The exclusive electroproduction process ep → e ′ p ′ π 0 was measured in the range of photon virtualities Q 2 = 0 . 4–1 . 0 GeV 2 and the invariant mass range of the p π 0 system of W = 1 . 1–1 . 8 GeV. These kinematics are covered in exclusive π 0 electroproduction off the proton with nearly complete angular coverage in the p π 0 center-of-mass system and with high statistical accuracy. Nearly 36 000 cross-section points were measured, and the structure functions σ T + ǫσ L , σ LT , and σ TT , were extracted via fitting the φ π 0 dependence of the cross section. A Legendre polynomial expansion analysis demonstrates the sensitivity of our data to high-lying N ∗ and (cid:6) ∗ resonances with M > 1 . 6 GeV. As part of a broad effort to determine the electrocouplings of the N ∗ and (cid:6) ∗ resonances using both single- and double-pion electroproduction, this dataset is crucial for the reliable extraction of the high-lying resonance electrocouplings from the combined isospin analysis of the N π and π + π − p channels.

The transition helicity amplitudes from the proton ground state to the $$P_{11}(1440)$$ and $$D_{13}(1520)$$ excited states ($$\gamma_{v}pN^*$$ electrocouplings) were determined from the analysis of nine independent one-fold differential $$\pi^{+} \pi^{-} p$$ electroproduction cross sections off a proton target, taken with CLAS at photon virtualities 0.25\enskip {\rm GeV$$^{2}$$} $<$ $$Q^{2}$$ $<$$ 0.60 \enskip {\rm GeV$$^{2}$}. The phenomenological reaction model was employed for separation of the resonant and non-resonant contributions to the final state. The $$P_{11}(1440)$$ and $$D_{13}(1520)$$ electrocouplings were obtained from the resonant amplitudes parametrized within the framework of a unitarized Breit-Wigner ansatz. They are consistent with results obtained in the previous CLAS analyses of the $$\pi^+n$$ and $$\pi^0p$$ channels. The successful description of a large body of data in dominant meson-electroproduction channels off protons with the same $$\gamma_{v}pN^*$$ electrocouplings offers clear evidence for the reliable extraction of these fundamental quantities from meson-electroproduction data. This analysis also led to the determination of the long-awaited hadronic branching ratios for the $$D_{13}(1520)$$ decay into $$\Delta\pi$$ (24%-32%) and $$N\rho$$ (8%-17%).

P. E. Bosted,35,* R. Fersch,39 G. Adams,31 M. Amarian,29 S. Anefalos,17 M. Anghinolfi,18 G. Asryan,40 H. Avakian,17,35 H. Bagdasaryan,29,40 N. Baillie,39 J. P. Ball,2 N. A. Baltzell,34 S. Barrow,13 V. Batourine,35 M. Battaglieri,18 K. Beard,21 I. Bedlinskiy,20 M. Bektasoglu,29 M. Bellis,5,31 N. Benmouna,14 A. S. Biselli,11 B. E. Bonner,32 S. Bouchigny,19,35 S. Boiarinov,20,35 R. Bradford,5 D. Branford,10 W. K. Brooks,35 S. Bültmann,29 V. D. Burkert,35 C. Butuceanu,39 J. R. Calarco,26 S. L. Careccia,29 D. S. Carman,35 B. Carnahan,6 A. Cazes,34 S. Chen,13 P. L. Cole,16,35 P. Collins,2 P. Coltharp,13 D. Cords,35,† P. Corvisiero,18 D. Crabb,38 H. Crannell,6 V. Crede,13 J. P. Cummings,31 R. De Masi,7 R. De Vita,18 E. De Sanctis,17 P. V. Degtyarenko,35 H. Denizli,30 L. Dennis,13 A. Deur,35 C. Djalali,34 G. E. Dodge,29 J. Donnelly,15 D. Doughty,8,35 P. Dragovitsch,13 M. Dugger,2 K. V. Dharmawardane,29,‡ S. Dytman,30 O. P. Dzyubak,34 H. Egiyan,35,39,§ K. S. Egiyan,40,† L. Elouadrhiri,8,35 P. Eugenio,13 R. Fatemi,38 G. Fedotov,25 R. J. Feuerbach,5 T. A. Forest,29 A. Fradi,19 H. Funsten,39 M. Garçon,7 G. Gavalian,26,29 G. P. Gilfoyle,33 K. L. Giovanetti,21 F. X. Girod,7 J. T. Goetz,3 E. Golovatch,18,‖ R. W. Gothe,34 K. A. Griffioen,39 M. Guidal,19 M. Guillo,34 N. Guler,29 L. Guo,35 V. Gyurjyan,35 C. Hadjidakis,19 K. Hafidi,1 R. S. Hakobyan,6 J. Hardie,8,35 D. Heddle,8,35 F. W. Hersman,26 K. Hicks,28 I. Hleiqawi,28 M. Holtrop,26 M. Huertas,34 C. E. Hyde-Wright,29 Y. Ilieva,14 D. G. Ireland,15 B. S. Ishkhanov,25 E. L. Isupov,25 M. M. Ito,35 D. Jenkins,37 H. S. Jo,19 K. Joo,9 H. G. Juengst,29 N. Kalantarians,29 C. Keith,35 J. D. Kellie,15 M. Khandaker,27 K. Y. Kim,30 K. Kim,22 W. Kim,22 A. Klein,29,¶ F. J. Klein,6,12 M. Klusman,31 M. Kossov,20 L. H. Kramer,12,35 V. Kubarovsky,31,35 J. Kuhn,5,31 S. E. Kuhn,29 S. V. Kuleshov,20 J. Lachniet,5,29 J. M. Laget,7,35 J. Langheinrich,34 D. Lawrence,24 Ji Li ,31 A. C. S. Lima,14 K. Livingston,15 H. Lu,34 K. Lukashin,6 M. MacCormick,19 N. Markov,9 S. McAleer,13 B. McKinnon,15 J. W. C. McNabb,5 B. A. Mecking,35 M. D. Mestayer,35 C. A. Meyer,5 T. Mibe,28 K. Mikhailov,20 R. Minehart,38 M. Mirazita,17 R. Miskimen,24 V. Mokeev,25 L. Morand,7 S. A. Morrow,7,19 M. Moteabbed,12 J. Mueller,30 G. S. Mutchler,32 P. Nadel-Turonski,14 R. Nasseripour,12,34 S. Niccolai,14,19 G. Niculescu,21 I. Niculescu,14,21 B. B. Niczyporuk,35 M. R. Niroula,29 R. A. Niyazov,29,35 M. Nozar,35 G. V. O’Rielly,14 M. Osipenko,18,25 A. I. Ostrovidov,13 K. Park,22 E. Pasyuk,2 C. Paterson,15 S. A. Philips,14 J. Pierce,38 N. Pivnyuk,20 D. Pocanic,38 O. Pogorelko,20 E. Polli,17 S. Pozdniakov,20 B. M. Preedom,34 J. W. Price,4 Y. Prok,38,** D. Protopopescu,15,26 L. M. Qin,29 B. A. Raue,12,35 G. Riccardi,13 G. Ricco,18 M. Ripani,18 G. Rosner,15 P. Rossi,17 D. Rowntree,23 P. D. Rubin,33 F. Sabatié,7,29 C. Salgado,27 J. P. Santoro,35,37,†† V. Sapunenko,18,35 R. A. Schumacher,5 V. S. Serov,20 Y. G. Sharabian,35 J. Shaw,24 N. V. Shvedunov,25 A. V. Skabelin,23 E. S. Smith,35 L. C. Smith,38 D. I. Sober,6 A. Stavinsky,20 S. S. Stepanyan,22 S. Stepanyan,8,35,40 B. E. Stokes,13 P. Stoler,31 S. Strauch,34 R. Suleiman,23 M. Taiuti,18 S. Taylor,32 D. J. Tedeschi,34 U. Thoma,35,‡‡ A. Tkabladze,14 S. Tkachenko,29 L. Todor,5 M. Ungaro,9 M. F. Vineyard,33,36 A. V. Vlassov,20 L. B. Weinstein,29 D. P. Weygand,35 M. Williams,5 E. Wolin,35 M. H. Wood,34,§§ A. Yegneswaran,35 J. Yun,29 L. Zana,26 J. Zhang,29 B. Zhao,9 and Z. Zhao34 (CLAS Collaboration) 1Argonne National Laboratory, Argonne, Illinois 60439, USA 2Arizona State University, Tempe, Arizona 85287-1504, USA 3University of California at Los Angeles, Los Angeles, California 90095-1547, USA 4California State University, Dominguez Hills, Carson, California 90747, USA 5Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA 6Catholic University of America, Washington, D.C. 20064, USA 7CEA-Saclay, Service de Physique Nucléaire, F-91191 Gif-sur-Yvette, France 8Christopher Newport University, Newport News, Virginia 23606, USA 9University of Connecticut, Storrs, Connecticut 06269, USA 10Edinburgh University, Edinburgh EH9 3JZ, United Kingdom 11Fairfield University, Fairfield, Connecticut 06824, USA 12Florida International University, Miami, Florida 33199, USA 13Florida State University, Tallahassee, Florida 32306, USA 14George Washington University, Washington, D.C. 20052, USA 15University of Glasgow, Glasgow G12 8QQ, United Kingdom 16Idaho State University, Pocatello, Idaho 83209, USA 17INFN, Laboratori Nazionali di Frascati, I-00044 Frascati, Italy 18INFN, Sezione di Genova, I-16146 Genova, Italy 19Institut de Physique Nucleaire ORSAY, Orsay, France 20Institute of Theoretical and Experimental Physics, RU-117259 Moscow, Russia 21James Madison University, Harrisonburg, Virginia 22807, USA 22Kyungpook National University, Daegu 702-701, South Korea 23Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA 24University of Massachusetts, Amherst, Massachusetts 01003, USA 25Moscow State University, General Nuclear Physics Institute, RU-119899 Moscow, Russia

Differential cross sections for the reaction gamma p -> K-*0 Sigma(+) are presented in the photon energy range of 1.7 to 3.0 GeV. The K-*0 was detected by its decay products, K+pi(-), in the Continuous Electron Beam Accelerator Facility's large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility. These data are the first K-*0 photoproduction cross sections ever published over a broad range of angles. Comparison with a theoretical model based on the vector and tensor K-*-quark couplings shows good agreement with the data, except at forward angles, suggesting that the role of scalar kappa meson exchange should be investigated.

The exclusive reactions (cid:1)p ! (cid:1) K 0 K (cid:1) n and (cid:1)p ! (cid:1) K 0 K 0 p have been studied in the photon energy range 1.6–3.8 GeV, searching for evidence of the exotic baryon (cid:2) (cid:1) (cid:2) 1540 (cid:3) in the decays (cid:2) (cid:1) ! nK (cid:1) and (cid:2) (cid:1) ! pK 0 . Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The integrated luminosity was about 70 pb (cid:4) 1 . The reactions have been isolated by detecting the K (cid:1) and proton directly, the neutral kaon via its decay to K S ! (cid:2) (cid:1) (cid:2) (cid:4) and the neutron or neutral kaon via the missing mass technique. The mass and width of known hyperons such as (cid:3) (cid:1) , (cid:3) (cid:4) and (cid:4) (cid:2) 1116 (cid:3) were used as a check of the mass determination accuracy and experimental resolution. Approximately 100 000 (cid:4) (cid:5) (cid:2) 1520 (cid:3) ’s and 150 000 (cid:3) ’s were observed in the (cid:1) K 0 K (cid:1) n and (cid:1) K 0 K 0 p final state, respectively. No evidence for the (cid:2) (cid:1) pentaquark was found in the nK (cid:1) or pK S invariant mass spectra. Upper limits were set on the production cross section of the reaction (cid:1)p ! (cid:1) K 0 (cid:2) (cid:1) as functions of center-of-mass angle, nK (cid:1) and pK S masses. Combining the results of the two reactions, the 95% C.L. upper limit on the total cross section for a resonance peaked at 1540 MeV was found to be 0.7 nb. Within most of the available theoretical models, this corresponds to an upper limit on the (cid:2) (cid:1) width, (cid:5) (cid:2) (cid:1) , ranging between 0.01 and 7 MeV.

The polarized longitudinal-transverse structure function sigma(LT') has been measured in the Delta(1232) resonance region at Q(2)=0.40 and 0.65 GeV2. Data for the p((e) over right arrow ,e'p)pi(0) reaction were taken at Jefferson Lab with the CEBAF large acceptance spectrometer (CLAS) using longitudinally polarized electrons at an energy of 1.515 GeV. For the first time a complete angular distribution was measured, permitting the separation of different nonresonant amplitudes using a partial wave analysis. Comparison with previous beam asymmetry measurements at MAMI indicate a deviation from the predicted Q(2) dependence of sigma(LT ') using recent phenomenological models.

S. Stepanyan, K. Hicks, D.S. Carman, E. Pasyuk, R.A. Schumacher, E.S. Smith, D.J. Tedeschi, L. Todor, G. Adams, P. Ambrozewicz, E. Anciant, M. Anghinolfi, B. Asavapibhop, G. Audit, H. Avakian, H. Bagdasaryan, J.P. Ball, S.P. Barrow, M. Battaglieri, K. Beard, M. Bektasoglu, M. Bellis, B.L. Berman, N. Bianchi, A.S. Biselli, S. Boiarinov, S. Bouchigny, R. Bradford, D. Branford, W.J. Briscoe, W.K. Brooks, V.D. Burkert, C. Butuceanu, J.R. Calarco, B. Carnahan, S. Chen, L. Ciciani, P.L. Cole, A. Coleman, D. Cords, P. Corvisiero, D. Crabb, H. Crannell, J.P. Cummings, E. De Sanctis, P.V. Degtyarenko, H. Denizli, L. Dennis, R. De Vita, K.V. Dharmawardane, K.S. Dhuga, C. Djalali, G.E. Dodge, D. Doughty, P. Dragovitsch, M. Dugger, S. Dytman, O.P. Dzyubak, H. Egiyan, K.S. Egiyan, L. Elouadrhiri, A. Empl, P. Eugenio, R. Fatemi, R.J. Feuerbach, J. Ficenec, T.A. Forest, H. Funsten, M. Garçon, G. Gavalian, G.P. Gilfoyle, K.L. Giovanetti, C.I.O. Gordon, R. Gothe, K. Griffioen, M. Guidal, M. Guillo, L. Guo, V. Gyurjyan, C. Hadjidakis, R.S. Hakobyan, J. Hardie, ,1 D. Heddle, ,9 P. Heimberg, F.W. Hersman, R.S. Hicks, M. Holtrop, J. Hu, C.E. Hyde-Wright, M.M. Ito, D. Jenkins, K. Joo, H.G. Juengst, J.D. Kellie, M. Khandaker, K.Y. Kim, K. Kim, W. Kim, A. Klein, F.J. Klein, A.V. Klimenko, M. Klusman, M. Kossov, L.H. Kramer, Y. Kuang, V. Kubarovsky, S.E. Kuhn, J. Kuhn, J. Lachniet, D. Lawrence, J. Li, A. Lima, K. Livingston, K. Lukashin, J.J. Manak, S. McAleer, J.W.C. McNabb, B.A. Mecking, S. Mehrabyan, J.J. Melone, M.D. Mestayer, C.A. Meyer, K. Mikhailov, R. Minehart, M. Mirazita, R. Miskimen, V. Mokeev, L. Morand, S. Morrow, V. Muccifora, J. Mueller, L.Y. Murphy, G.S. Mutchler, J. Napolitano, R. Nasseripour, S. Niccolai, G. Niculescu, I. Niculescu, B.B. Niczyporuk, R.A. Niyazov, M. Nozar, J. O’Brien, G.V. O’Rielly, A.K. Opper, M. Osipenko, K. Park, G. Peterson, S.A. Philips, N. Pivnyuk, D. Pocanic, O. Pogorelko, E. Polli, S. Pozdniakov, B.M. Preedom, J.W. Price, Y. Prok, D. Protopopescu, L.M. Qin, B.A. Raue, ,1 G. Riccardi, G. Ricco, M. Ripani, B.G. Ritchie, F. Ronchetti, P. Rossi, D. Rowntree, P. Rubin, F. Sabatié, C. Salgado, J. Santoro, V. Sapunenko, V.S. Serov, Y.G. Sharabian, J. Shaw, S. Simionatto, A.V. Skabelin, L.C. Smith, D.I. Sober, I.I. Strakovsky, A. Stavinsky, P. Stoler, R. Suleiman, M. Taiuti, S. Taylor, U. Thoma, R. Thompson, C. Tur, M. Ungaro, M.F. Vineyard, A.V. Vlassov, K. Wang, L.B. Weinstein, H. Weller, D.P. Weygand, C.S. Whisnant, E. Wolin, M.H. Wood, A. Yegneswaran, J. Yun

L. Zana, 27 and The CLAS Collaboration University of Connecticut, Storrs, Connecticut 06269, USA University of Virginia, Charlottesville, Virginia 22901, USA Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA Arizona State University, Tempe, Arizona 85287-1504, USA CEA-Saclay, Service de Physique Nucléaire, F91191 Gif-sur-Yvette, Cedex, France University of California at Los Angeles, Los Angeles, California 90095-1547, USA Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA Catholic University of America, Washington, D.C. 20064, USA Christopher Newport University, Newport News, Virginia 23606, USA Duke University, Durham, North Carolina 27708-0305, USA Edinburgh University, Edinburgh EH9 3JZ, United Kingdom Florida International University, Miami, Florida 33199, USA Florida State University, Tallahassee, Florida 32306, USA Physikalisches Institut der Universitaet Giessen, 35392 Giessen, Germany The George Washington University, Washington, D.C. 20052, USA University of Glasgow, Glasgow G12 8QQ, United Kingdom INFN, Laboratori Nazionali di Frascati, Frascati, Italy INFN, Sezione di Genova, 16146 Genova, Italy Idaho State University, Pocatello, Idaho 83209, USA Institut de Physique Nucleaire ORSAY, Orsay, France Institute of Theoretical and Experimental Physics, Moscow, 117259, Russia James Madison University, Harrisonburg, Virginia 22807, USA Kungpook National University, Taegu 702-701, South Korea Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA University of Massachusetts, Amherst, Massachusetts 01003, USA Moscow State University, General Nuclear Physics Institute, 119899 Moscow, Russia University of New Hampshire, Durham, New Hampshire 03824-3568, USA Norfolk State University, Norfolk, Virginia 23504, USA PHYSICAL REVIEW C 70, 042201(R) (2004) RAPID COMMUNICATIONS

Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q(2) dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the gamma* p --> Delta(+) --> ppi(0) transition. We report new experimental values for the ratios E1+/M1+ and S1+/M1+ over the range Q(2) = 0.4-1.8 GeV2, extracted from precision p(e,e'p)pi(0) data using a truncated multipole expansion. Results are best described by recent unitary models in which the pion cloud plays a dominant role.

Cross sections are presented for the O-16(<(gamma)over right arrow>, pi(-) p) reaction at incident photon energies between 290 and 325 MeV. The data are presented for specific proton and pion angles as a function of proton energy, which are compared with calculations in a local distorted wave impulse approximation model. The results are in agree ment at most kinematics, although at some kinematics the data and calculations disagree by a factor of 2 or more. These data do not support the conclusion of a large modification to the mass of the Delta resonance in the nucleus.

The (γ↘,π−p) reaction was measured for 16O at photon energies of 200 to 320 MeV, and angles ranging from about 20° to 160° for the proton and 32° to 135° for the pion. The photon asymmetry data are compared with calculations in a DWIA framework. The agreement between the present data and calculations is reasonable at quasifree kinematics, but disagree as the momentum transfer to the residual nucleus becomes large.

The first measurement of the reaction He-3(gamma over arrow pointing right, p)X using linearly polarized photons is reported. Cross sections and beam-polarization asymmetries for theta(p)lab = 60-degrees - 100-degrees and E(gamma) - 195-304 MeV are compared with a microscopic calculation which includes one-, two-, and three-nucleon absorption mechanisms. One- and two-nucleon absorption alone fails to describe the data at low proton momenta. The inclusion of three-nucleon absorption significantly improves the comparison with the measured cross sections. However, some features of the asymmetry distributions are not explained.

Pion absorption by 3He was studied at T-pi = 165 MeV in a kinematically complete experiment. The cross section for absorption on a (pn) pair of nucleons, sigma-pn (pi+), was found to be 17.0 +/- 2.6 mb; that for absorption on a (pp) pair, sigma-pp (pi-), 0.91 +/- 0.20 mb. The angular distribution in the pi-NN center-of-mass system for sigma-pn (pi+) resembles that for the pi+ +d-->p + p reaction while the angular distribution for sigma-pp (pi-) is strongly backward peaked. Evidence that a significant fraction of the absorptions involves all three target nucleons is seen in the angular correlation between the two detected nucleons as well as in the momentum distribution of the unobserved nucleon. For pi+ and pi- absorption, the three-body cross sections were found to be 9.6 +/- 2.1 and 4.2 +/- 01.2 mb, respectively. Neither initial- nor final-state interactions appear to be major contributors to the observed three-body absorption, though initial-state interactions may be contributing to the enhancement of the three-body pi+ absorption at the DELTA resonance.

Inclusive electron-scattering cross sections have been measured for Fe-56 in the quasielastic region at electron energies between 0.9 and 4.3 GeV, at scattering angles of 15-degrees and 85-degrees. Longitudinal and transverse response functions at a q of 1.14 GeV/c have been extracted using a Rosenbluth separation. The experimental Coulomb sum has been obtained with the aid of an extrapolation. The longitudinal response function, after correction for Coulomb distortion, is lower than quasifree-scattering-model predictions at the quasielastic peak and on the high-omega side.