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Now showing items 17 - 32 of 36

  • Measurement of the nucleon structure function F(2) in the nuclear medium and evaluation of its moments RID A-2439-2012 RID E-8618-2010 RID B-4083-2012

    Osipenko, M.   Ricco, G.   Simula, S.   Ripani, M.   Taiuti, M.   Adhikari, K. P.   Amaryan, M. J.   Anghinolfi, M.   Avakian, H.   Baghdasaryan, H.   Battaglieri, M.   Batourine, V.   Bedlinskiy, I.   Biselli, A. S.   Branford, D.   Briscoe, W. J.   Brooks, W. K.   Burkert, V. D.   Careccia, S. L.   Carman, D. S.   Cole, P. L.   Collins, P.   Crede, V.   D'Angelo, A.   Daniel, A.   Dashyan, N.   De Vita, R.   De Sanctis, E.   Deur, A.   Dey, B.   Dhamija, S.   Dickson, R.   Djalali, C.   Doughty, D.   Dupre, R.   Egiyan, H.   El Alaoui, A.   Eugenio, P.   Fegan, S.   Forest, T. A.   Fradi, A.   Gabrielyan, M. Y.   Gevorgyan, N.   Gilfoyle, G. P.   Giovanetti, K. L.   Gohn, W.   Gothe, R. W.   Griffioen, K. A.   Guo, L.   Hafidi, K.   Hakobyan, H.   Hanretty, C.   Hassall, N.   Heddle, D.   Hicks, K.   Holtrop, M.   Ilieva, Y.   Ireland, D. G.   Isupov, E. L.   Jawalkar, S. S.   Jo, H. S.   Joo, K.   Keller, D.   Khandaker, M.   Khetarpal, P.   Kim, W.   Klein, A.   Klein, F. J.   Kubarovsky, V.   Kuhn, S. E.   Kuleshov, S. V.   Kuznetsov, V.   Livingston, K.   Lu, H. Y.   Martinez, D.   Mayer, M.   McAndrew, J.   McCracken, M. E.   McKinnon, B.   Meyer, C. A.   Mirazita, M.   Mokeev, V.   Moreno, B.   Moriya, K.   Morrison, B.   Moutarde, H.   Munevar, E.   Nadel-Turonski, P.   Nasseripour, R.   Niccolai, S.   Niculescu, I.   Ostrovidov, A. I.   Paremuzyan, R.   Park, K.   Park, S.   Pasyuk, E.   Pereira, S. Anefalos   Pisano, S.   PogoreIko, O.   Pozdniakov, S.   Price, J. W.   Procureur, S.   Prok, Y.   Protopopescu, D.   Raue, B. A.   Rosner, G.   Rossi, P.   Sabatie, F.   Saini, M. S.   Salamanca, J.   Salgado, C.   Saracco, P.   Schumacher, R. A.   Seraydaryan, H.   Sharabian, Y. G.   Smith, E. S.   Sober, D.   Sokhan, D.   Stepanyan, S. S.   Stepanyan, S.   Stoler, P.   Strauch, S.   Tedeschi, D. J.   Tkachenko, S.   Ungaro, M.   Vernarsky, B.   Vineyard, M. F.   Voutier, E.   Watts, D. P.   Weygand, D. P.   Wood, M. H.   Yegneswaran, A.   Zhang, J.   Zhao, B.  

    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 final-state hadronic system W approximate to 2.4 GeV with four-momentum transfers Q(2) ranging from 0.2 to 5 (GeV/c)(2). These data, together with previous measurements of the inclusive electron scattering off proton and deuteron, which cover a similar continuous two-dimensional region of Q(2) 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 F(2) structure function and its moments. Using an OPE-based twist expansion, we studied the Q(2)-evolution of the moments, obtaining a separation of the leading-twist and the total higher-twist terms. The carbon-to-deuteron ratio of the leading-twist contributions to the F(2) moments exhibits the well-known EMC effect, compatible with that discovered previously in x-space. The total higher-twist term in the carbon nucleus appears, although with large systematic uncertainties, 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. (C) 2010 Elsevier B.V. All rights reserved.
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  • The G0 experiment: Apparatus for parity-violating electron scattering measurements at forward and backward angles

    Androic, D.   Armstrong, D. S.   Arvieux, J.   Asaturyan, R.   Averett, T. D.   Bailey, S. L.   Batigne, G.   Beck, D. H.   Beise, E. J.   Benesch, J.   Benmokhtar, F.   Bimbot, L.   Birchall, J.   Biselli, A.   Bosted, P.   Breuer, H.   Brindza, P.   Capuano, C. L.   Carlini, R. D.   Carr, R.   Chant, N.   Chao, Y. -C.   Clark, R.   Coppens, A.   Covrig, S. D.   Cowley, A.   Dale, D.   Davis, C. A.   Ellis, C.   Falk, W. R.   Fenker, H.   Finn, J. M.   Forest, T.   Franklin, G.   Frascari, R.   Furget, C.   Gaskell, D.   Gericke, M. T. W.   Grames, J.   Griffioen, K. A.   Grimm, K.   Guillard, G.   Guillon, B.   Guler, H.   Gustafsson, K.   Hannelius, L.   Hansknecht, J.   Hasty, R. D.   Allen, A. M. Hawthorne   Horn, T.   Ito, T. M.   Johnston, K.   Jones, M.   Kammel, P.   Kazimi, R.   King, P. M.   Kolarkar, A.   Korkmaz, E.   Korsch, W.   Kox, S.   Kuhn, J.   Lachniet, J.   Laszewski, R.   Lee, L.   Lenoble, J.   Liatard, E.   Liu, J.   Lung, A.   MacLachlan, G. A.   Mammei, J.   Marchand, D.   Martin, J. W.   Mack, D. J.   McFarlane, K. W.   McKee, D. W.   McKeown, R. D.   Merchez, F.   Mihovilovic, M.   Micherdzinska, A.   Mkrtchyan, H.   Moffit, B.   Morlet, M.   Muether, M.   Musson, J.   Nakahara, K.   Neveling, R.   Niccolai, S.   Nilsson, D.   Ong, S.   Page, S. A.   Papavassiliou, V.   Pate, S. F.   Phillips, S. K.   Pillot, P.   Pitt, M. L.   Poelker, M.   Porcelli, T. A.   Quemener, G.   Quinn, B. P.   Ramsay, W. D.   Rauf, A. W.   Real, J. -S.   Ries, T.   Roche, J.   Roos, P.   Rutledge, G. A.   Schaub, J.   Secrest, J.   Seva, T.   Simicevic, N.   Smith, G. R.   Spayde, D. T.   Stepanyan, S.   Stutzman, M.   Suleiman, R.   Tadevosyan, V.   Tieulent, R.   van de Wiele, J.   van Oers, W. T. H.   Versteegen, M.   Voutier, E.   Vulcan, W. F.   Wells, S. P.   Warren, G.   Williamson, S. E.   Woo, R. J.   Wood, S. A.   Yan, C.   Yun, J.   Zeps, V.  

    In the GO experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part-per-million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cherenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed. (C) 2011 Elsevier B.V. All rights reserved.
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  • Target and double spin asymmetries of deeply virtual pi(0) production with a longitudinally polarized proton target and CLAS

    Kim, A.   Avakian, H.   Burkert, V.   Joo, K.   Kim, W.   Adhikari, K. P.   Akbar, Z.   Pereira, S. Anefalos   Badui, R. A.   Battaglieri, M.   Batourine, V.   Bedlinskiy, I.   Biselli, A. S.   Boiarinov, S.   Bosted, P.   Briscoe, W. J.   Brooks, W. K.   Bultmann, S.   Cao, T.   Carman, D. S.   Celentano, A.   Chandavar, S.   Charles, G.   Chetry, T.   Colaneri, L.   Cole, P. L.   Compton, N.   Contalbrigo, M.   Cortes, O.   Crede, V.   D'Angelo, A.   Dashyan, N.   De Vita, R.   De Sanctis, E.   Djalali, C.   Egiyan, H.   El Alaoui, A.   El Fassi, L.   Eugenio, P.   Fedotov, G.   Fersch, R.   Filippi, A.   Fleming, J. A.   Fradi, A.   Con, M. Garc   Ghandilyan, Y.   Gilfoyle, G. P.   Giovanetti, K. L.   Girod, F. X.   Gohn, W.   Golovatch, E.   Gothe, R. W.   Griffioen, K. A.   Guo, L.   Hafidi, K.   Hanretty, C.   Hattawy, M.   Heddle, D.   Hicks, K.   Holtrop, M.   Ilieva, Y.   Ireland, D. G.   Ishkhanov, B. S.   Jenkins, D.   Jiang, H.   Jo, H. S.   Joosten, S.   Keller, D.   Khachatryan, G.   Khandaker, M.   Klein, A.   Klein, F. J.   Kubarovsky, V.   Kuhn, S. E.   Kuleshov, S. V.   Lanza, L.   Lenisa, P.   Lu, H. Y.   MacGregor, I. J. D.   Markov, N.   Mattione, P.   McCracken, M. E.   McKinnon, B.   Mokeev, V.   Movsisyan, A.   Munevar, E.   Nadel-Turonski, P.   Net, L. A.   Niccolai, S.   Osipenko, M.   Ostrovidov, A. I.   Paolone, M.   Park, K.   Pasyuk, E.   Phelps, W.   Pisano, S.   Pogorelko, O.   Price, J. W.   Prok, Y.   Ripani, M.   Rizzo, A.   Rosner, G.   Rossi, P.   Roy, P.   Salgado, C.   Schumacher, R. A.   Seder, E.   Sharabian, Y. G.   Skorodumina, Iu.   Smith, G. D.   Sokhan, D.   Sparveris, N.   Stepanyan, S.   Stoler, P.   Strakovsky, I. I.   Strauch, S.   Sytnik, V.   Taiuti, M.   Torayev, B.   Ungaro, M.   Voskanyan, H.   Voutier, E.   Watts, D. P.   Wei, X.   Weinstein, L. B.   Zachariou, N.   Zana, L.   Zhang, J.  

    The target and double spin asymmetries of the exclusive pseudoscalar channel (e) over right arrow(p) over right arrow -> ep pi(0) ere measured for the first time in the deep-inelastic regime using a longitudinally polarized 5.9 GeV electron beam and a longitudinally polarized proton target at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS). The data were collected over a large kinematic phase space and divided into 110 four-dimensional bins of Q(2), x(B), -t and phi. Large values of asymmetry moments clearly indicate a substantial contribution to the polarized structure functions from transverse virtual photon amplitudes. The interpretation of experimental data in terms of generalized parton distributions (GPDs) provides the first insight on the chiral-odd GPDs (I) over tildeI(T) and E-T, and complement previous measurements of unpolarized structure functions sensitive to the GPDs H-T and (E) over bar (T). These data provide a crucial input for parametrizations of essentially unknown chiral-odd GPDs and will strongly influence existing theoretical calculations based on the handbag formalism. (C) 2017 The Author(s). Published by Elsevier B.V.
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  • [AIP INTERSECTIONS OF PARTICLE AND NUCLEAR PHYSICS: 9th Conference CIPAN2006 - Rio Grande, Puerto Rico (USA) (30 May-3June 2006)] AIP Conference Proceedings - Overview of the CLAS/JLAB Physics Program

    Stepanyan, S.  

    The CLAS collaboration has developed a broad program for studying electromagnetically induced processes with both electron and photon beams. This program includes topics such as excited baryon resonances, meson production, hadron structure, search for pentaquarks, and the structure of nuclei. In this report, highlights of recent CLAS results will be presented
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  • Measurement of transparency ratios for protons from short-range correlated pairs

    Hen, O.   Hakobyan, H.   Shneor, R.   Piasetzky, E.   Weinstein, L. B.   Brooks, W. K.   Beck, S. May-Tal   Gilad, S.   Korover, I.   Beck, A.   Adhikari, K. P.   Aghasyan, M.   Amaryan, M. J.   Pereira, S. Anefalos   Arrington, J. R.   Baghdasaryan, H.   Ball, J.   Battaglieri, M.   Batourine, V.   Bedlinskiy, I.   Biselli, A. S.   Bono, J.   Boiarinov, S.   Briscoe, W. J.   Burkert, V. D.   Carman, D. S.   Celentano, A.   Chandavar, S.   Cole, P. L.   Contalbrigo, M.   Crede, V.   D'Angelo, A.   Dashyan, N.   De Vita, R.   De Sanctis, E.   Deur, A.   Djalali, C.   Dodge, G. E.   Doughty, D.   Dupre, R.   Egiyan, H.   El Alaoui, A.   El Fassi, L.   Eugenio, P.   Fedotov, G.   Fegan, S.   Fleming, J. A.   Gabrielyan, M. Y.   Gevorgyan, N.   Gilfoyle, G. P.   Giovanetti, K. L.   Girod, F. X.   Goetz, J. T.   Gohn, W.   Golovatch, E.   Gothe, R. W.   Griffioen, K. A.   Guo, L.   Hafidi, K.   Harrison, N.   Heddle, D.   Hicks, K.   Holtrop, M.   Hyde, C. E.   Ilieva, Y.   Ireland, D. G.   Ishkhanov, B. S.   Isupov, E. L.   Jo, H. S.   Joo, K.   Keller, D.   Khandaker, M.   Khetarpal, P.   Kim, A.   Klein, F. J.   Koirala, S.   Kubarovsky, A.   Kubarovsky, V.   Kuhn, S. E.   Livingston, K.   Lu, H. Y.   MacGregor, I. J. D.   Martinez, D.   Mayer, M.   McKinnon, B.   Mineeva, T.   Mokeev, V.   Montgomery, R. A.   Moutarde, H.   Munevar, E.   Camacho, C. Munoz   Mustapha, B.   Nadel-Turonski, P.   Nasseripour, R.   Niccolai, S.   Niculescu, G.   Niculescu, I.   Osipenko, M.   Ostrovidov, A. I.   Pappalardo, L. L.   Paremuzyan, R.   Park, K.   Park, S.   Pasyuk, E.   Phelps, E.   Phillips, J. J.   Pisano, S.   Pivnyuk, N.   Pogorelko, O.   Pozdniakov, S.   Price, J. W.   Procureur, S.   Protopopescu, D.   Puckett, A. J. R.   Raue, B. A.   Rimal, D.   Ripani, M.   Ritchie, B. G.   Rosner, G.   Rossi, P.   Sabatie, F.   Saini, M. S.   Schott, D.   Schumacher, R. A.   Seraydaryan, H.   Sharabian, Y. G.   Smith, G. D.   Sober, D. I.   Sokhan, D.   Stepanyan, S. S.   Stepanyan, S.   Strauch, S.   Taiuti, M.   Tang, W.   Taylor, C. E.   Tian, Ye   Tkachenko, S.   Ungaro, M.   Vernarsky, B.   Vlassov, A.   Voskanyan, H.   Voutier, E.   Walford, N. K.   Watts, D. P.   Wood, M. H.   Zachariou, N.   Zana, L.   Zhang, J.   Zheng, X.   Zonta, I.  

    Nuclear transparency, T-p(A), is a measure of the average probability for a struck proton to escape the nucleus without significant re-interaction. Previously, nuclear transparencies were extracted for quasi-elastic A(e, e' p) knockout of protons with momentum below the Fermi momentum, where the spectral functions are well known. In this Letter we extract a novel observable, the transparency ratio, T-p(A)/T-p(C-12), for knockout of high-missing-momentum protons from the breakup of short-range correlated pairs (2N-SRC) in Al, Fe and Pb nuclei relative to C. The ratios were measured at momentum transfer Q(2) >= 1.5 (GeV/c)(2) and x(B) >= 1.2 where the reaction is expected to be dominated by electron scattering from 2N-SRC. The transparency ratios of the knocked-out protons coming from 2N-SRC breakup are 20-30% lower than those of previous results for low missing momentum. They agree with Glauber calculations and agree with renormalization of the previously published transparencies as proposed by recent theoretical investigations. The new transparencies scale as A(-1/3), which is consistent with dominance of scattering from nucleons at the nuclear surface. (C) 2013 Elsevier B.V. All rights reserved.
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  • Measurement of the x- and Q(2)-dependence of the asymmetry A(1) on the nucleon RID A-2074-2012 RID E-8618-2010 RID B-4083-2012

    Dharmawardane, K. V.   Kuhn, S. E.   Bosted, P.   Prok, Y.   Adams, G.   Ambrozewicz, P.   Anghinolfi, M.   Asryan, G.   Avakian, H.   Bagdasaryan, H.   Baillie, N.   Ball, J. P.   Baltzell, N. A.   Barrow, S.   Batourine, V.   Battaglieri, M.   Beard, K.   Bedlinskiy, I.   Bektasoglu, M.   Bellis, M.   Benmouna, N.   Biselli, A. S.   Bonner, B. E.   Bouchigny, S.   Boiarinov, S.   Bradford, R.   Branford, D.   Brooks, W. K.   Bultmann, S.   Burkert, V. D.   Butuceanu, C.   Calarco, J. R.   Careccia, S. L.   Carman, D. S.   Carnahan, B.   Cazes, A.   Chen, S.   Cole, P. L.   Collins, P.   Coltharp, P.   Cords, D.   Corvisiero, P.   Crabb, D.   Crannell, H.   Crede, V.   Cummings, J. P.   De Masi, R.   DeVita, R.   De Sanctis, E.   Degtyarenko, P. V.   Denizli, H.   Dennis, L.   Deur, A.   Djalali, C.   Dodge, G. E.   Donnelly, J.   Doughty, D.   Draigovitsch, P.   Dugger, M.   Dytman, S.   Dzyubak, O. P.   Egiyan, H.   Egiyan, K. S.   Elouadrhiri, L.   Eugenio, P.   Fatemi, R.   Fedotov, G.   Feuerbach, R. J.   Forest, T. A.   Funsten, H.   Garcon, M.   Gavalian, G.   Gilfoyle, G. P.   Giovanetti, K. L.   Girod, F. X.   Goetz, J. T.   Golovatch, E.   Gonenc, A.   Gothe, R. W.   Griffioen, K. A.   Guidal, M.   Guillo, M.   Guler, N.   Guo, L.   Gyurjyan, V.   Hadjidakis, C.   Hafidi, K.   Hakobyan, R. S.   Hardie, J.   Heddle, D.   Hersman, F. W.   Hicks, K.   Hleiqawi, I.   Holtrop, M.   Huertas, M.   Hyde-Wriyht, C. E.   Ilieva, Y.   Ireland, D. G.   Ishkhanov, B. S.   Isupov, E. L.   Ito, M. M.   Jenkins, D.   Jo, H. S.   Joo, K.   Juengst, H. G.   Keith, C.   Kellie, J. D.   Khandaker, M.   Kim, K. Y.   Kim, K.   Kim, W.   Klein, A.   Klein, F. J.   Klusman, M.   Kossov, M.   Kramer, L. H.   Kubarovsky, V.   Kuhn, J.   Kuleshov, S. V.   Lachniet, J.   Laget, J. M.   Langheinrich, J.   Lawrence, D.   Li, Ji   Lima, A. C. S.   Livingston, K.   Lu, H.   Lukashin, K.   MacCormick, M.   Manak, J. J.   Markov, N.   McAleer, S.   McKinnon, B.   McNabb, J. W. C.   Mecking, B. A.   Mestayer, M. D.   Meyer, C. A.   Mibe, T.   Mikhailov, K.   Minehart, R.   Mirazita, M.   Miskimen, R.   Mokeev, V.   Morand, L.   Morrow, S. A.   Moteabbed, M.   Mueller, J.   Mutchler, G. S.   Nadel-Turonski, P.   Napolitano, J.   Nasseripour, R.   Niccolai, S.   Niculescu, G.   Niculescu, I.   Niczyporuk, B. B.   Niroula, M. R.   Nyazov, R. A.   Nozar, M.   O'Rielly, G. V.   Osipenko, M.   Ostrovidov, A. I.   Park, K.   Pasyuk, E.   Paterson, C.   Philips, S. A.   Pierce, J.   Pivnyuk, N.   Pocanic, D.   Pogorelko, O.   Polli, E.   Pozdniakov, S.   Preedom, B. M.   Price, J. W.   Protopopescu, D.   Qin, L. M.   Raue, B. A.   Riccardi, G.   Ricco, G.   Ripani, M.   Ritchie, B. G.   Ronchetti, F.   Rosner, G.   Rossi, P.   Rowntree, D.   Rubin, P. D.   Sabatie, E.   Salgado, C.   Santoro, J. P.   Sapunenko, V.   Schumacher, R. A.   Serov, V. S.   Sharabian, Y. G.   Shaw, J.   Shvedunov, N. V.   Skabelin, A. V.   Smith, E. S.   Smith, L. C.   Sober, D. I.   Stavinsky, A.   Stepanyan, S. S.   Stepanyan, S.   Stokes, B. E.   Stoler, P.   Strakovsky, I. I.   Strauch, S.   Suleiman, R.   Taiuti, M.   Taylor, S.   Tedeschi, D. J.   Thoma, U.   Thompson, R.   Tkabladze, A.   Tkachenko, S.   Todor, L.   Tur, C.   Ungaro, M.   Vineyard, M. F.   Vlassov, A. V.   Weinstein, L. B.   Weygand, D. P.   Williams, M.   Wolin, E.   Wood, M. H.   Yegneswaran, A.   Yun, J.   Zana, L.   Zhang, J.   Zhao, B.   Zhao, Z.  

    We report results for the virtual photon asymmetry A I on the nucleon from new Jefferson Lab measurements. The experiment, which used the CEBAF Large Acceptance Spectrometer and longitudinally polarized proton ((NH3)-N-15) and deuteron ((ND3)-N-15) targets, collected data with a longitudinally polarized electron beam at energies between 1.6 GeV and 5.7 GeV. In the present. Letter, we concentrate on our results for A(1) (x, Q(2)) and the related ratio g(1)/F-1 (x, Q(2))) in the resonance and the deep inelastic regions for our J west and highest beam energies, covering a range in momentum transfer Q(2) from 0.05 to 5.0 (GeV/c)(2) and in final-state invariant mass W up to about 3 GeV. Our data show detailed structure in the resonance re-ion, which leads to a strong Q(2) dependence of A(1) (x, Q(2)) to. W below 2 GeV. At higher W, a smooth approach to the scaling limit, established by earlier experiments, can be seen, but A I (x, Q(2)) is not strictly Q(2)-independent. We add significantly to the world data set at high x, up to x = 0.6. Our data exceed the SU(6)-symmetric quark model expectation for both the proton and the deuteron while being consistent with a negative d-quark polarization up to our highest x. This data set should improve next-to-leading order (NLO) pQCD fits of the parton polarization distributions. (c) 2006 Elsevier B.V.All rights reserved.
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  • The Heavy Photon Search beamline and its performance

    Baltzell, N.   Egiyan, H.   Ehrhart, M.   Field, C.   Freyberger, A.   Girod, F. -X.   Holtrop, M.   Jaros, J.   Kalicy, G.   Maruyama, T.   McKinnon, B.   Moffeit, K.   Nelson, T.   Odian, A.   Oriunno, M.   Paremuzyan, R.   Stepanyan, S.   Tiefenback, M.   Uemura, S.   Ungaro, M.   Vance, H.  

    The Heavy Photon Search (HPS) is an experiment to search for a hidden sector photon, aka a heavy photon or dark photon, in fixed target electroproduction at the Thomas Jefferson National Accelerator Facility (JLab). The HPS experiment searches for the e(+)e(-) decay of the heavy photon with bump hunt and detached vertex strategies using a compact, large acceptance forward spectrometer, consisting of a silicon microstrip detector (SVT) for tracking and vertexing, and a PbWO4 electromagnetic calorimeter for energy measurement and fast triggering. To achieve large acceptance and good vertexing resolution, the first layer of silicon detectors is placed just 10 cm downstream of the target with the sensor edges only 500 mu m above and below the beam. Placing the SVT in such close proximity to the beam puts stringent requirements on the beam profile and beam position stability. As part of an approved engineering run, HPS took data in 2015 and 2016 at 1.05 GeV and 2.3 GeV beam energies, respectively. This paper describes the beam line and its performance during that data taking.
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  • A double-target system for precision measurements of nuclear medium effects

    Hakobyan, H.   Brooks, W. K.   Bruhwel, K.   Burkert, V. D.   Carstens, T.   Christo, S.   Egiyan, H.   Gevorgyan, N.   Gram, J.   Hafidi, K.   Hemler, P.   Insley, D.   Jacobs, G.   Kashy, D.   Mecking, B. A.   Sharabian, Y.   Stepanyan, S.   Tilles, D.   Weinstein, L.   Zheng, X.  

    A double-target system has been developed for precision measurements of nuclear medium effects in unpolarized electron scattering with 4-5 GeV electron beams. This system allows for a precise comparison of elementary targets such as deuterium and hydrogen to heavy solid targets to study subtle medium effects such as color transparency, transverse momentum broadening, and hadron attenuation. One cryo-target and one solid target were located in the beam simultaneously, separated by 4 cm to minimize acceptance correction differences in the large CLAS spectrometer while maintaining the ability to identify the target event-by-event. Because both targets were positioned in the beam simultaneously, time-dependent systematic effects such as drifting gains or inefficient detector channels cancel in ratios of observables, increasing the precision of the final results. Measurements were performed with hydrogen and deuterium in combination with 3 mm diameter targets of carbon, aluminum, iron, tin, and lead. The solid targets and deuterium target were comparable in thicknesses except for specialized diagnostic runs with ultra-thin aluminum. Switching of the solid targets was performed remotely and required only a few seconds to complete. An ultra-low mass vacuum chamber made from Rohacell(C) foam provided vacuum isolation of the cryotarget without adding significantly to multiple scattering of final-state particles. (C) 2008 Elsevier B.V. All rights reserved.
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  • Measurement of spin structure functions at moderate Q 2 using CLAS

    Kuhn, S.E.   Dharmawardane, V.   Dodge, G.E.   Stepanyan, S.   Prok, Y.   Minehart, R.   Burkert, V.  

    Spin structure functions of the nucleon in the region of large x and small to moderate Q 2 continue to be of high current interest. Among the topics one can study in this kinematic regime are spin-dependent resonance transition amplitudes and their interference with each other and the nonresonant background, the behavior of the asymmetry A 1 at large x, and the presence or absence of local duality in spin structure functions. The first moment of the spin structure function g 1 goes through a rapid transition from the photon point (Q 2=0), where it is constrained by the Gerasimov-Drell-Hearn sum rule, to the deep inelastic limit where it is sensitive to the nucleon spin fraction carried by quarks. This opens up the possibility to study the transition from hadronic to quark degrees of freedom over the whole range of Q 2. Recently, we concluded a large experimental program to measure these observables with polarized proton and deuteron targets at Jefferson Lab. A highly polarized electron beam, solid polarized NH 3 and ND 3 targets and the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B were used to accumulate over 23 billion events with 4 different beam energies of 1.6, 2.5, 4.2 and 5.7 GeV. We present an overview of the experiment, its kinematic coverage and its statistical power. We show final results from the first run at 2.5 GeV and 4 GeV and preliminary results from the 5.7 GeV and the 1.6 GeV data sets
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  • Timelike Compton Scattering at JLab 12 GeV

    Nadel-Turonski, P.   Guidal, M.   Horn, T.   Paremuzyan, R.   Stepanyan, S.  

    A major goal of Jefferson Lab at 12 GeV is to map out the 3-D structure of the proton through Generalized Parton Distributions (GPDs). An important tool in this endeavor is Deeply Virtual Compton Scattering, traditionally performed in kinematics where the incoming photon has a spacelike virtuality and the outgoing photon is real. However, measuring the corresponding timelike process, known as Timlike Compton Scattering (TCS), where the incoming photon is real and the outgoing one timelike, offers a unique opportunity to test the universality of GPDs. It also allows to take advantage of the straightforward access in TCS to the real part of the Compton Form Factors, providing constraints on global GPD fits. In addition, the experiment will provide a high-statistics measurement of the J/psi photoproduction cross section near threshold, as this process shares the same final state.
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  • Spatial evolution of the plasma kernel produced by nanosecond discharges in air

    Stepanyan, S.   Minesi, N.   Tibere-Inglesse, A.   Salmon, A.   Stancu, G. D.   Laux, C. O.  

    This work presents an experimental investigation of the hydrodynamic effects induced by nanosecond and conventional spark discharges. The energy deposited in sparks in the short breakdown time (similar to 1 mJ mm(-1)) induces hydrodynamic effects that redistribute the energy over a large volume (similar to 1 cm(3)) surrounding the initial plasma channel. This process influences the subsequent formation of the ignition kernel and the initiation of combustion. The experimental results presented in this paper were obtained with a set of synchronized diagnostics including schlieren, OH planar laser induced fluorescence and electrical measurements of the energy deposited in the plasma. It is shown that the motion of the gas excited after the discharge breakdown depends not only on the total deposited energy but also on the dynamics of the energy input in the plasma. Finally, the effects of nanosecond sparks are compared with those of conventional sparks used for internal combustion engines. We show that, with 20 times less energy, the nanosecond spark produces a twice bigger excited gas volume than the conventional spark. This is because the energy deposited by the nanosecond spark during the breakdown stage is three times higher than for the conventional spark.
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  • Energy calibration of the JLab bremsstrahlung tagging system

    Stepanyan, S.   Boyarinov, S.   Egiyan, H.   Guo, L.   Dale, D.   Gabrielyan, M.   Gan, L.   Gasparian, A.   Glamazdin, A.   Mecking, B.   Nakagawa, I.   Teymurazyan, A.   Wood, M. H.  

    In this report, we present the energy calibration of the Hall B bremsstrahlung tagging system at the Thomas Jefferson National Accelerator Facility. The calibration was performed using a magnetic pair spectrometer. The tagged photon energy spectrum was measured in coincidence with e(+)e(-) pairs as a function of the pair spectrometer magnetic field. Taking advantage of the internal linearity of the pair spectrometer, the energy of the tagging system was calibrated at the level of +/- 0.1%E. The absolute energy scale was determined using the e+e- rate measurements close to the end-point of the photon spectrum. The energy variations across the full tagging range were found to be < 3 MeV. (c) 2007 Elsevier B.V. All rights reserved.
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  • High precision measurement of Compton scattering in the 5 GeV region

    Ambrozewicz, P.   Ye, L.   Prok, Y.   Larin, I   Ahmidouch, A.   Baker, K.   Baturin, V   Benton, L.   Bernstein, A.   Burkert, V   Clinton, E.   Cole, P. L.   Collins, P.   Dale, D.   Danagoulian, S.   Davidenko, G.   Demirchyan, R.   Deur, A.   Dolgolenko, A.   Dutta, D.   Dzyubenko, G.   Evdokimov, A.   Fedotov, G.   Feng, J.   Gabrielyan, M.   Gan, L.   Gao, H.   Gasparian, A.   Gevorkyan, N.   Gevorkyan, S.   Glamazdin, A.   Goryachev, V   Guo, L.   Gyurjyan, V   Hardy, K.   He, J.   Isupov, E.   Ito, M. M.   Jiang, L.   Kang, H.   Kashy, D.   Khandaker, M.   Kingsberry, P.   Klein, F.   Kolarkar, A.   Konchatnyi, M.   Korchin, O.   Korsch, W.   Kosinov, O.   Kowalski, S.   Kubantsev, M.   Kubarovsky, A.   Kubarovsky, V   Lawrence, D.   Li, X.   Levillain, M.   Lu, H.   Ma, L.   Martel, P.   Matveev, V   McNulty, D.   Mecking, B.   Micherdzinska, A.   Milbrath, B.   Minehart, R.   Miskimen, R.   Mochalov, V   Morrison, B.   Mtingwa, S.   Nakagawa, I   Overby, S.   Pasyuk, E.   Payen, M.   Park, K.   Pedroni, R.   Phelps, W.   Protopopescu, D.   Rimal, D.   Ritchie, B. G.   Romanov, D.   Salgado, C.   Shahinyan, A.   Sitnikov, A.   Sober, D.   Stepanyan, S.   Stephens, W.   Tarasov, V   Taylor, S.   Teymurazyan, A.   Underwood, J.   Vasiliev, A.   Vishnyakov, V.   Weygand, D. P.   Wood, M.   Zhang, Y.   Zhou, S.   Zihlmann, B.  

    The cross section of atomic electron Compton scattering gamma + e -> gamma' + e' was measured in the 4.400-5.475 GeV photon beam energy region by the PrimEx collaboration at Jefferson Lab with an accuracy of 2.6% and less. The results are consistent with theoretical predictions that include next-to-leading order radiative corrections. The measurements provide the first high precision test of this elementary QED process at beam energies greater than 0.1 GeV. (C) 2019 The Author(s). Published by Elsevier B.V.
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  • Hadron Physics with CLAS12

    Stepanyan, S.  

    Hadron spectroscopy has been an essential part of the physics program with the CLAS detector in experimental Hall B at Jefferson Lab. Production of baryon and meson resonances with high energy (polarized) electron and photon beams was studied on a veriety of targets, ranging from hydrogen to lead. Physics topics of interest include: investigation of the spectrum of baryon and meson resonances, transition form-factors, meson-nucleon couplings (mesons in nuclei), and search for exotic and missing states. With the 12 GeV upgrade of the CEBAF machine, hadron spectroscopy in Hall B will be extended to a new domain of higher mass resonances and the range of higher transferred momentum using up to 11 GeV electron beams and the upgraded CLAS12 detector. In this paper a brief description of the CLAS12 detector and the physics program adopted for 12 GeV with emphasis to baryon and meson spectroscopy is presented.
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  • Near-threshold photoproduction of phi mesons from deuterium RID G-2589-2011 RID E-8618-2010

    Qian, X.   Chen, W.   Gao, H.   Hicks, K.   Kramer, K.   Laget, J. M.   Mibe, T.   Qiang, Y.   Stepanyan, S.   Tedeschi, D. J.   Xu, W.   Adhikari, K. P.   Amaryan, M.   Anghinolfi, M.   Ball, J.   Battaglieri, M.   Batourine, V.   Bedlinskiy, I.   Bellis, M.   Biselli, A. S.   Bookwalter, C.   Branford, D.   Briscoe, W. J.   Brooks, W. K.   Burkert, V. D.   Careccia, S. L.   Carman, D. S.   Cole, P. L.   Collins, P.   Crede, V.   D'Angelo, A.   Daniel, A.   Dashyan, N.   De Vita, R.   De Sanctis, E.   Deur, A.   Dey, B.   Dhamija, S.   Djalali, C.   Doughty, D.   Dupre, R.   Egiyan, H.   El Alaoui, A.   Eugenio, P.   Fegan, S.   Gabrielyan, M. Y.   Gevorgyan, N.   Gilfoyle, G. P.   Giovanetti, K. L.   Girod, F. X.   Goetz, J. T.   Gohn, W.   Gothe, R. W.   Graham, L.   Griffioen, K. A.   Guidal, M.   Guo, L.   Hafidi, K.   Hakobyan, H.   Hanretty, C.   Hassall, N.   Holtrop, M.   Ilieva, Y.   Ireland, D. G.   Jawalkar, S. S.   Jo, H. S.   Joo, K.   Keller, D.   Khandaker, M.   Khetarpal, P.   Kim, A.   Kim, W.   Klein, A.   Klein, F. J.   Konczykowski, P.   Kubarovsky, V.   Kuleshov, S. V.   Kuznetsov, V.   Livingston, K.   Martinez, D.   Mayer, M.   McAndrew, J.   McCracken, M. E.   McKinnon, B.   Meyer, C. A.   Mikhailov, K.   Mineeva, T.   Mirazita, M.   Mokeev, V.   Moreno, B.   Moriya, K.   Morrison, B.   Moutarde, H.   Munevar, E.   Nadel-Turonski, P.   Ni, A.   Niccolai, S.   Niculescu, I.   Niroula, M. R.   Osipenko, M.   Ostrovidov, A. I.   Paremuzyan, R.   Park, K.   Park, S.   Pereira, S. Anefalos   Pisano, S.   Pogorelko, O.   Pozdniakov, S.   Price, J. W.   Procureu, S.   Protopopescu, D.   Ricco, G.   Ripani, M.   Ritchie, B. G.   Rosner, G.   Rossi, P.   Sabatie, F.   Saini, M. S.   Salgado, C.   Schott, D.   Schumacher, R. A.   Seder, E.   Seraydaryan, H.   Sharabian, Y. G.   Smith, E. S.   Smith, G. D.   Sober, D. I.   Sokhan, D.   Stepanyan, S. S.   Stoler, P.   Strakovsky, I. I.   Strauch, S.   Taiuti, M.   Taylor, C. E.   Tkachenko, S.   Ungaro, M.   Vernarsky, B.   Vineyard, M. F.   Voutier, E.   Weinstein, L. B.   Weygand, D. P.   Wood, M. H.   Zachariou, N.   Zana, L.   Zhang, J.   Zhao, B.   Zhao, Z. W.  

    We report the first, kinematically-complete measurement of the differential cross section of phi-meson photoproduction from deuterium near the production threshold for a proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson Lab. The measurement was carried out by a triple coincidence detection of a proton, K+ and K- near the theoretical production threshold of 1.57 GeV. The extracted differential cross sections d sigma/dt for the initial photon energy range of 1.65-1.75 GeV are consistent with predictions based on a quasifree mechanism. Our finding is different from recent LEPS results on phi-meson photoproduction from deuterium in a similar incident photon energy range, but in a different momentum transfer region. (C) 2011 Elsevier B.V. All rights reserved.
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  • Heavy Photon Search Experiment at JLAB

    Stepanyan, S.  

    The Heavy Photon Search (HPS) experiment in Hall-B at Jefferson Lab will search for new heavy vector boson(s), aka "heavy photons", in the mass range of 20 MeV/c(2) to 1000 MeV/c(2) using the scattering of high energy, high intensity electron beams off a high Z target. The proposed measurements will cover the region of parameter space favored by the mum g-2 anomaly, and will explore a significant region of parameter space, not only at large couplings (alpha'/alpha > 10(-7)), but also in the regions of small couplings, down to alpha'/alpha similar to 10(-10). The excellent vertexing capability of the Si-tracker uniquely enables HPS to cover the small coupling region. Also, HPS will search for heavy photons in an alternative to the e(+)e(-) decay mode, in the heavy photon's decay to mu(+) mu(-).
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