K. Ackerstaff6, A. Airapetian36, N. Akopov36, I. Akushevich7, M. Amarian26,31,36, E.C. Aschenauer7,14,26, H. Avakian11, R. Avakian36, A. Avetissian36, B. Bains16, S. Barrow28, C. Baumgarten24, M. Beckmann13, S. Belostotski29, J.E. Belz32,33, Th. Benisch9, S. Bernreuther9, N. Bianchi11, S. Blanchard25, J. Blouw26, H. Böttcher7, A. Borissov6,15, J. Brack5, B. Bray4, S. Brauksiepe13, B. Braun9,24, St. Brons7, W. Brückner15, A. Brüll15, E.E.W. Bruins21, H.J. Bulten19,26,35, R.V. Cadman16, G.P. Capitani11, P. Carter4, P. Chumney25, E. Cisbani31, G.R. Court18, P. F. Dalpiaz10, R. De Leo3, P.P.J. Delheij33, E. De Sanctis11, D. De Schepper2,21, E. Devitsin23, P.K.A. de Witt Huberts26, P. Di Nezza11, M. Düren9, A. Dvoredsky4, J. Ely5, G. Elbakian36, J. Emerson, A. Fantoni, A. Fechtchenko, M. Ferstl, D. Fick, K. Fiedler, B.W. Filippone, H. Fischer, H.T. Fortune28, B. Fox5, S. Frabetti10, J. Franz13, S. Frullani31, M.-A. Funk6, N.D. Gagunashvili8, P. Galumian1, H. Gao2,16,21, Y. Gärber7, F. Garibaldi31, G. Gavrilov29, P. Geiger15, V. Gharibyan36, A. Golendukhin6,20,24,36, G. Graw24, O. Grebeniouk29, P.W. Green1,33, L.G. Greeniaus1,33, C. Grosshauser9, M. Guidal26, A. Gute9, V. Gyurjyan11, J.P. Haas25, W. Haeberli19, J.-O. Hansen2, D. Hasch7, O. Häusser†32,33, R. Henderson33, F.H. Heinsius13, Th. Henkes26, M. Henoch9, R. Hertenberger24, Y. Holler6, R.J. Holt16, W. Hoprich15, H. Ihssen6,26, M. Iodice31, A. Izotov29, H.E. Jackson2, A. Jgoun29, C. Jones2, R. Kaiser7,32,33, M. Kestel13, E. Kinney5, M. Kirsch9, A. Kisselev29, P. Kitching1, H. Kobayashi34, N. Koch20, K. Königsmann13, M. Kolstein26, H. Kolster24, V. Korotkov, W. Korsch, V. Kozlov, L.H. Kramer, B. Krause, V.G. Krivokhijine, M. Kückes, F. Kümmell13, M. Kurisuno34, G. Kyle25, W. Lachnit9, W. Lorenzon22,28, A. Lung4, N.C.R. Makins2,16, F.K. Martens1, J.W. Martin21, H. Marukyan36, F. Masoli10, A. Mateos21, M. Maul30, M. McAndrew18, K. McIlhany4,21, R.D. McKeown4, F. Meissner7, F. Menden13,33, D. Mercer5, A. Metz24, N. Meyners6 O. Mikloukho29, C.A. Miller1,33, M.A. Miller16, R. Milner21, V. Mitsyn8, A. Most16,22,28, R. Mozzetti11, V. Muccifora11, A. Nagaitsev8, E. Nappi3, Yu. Naryshkin29, A.M. Nathan16, F. Neunreither9, J.M. Niczyporuk16,21, W.-D. Nowak7, M. Nupieri11, P. Oelwein15, H. Ogami34, T.G. O’Neill2, R. Openshaw33, B.R. Owen16, J. Ouyang33, V. Papavassiliou25, S.F. Pate21,25, M. Pitt4, H.R. Poolman26, S. Potashov23, D.H. Potterveld2, G. Rakness5, A. Reali, R. Redwine, A.R. Reolon, R. Ristinen, K. Rith, G. Röper, P. Rossi, S. Rudnitsky, M. Ruh13, D. Ryckbosch14, Y. Sakemi34, I. Savin8, C. Scarlett22, A. Schäfer30, F. Schmidt9, H. Schmitt13, G. Schnell25, K.P. Schüler6, A. Schwind7, J. Seibert13, T.-A. Shibata34, K. Shibatani34, T. Shin21, V. Shutov8, C. Simani10, A. Simon13,25, K. Sinram6, P. Slavich10,11, W.R. Smythe5, J. Sowinski15, M. Spengos6,28, E. Steffens9, J. Stenger9, J. Stewart18, F. Stock9,15, U. Stoesslein7, M. Sutter21, H. Tallini18, S. Taroian36, A. Terkulov23, D.M. Thiessen32,33, B. Tipton21, E. Thomas11, A. Trudel33, M. Tytgat14, G.M. Urciuoli31, J.J. van Hunen26, R. van de Vyver14, J.F.J. van den Brand26,35, G. van der Steenhoven26, M.C. Vetterli32,33, V. Vikhrov29, M. Vincter33, J. Visser26, E. Volk15, W. Wander9,21, T.P. Welch27, J. Wendland32,33, S.E. Williamson16, T. Wise19, K. Woller6, S. Yoneyama, K. Zapfe, H. Zohrabian, R. Zurmühle Department of Physics, University of Alberta, Edmonton, Alberta T6G 2J1, Canada Physics Division, Argonne National Laboratory, Argonne, Illinois 60439-4843, USA Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70124 Bari, Italy W.K. Kellogg Radiation Lab, California Institute of Technology, Pasadena, California 91125, USA Nuclear Physics Laboratory, University of Colorado, Boulder, Colorado 80309-0446, USA DESY, Deutsches Elektronen Synchrotron, 22603 Hamburg, Germany DESY Zeuthen, 15738 Zeuthen, Germany Joint Institute for Nuclear Research, 141980 Dubna, Russia Physikalisches Institut, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara and Dipartimento di Fisica, Università di Ferrara, 44100 Ferrara,

K. Ackerstaff, A. Airapetian, I. Akushevich, N. Akopov, M. Amarian, E.C. Aschenauer, R. Avakian, H. Avakian, A. Avetissian, B. Bains, S. Barrow, M. Beckmann, S. Belostotski, J.E. Belz, Th. Benisch, S. Bernreuther, N. Bianchi, S. Blanchard, J. Blouw, H. Böttcher, A. Borissov, J. Brack, B. Braun, B. Bray, W. Brückner, A. Brüll, E.E.W. Bruins, H.J. Bulten, G.P. Capitani, P. Carter, E. Cisbani, G.R. Court, P.P.J. Delheij, E. Devitsin, C.W. de Jager, E. De Sanctis, D. De Schepper, P.K.A. de Witt Huberts, M. Düren, A. Dvoredsky, G. Elbakian, J. Emerson, A. Fantoni, A. Fechtchenko, M. Ferstl, D. Fick, K. Fiedler, B.W. Filippone, H. Fischer, H.T. Fortune, J. Franz, S. Frullani, M.-A. Funk, N.D. Gagunashvili, P. Galumian, H. Gao, Y. Gärber, F. Garibaldi, P. Geiger, V. Gharibyan, A. Golendoukhin, G. Graw, O. Grebeniouk, P.W. Green, L.G. Greeniaus, C. Grosshauser, A. Gute, V. Gyurjyan, J.P. Haas, W. Haeberli, J.-O. Hansen, D. Hasch, O. Häusser, R.S. Henderson, Th. Henkes, R. Hertenberger, Y. Holler, R.J. Holt, H. Ihssen, M. Iodice, A. Izotov, H.E. Jackson, A. Jgoun, C. Jones, R. Kaiser, E. Kinney, M. Kirsch, A. Kisselev, P. Kitching, N. Koch, K. Königsmann, M. Kolstein, H. Kolster, W. Korsch, V. Kozlov, L.H. Kramer, B. Krause, V.G. Krivokhijine, M. Kückes, G. Kyle, W. Lachnit, W. Lorenzon, A. Lung, N.C.R. Makins, S.I. Manaenkov, F.K. Martens, J.W. Martin, A. Mateos, K. McIlhany, R.D. McKeown, F. Meissner, D. Mercer, A. Metz, N. Meyners, O.Mikloukho, C.A. Miller, M.A. Miller, R.G. Milner, V. Mitsyn, A. Most, R. Mozzetti, V. Muccifora, A. Nagaitsev, Y. Naryshkin, A.M. Nathan, F. Neunreither M. Niczyporuk, W.-D. Nowak, M. Nupieri, P. Oelwein, H. Ogami, T.G. O’Neill, R. Openshaw, V. Papavassiliou, S.F. Pate, M. Pitt, S. Potashov, D.H. Potterveld, B. Povh, G. Rakness, R. Redwine, A.R. Reolon, R. Ristinen, K. Rith, G. Röper, H. Roloff, P. Rossi, S. Rudnitsky, M. Ruh, D. Ryckbosch, Y. Sakemi, I. Savin, K.P. Schüler, A. Schwind, T.-A. Shibata, T. Shin, A. Simon, K. Sinram, W.R. Smythe, J. Sowinski, M. Spengos, E. Steffens, J. Stenger, J. Stewart, F. Stock, U. Stoesslein, M. Sutter, H. Tallini, S. Taroian, A. Terkulov, D.M. Thiessen, B. Tipton, A. Trudel, M. Tytgat, G.M. Urciuoli, R. Van de Vyver, J.F.J. van den Brand, G. van der Steenhoven, M.C. Vetterli, E. Volk, W. Wander, T.P. Welch, S.E. Williamson, T. Wise, T. Wölfel, K. Zapfe-Düren, H. Zohrabian, R. Zurmühle

Spin transfer in deep-inelastic Lambda electroproduction has been studied with the HERMES detector using the 27.6 GeV polarized positron beam in the DESY HERA storage ring. For an average fractional energy transfer [z] = 0.45, the longitudinal spin transfer from the virtual photon to the Lambda has been extracted. The spin transfer along the Lambda momentum direction is found to be 0.11+/-0.17(stat)+/-0.03(syst); similar values are found for other possible choices for the longitudinal spin direction of the Lambda. This result is the most precise value obtained to date from deep-inelastic scattering with charged lepton beams, and is sensitive to polarized up quark fragmentation to hyperon states. The experimental result is found to be in general agreement with various models of the Lambda spin content, and is consistent with the assumption of helicity conservation in the fragmentation process.

E. Kinney, M. Kirsch, A. Kisselev, 2,25 P. Kitching, H. Kobayashi, 29 N. Koch, K. Königsmann, 12 M. Kolstein, H. Kolster,V. Korotkov, W. Korsch, 3,16 V. Kozlov, L. H. Kramer, V. G. Krivokhijine, M. Kurisuno, G. Kyle, W. Lachnit, P. Lenisa, 9 W. Lorenzon, 20 N. C. R. Makins, 15 S. I. Manaenkov, 25 F. K. Martens, 1 J. W. Martin, F. Masoli, A. Mateos, 19 M. McAndrew, K. McIlhany, R. D. McKeown, 3 F. Meissner, 6,22 F. Menden, 12 A. Metz,

Cross section ratios for deep-inelastic scattering from 14N and 3He with respect to 2H have been measured by the HERMES experiment at DESY using a 27.5 GeV positron beam. The data cover a range in the Bjorken scaling variable x between 0.013 and 0.65, while the negative squared four-momentum transfer Q2 varies from 0.5 to 15 GeV2. The data are compared to measurements performed by NMC, E665, and SLAC on 4He and 12C, and are found to be different for x<0.06 and Q2<1.5 GeV2. The observed difference is attributed to an A-dependence of the ratio R=σL/σT of longitudinal to transverse deep-inelastic scattering cross sections at low x and low Q2.

Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the ρ(770) meson over a range in the virtual photon negative four-momentum squared 0.5 < Q < 4 GeV and the photon-nucleon invariant mass range 3.8 < W < 6.5 GeV. The experiment was performed with the Hermes spectrometer, using a longitudinally polarized positron beam and a He gas target internal to the HERA e storage ring. The event sample combines ρ mesons produced incoherently off individual nucleons and coherently off the nucleus as a whole. The distributions in one production angle and two angles describing the ρ → ππ decay yielded measurements of eight elements of the spin-density matrix, including one that had not been measured before. The results are consistent 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.

Cross section ratios for deep-inelastic scattering from N-14 and He-3 with respect to H-2 have been measured by the HERMES experiment at DESY using a 27.5 GeV positron beam. The data cover a range in the Bjorken scaling variable x between 0.013 and 0.65, while the negative squared four-momentum transfer Q(2) Varies from 0.5 to 15 GeV2. The data are compared to measurements performed by NMC, E665, and SLAG on He-4 and C-12, and rue found to be different for x < 0.06 and Q(2) < 1.5 GeV2. The observed difference is attributed to an A-dependence of the ratio R = sigma(L)/sigma(Gamma) of longitudinal to transverse deep-inelastic scattering cross sections at low x and low Q(2). (C) 2000 Elsevier Science B.V. All rights reserved.

Exclusive incoherent electroproduction of the rho^0(770) meson from 1H, 2H, 3He, and 14N targets has been studied by the HERMES experiment at squared four-momentum transfer Q**2>0.4 GeV**2 and positron energy loss nu from 9 to 20 GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the nuclear transparency, was found to decrease with increasing coherence length of quark-antiquark fluctuations of the virtual photon. The data provide clear evidence of the interaction of the quark- antiquark fluctuations with the nuclear medium.

Spin-polarized atomic hydrogen is used as a gaseous polarized-proton target in high-energy and nuclear-physics experiments operating with internal beams in storage rings. When such beams are intense and bunched, this type of target can be depolarized by a resonant interaction with the transient magnetic field generated by the beam bunches. This effect has been studied with the HERA positron beam in the HERMES experiment at DESY. Resonances have been observed and a simple analytic model has been used to explain their shape and position. Operating conditions for the experiment have been found where there is no significant target depolarization due to this effect. [S0031-9007(98)08340-9].

Measurements were made at SLAC of the cross section for scattering 29 GeV electrons from carbon at a laboratory angle of 4.5 degrees, corresponding to 0.03<x<0.1 and 1.3<Q^2<2.7 GeV^2. Values of R=sigma_L/sigma_T were extracted in this kinematic range by comparing these data to cross sections measured at a higher beam energy by the NMC collaboration. The results are in reasonable agreement with pQCD calculations and with extrapolations of the R1990 parameterization of previous data. A new fit is made including these data and other recent results.

Spin asymmetries of semi-inclusive cross sections for the production of positively and negatively charged hadrons have been measured in deep-inelastic scattering of polarized positrons on polarized hydrogen and He-3 targets, in the kinematic range 0.023 < x < 0.6 and 1 GeV2 < Q(2) < 10 GeV2. Polarized quark distributions are extracted as a function of x for up (u + (u) over bar) and down (d + (d) over bar) flavors. The up quark polarization is positive and the down quark polarization is negative in the measured range. The polarization of the sea is compatible with zero. The first moments of the polarized quark distributions are presented. The isospin non-singlet combination dq, is consistent with the prediction based on the Bjorken sum rule. The moments of the polarized quark distributions are compared to predictions based on SU(3)(f) flavor symmetry and to a prediction from lattice QCD. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

A measurement of the proton spin structure function g(l)(p)(x, Q(2)) in deep-inelastic scattering is presented. The data were taken with the 27.6 GeV longitudinally polarised positron beam at HERA incident on a longitudinally polarised pure hydrogen gas target internal to the storage ring. The kinematic range is 0.021 < x < 0.85 and 0.8 GeV2 < Q(2) < 20 GeV2. The integral integral(0.021)(0.85) g(l)(p)(x) dx evaluated at Q(0)(2) of 2.5 GeV2 is 0.122 +/- 0.003(stat.) +/- 0.010(syst.). (C) Elsevier Science B.V. All rights reserved.

The virtual photon absorption cross section differences [alpha(1/2) - alpha(3/2)] for the proton and neutron have been determined from measurements of polarised cross section asymmetries in deep inelastic scattering of 27.5 GeV longitudinally polarised positrons from polarised H-1 and He-3 internal gas targets. The data were collected in the region above the nucleon resonances in the kinematic range v < 23.5 GeV and 0.8 GeV2 < Q(2) < 12 GeV2. For the proton the contribution to the generalised Gerasimov-Drell-Hearn integral was found to be substantial and must be included for an accurate determination of the full integral. Furthermore the data are consistent with a QCD next-to-leading order fit based on previous deep inelastic scattering data. Therefore higher twist effects do not appear significant. (C) 1998 Elsevier Science B.V. All rights reserved.

Measurements of inclusive electron-scattering cross sections using hydrogen and deuterium targets in the region of the {Delta}(1232) resonance are reported. A global fit to these new data and previous data in the resonance region is also reported for the proton. Transition form factors have been extracted from the proton cross sections for this experiment over the four-momentum transfer squared range 1.64{lt}Q{sup 2}{lt}6.75 (GeV/c){sup 2} and from previous data over the range 2.41{lt}Q{sup 2}{lt}9.82 (GeV/c){sup 2}. The results confirm previous reports that the {Delta}(1232) transition form factor decreases more rapidly with Q{sup 2} than expected from perturbative QCD. The ratio of {sigma}{sub n}/{sigma}{sub p} in the {Delta}(1232) resonance region has been extracted from the deuteron data for this experiment in the range 1.64{lt}Q{sup 2}{lt}3.75 (GeV/c){sup 2} and for a previous experiment in the range 2.4{lt}Q{sup 2}{lt}7.9 (GeV/c){sup 2}. A study has been made of the model dependence of these results. This ratio {sigma}{sub n}/{sigma}{sub p} for {Delta}(1232) production is slightly less than unity, while {sigma}{sub n}/{sigma}{sub p} for the nonresonant cross sections is approximately 0.5, which is consistent with deep inelastic scattering results. thinsp {copyright} {ital 1998} {ital The American Physical Society}

The HERMES experiment is collecting data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of H, D, and He. These data give information on the spin structure of the nucleon. This paper describes the forward angle spectrometer built for this purpose. The spectrometer includes numerous tracking chambers (micro-strip gas chambers, drift and proportional chambers) in front of and behind a 1.3 T.m magnetic field, as well as an extensive set of detectors for particle identification (a lead-glass calorimeter, a pre-shower detector, a transition radiation detector, and a threshold Čerenkov detector). Two of the main features of the spectrometer are its good acceptance and identification of both positrons and hadrons, in particular pions. These characteristics, together with the purity of the targets, are allowing HERMES to make unique contributions to the understanding of how the spins of the quarks contribute to the spin of the nucleon. (Submitted to Nuclear Instruments and Methods)

The HERMES experiment is collecting data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of H, D, and 3He. These data give information on the spin structure of the nucleon. This paper describes the forward angle spectrometer built for this purpose. The spectrometer includes numerous tracking chambers (micro-strip gas chambers, drift and proportional chambers) in front of and behind a 1.3T.m magnetic field, as well as an extensive set of detectors for particle identification (a lead-glass calorimeter, a pre-shower detector, a transition radiation detector, and a threshold Cherenkov detector). Two of the main features of the spectrometer are its good acceptance and identification of both positrons and hadrons, in particular pions. These characteristics, together with the purity of the targets, are allowing HERMES to make unique contributions to the understanding of how the spins of the quarks contribute to the spin of the nucleon.