First Measurement of Z/γ Production in Compton Scattering of Quasi-real Photons

We report the first observation of Z/γ production in Compton scattering of quasi-real photons. This is a subprocess of the reaction ee → eeZ/γ, where one of the final state electrons is undetected. Approximately 55 pb of data collected in the year 1997 at an ee centre-of-mass energy of 183 GeV with the OPAL detector at LEP have been analysed. The Z/γ from Compton scattering has been detected in the hadronic decay channel. Within well defined kinematic bounds, we measure the product of cross-section and Z/γ branching ratio to hadrons to be (0.9±0.3±0.1) pb for events with a hadronic mass larger than 60 GeV, dominated by (e)eZ production. In the hadronic mass region between 5 GeV and 60 GeV, dominated by (e)eγ production, this product is found to be (4.1±1.6±0.6) pb. Our results agree with the predictions of two Monte Carlo event generators, grc4f and PYTHIA. (Submitted to Physics Letters B) The OPAL Collaboration G.Abbiendi, K.Ackerstaff, G.Alexander, J. Allison, N.Altekamp, K.J.Anderson, S.Anderson, S.Arcelli, S.Asai, S.F.Ashby, D.Axen, G.Azuelos, A.H.Ball, E. Barberio, R.J. Barlow, R.Bartoldus, J.R.Batley, S. Baumann, J. Bechtluft, T.Behnke, K.W.Bell, G.Bella, A.Bellerive, S. Bentvelsen, S. Bethke, S. Betts, O.Biebel, A.Biguzzi, S.D.Bird, V.Blobel, I.J. Bloodworth, M.Bobinski, P. Bock, J. Böhme, D.Bonacorsi, M.Boutemeur, S. Braibant, P. Bright-Thomas, L. Brigliadori, R.M.Brown, H.J. Burckhart, C.Burgard, R.Bürgin, P.Capiluppi, R.K.Carnegie, A.A.Carter, J.R.Carter, C.Y.Chang, D.G.Charlton, D.Chrisman, C.Ciocca, P.E.L.Clarke, E.Clay, I. Cohen, J.E.Conboy, O.C.Cooke, C.Couyoumtzelis , R.L.Coxe, M.Cuffiani, S.Dado, G.M.Dallavalle, R.Davis, S.De Jong, L.A. del Pozo, A. de Roeck, K.Desch, B.Dienes, M.S.Dixit, J.Dubbert, E.Duchovni, G.Duckeck, I.P.Duerdoth, D. Eatough, P.G.Estabrooks, E. Etzion, H.G.Evans, F. Fabbri, M.Fanti, A.A. Faust, F. Fiedler, M.Fierro, I. Fleck, R. Folman, A. Fürtjes, D.I. Futyan, P.Gagnon, J.W.Gary, J.Gascon, S.M.Gascon-Shotkin, G.Gaycken, C.Geich-Gimbel, G.Giacomelli, P.Giacomelli, V.Gibson, W.R.Gibson, D.M.Gingrich, D.Glenzinski, J.Goldberg, W.Gorn, C.Grandi, E.Gross, J.Grunhaus, M.Gruwé, G.G.Hanson, M.Hansroul, M.Hapke, K.Harder, C.K.Hargrove, C.Hartmann, M.Hauschild, C.M.Hawkes, R.Hawkings, R.J.Hemingway, M.Herndon, G.Herten, R.D.Heuer, M.D.Hildreth, J.C.Hill, S.J.Hillier, P.R.Hobson, A.Hocker, R.J.Homer, A.K.Honma, D.Horváth, K.R.Hossain, R.Howard, P.Hüntemeyer, P. Igo-Kemenes, D.C. Imrie, K. Ishii, F.R. Jacob, A. Jawahery, H. Jeremie, M. Jimack, C.R. Jones, P. Jovanovic, T.R. Junk, D.Karlen, V.Kartvelishvili, K.Kawagoe, T.Kawamoto, P.I.Kayal, R.K.Keeler, R.G.Kellogg, B.W.Kennedy, A.Klier, S.Kluth, T.Kobayashi, M.Kobel, D.S.Koetke, T.P.Kokott, M.Kolrep, S.Komamiya, R.V.Kowalewski, T.Kress, P.Krieger, J. von Krogh, T.Kuhl, P.Kyberd, G.D. Lafferty, D. Lanske, J. Lauber, S.R. Lautenschlager, I. Lawson, J.G. Layter, D. Lazic, A.M.Lee, D. Lellouch, J. Letts, L. Levinson, R. Liebisch, B. List, C. Littlewood, A.W.Lloyd, S.L. Lloyd, F.K. Loebinger, G.D. Long, M.J. Losty, J. Ludwig, D. Liu, A.Macchiolo, A.Macpherson, W.Mader, M.Mannelli, S.Marcellini, C.Markopoulos, A.J.Martin, J.P.Martin, G.Martinez, T.Mashimo, P.Mättig, W.J.McDonald, J.McKenna, E.A.Mckigney, T.J.McMahon, R.A.McPherson, F.Meijers, S.Menke, F.S.Merritt, H.Mes, J.Meyer, A.Michelini, S.Mihara, G.Mikenberg, D.J.Miller, R.Mir, W.Mohr, A.Montanari, T.Mori, K.Nagai, I. Nakamura, H.A.Neal, B.Nellen, R.Nisius, S.W.O’Neale, F.G.Oakham, F.Odorici, H.O.Ogren, M.J.Oreglia, S.Orito, J. Pálinkás, G. Pásztor, J.R.Pater, G.N.Patrick, J. Patt, R. Perez-Ochoa, S. Petzold, P. Pfeifenschneider, J.E. Pilcher, J. Pinfold, D.E.Plane, P. Poffenberger, J. Polok, M.Przybycień, C.Rembser, H.Rick, S. Robertson, S.A.Robins, N.Rodning, J.M.Roney, K.Roscoe, A.M.Rossi, Y.Rozen, K.Runge, O.Runolfsson, D.R.Rust, K. Sachs, T. Saeki, O. Sahr, W.M. Sang, E.K.G. Sarkisyan, C. Sbarra, A.D. Schaile, O. Schaile, F. Scharf, P. Scharff-Hansen, J. Schieck, B. Schmitt, S. Schmitt, A. Schöning, M. Schröder, M. Schumacher, C. Schwick, W.G. Scott, T. Seiler, R. Seuster, T.G. Shears, B.C. Shen, C.H. Shepherd-Themistocleous , P. Sherwood, G.P. Siroli, A. Sittler, A. Skuja, A.M. Smith, G.A. Snow, R. Sobie, S. Söldner-Rembold, M. Sproston, A. Stahl, K. Stephens, J. Steuerer, K. Stoll,