Eur. Phys. J. C 21, 599-606 (2001)
DOI: 10.1007/s100520100765

Multiplicity of charged and neutral pions in deep-inelastic scattering of 27.5 GeV positrons on hydrogen

The HERMES Collaboration

A. Airapetian², N. Akopov², Z. Akopov², M. Amarian^{3, 4, 2}, J. Arrington⁵, E.C. Aschenauer^{6, 7, 3}, H. Avakian⁸, R. Avakian², A. Avetissian², E. Avetissian², P. Bailey⁹, B. Bains⁹, C. Baumgarten¹⁰, M. Beckmann¹¹, S. Belostotski¹², S. Bernreuther¹³, N. Bianchi⁸, H. Böttcher⁶, A. Borissov^{14, 15}, M. Bouwhuis⁹, J. Brack¹⁶, S. Brauksiepe¹¹, B. Braun^{13, 10}, W. Brückner¹⁵, A. Brüll^{15, 17}, P. Budz¹³, H.J. Bulten^{18, 3, 19}, G.P. Capitani⁸, P. Carter²⁰, P. Chumney²¹, E. Cisbani⁴, G.R. Court²², P.F. Dalpiaz²³, R. De Leo²⁴, L. De Nardo¹, E. De Sanctis⁸, D. De Schepper^{5, 17}, E. Devitsin²⁵, P.K.A. de Witt Huberts³, P. Di Nezza⁸, V. Djordjadze⁶, M. Düren¹³, A. Dvoredsky²⁰, G. Elbakian², J. Ely¹⁶, A. Fantoni⁸, A. Fechtchenko²⁶, M. Ferro-Luzzi³, K. Fiedler¹³, B.W. Filippone²⁰, H. Fischer¹¹, B. Fox¹⁶, J. Franz¹¹, S. Frullani⁴, Y. Gärber⁶, F. Garibaldi⁴, E. Garutti³, G. Gavrilov¹², V. Gharibyan², A. Golendukhin^{14, 10, 2}, G. Graw¹⁰, O. Grebeniouk¹², P.W. Green^{1, 27}, L.G. Greeniaus^{1, 27}, A. Gute¹³, W. Haeberli¹⁸, M. Hartig²⁷, D. Hasch^{6, 8}, D. Heesbeen³, F.H. Heinsius¹¹, M. Henoch¹³, R. Hertenberger¹⁰, W.H.A. Hesselink³, P. Hoffmann-Rothe³, G. Hofman¹⁶, Y. Holler¹⁴, R.J. Holt⁹, B. Hommez⁷, W. Hoprich¹⁵, G. Iarygin²⁶, H. Ihssen^{14, 3}, M. Iodice⁴, A. Izotov¹², H.E. Jackson⁵, A. Jgoun¹², R. Kaiser^{6, 28, 27}, J. Kanesaka²⁹, E. Kinney¹⁶, A. Kisselev¹², P. Kitching¹, H. Kobayashi²⁹, N. Koch¹³, K. Königsmann¹¹, H. Kolster^{10, 3}, V. Korotkov⁶, E. Kotik¹, V. Kozlov²⁵, V.G. Krivokhijine²⁶, G. Kyle²¹, L. Lagamba²⁴, A. Laziev³, P. Lenisa²³, T. Lindemann¹⁴, W. Lorenzon³⁰, N.C.R. Makins^{5, 9}, J.W. Martin¹⁷, H. Marukyan², F. Masoli²³, M. McAndrew²², K. McIlhany^{20, 17}, R.D. McKeown²⁰, F. Meissner^{6, 10}, F. Menden¹¹, A. Metz¹⁰, N. Meyners¹⁴, O. Mikloukho¹², C.A. Miller^{1, 27}, R. Milner¹⁷, V. Muccifora⁸, R. Mussa²³, A. Nagaitsev²⁶, E. Nappi²⁴, Y. Naryshkin¹², A. Nass¹³, W.-D. Nowak⁶, T.G. O'Neill⁵, R. Openshaw²⁷, J. Ouyang²⁷, B.R. Owen⁹, S.F. Pate^{17, 21}, S. Potashov²⁵, D.H. Potterveld⁵, G. Rakness¹⁶, R. Redwine¹⁷, D. Reggiani²³, A.R. Reolon⁸, R. Ristinen¹⁶, K. Rith¹³, D. Robinson⁹, A. Rostomyan², M. Ruh¹¹, D. Ryckbosch⁷, Y. Sakemi²⁹, F. Sato²⁹, I. Savin²⁶, C. Scarlett³⁰, A. Schäfer³¹, C. Schill¹¹, F. Schmidt¹³, M. Schmitt¹³, G. Schnell²¹, K.P. Schüler¹⁴, A. Schwind⁶, J. Seibert¹¹, T.-A. Shibata²⁹, T. Shin¹⁷, V. Shutov²⁶, M.C. Simani^{23, 3, 19}, A. Simon¹¹, K. Sinram¹⁴, E. Steffens¹³, J.J.M. Steijger³, J. Stewart^{22, 27}, U. Stösslein⁶, K. Suetsugu²⁹, M. Sutter¹⁷, H. Tallini²², S. Taroian², A. Terkulov²⁵, S. Tessarin²³, E. Thomas⁸, B. Tipton^{17, 20}, M. Tytgat⁷, G.M. Urciuoli⁴, J.F.J. van den Brand^{3, 19}, G. van der Steenhoven³, R. van de Vyver⁷, J.J. van Hunen³, M.C. Vetterli^{28, 27}, V. Vikhrov¹², M.G. Vincter^{1, 27}, J. Visser³, E. Volk¹⁵, C. Weiskopf¹³, J. Wendland^{28, 27}, J. Wilbert¹³, T. Wise¹⁸, K. Woller¹⁴, S. Yoneyama²⁹ and H. Zohrabian<sup>2

1</sup>  Department of Physics, University of Alberta, Edmonton, Alberta T6G 2J1, Canada
²  Yerevan Physics Institute, 375036, Yerevan, Armenia
³  Nationaal Instituut voor Kernfysica en Hoge-Energiefysica (NIKHEF), 1009 DB Amsterdam, The Netherlands
⁴  Istituto Nazionale di Fisica Nucleare, Sezione Roma 1 - Gruppo Sanità and Physics Laboratory, Istituto Superiore di Sanità, 00161 Roma, Italy
⁵  Physics Division, Argonne National Laboratory, Argonne, IL 60439-4843, USA
⁶  DESY Zeuthen, 15738 Zeuthen, Germany
⁷  Department of Subatomic and Radiation Physics, University of Gent, 9000 Gent, Belgium
⁸  Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, 00044 Frascati, Italy
⁹  Department of Physics, University of Illinois, Urbana, IL 61801, USA
¹⁰  Sektion Physik, Universität München, 85748 Garching, Germany
¹¹  Fakultät für Physik, Universität Freiburg, 79104 Freiburg, Germany
¹²  Petersburg Nuclear Physics Institute, St. Petersburg, Gatchina, 188350 Russia
¹³  Physikalisches Institut, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
¹⁴  DESY, Deutsches Elektronen Synchrotron, 22603 Hamburg, Germany
¹⁵  Max-Planck-Institut für Kernphysik, 69029 Heidelberg, Germany
¹⁶  Nuclear Physics Laboratory, University of Colorado, Boulder, CO 80309-0446, USA
¹⁷  Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁸  Department of Physics, University of Wisconsin-Madison, Madison, WI 53706, USA
¹⁹  Department of Physics and Astronomy, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands
²⁰  W.K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USA
²¹  Department of Physics, New Mexico State University, Las Cruces, NM 88003, USA
²²  Physics Department, University of Liverpool, Liverpool L69 7ZE, UK
²³  Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara and Dipartimento di Fisica, Università di Ferrara, 44100 Ferrara, Italy
²⁴  Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70124 Bari, Italy
²⁵  Lebedev Physical Institute, 117924 Moscow, Russia
²⁶  Joint Institute for Nuclear Research, 141980 Dubna, Russia
²⁷  TRIUMF, Vancouver, British Columbia V6T 2A3, Canada
²⁸  Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
²⁹  Department of Physics, Tokyo Institute of Technology, Tokyo 152, Japan
³⁰  Randall Laboratory of Physics, University of Michigan, Ann Arbor, MI 48109-1120, USA
³¹  Institut für Theoretische Physik, Unversität Regensburg, 93040 Regensburg, Germany

(Received: 2 April 2001 / Revised version: 27 June 2001 / Published online: 7 September 2001 -© Springer-Verlag / Società Italiana di Fisica 2001 )

Abstract
Measurements of the individual multiplicities of , and produced in the deep-inelastic scattering of 27.5 GeV positrons on hydrogen are presented. The average charged pion multiplicity is the same as for neutral pions, up to , where z is the fraction of the energy transferred in the scattering process carried by the pion. This result (below ) is consistent with isospin invariance. The total energy fraction associated with charged and neutral pions is (syst.) and , respectively. For fixed z, the measured multiplicities depend on both the negative squared four momentum transfer Q² and the Bjorken variable x. The observed dependence on Q² agrees qualitatively with the expected behaviour based on NLO-QCD evolution, while the dependence on x is consistent with that of previous data after corrections have been made for the expected Q²-dependence.

© Società Italiana di Fisica, Springer-Verlag 2001