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Measurement of the $x$- and $Q^2$-Dependence of the Asymmetry $A_1$ on the Nucleon

K. V. Dharmawardane S. E. Kuhn P. Bosted Y. Prok G. Adams P. Ambrozewicz M. Anghinolo G. Asryan H. Avakian H. Bagdasaryan N. Baillie J. P. Ball N. A. Baltzell S. Barrow V. Batourine M. Battaglieri K. Beard I. Bedlinskiy M. Bektasoglu M. Bellis N. Benmouna A. S. Biselli B. E. Bonner S. Bouchigny 1 S. Boiarinov R. Bradford D. Branford W. K. Brooks S. Bltmann V. D. Burkert C. Butuceanu J. R. Calarco S. L. Careccia D. S. Carman B. Carnahan A. Cazes S. Chen P. L. Cole P. Collins P. Coltharp D. Cords P. Corvisiero D. Crabb H. Crannell V. Credé J. P. Cummings R. de Masi 2 R. de Vita E. de Sanctis P. V. Degtyarenko H. Denizli L. Dennis A. Deur C. Djalali G. E. Dodge J. Donnelly D. Doughty P. Dragovitsch M. Dugger S. Dytman O. P. Dzyubak H. Egiyan K. S. Egiyan L. Elouadrhiri P. Eugenio R. Fatemi G. Fedotov R. J. Feuerbach T. A. Forest H. Funsten M. Garçon 2 G. Gavalian G. P. Gilfoyle K. L. Giovanetti F.X. Girod 2 J. T. Goetz E. Golovatch A. Gonenc R. W. Gothe K. A. Grioen M. Guidal 1 M. Guillo N. Guler L. Guo V. Gyurjyan C. Hadjidakis 1 K. Haodi R. S. Hakobyan J. Hardie D. Heddle F. W. Hersman K. Hicks I. Hleiqawi M. Holtrop M. Huertas C. E. Hyde-Wright Y. Ilieva D. G. Ireland B. S. Ishkhanov E. L. Isupov M. M. Ito D. Jenkins H.S. Jo 1 K. Joo H. G. Jüngst C. Keith J. D. Kellie M. Khandaker K. Y. Kim K. Kim W. Kim A. Klein F. J. Klein M. Klusman M. Kossov L. H. Kramer V. Kubarovski J. Kühn S. V. Kuleshov J. Lachniet J.M. Laget 2 J. Langheinrich D. Lawrence A. C. S. Lima K. Livingston H. Lü K. Lukashin M. Maccormick 1 J. J. Manak N. Markov S. Mcaleer B. Mckinnon J. W. C. Mcnabb B. A. Mecking M. D. Mestayer C. A. Meyer T. Mibe K. Mikhailov R. Minehart M. Mirazita R. Miskimen V. Mokeev L. Morand 2 S.A. Morrow 1, 2 M. Moteabbed J. Müller G. S. Mutchler P. Nadel-Turonski J. Napolitano R. Nasseripour S. Niccolai 1 G. Niculescu I. Niculescu B. B. Niczyporuk M. R. Niroula R. A. Niyazov M. Nozar G. V. O'Rielly M. Osipenko A. I. Ostrovidov K. Park E. Pasyuk C. Paterson S. A. Philips J. Pierce N. Pivnyuk D. Pocanic O. Pogorelko E. Polli S. Pozdniakov B. M. Preedom J. W. Price D. Protopopescu L. M. Qin B. A. Raue G. Riccardi G. Ricco M. Ripani B. G. Ritchie F. Ronchetti G. Rosner P. Rossi D. Rowntree P. D. Rubin F. Sabatie 2 C. Salgado J. P. Santoro V. Sapunenko R. A. Schumacher V. S. Serov Yu G Sharabyan J. Shaw N. V. Shvedunov A. V. Skabelin E. S. Smith L. C. Smith D. I. Sober A. Stavinsky S. S. Stepanyan S. Stepanyan B. E. Stokes P. Stoler I. I. Strakovsky S. Strauch R. Suleiman M. Taiuti S. Taylor D. J. Tedeschi U. Thoma R. Thompson A. Tkabladze S. Tkachenko L. Todor C. Tur M. Ungaro M. F. Vineyard A. V. Vlassov L. B. Weinstein D. P. Weygand M. Williams E. Wolin M. H. Wood A. Yegneswaran J. Yun L. Zana J. Zhang B. Zhao
Abstract : We report results for the virtual photon asymmetry $A_1$ on the nucleon from new Jefferson Lab measurements. The experiment, which used the CEBAF Large Acceptance Spectrometer and longitudinally polarized proton ($^{15}$NH$_3$) and deuteron ($^{15}$ND$_3$) targets, collected data with a longitudinally polarized electron beam at energies between 1.6 GeV and 5.7 GeV. In the present paper, 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 lowest and highest beam energies, covering a range in momentum transfer $Q^2$ from 0.05 to 5.0 GeV$^2$ and in final-state invariant mass $W$ up to about 3 GeV. Our data show detailed structure in the resonance region, which leads to a strong $Q^2$--dependence of $A_1(x,Q^2)$ for $W$ below 2 GeV. At higher $W$, a smooth approach to the scaling limit, established by earlier experiments, can be seen, but $A_1(x,Q^2)$ 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 setshould improve next-to-leading order (NLO) pQCD fits of the parton polarization distributions.
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Submitted on : Friday, October 13, 2006 - 3:52:13 PM
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K. V. Dharmawardane, S. E. Kuhn, P. Bosted, Y. Prok, G. Adams, et al.. Measurement of the $x$- and $Q^2$-Dependence of the Asymmetry $A_1$ on the Nucleon. Physics Letters B, Elsevier, 2006, 641, pp.11-17. ⟨10.1016/j.physletb.2006.08.011⟩. ⟨in2p3-00106294⟩



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