Measurement of angular distributions and R = sigma(L)/sigma(T) in diffractive electroproduction of p(0) mesons

Authors
Ackerstaff, K Airapetian, A Akopov, N Amarian, M Aschenauer, EC Avakian, H Avakian, R Avetissian, A Bains, B Beckmann, M Belostotski, S Belz, JE Benisch, T Bernreuther, S Bianchi, N Blanchard, S Blouw, J Bottcher, H Borissov, A Brack, J Bray, B Bruckner, W Brull, A Bruins, EEW Bulten, HJ Capitani, GP Carter, P Cisbani, E Court, GR Delheij, PPJ De Sanctis, E De Schepper, D Devitsin, E Huberts, PKAD Duren, M Dvoredsky, A Elbakian, G Emerson, J Fantoni, A Fechtchenko, A Ferstl, M Fiedler, K Filippone, BW Fischer, H Fox, B Franz, J Frullani, S Funk, MA Garber, Y Gagunashvili, ND Galumian, P Gao, H Garibaldi, F Gavrilov, G Geiger, P Gharibyan, V Golendukhin, A Graw, G Grebeniouk, O Green, PY Greeniaus, LG Grosshauser, C Gute, A Gyurjyan, V Haas, JP Haeberli, W Hausser, O Hansen, JO Hasch, D Henderson, R Henkes, T Hertenberger, R Holler, Y Holt, RJ Ihssen, H Iodice, M Izotov, A Jackson, HE Jgoun, A Jones, C Kaiser, R Kinney, E Kirsch, M Kisselev, A Kitching, P Konigsmann, K Kolstein, M Kolster, H Korsch, W Kozlov, V Kramer, LH Krause, B Krivokhijine, VG Kuckes, M Kyle, G Lachnit, W Lorenzon, W Lung, A Makins, NCR Manaenkov, SI Martens, FK Martin, JW Mateos, A McIlhany, K McKeown, RD Meissner, F Menden, F Mercer, D Metz, A Meyners, N Mikloukho, B Miller, CA Miller, MA Milner, R Mitsyn, V Most, A Mozzetti, R Muccifora, V Nagaitsev, A Naryshkin, Y Nathan, AM Neunreither, F Niczyporuk, JM Nowak, WD Nupieri, M Oelwein, P Ogami, H O'Neill, TG Openshaw, R Ouyang, J Pate, SF Pitt, M Poolman, HR Potashov, S Potterveld, DH Rakness, G Redwine, R Reolon, AR Ristinen, R Rith, K Roper, G Roloff, HO Rossi, P Ruh, M Ryckbosch, D Sakemi, Y Savin, I Schuler, KP Schwind, A Shibata, TA Shin, T Simon, A Sinram, K Smythe, WR Sowinski, J Spengos, M Steffens, E Stenger, J Stewart, J Stock, F Stosslein, U Sutter, M Tallini, H Taroian, S Terkulov, A Thiessen, DM Tipton, B Trudel, A Tytgat, M Urciuoli, GM van den Brand, JFJ van der Steenhoven, G van de Vyver, R Vetterli, MC Vincter, MG Volk, E Wander, W Welch, TP Williamson, SE Wise, T Zapfe, K Zohrabian, H
Citation
K. Ackerstaff et al., Measurement of angular distributions and R = sigma(L)/sigma(T) in diffractive electroproduction of p(0) mesons, EUR PHY J C, 18(2), 2000, pp. 303-316
Citations number
49
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physics
Journal title
EUROPEAN PHYSICAL JOURNAL C
ISSN journal
1434-6044 → ACNP
Volume
18
Issue
2
Year of publication
2000
Pages
303 - 316
Database
ISI
SICI code
1434-6044(200012)18:2<303:MOADAR>2.0.ZU;2-0
Abstract
Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the rho (0)(770) meson over a range in t he virtual photon negative four-momentum squared 0.5 < Q(2) < 4 GeV2 and th e photon-nucleon invariant mass range 3.8 < W < 6.5 GeV. The experiment was performed with the HERMES spectrometer, using a longitudinally polarized p ositron beam and a He-3 gas target internal to the HERA e(+/-) storage ring . The event sample combines rho (0) masons produced incoherently off indivi dual nucleons and coherently off the nucleus as a whole. The distributions in one production angle and two angles describing the rho (0) --> pi (+)pi (-) decay yielded measurements of eight elements of the spin-density matrix , including one that had not been measured before. The results are consiste nt with the dominance of helicity conserving amplitudes and natural parity exchange. The improved precision achieved at 4 < W < 7 GeV, in combination with other data at W > 7 GeV, reveals evidence for an energy dependence in the ratio R of the longitudinal to transverse cross sections at constant Q( 2).