^p)