K. Park, 2, ∗ V.D. Burkert, W. Kim, I.G. Aznauryan, 2 R. Minehart, L.C. Smith, K. Joo, 41 L. Elouadrhiri, 2 G. Adams, M.J. Amaryan, P. Ambrozewicz, M. Anghinolfi, G. Asryan, H. Avakian, 2 H. Bagdasaryan, 32 N. Baillie, J.P. Ball, N.A. Baltzell, S. Barrow, V. Batourine, M. Battaglieri, I. Bedlinskiy, M. Bektasoglu, M. Bellis, N. Benmouna, B.L. Berman, A.S. Biselli, 7, 15 L. Blaszczyk, B.E. Bonner, C. Bookwalter, S. Bouchigny, S. Boiarinov, 2 R. Bradford, D. Branford, W.J. Briscoe, W.K. Brooks, S. Bültmann, C. Butuceanu, J.R. Calarco, S.L. Careccia, D.S. Carman, 2 L. Casey, A. Cazes, S. Chen, L. Cheng, P.L. Cole, 8, 20 P. Collins, P. Coltharp, D. Cords, P. Corvisiero, D. Crabb, V. Crede, J.P. Cummings, D. Dale, N. Dashyan, R. De Masi, 23 R. De Vita, E. De Sanctis, P.V. Degtyarenko, H. Denizli, L. Dennis, A. Deur, S. Dhamija, K.V. Dharmawardane, K.S. Dhuga, R. Dickson, C. Djalali, G.E. Dodge, J. Donnelly, D. Doughty, 2 M. Dugger, S. Dytman, O.P. Dzyubak, H. Egiyan, 2, † K.S. Egiyan, L. El Fassi, P. Eugenio, 17 R. Fatemi, G. Fedotov, G. Feldman, R.J. Feuerbach, T.A. Forest, 20 A. Fradi, H. Funsten, M.Y. Gabrielyan, M. Garçon, G. Gavalian, 32 N. Gevorgyan, G.P. Gilfoyle, K.L. Giovanetti, F.X. Girod, 2 J.T. Goetz, W. Gohn, E. Golovatch, ‡ A. Gonenc, C.I.O. Gordon, R.W. Gothe, L. Graham, K.A. Griffioen, M. Guidal, M. Guillo, N. Guler, L. Guo, V. Gyurjyan, C. Hadjidakis, K. Hafidi, K. Hafnaoui, H. Hakobyan, R.S. Hakobyan, C. Hanretty, J. Hardie, 2 N. Hassall, § D. Heddle, F.W. Hersman, K. Hicks, I. Hleiqawi, M. Holtrop, C.E. Hyde-Wright, Y. Ilieva, D.G. Ireland, B.S. Ishkhanov, E.L. Isupov, M.M. Ito, D. Jenkins, H.S. Jo, J.R. Johnstone, H.G. Juengst, 32 N. Kalantarians, D. Keller, J.D. Kellie, M. Khandaker, K.Y. Kim, A. Klein, F.J. Klein, 8 A.V. Klimenko, M. Klusman, M. Kossov, Z. Krahn, L.H. Kramer, 2 V. Kubarovsky, J. Kuhn, 7 S.E. Kuhn, S.V. Kuleshov, V. Kuznetsov, J. Lachniet, 32 J.M. Laget, 2 J. Langheinrich, D. Lawrence, T. Lee, Ji Li, A.C.S. Lima, K. Livingston, H.Y. Lu, K. Lukashin, M. MacCormick, N. Markov, P. Mattione, S. McAleer, B. McKinnon, J.W.C. McNabb, B.A. Mecking, S. Mehrabyan, J.J. Melone, M.D. Mestayer, C.A. Meyer, T. Mibe, K. Mikhailov, M. Mirazita, R. Miskimen, V. Mokeev, 2 L. Morand, B. Moreno, K. Moriya, S.A. Morrow, 9 M. Moteabbed, J. Mueller, E. Munevar, G.S. Mutchler, P. Nadel-Turonski, R. Nasseripour, 37 S. Niccolai, 23 G. Niculescu, 25 I. Niculescu, 2, 25 B.B. Niczyporuk, M.R. Niroula, R.A. Niyazov, 2 M. Nozar, ¶ G.V. O’Rielly, M. Osipenko, 28 A.I. Ostrovidov, S. Park, E. Pasyuk, C. Paterson, S. Anefalos Pereira, S.A. Philips, J. Pierce, N. Pivnyuk, D. Pocanic, O. Pogorelko, E. Polli, I. Popa, S. Pozdniakov, B.M. Preedom, J.W. Price, Y. Prok, 2, ∗∗ D. Protopopescu, 19 L.M. Qin, B.A. Raue, 2 G. Riccardi, G. Ricco, M. Ripani, B.G. Ritchie, F. Ronchetti, G. Rosner, P. Rossi, D. Rowntree, P.D. Rubin, F. Sabatié, 9 M.S. Saini, J. Salamanca, C. Salgado, J.P. Santoro, 8, 2 V. Sapunenko, 2 D. Schott, R.A. Schumacher, V.S. Serov, Y.G. Sharabian, D. Sharov, J. Shaw, N.V. Shvedunov, A.V. Skabelin, E.S. Smith, D.I. Sober, D. Sokhan, A. Stavinsky, S.S. Stepanyan, S. Stepanyan, B.E. Stokes, P. Stoler, I.I. Strakovsky, S. Strauch, 37 R. Suleiman, M. Taiuti, T. Takeuchi, D.J. Tedeschi, 14 A. Tkabladze, 18 S. Tkachenko, L. Todor, 36 C. Tur, M. Ungaro, 11 M.F. Vineyard, 36 A.V. Vlassov, D.P. Watts, †† L.B. Weinstein, D.P. Weygand, M. Williams, E. Wolin, M.H. Wood, ‡‡ A. Yegneswaran, J. Yun, M. Yurov, L. Zana, B. Zhang, J. Zhang, B. Zhao, and Z.W. Zhao

High-quality cross sections for the reaction γ d → π 0 d have been measured using the CLAS at Jefferson Lab over a wide energy range near and above the η -meson photoproduction threshold. At backward c.m. angles for the outgoing pions, we observe a resonance-like structure near E γ = 700 MeV. Our model analysis shows that it can be explained by η excitation in the intermediate state. The effect is the result of the contribution of the N (1535) S 11 -resonance to the amplitudes of the subprocesses occurring between the two nucleons and of a two-step process in which the excitation of an intermediate η -meson dominates.

A search for exotic mesons in the pi;{+}pi;{+}pi;{-} system photoproduced by the charge exchange reaction gammap-->pi;{+}pi;{+}pi;{-}(n) was carried out by the CLAS Collaboration at Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range, produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on a liquid-hydrogen target. A partial wave analysis was performed on a sample of 83 000 events, the highest such statistics to date in this reaction at these energies. The main objective of this study was to look for the photoproduction of an exotic J;{PC}=1;{-+} resonant state in the 1 to 2 GeV mass range. Our partial wave analysis shows production of the a_{2}(1320) and the pi_{2}(1670) mesons, but no evidence for the a_{1}(1260), nor the pi_{1}(1600) exotic state at the expected levels. An upper limit of 13.5 nb is determined for the exotic pi_{1}(1600) cross section, less than 2% of the a_{2}(1320) production.

The spin structure functions g, for the proton and the deuteron have been measured over a wide kinematic range in x and Q(2) using 1.6 and 5.7 GeV longitudinally polarized electrons incident upon polarized NH3 and ND3 targets at Jefferson Lab. Scattered electrons were detected in the CEBAF Large Acceptance Spectrometer, for 0.05 < Q(2) < 5 GeV2 and W < 3 GeV. The first moments of g(1) for the proton and deuteron are presented - both have a negative slope at low Q(2), as predicted by the extended Gerasimov-Drell-Hearn sum rule. The first extraction of the generalized forward spin polarizability of the proton gamma(p)(0) is also reported. This quantity shows strong Q(2) dependence at low Q(2). Our analysis of the Q(2) evolution of the first moment of g, shows agreement in leading order with Heavy Baryon Chiral Perturbation Theory. However, a significant discrepancy is observed between the gamma(p)(0) data and Chiral Perturbation calculations for gamma(p)(0), even at the lowest Q(2). (C) 2009 Elsevier B.V. All rights reserved.

This paper reports on the most comprehensive data set obtained on differential and fully integrated cross sections for the process $e p \to e' p \pi^{+} \pi^{-} $. The data were collected with the CLAS detector at Jefferson Laboratory. Measurements were carried out in the so-far unexplored kinematic region of photon virtuality 0.2 $<$ $Q^{2}$ $<$ 0.6 GeV$^{2}$ and invariant mass of the final hadron system $W$ from 1.3 to 1.57 GeV. For the first time, nine independent 1-fold differential cross sections were determined in each bin of $W$ and $Q^{2}$ covered by the measurements. A phenomenological analysis of the data allowed us to establish the most significant mechanisms contributing to the reaction. The non-resonant mechanisms account for a major part of cross-sections. However, we find sensitivity to s-channel excitations of low-mass nucleon resonances, especially to the $N(1440)P_{11}$ and $N(1520)D_{13}$ states in kinematical dependencies of the 1-fold differential cross-sections.

This paper reports on the most comprehensive data set obtained on differential and fully integrated cross sections for the process ep. e -> p pi(+)pi(-). The data were collected with the CLAS detector at Jefferson Laboratory. Measurements were carried out in the as yet unexplored kinematic region of photon virtuality 0.2 < Q(2) < 0.6 GeV2 and invariant mass of the final hadron system W from 1.3 to 1.57 GeV. For the first time, nine independent one-fold differential cross sections were determined in each bin of W and Q(2) covered by the measurements. A phenomenological analysis of the data allowed us to establish the most significant mechanisms contributing to the reaction. The nonresonant mechanisms account for a major part of cross sections. However, we find sensitivity to s-channel excitations of low-mass nucleon resonances, especially to the N(1440)P-11 and N(1520)D-13 states in kinematic dependencies of the one-fold differential cross sections.

We report on the results of the first measurement of exclusive f_{0}(980) meson photoproduction on protons for E_{gamma}=3.0-3.8 GeV and -t=0.4-1.0 GeV2. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The resonance was detected via its decay in the pi;{+}pi;{-} channel by performing a partial wave analysis of the reaction gammap-->ppi;{+}pi;{-}. Clear evidence of the f_{0}(980) meson was found in the interference between P and S waves at M_{pi;{+}pi;{-}} approximately 1 GeV. The S-wave differential cross section integrated in the mass range of the f_{0}(980) was found to be a factor of about 50 smaller than the cross section for the rho meson. This is the first time the f_{0}(980) meson has been measured in a photoproduction experiment.

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)$^2$ $

Semi-inclusive pi+ electroproduction on protons has been measured with the CLAS detector at Jefferson Lab. The measurement was performed on a liquid-hydrogen target using a 5.75 GeV electron beam. The complete five-fold differential cross sections were measured over a wide kinematic range including the complete range of azimuthal angles between hadronic and leptonic planes, phi, enabling us to separate the phi-dependent terms. Our measurements of phi-independent term of the cross section at low Bjorken x were found to be in fairly good agreement with pQCD calculations. Indeed, the conventional current fragmentation calculation can account for almost all of the observed cross section, even at small pi+ momentum. The measured center-of-momentum spectra are in qualitative agreement with high energy data, which suggests a surprising numerical similarity between the spectator diquark fragmentation in the present reaction and the anti-quark fragmentation measured in e+e- collisions. We have observed that the two phi-dependent terms of the cross section are small. Within our precision the cos(2phi) term is compatible with zero, except for low-z region, and the measured cos(phi) term is much smaller in magnitude than the sum of the Cahn and Berger effects.

A search for exotic mesons in the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ system photoproduced by the charge exchange reaction $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}(n)$ was carried out by the CLAS Collaboration at Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range, produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on a liquid-hydrogen target. A partial wave analysis was performed on a sample of 83 000 events, the highest such statistics to date in this reaction at these energies. The main objective of this study was to look for the photoproduction of an exotic ${J}^{PC}={1}^{\ensuremath{-}+}$ resonant state in the 1 to 2 GeV mass range. Our partial wave analysis shows production of the ${a}_{2}(1320)$ and the ${\ensuremath{\pi}}_{2}(1670)$ mesons, but no evidence for the ${a}_{1}(1260)$, nor the ${\ensuremath{\pi}}_{1}(1600)$ exotic state at the expected levels. An upper limit of 13.5 nb is determined for the exotic ${\ensuremath{\pi}}_{1}(1600)$ cross section, less than 2% of the ${a}_{2}(1320)$ production.

M. Battaglieri, R. De Vita, A. P. Szczepaniak, K. P. Adhikari, M. Aghasyan, M. J. Amaryan, P. Ambrozewicz, M. Anghinolfi, G. Asryan, H. Avakian, H. Bagdasaryan, N. Baillie, J. P. Ball, N. A. Baltzell, V. Batourine, I. Bedlinskiy, M. Bellis, N. Benmouna, B. L. Berman, L. Bibrzycki, A. S. Biselli, C. Bookwalter, S. Bouchigny, S. Boiarinov, R. Bradford, D. Branford, W. J. Briscoe, W.K. Brooks, S. Bultmann, V.D. Burkert, J. R. Calarco, S. L. Careccia, D. S. Carman, L. Casey, S. Chen, L. Cheng, E. Clinton, P. L. Cole, P. Collins, D. Crabb, H. Crannell, V. Crede, J. P. Cummings, D. Dale, A. Daniel, N. Dashyan, R. De Masi, E. De Sanctis, P. V. Degtyarenko, A. Deur, S. Dhamija, K.V. Dharmawardane, R. Dickson, C. Djalali, G. E. Dodge, J. Donnelly, D. Doughty, M. Dugger, O. P. Dzyubak, H. Egiyan, K. S. Egiyan, L. El Fassi, L. Elouadrhiri, P. Eugenio, G. Fedotov, R. Fersch, T. A. Forest, A. Fradi, M.Y. Gabrielyan, L. Gan, M. Garcon, A. Gasparian, G. Gavalian, N. Gevorgyan, G. P. Gilfoyle, K. L. Giovanetti, F. X. Girod, O. Glamazdin, J. Goett, J. T. Goetz, W. Gohn, E. Golovatch, C. I. O. Gordon, R.W. Gothe, L. Graham, K.A. Griffioen, M. Guidal, N. Guler, L. Guo, V. Gyurjyan, C. Hadjidakis, K. Hafidi, H. Hakobyan, R. S. Hakobyan, C. Hanretty, J. Hardie, N. Hassall, D. Heddle, F.W. Hersman, K. Hicks, I. Hleiqawi, M. Holtrop, C. E. Hyde, Y. Ilieva, D.G. Ireland, B. S. Ishkhanov, E. L. Isupov, M.M. Ito, D. Jenkins, H. S. Jo, J. R. Johnstone, K. Joo, H. G. Juengst, T. Kageya, N. Kalantarians, D. Keller, J. D. Kellie, M. Khandaker, P. Khetarpal, W. Kim, A. Klein, F. J. Klein, A.V. Klimenko, P. Konczykowski, M. Kossov, Z. Krahn, L. H. Kramer, V. Kubarovsky, J. Kuhn, S. E. Kuhn, S. V. Kuleshov, V. Kuznetsov, J. Lachniet, J.M. Laget, J. Langheinrich, D. Lawrence, T. Lee, L. Lesniak, Ji Li, K. Livingston, M. Lowry, H. Y. Lu, M.MacCormick, S. Malace, N.Markov, P. Mattione, M. E. McCracken, B. McKinnon, B. A. Mecking, J. J. Melone, M.D. Mestayer, C. A. Meyer, T. Mibe, K. Mikhailov, T Mineeva, R. Minehart, M. Mirazita, R. Miskimen, V. Mochalov, V. Mokeev, B. Moreno, K. Moriya, S. A. Morrow, M. Moteabbed, E. Munevar, G. S. Mutchler, P. Nadel-Turonski, I. Nakagawa, R. Nasseripour, S. Niccolai, G. Niculescu, I. Niculescu, B. B. Niczyporuk, M.R. Niroula, R.A. Niyazov, M. Nozar, M. Osipenko, A. I. Ostrovidov, K. Park, S. Park, E. Pasyuk, M. Paris, C. Paterson, S. Anefalos Pereira, J. Pierce, N. Pivnyuk, D. Pocanic, O. Pogorelko, S. Pozdniakov, J.W. Price, Y. Prok, D. Protopopescu, B. A. Raue, G. Riccardi, G. Ricco, M. Ripani, B.G. Ritchie, G. Rosner, P. Rossi, F. Sabatie, M. S. Saini, J. Salamanca, C. Salgado, A. Sandorfi, J. P. Santoro, V. Sapunenko, D. Schott, R.A. Schumacher, V. S. Serov, Y.G. Sharabian, D. Sharov, N.V. Shvedunov, E. S. Smith, L. C. Smith, D. I. Sober, D. Sokhan, A. Starostin, A. Stavinsky, S. Stepanyan, S. S. Stepanyan, B. E. Stokes, P. Stoler, K.A. Stopani, I. I. Strakovsky, S. Strauch, M. Taiuti, D. J. Tedeschi, A. Teymurazyan, A. Tkabladze, S. Tkachenko, L. Todor, C. Tur, M. Ungaro, M. F. Vineyard, A. V. Vlassov, D. P. Watts, X. Wei, L. B. Weinstein, D. P. Weygand, M. Williams, E. Wolin, M.H. Wood, A. Yegneswaran, M. Yurov, L. Zana, J. Zhang, B. Zhao, and Z.W. Zhao

The neutron elastic magnetic form factor was extracted from quasielastic electron scattering on deuterium over the range Q(2)=1.0-4.8 GeV2 with the CLAS detector at Jefferson Lab. High precision was achieved with a ratio technique and a simultaneous in situ calibration of the neutron detection efficiency. Neutrons were detected with electromagnetic calorimeters and time-of-flight scintillators at two beam energies. The dipole parametrization gives a good description of the data.