P. Bosted

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.

Transverse momentum dependence of semi-inclusive pion production

Abstract Cross sections for semi-inclusive electroproduction of charged pions ( π ± ) from both proton and deuteron targets were measured for 0.2 x 0.5 , 2 Q 2 4 GeV 2 , 0.3 z 1 , and P t 2 0.2 GeV 2 . For P t 0.1 GeV , we find the azimuthal dependence to be small, as expected theoretically. For both π + and π − , the P t dependence from the deuteron is found to be slightly weaker than from the proton. In the context of a simple model, this implies that the initial transverse momenta width of d quarks is larger than for u quarks and, contrary to expectations, the transverse momentum width of the favored fragmentation function is larger than the unfavored one.

Compton-scattering cross section on the proton at high momentum transfer.

Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s=5-11 and -t=2-7 GeV2 with a statistical accuracy of a few percent. The scaling power for the s dependence of the cross section at fixed center-of-mass angle was found to be 8.0+/-0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross-section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark.

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.

Probing the high momentum component of the deuteron at high Q2.

W.U. Boeglin, L. Coman, P. Ambrozewicz, K. Aniol, J. Arrington, G. Batigne, P. Bosted, A. Camsonne, G. Chang, J.P. Chen, S. Choi, A. Deur, M. Epstein, J.M. Finn, ∗ S. Frullani, C. Furget, F. Garibaldi, O. Gayou, 5 R. Gilman, 5 O. Hansen, D. Hayes, D.W. Higinbotham, W. Hinton, C. Hyde, H. Ibrahim, 11 C.W. de Jager, X. Jiang, M. K. Jones, L.J. Kaufman, † A. Klein, S. Kox, L. Kramer, G. Kumbartzki, J.M. Laget, J. LeRose, R. Lindgren, D.J. Margaziotis, P. Markowitz, K. McCormick, Z. Meziani, R. Michaels, B. Milbrath, J. Mitchell, ‡ P. Monaghan, M. Moteabbed, P. Moussiegt, R. Nasseripour, K. Paschke, C. Perdrisat, E. Piasetzky, V. Punjabi, I.A. Qattan, 3 G. Quéméner, R.D. Ransome, B. Raue, J.S. Réal, J. Reinhold, B. Reitz, R. Roché, M. Roedelbronn, A. Saha, ∗ K. Slifer, P. Solvignon, V. Sulkosky, § P.E. Ulmer, ‡ E. Voutier, L.B. Weinstein, B. Wojtsekhowski, and M. Zeier

Proton Spin Structure in the Resonance Region

We have examined the spin structure of the proton in the region of the nucleon resonances (1.085 GeV<W<1.910 GeV) at an average four momentum transfer of Q2=1.3 GeV2. Using the Jefferson Lab polarized electron beam, a spectrometer, and a polarized solid target, we measured the asymmetries A|| and A(perpendicular) to high precision, and extracted the asymmetries A1 and A2, and the spin structure functions g1 and g2. We found a notably nonzero A(perpendicular), significant contributions from higher-twist effects, and only weak support for polarized quark-hadron duality.

Probing Quark-Gluon Interactions with Transverse Polarized Scattering

We have extracted QCD matrix elements from our data on doubly polarized inelastic scattering of electrons on nuclei. We find the higher twist matrix element d˜2, which arises strictly from quark-gluon interactions, to be unambiguously nonzero. The data also reveal an isospin dependence of higher twist effects if we assume that the Burkhardt-Cottingham sum rule is valid. The fundamental Bjorken sum rule obtained from the a0 matrix element is satisfied at our low momentum transfer.

Single spin asymmetry in open charm photoproduction and decay as a test of pQCD

In the framework of perturbative QCD, the basic spin-averaged characteristics of heavy flavor hadro-, photo- and electroproduction are known exactly up to the next-to-leading order (NLO). During the last ten years, these NLO results have been widely used for a phenomenological description of available data (for a review see [1]). At the same time, the key question still remains open: How to test the applicability of QCD at fixed order to the heavy quark production? The problem is twofold. On the one hand, the NLO corrections are large; they increase the leading order (LO) predictions for both charm and bottom production cross sections approximately by a factor of two. For this reason, one could expect that higher-order corrections, as well as nonperturbative contributions, can be essential in these processes, especially for the c-quark case. On the other hand, it is very difficult to compare directly, without additional assumptions, pQCD predictions for spin-averaged cross sections with experimental data because of a high sensivity of the theoretical calculations to standard uncertainties in the input QCD parameters: m Q, the factorization and renormalization scales, μ F and μ R , Λ QCD and the parton distribution functions [2, 3].

Experimental tudy of the A(e,e'

Cross sections for the 1 H(e,eπ + )n process on 1 H, 2 H, 12 C, 27 Al, 63 Cu, and 197 Au targets were measured at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) to extract nuclear transparencies. Data were taken from Q 2 = 1.1-4.7 GeV 2 for a fixed center-of-mass energy of W = 2.14 GeV. The ratio of σ L and σ T was extracted from the measured cross sections for 1 H, 2 H, 12 C, and 63 Cu targets at Q 2 = 2.15 and 4.0 GeV 2 , allowing for additional studies of the reaction mechanism. In this article, we present the experimental setup and the analysis of the data in detail, including systematic uncertainty studies. Differential cross sections and nuclear transparencies as a function of the pion momentum at different values of Q 2 are presented. Our results are consistent with the predicted early onset of color transparency in mesons. Global features of the data are discussed and the data are compared with model calculations for the 1 H(e,eπ + )n reaction from nuclear targets.Cross sections for the {sup 1}H(e,e{pi}{sup +})n process on {sup 1}H, {sup 2}H, {sup 12}C, {sup 27}Al, {sup 63}Cu, and {sup 197}Au targets were measured at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) to extract nuclear transparencies. Data were taken from Q{sup 2}=1.1-4.7 GeV{sup 2} for a fixed center-of-mass energy of W=2.14 GeV. The ratio of {sigma}{sub L} and {sigma}{sub T} was extracted from the measured cross sections for {sup 1}H, {sup 2}H, {sup 12}C, and {sup 63}Cu targets at Q{sup 2}=2.15 and 4.0 GeV{sup 2}, allowing for additional studies of the reaction mechanism. In this article, we present the experimental setup and the analysis of the data in detail, including systematic uncertainty studies. Differential cross sections and nuclear transparencies as a function of the pion momentum at different values of Q{sup 2} are presented. Our results are consistent with the predicted early onset of color transparency in mesons. Global features of the data are discussed and the data are compared with model calculations for the {sup 1}H(e,e{pi}{sup +})n reaction from nuclear targets.