Phys. Rev. Lett.
81,
5519–5523
(1998)
Flavor Asymmetry of the Light Quark Sea from Semi-inclusive Deep-Inelastic Scattering
K. Ackerstaff et al. (HERMES Collaboration)
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K. Ackerstaff5, A. Airapetian32, N. Akopov32, I. Akushevich6, M. Amarian32,27, E. C. Ashenauer13,14, H. Avakian10, R. Avakian32, A. Avetissian32, B. Bains15, C. Baumgarten23, M. Beckmann12, St. Belostotski26, J. E. Belz28,29, Th. Benisch8, S. Bernreuther8, N. Bianchi10, J. Blouw25, H. Böttcher6, A. Borissov6,14, J. Brack4, S. Brauksiepe12, B. Braun8, B. Bray3, St. Brons6, W. Brückner14, A. Brüll14, E. E. W. Bruins20, H. J. Bulten18,25,31, R. V. Cadman15, G. P. Capitani10, P. Carter3, P. Chumney24, E. Cisbani27, G. R. Court17, P. F. Dalpiaz9, E. De Sanctis10, D. De Schepper20, E. Devitsin22, P. K. A. de Witt Huberts25, P. Di Nezza10, M. Düren8, A. Dvoredsky3, G. Elbakian32, A. Fantoni10, A. Fechtchenko7, M. Ferstl8, K. Fiedler8, B. W. Filippone3, H. Fischer12, B. Fox4, J. Franz12, S. Frullani27, M.-A. Funk5, N. D. Gagunashvili7, H. Gao2,15, Y. Gärber6, F. Garibaldi27, G. Gavrilov26, P. Geiger14, V. Gharibyan32, V. Giordjian10, A. Golendukhin19,32, G. Graw23, O. Grebeniouk26, P. W. Green1,29, L. G. Greeniaus1,29, C. Grosshauser8, A. Gute8, W. Haeberli18, J.-O. Hansen2, D. Hasch6, O. Häusser28,29,*, R. Henderson29, Th. Henkes25, M. Henoch8, R. Hertenberger23, Y. Holler5, R. J. Holt15, W. Hoprich14, H. Ihssen5,25, M. Iodice27, A. Izotov26, H. E. Jackson2, A. Jgoun26, R. Kaiser28,29, E. Kinney4, A. Kisselev26, P. Kitching1, H. Kobayashi30, N. Koch19, K. Königsmann12, M. Kolstein25, H. Kolster23, V. Korotkov6, W. Korsch3,16, V. Kozlov22, L. H. Kramer20,11, V. G. Krivokhijine7, M. Kurisuno30, G. Kyle24, W. Lachnit8, W. Lorenzon21, N. C. R. Makins2,15, S. I. Manaenkov26, F. K. Martens1, J. W. Martin20, F. Masoli9, A. Mateos20, M. McAndrew17, K. McIlhany3, R. D. McKeown3, F. M. Menden29, F. Meissner6, A. Metz23, N. Meyners5, O. Mikloukho26, C. A. Miller1,29, M. A. Miller15, R. Milner20, V. Mitsyn7, A. Most15,21, R. Mozzetti10, V. Muccifora10, A. Nagaitsev7, Y. Naryshkin26, A. M. Nathan15, F. Neunreither8, M. Niczyporuk20, W.-D. Nowak6, M. Nupieri10, T. G. O'Neill2, J. Ouyang29, B. R. Owen15, V. Papavassiliou24, S. F. Pate20,24, M. Pitt3, S. Potashov22, D. H. Potterveld2, G. Rakness4, A. Reali9, R. Redwine20, A. R. Reolon10, R. Ristinen4, K. Rith8, H. Roloff6, P. Rossi10, S. Rudnitsky21, M. Ruh12, D. Ryckbosch13, Y. Sakemi30, I. Savin7, F. Schmidt8, H. Schmitt12, G. Schnell24, K. P. Schüler5, A. Schwind6, T.-A. Shibata30, K. Shibatani30, T. Shin20, V. Shutov7, C. Simani9, A. Simon12, K. Sinram5, P. Slavich9,10, M. Spengos5, E. Steffens8, J. Stenger8, J. Stewart17, U. Stoesslein6, M. Sutter20, H. Tallini17, S. Taroian32, A. Terkulov22, B. Tipton20, M. Tytgat13, G. M. Urciuoli27, J. J. van Hunen25, R. van de Vyver13, J. F. J. van den Brand25,31, G. van der Steenhoven25, M. C. Vetterli28,29, M. G. Vincter29, E. Volk14, W. Wander8, S. E. Williamson15, T. Wise18, K. Woller5, S. Yoneyama30, and H. Zohrabian32 (HERMES Collaboration)
1Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2J1
2Physics Division, Argonne National Laboratory, Argonne, Illinois 60439
3W. K. Kellogg Radiation Lab, California Institute of Technology, Pasadena, California 91125
4Nuclear Physics Laboratory, University of Colorado, Boulder, Colorado 80309-0446
5DESY, Deutsches Electronen Synchrotron, 22603 Hamburg, Germany
6DESY, 15738 Zeuthen, Germany
7Joint Institute for Nuclear Research, 141980 Dubna, Russia
8Physikalisches Institut, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
9Dipartimento di Fisica, Università di Ferrara, 44100 Ferrara, Italy
10Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, 00044 Frascati, Italy
11Department of Physics, Florida International University, Miami, Florida 33199
12Fakultaet fuer Physik, Universität Freiburg, 79104 Freiburg, Germany
13Department of Subatomic and Radiation Physics, University of Gent, 9000 Gent, Belgium
14Max-Planck-Institut für Kernphysik, 69029 Heidelberg, Germany
15Department of Physics, University of Illinois, Urbana, Illinois 61801
16Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506
17Physics Department, University of Liverpool, Liverpool L69 7ZE, United Kingdom
18Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706
19Physikalisches Institut, Philipps-Universität Marburg, 35037 Marburg, Germany
20Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
21Randall Laboratory of Physics, University of Michigan, Ann Arbor, Michigan 48109-1120
22Lebedev Physical Institute, 117924 Moscow, Russia
23Sektion Physik, Universität München, 85748 Garching, Germany
24Department of Physics, New Mexico State University, Las Cruces, New Mexico 88003
25Nationaal Instituut voor Kernfysica en Hoge-Energiefysica (NIKHEF), 1009 DB Amsterdam, The Netherlands
26Petersburg Nuclear Physics Institute, St. Petersburg, 188350 Russia
27Istituto Nazionale di Fisica Nucleare, Sezione Sanitá and Istituto Superiore di Sanitá, Physics Laboratory, 00161 Roma, Italy
28Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
29TRIUMF, Vancouver, British Columbia, Canada V6T 2A3
30Tokyo Institute of Technology, Tokyo 152, Japan
31Department of Physics and Astronomy, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands
32Yerevan Physics Institute, 375036, Yerevan, Armenia
Received 15 July 1998; revised 12 October 1998; published in the issue dated 21 December 1998
The flavor asymmetry of the light quark sea of the nucleon is determined in the kinematic range 0.02<x<0.3 and 1<Q2<10GeV2 for the first time from semi-inclusive deep-inelastic scattering. The quantity [d̅ (x)-u̅ (x)]/[u(x)-d(x)] is derived from a relationship between the yields of positive and negative pions from unpolarized hydrogen and deuterium targets. The flavor asymmetry d̅ -u̅ is found to be nonzero and x dependent, showing an excess of d̅ over u̅ quarks in the proton.
© 1998 The American Physical Society
URL:
http://link.aps.org/doi/10.1103/PhysRevLett.81.5519
DOI:
10.1103/PhysRevLett.81.5519
PACS:
13.60.Hb, 11.30.Hv, 14.20.Dh, 25.30.Fj
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