The product ion rate o f electrons with momentum p > 4 G e V / c and large m o m e n t u m transverse to the jet containing the electron has been measured in 136 000 hadronic decays o f the Z ~ recorded with the O P A L detector at LEP in 1990. The dominan t source o f these electrons is the semileptonic decay of hadrons containing b quarks. I f we assume that the semileptonic branching fraction o f b hadrons produced on the Z ~ resonance is the same as the branching fraction measured at the r ( 4 S) resonance, we determine Fse = 394 + 13 + 32 MeV, where the first error is statistical and the second error is systematic. The sensitivity o f the result to this assumption is discussed. We have reduced the dependence o f our result on the model o f b hadron semileptonic decay by taking into account the correlat ion between the model dependence o f the branching fractions measured at the Y (4 S ) and of our kinematic acceptance for electrons.

Results are presented on the production of excited charm and excited charm-strange mesons in hadronic Z0 decays. The results are obtained from approximately 4.3 million hadronic Z0 decays, collected on or near the Z0 resonance using the OPAL detector at LEP. The D~(2420) and D2°(2460) mesons are reconstructed in the n•+"final state and their separate production rates in charm fragmentation and in weak decays of bhadrons are determined. From these measurements, the charm hadronization fractions and the inclusive branching ratios ofb-hadrons to these neutral P-wave charm mesons are determined to be f(cD~) f(c-D2°) f(bD~) f(bD2°) 0.021 ± 0.007( stat) ± 0.003( syst ), 0.052 ± 0.022(stat) ± 0.013( syst ), 0.050 ± 0.014(stat) ± 0.006(syst), 0.04 7 ± 0.024(stat) ± 0.013( syst ). We also present the first observation at LEP of the D;i (2536) meson which is reconstructed in both the D*+K~ and D*°K+ final states. After correcting for the expected contribution from bb events, these results are used to derive the charm hadronization fraction f( c ~ D;i): f(c ~ D;i) = 0.016 ± 0.004(stat) ± 0.003(syst). (To be submitted to Zeitschrift fiir Physik C) The OPAL Collaboration K. Ackersta:ffS, G. Alexander23 , J. Allison16 , N. Altekamp5 , K.J. Anderson9 , S. Anderson12 , S.Arcell?, S.Asai , D.Axen 29 , G.Azuelos18·a, A.H.BalF 7 , E.Barberio , R.J.Barlow , R.Bartoldus3 , J.R.Batley5 , S.Baumann3 , J.Bechtluft1\ C.Beeston , T.Behnke , A.N.BelF, K.W. Bell20 , G. Bella , S. Bentvelsen , P. Berlich , S. Bethke1\ 0. BiebeF\ A. Biguzzi5 , S.D. Bird16 , V. BlobeJ2 , I.J. Bloodworth1 , J .E. Bloomer , M. Bobinski , P. BocPl, D. Bonacors?, M. Boutemeur3\ B.T. Bouwens , S. Braibant , L. Brigliador?, R.M. Brown , H.J. Burckhart8 , C. Burgard8 , R. Biirgin10 , P. Capilupp?, R.K. Carnegie6 , A.A. Carter13, J.R. Carter5 , C.Y. Chang17 , D.G. Charlton1•b, D. Chrisman\ P.E.L. Clarke15 , I. Cohen23 , J.E.Conboy15 , O.C.Cooke16 , M.Cuffian?, S.Dado , C.Dallapiccola , G.M.Dallavalle , S.De Jong , L.A. del Pozo\ K.Desch , M.S.Dixit 7 , E. do Couto e Silva , M.Doucet , E. Duchovn?6 , G. Duckeck\ I.P. Duerdoth , D. Eatough , J.E.G. Edwards , P.G. Estabrooks6 , H.G. Evans9 , M. Evans13 , F. Fabbr?, M. Fanti2 , A.A. Faust30 , F. Fiedler27 , M. Fierro , H.M. Fischer\ I. Fleck , R. Folman , D.G. Fong , M. Foucher , A. Fiirtjes , D.I. Futyan16, P. Gagnon', J.W. Gary\ J. Gascon , S.M. Gascon-Shotkin17 , N.I. Geddes 20 , C. Geich-Gimbel , T. Geralis20 , G. Giacomelli , P. Giacomelli , R. Giacomell?, V. Gibson , W.R.Gibson13 , D.M.Gingrich30·", D.Glenzinski , J.Goldberg , M.J.Goodrick , W.Gorn\ C.Grandi2 , E.Gross 26 , J.Grunhaus 23 , M.Gruwe , C.Hajdu32 , G.G.Hanson , M.Hansroul8 , M. Hapke13 , C.K. Hargrove , P.A. Hart , C. Hartmann , M. Hauschild , C.M. Hawkes", R.Hawkings27 , R.J.Hemingway , M.Herndon, G.Herten, R.D.Heuer , M.D.Hildreth , J .C. HillS, S.J. Hillier1 , T. Hilse10 , P.R. Hobson25 , R.J. Homer\ A.K. Honma28·", D. Horvath ·c, R. Howard29 , D.E. Hutchcroft5 , P. Igo-Kemenes , D.C. Imrie , M.R. Ingram , K. Ishii\ A.Jawahery17 , P.W.Jeffreys20 , H.Jeremie, M.Jimackl, A.Joly , C.R.Jones , G.Jones , M.Jones6 , U.Jost11, P.Jovanovic , T.R.Junk", D.Karlen6 , V.Kartvelishvili , K.Kawagoe\ T. Kawamoto2\ R.K. Keeler28 , R.G. Kellogg , B.W. Kennedy, J. Kirk , A. Klier , S. Kluth8 , T. Kobayash?\ M. KobeF0 , D.S. Koetke , T.P. Kokotts, M. Kolrep , S. Komamiya2\ T. Kress 11 , P. Krieger6 , J. von Krogh1 \ P. Kyberds, G.D. Lafferty , R. Lahmann17 , W.P. Lai19 , D. Lanske1\ J. Lauber15 , S.R. Lautenschlagers\ J.G. Layter\ D.Lazic22 , A.M.Lee31, E.Lefebvre18 , D.Lellouch , J.Letts12 , L.Levinson , S.L.Lloyds, F .K. Loebinger16 , G.D. Long28 , M.J. Losty7 , J. Ludwig10 , A. Macchiolo , A. Macpherson so, M. Mannelli8 , S. Marcellini2 , C. Markuss, A.J. Martin1s, J.P. Martin18 , G. Martinez , T. Mashimo2\ P. Miittigs, W.J. McDonald , J. McKenna , E.A. Mckigney, T.J. McMahon\ R.A. McPherson8 , F. Meijers8 , S. Menkes, F.S. Merritt9 , H. Mes7 , J. Meyer27, A. Michelin?, G. Mikenberg26 , D.J. Miller15 , A. Mincer22·e, R. Mir , W. Mohr10 , A. Montanari , T. Mor?\ M.Morii2\ U.Miillers, K.Nagai26 , I.Nakamura\ H.A.Neal , B.Nellen , R.Nisius , S.W. O'Neale\ F.G. Oakham , F. Odorici , H.O. Ogren , N.J. Oldershaw , M.J. Oreglia , S.Orito2\ J.Palinkas33·d, G.Pasztor32 , J.R.Pater16 , G.N.Patrick , J.Patt10 , M.J.Pearcel, S. Petzold27 , P. Pfeifenschneider14 , J .E. Pilcher9 , J. Pinfold , D.E. Plane , P. Poffenberger , B.Poli , A.Posthaus , H.Przysiezniak , D.L.Rees\ D. Rigby\ S.Robertson , S.A.Robins , N. Rodning , J.M. Roney, A. Rooke , E. Ros , A.M. Rossi', M. Rosvick , P. Routenburg , Y. Rozen22 , K. Runge10 , 0. Runolfsson8 , U. Ruppel\ D.R. Rust , R. Rylko , K. Sachs , T. Saeki2\ E.K.G. Sarkisyan2S, C. Sbarra29 , A.D. Schailes\ 0. Schaile\ F. Scharf\ P. Scharff-Hansen8 , P. Schenk3\ J. Schieck11 , P. Schleper11 , B. Schmitt , S. Schmitt ,

The cross section of the pure QED process e+ e-> "/"/ has been measured using data accumulated during the 1989 and 1990 scans of the Z resonance at LEP. Both the energy dependence and the angular distribution are in good agreement with the QED prediction, Upper limits on the branching ratios of Z -> "f"f, Z -> 1r "f and Z -> rn have been set at lAx I o-4 , 1 Ax 10-'1 and 2.0 x 10-4 respectively. Lower limits on the cutoff parameters of the modified electron propagator have been found to be A+> 117 GeV and A_ > 110 GeV. The reaction e+e-> "/"1"1 has also been studied and was found to be consistent with the QED prediction_ An upper limit on the branching ratio of Z _,"/"/"/has been set at 6 .. 6 x 10• All the limits are given at 95% confidence leveL (Submitted to Physics Letters D) The OPAL Collaboration lii.Z. Akrawy 12 , G. Alexander22 , J. Allison 15 , P.P. Allport5 , K.J. Anderson9 , J.C. Armitage6 , G.T.J. Arnison 9, P. Ashton15 , G. Azuelos·d, J.T.l\I. Baines15 , A. H. Ball 16 , J. Banks15 , G.J. Barker , R.J. Barlow 15 , .I.R. Batley5 , G. Beaudoin'\ A. Beck 22 , J. Becker10 , T. Behnkes, K.W. Bell' 9 , G. Bella22 , S. Bethken, 0. Bicbel , U. Binder 10 , I.J. Bloodworth', P. Bockn, II. Breukers, R.l\1. Brown 19 , R. Bruns, A. Buijss, H.J. Burckharts, P. Capiluppi2 , R. K. Carncgie , A.A. Carler12 , J .R. Carter5 , C.Y. Chang16 , D.G. Charltons, J .T.l\1. Chrin 15 , P.E.L. Clarkc , I. Cohen , W.J. Collins , J .E. Conboy14 , i\1. Couch , 1\l. Coupland , 1\l. Cuffiani , S. Dado21 , G.l\1. Dallamlle , S. De Jongs, P. Dcbu20 , 1\l.l\l. Deninno , A. Dieckmann ll, 1\l. Dittmar', 1\l.S. Dixit 1 , E. Duchovni25 , l.P. Duerdoth 15 , D .. J.P. Dumas6 , P.A. Elcombe , P.G. Estabrooks6 , E. Etzion , F. Fabbr?, P. Farthouat20 , H.l\1. Fischer , D.G. Fong , 1\LT. French19 , C. Fukunaga , A. Gaidot20 , 0. GaneF5 , J.W. Garyll, .) . Gascon , N .I. Geddes19 , C.N .P. Gee19 , C. Geich-GimbeP, S. W. Gensler9 , F .X. Gentit20 , G. Giacomcll?, V. Gibson 5 , W.R. Gibson 12 , J.D. Gillies , J. Goldberg21 , i\I.J. Goodrick5 , W. Gorn4 , D. Granite21 , E. Gross25 , J. Grunhaus , H. Hagedorn 10 , J. llagemanns, 1\l.llansrouls, C.K.IIargrove7, I. Harrus21 , J. Hart5 , P.l\1. Hattersley', 1\l.llauschilds, C.l\1. Haw kess, E. Heflin 4 , R.J. llemingway6 , ltD. Heuers, J .C. llill5 , S.J. Hillier1 , D.A.llinshaw 17 , C. Ho4, J.D. Hobbs9 , P.R. Hobson', D. Hochman25 , B. HoUS, R.J. l!omer1 , S.R. Ilou16 , C.P.llowarth1\ R.E.llughcs-Jones , R. Humbert10 , P.lgo-Kemcnesn, H. lhssenll, D.C. lmrie24 , L. Janissen6 , A. Jawahery , P.\V. Jcffreys19 , H. Jeremie , M.Jimacks,.M.Jobes1 , R.W.L.Jones12 , P.Jovanovic1 , D. Karlen6 , K.Kawagoe23 , T. Kawamoto23 , R.G. Kcllogg16 , B.W. Kennedy 14 , C. Klein worts, D.E. Klem1s, G. Knop3 , T. Kobayash? , T.P. Kokott3 , L. Kopkes, R. Kowalewski6 , H. Kreutzmann\ J. Kroll , 1\I. Kuwano , P. Kyberd 12 , G.D. Lalferty'5 , F. Lamarche17 , W.J. Larson', J.G. Layter , P. Le Du20 , P. Leblanc17 , A.M. Lee16 , I\!. H. Lehto14 , D. Lellouchs, P. Lennertn, C. Leroy17 , L. Lessard17 , S. Levegriin3 , L. Levinson25 , S.L. Lloyd , F.K. Loebinger15 , J.l\1. Lorah16 , B. Lora.zo17 , 1\l.J. Losty 7, J. Ludwig10 , J. l\Ia4•b, A.A.l\!acbeth15 , 1\L 1\Iannellis, S. Marcellini2, G.l\Iaringer , A.J.l\Iartin12 , J.P. i\Iartin , T. Mashimo , P.l\Iiittig , U.l\Iaur , T.J. Mcl\!ahon 1 , J.R.l\IcNutt24 , F. Meijerss, D. Mensznern, F.S.l\Ierritt9 , H.l\Ies 7, A.l\Iichelinis, R.P. Middleton 19 , G.l\Iikenberg, J. l\!ildenbcrger6 , D.J. Miller 14 , C.l\Iilstcne22 , l\l.l\Iinowa23 , W.l\lohr10 , C.l\loisan17 , A. Montanari2 , T. Mori23 , 1\l.W. Moss , P.G.l\Iurphy' 5 , W.J.l\lurray , B. Ncllen , lUI. Nguyen , 1\l. Nozaki , A.J.P. O'Dowd15 , S.W. O'Neales,c, B.P. O'Neill', F.G. Oakham', F. Odorici2 , 1\I. Ogg6 , II. Oh 4 , 1\I.J. Oreglia9 , S. Orito23 , J.P. Pansart , G.N. Patrick19 , S.J. Pawley' 5 , P. Pfister10 , J.E. Pilcher9 , J.L. Pinfold25 , D.E. Planes, B. Pol?, A. Pouladdej", E. Prebyss, T.W. Pritchard 12 , II. Przysiezniak17 , G. Quasts, M.W. Redmond 9 , D.L. Rees1 , 1\1. Regimbald11 , K. Riles', C.M. Roach , S.A. Robins 12 , A. Rollnik3 , J.l\1. Roney9 , S. Rossberg 10 , A.M. Rossi2·•, P. Routenburg , K. Runge 10 , 0. Runolfssons, S. Sanghera6 , R.A. Sansum , 1\1. Sasaki23 , B.J. Saunders , A.D. Schaile10 , 0. Scha.ile10 , W. Schappert6 , P. Scha.rlf-Ha.nsens, S. Schreiber3 , J. Schwarz , A. Shapira.25 , B.C. Shen\ P. Sherwood", A. Simon3 , P. Singh 12 , G.P. Siroli2 , A. Skuja16 , A.M. Smiths, T.J. Smiths, G.A. Snow 16 , R.W. Springer , 1\I. Sproston , K. Stephens , H.E. Stier10 , R. Stroehmerll, D. Strom9 , H. Ta.kcda , T. Takeshita. , P. Taras, N.J. Tha.ckra.y', T. Tsukamoto23 , I\!. F. Turner5 , G. Tysarczyk-Niemeyeru, D. Va.n den pla.s , R. Va.n Kootens, G.J. VanDalen', G. Va.sseur20 ,

Events with four distinct jets from e + e − collisions, collected by the OPAL detector at centre-of-mass energies between 130 and 184 GeV, are analysed for a peak in the sum of dijet masses. This search is motivated by the ALEPH Collaboration's observation of a clear excess of events with dijet mass sums close to 105 GeV in data taken at centre-of-mass energies of 130 and 136 GeV in 1995. We have observed no significant excess of four-jet events compared to the Standard Model expectation for any dijet mass sum at any energy. Our observation is inconsistent with the excess observed by ALEPH in 1995. Upper limits are determined on the production cross-section as a function of the dijet mass sum.

A search for stable and long-lived massive particles of electric charge |Q/e| = 1 or 2/3, pair-produced in ee collisions at centre-of-mass energies from 130 to 183 GeV, is reported by the OPAL collaboration at LEP. No evidence for production of these particles was observed in a mass range between 45 and 89.5 GeV. Model-independent upper limits on the production cross-section between 0.05 and 0.19 pb have been derived for scalar and spin-1/2 particles with charge ±1. Within the framework of the minimal supersymmetric model (MSSM), this implies a lower limit of 82.5 (83.5) GeV on the mass of long-lived right(left-)handed scalar muons and scalar taus. Long-lived charged leptons and charginos are excluded for masses below 89.5 GeV. For particles with charge ±2/3 the upper limits on the production cross-section vary between 0.05 and 0.2 pb. All limits, on masses and on cross-sections, are valid at the 95% confidence level for particles with lifetimes longer than 10 s. (Submitted to Physics Letters B) The OPAL Collaboration 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, S. Bentvelsen, S. Bethke, S. Betts, O.Biebel, A.Biguzzi, S.D.Bird, V.Blobel, I.J. Bloodworth, M.Bobinski, P. Bock, D.Bonacorsi, M.Boutemeur, S. Braibant, 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, P.E.L.Clarke, I. Cohen, J.E.Conboy, O.C.Cooke, C.Couyoumtzelis , R.L.Coxe, M.Cuffiani, S.Dado, C.Dallapiccola, G.M.Dallavalle, R.Davis, S.De Jong, L.A. del Pozo, A. de Roeck, K.Desch, B.Dienes, M.S.Dixit, M.Doucet, E.Duchovni, G.Duckeck, I.P.Duerdoth, D. Eatough, P.G.Estabrooks, E. Etzion, H.G.Evans, M.Evans, F. Fabbri, A. Fanfani, M.Fanti, A.A. Faust, L. Feld, F. Fiedler, M.Fierro, H.M.Fischer, I. Fleck, R. Folman, D.G.Fong, M.Foucher, A. Fürtjes, D.I. Futyan, P.Gagnon, J.W.Gary, J.Gascon, S.M.Gascon-Shotkin, N.I.Geddes, C.Geich-Gimbel, T.Geralis, G.Giacomelli, P.Giacomelli, R.Giacomelli, V.Gibson, W.R.Gibson, D.M.Gingrich, D.Glenzinski, J.Goldberg, M.J.Goodrick, W.Gorn, C.Grandi, E.Gross, J.Grunhaus, M.Gruwé, C.Hajdu, G.G.Hanson, M.Hansroul, M.Hapke, C.K.Hargrove, P.A.Hart, 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, D.E.Hutchcroft, P. Igo-Kemenes, D.C. Imrie, K. Ishii, A. Jawahery, P.W. Jeffreys, H. Jeremie, M. Jimack, A. Joly, C.R. Jones, M. Jones, U. Jost, P. Jovanovic, T.R. Junk, J.Kanzaki, D.Karlen, V.Kartvelishvili, K.Kawagoe, T.Kawamoto, P.I.Kayal, R.K.Keeler, R.G.Kellogg, B.W.Kennedy, J.Kirk, 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, P.Kyberd, G.D. Lafferty, R. Lahmann, W.P. Lai, D. Lanske, J. Lauber, S.R. Lautenschlager, I. Lawson, J.G. Layter, D. Lazic, A.M.Lee, E. Lefebvre, D. Lellouch, J. Letts, L. Levinson, B. List, S.L. Lloyd, F.K. Loebinger, G.D. Long, M.J. Losty, J. Ludwig, D. Lui, A.Macchiolo, A.Macpherson, M.Mannelli, S.Marcellini, C.Markopoulos, C.Markus, 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, A.Mincer, 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, A.Oh, N.J.Oldershaw, 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, B. Poli, A. Posthaus, C.Rembser, S. Robertson, S.A.Robins, N.Rodning, J.M.Roney, A.Rooke, A.M.Rossi, P.Routenburg, Y.Rozen, K.Runge, O.Runolfsson, U.Ruppel, 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, P. Schleper, B. Schmitt, S. Schmitt, A. Schöning, M. Schröder, M. Schumacher, C. Schwick , W.G. Scott,

Cross-sections for hadronic and leptonic two-fermion events, and leptonic forward-backward asymmetries, have been measured in e + e ? collisions at a centre-of-mass energy of 161 GeV, using the OPAL detector at LEP. Results are presented both including and excluding the dominant production of radiative Z 0 events. We have measured R b , the ratio of the number of bb to all multihadronic events at 161 GeV, and compared it to the result obtained at 130{136 GeV. All results agree well with the Standard Model expectations. In a model-independent t to the Z 0 lineshape, the data presented here give an improved precision on the Z 0-interference term. The data have also been used to obtain new limits on extensions of the Standard Model described by eeective four-fermion contact interactions.

The forward-backward asymmetry of e + e ? ! Z 0 ! bb has been measured using approximately 2.15 million hadronic Z 0 decays collected at the LEP e + e ? collider with the OPAL detector. A lifetime tag technique was used to select an enriched bb event sample. The measurement of the bb asymmetry was then performed using a jet charge algorithm to determine the direction of the primary quark. were measured where, in each case, the rst error is statistical, the second is systematic and the third term gives the variation due to a change (? bb =? had) in the value of ? bb =? had = 0:216 assumed. The dependence on the assumed charm asymmetry at the same energy is (A b FB) +0:077(A c FB). Assuming the Standard Model form for the couplings, these measurements correspond to an eeective weak mixing angle of: sin 2 ee;e +16 ?19 GeV/c 2 , where the rst error is statistical and the second is systematic. The Higgs mass assumed is 300 GeV/c 2. A variation in the assumed mass of the Higgs boson between 60 and 1000 GeV/c 2 corresponds to an uncertainty in sin 2 ee;e W of 0:00006 and on M top of +20 ?26 GeV/c 2 .

A study of b quark fragmentation at LEP is presented using a sample of semileptonic B decays containing a fully reconstructed charm meson. The data are compared to several theoretical models for heavy quark fragmentation; the free parameters in these models are tted and the sensitivity of the model parameters to the rate of P-wave B meson production is studied. The mean scaled energy fraction of B 0 and B + mesons has been determined to be hx E i = 0:695 0:006 0:003 0:007, where the errors are statistical, systematic and model dependence respectively. This result is consistent with previous, less direct measurements from inclusive leptonic B decays. Also presented is a model independent t to the shape of the energy distribution of weakly decaying B mesons at LEP.

We report a measurement of the branching ratio B(D + ! 0 ` + `)/ B(D + ! K 0 ` + `) from the Fermilab charm hadroproduction experiment E791. Based on signals of 49 17 events in the D + ! 0 e + e mode and 54 18 events in the D + ! 0 + mode, we measure Combining the results from both the electronic and muonic modes, we obtain 2 Semileptonic charm decays are useful in probing the dynamics of hadronic currents since the Cabibbo-Kobayashi-Maskawa matrix elements for the charm sector are well-known from unitarity constraints. Form factors for Cabibbo-suppressed (CS) c ! d semileptonic decays can be related via Heavy Quark EEective Theory (HQET) to those for b ! u semileptonic decays at the same four-velocity transfer 1]. Since knowledge of the form factors in b ! u transitions is vital for extracting V ub from b ! u semileptonic decays in a model-independent way, study of c ! d semileptonic decays can improve our knowledge of V ub. Although considerable progress has been made in studying CS semileptonic charm decays to pseudoscalar mesons 2], the only previous result on CS semileptonic charm decay to a vector meson is based on four D + ! 0 + events 3]. In this Letter, we report a new measurement from the Fermilab hadroproduction experiment E791 of B(D + ! 0 ` + `)=B(D + ! K 0 ` + `) based on more than 100 D + ! 0 ` + ` decays in the combined electronic and muonic modes. The E791 experiment 4] recorded 2 10 10 events from 500 GeV/c ? interactions in ve thin targets (one platinum, four diamond) separated by gaps of 1.34 to 1.39 cm. Precision tracking and vertexing information was provided by 23 silicon microstrip detectors (6 upstream and 17 downstream of the targets) and 35 drift chamber planes. Momentum was measured with two dipole magnets. Two segmented threshold Cerenkov counters provided =K separation in the 6 ? 60 GeV/c momentum range 5]. (charge-conjugate states are implied throughout this Letter) are selected by requiring a three-prong decay vertex of charge 1 with one of the decay particles being identiied as a lepton. A segmented lead and liquid-scintillator calorimeter 6] is used to identify the electrons, based on energy deposition and transverse shower shape. The probability that a (K) is misidentiied as …

From 1 105 045 hadronic Z 0 decays observed with the OPAL detector at the LEP e + e ? collider, 21 732 four-jet events are selected. A simultaneous t of three selected angular variables from these events by the second order QCD matrix element calculation yields for the ratios of colour factors, in agreement with SU(3) expectations of C A =C F = 9=4 and T F =C F = 3=8.

A search is described for the neutral Higgs bosons h0 and A0 predicted by models with two scalar field doublets and, in particular, the Minimal Supersymmetric Standard Model (MSSM). The search in the Z0h0 and h0A0 production channels is based on data corresponding to an integrated luminosity of 25 pb−1 from e+e− collisions at centre-of-mass energies between 130 and 172 GeV collected with the OPAL detector at LEP. The observation of a number of candidates consistent with Standard Model background expectations is used in combination with earlier results from data collected at the Z0 resonance to set limits on mh and ma in general models with two scalar field doublets and in the MSSM. For example, in the MSSM, for tan β > 1, minimal and maximal scalar top quark mixing and soft SUSY-breaking masses of 1 TeV, the 95% confidence level limits mh > 59.0 GeV and ma > 59.5 GeV are obtained. For the first time, the MSSM parameter space is explored in a detailed scan.

The process e+e− →, γγ(γ) is studied using data recorded with the OPAL detector at LEP. The data sample corresponds to a total integrated luminosity of 25.38 pb−1 taken at centre-of-mass energies of 130–172 GeV. The measured cross-sections agree well with the expectation from QED. In a combined fit using data from all centre-of-mass energies, the angular distribution is used to obtain improved limits on the cut-off parameters: Λ+ > 195 GeV and Λ− > 210 GeV (95% CL). In addition, limits on nonstandard e+e−γ couplings and contact interactions, as well as a 95% CL mass limit for an excited electron,Me*= > 194 GeV for an e+e−γ coupling κ = 1, are determined.

An investigation of CP violation was performed using a total of 24 candidates for B0 → J/ψKS decay, with a purity of about 60%. These events were selected from 4.4 million hadronic Z0 decays recorded by the OPAL detector at LEP. An analysis procedure, involving techniques to reconstruct the proper decay times and tag the produced b-flavours, B0 or B̄0, has been developed to allow a first direct study of the time dependent CP asymmetry that, in the Standard Model, is sin 2β. The result is sin 2β = 3.2 −2.0 ± 0.5 , where the first error is statistical and the second systematic. This result is used to determine probabilities for different values of sin 2β in the physical region from −1 to +1. (Submitted to Physics Letters B) The OPAL Collaboration 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, S. Bentvelsen, S. Bethke, S. Betts, O. Biebel, A. Biguzzi, S.D. Bird, V. Blobel, I.J. Bloodworth, M. Bobinski, P. Bock, D. Bonacorsi, M. Boutemeur, S. Braibant, 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, P.E.L. Clarke, I. Cohen, J.E. Conboy, O.C. Cooke, C. Couyoumtzelis , R.L. Coxe, M. Cuffiani, S. Dado, C. Dallapiccola, G.M. Dallavalle, R. Davis, S. De Jong, L.A. del Pozo, A. de Roeck, K. Desch, B. Dienes, M.S. Dixit, M. Doucet, E. Duchovni, G. Duckeck, I.P. Duerdoth, D. Eatough, P.G. Estabrooks, E. Etzion, H.G. Evans, M. Evans, F. Fabbri, A. Fanfani, M. Fanti, A.A. Faust, L. Feld, F. Fiedler, M. Fierro, H.M. Fischer, I. Fleck, R. Folman, D.G. Fong, M. Foucher, A. Fürtjes, D.I. Futyan, P. Gagnon, J.W. Gary, J. Gascon, S.M. Gascon-Shotkin, N.I. Geddes, C. Geich-Gimbel, T. Geralis, G. Giacomelli, P. Giacomelli, R. Giacomelli, V. Gibson, W.R. Gibson, D.M. Gingrich, D. Glenzinski, J. Goldberg, M.J. Goodrick, W. Gorn, C. Grandi, E. Gross, J. Grunhaus, M. Gruwé, C. Hajdu, G.G. Hanson, M. Hansroul, M. Hapke, C.K. Hargrove, P.A. Hart, 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, D.E. Hutchcroft, P. Igo-Kemenes, D.C. Imrie, K. Ishii, A. Jawahery, P.W. Jeffreys, H. Jeremie, M. Jimack, A. Joly, C.R. Jones, M. Jones, U. Jost, P. Jovanovic, T.R. Junk, J. Kanzaki, D. Karlen, V. Kartvelishvili, K. Kawagoe, T. Kawamoto, P.I. Kayal, R.K. Keeler, R.G. Kellogg, B.W. Kennedy, J. Kirk, 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, P. Kyberd, G.D. Lafferty, R. Lahmann, W.P. Lai, D. Lanske, J. Lauber, S.R. Lautenschlager, I. Lawson, J.G. Layter, D. Lazic, A.M. Lee, E. Lefebvre, D. Lellouch, J. Letts, L. Levinson, B. List, S.L. Lloyd, F.K. Loebinger, G.D. Long, M.J. Losty, J. Ludwig, D. Lui, A. Macchiolo, A. Macpherson, M. Mannelli, S. Marcellini, C. Markopoulos, C. Markus, 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, A. Mincer, R. Mir, W. Mohr, A. Montanari, T. Mori, S. Mihara, K. Nagai, I. Nakamura, H.A. Neal, B. Nellen, R. Nisius, S.W. O’Neale, F.G. Oakham, F. Odorici, H.O. Ogren, A. Oh, N.J. Oldershaw, 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, B. Poli, A. Posthaus, C. Rembser, S. Robertson, S.A. Robins, N. Rodning, J.M. Roney, A. Rooke, A.M. Rossi, P. Routenburg, Y. Rozen, K. Runge, O. Runolfsson, U. Ruppel, 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, P. Schleper, B. Schmitt, S. Schmitt, A. Schöning, M. Schröder, M. Schumacher, C. Schwick, W.G. Scott, T.G. Shears, B.C. Shen, C.H. Shepherd-Themistocleous ,

A search for decays of the B-c meson was performed using data collected from 1990-1995 with the OPAL detector on or near the Z(o) peak at LEP. The decay channels B-c(+) --> J/psi pi(+), B-c(+) --> J/psi a(1)(+) and B-c(+) --> J/psi l(+) nu were investigated, where l denotes an electron or a muon. Two candidates are observed in the mode B-c(+) --> J/psi pi(+), With an estimated background of (0.63 +/- 0.20) events. The weighted mean of the masses of the two candidates is (6.32 +/- 0.06) GeV/c(2), which is consistent with the predicted mass of the B-c meson. One candidate event is observed in the mode B-c(+) --> J/psi l(+) nu, with an estimated background of (0.82 +/- 0.19) events. No candidate events are observed in the B-c(+) --> J/psi a(1)(+) decay mode, with an estimated background of (1.10 +/- 0.22) events, Upper bounds at the 90% confidence level ate set on the production rates for these processes. (C) 1998 Published bq Elsevier Science B.V.

An investigation of CP violation was performed using a total of 24 candidates for B^0 -> J/psi K^0_S decay, with a purity of about 60%. These events were selected from 4.4 million hadronic Z^0 decays recorded by the OPAL detector at LEP. An analysis procedure, involving techniques to reconstruct the proper decay times and tag the produced b-flavours, B^0 or B^0(bar), has been developed to allow a first direct study of the time dependent CP asymmetry that, in the Standard Model, is sin(2beta). The result is sin(2beta) = 3.2_{-2.0}^{+1.8} +/- 0.5, where the first error is statistical and the second systematic. This result is used to determine probabilities for different values of sin(2beta) in the physical region from -1 to +1.

In e+e2212 collisions at centre-of-mass energies around 91 GeV, D*0 mesons have been reconstructed using data collected with the OPAL detector at LEP. The hadronisation fraction has been measured to be f(c→D*0)=0.218±0.054±0.045±0.007, where the errors correspond to the statistical and systematic errors specific to this analysis, and to systematic uncertainties from externally measured branching fractions, respectively. Together with previous OPAL measurements of the hadronisation fractions of other charmed mesons, this value is used to investigate the relative production of observed vector and pseudoscalar charmed mesons in $$Z^0 \to c\bar c$$ decays. The production ratio is determined to be P effV = V/(V+P)=0.57±0.05. The relative primary production of vector and pseudoscalar mesons, P vrim, is studied in the context of the production and decay of orbitally excited charmed resonances. The first measurement of the inclusive Ds*+ production rate in hadronic Z0 decays is presented.

This paper describes a search for the Standard Model Higgs boson using data from e(+)e(-) collisions collected at center-of-mass energies of 161, 170 and 172 GeV by the OPAL detector at LEP. The data collected at these energies correspond to integrated luminosities of 10.0, 1.0 and 9.4 pb(-1), respectively. The search is sensitive to the main final states from the process in which the Higgs boson is produced in association with a fermion anti-fermion pair, namely four jets, two jets with missing energy. and two jets produced together with a pair of electron, muon or tau leptons. One candidate event is observed, in agreement with the Standard Model background expectation. In combination with previous OPAL searches at center-of-mass Energies close to the Z(0) resonance and the revised previous OPAL searches at 161 GeV, we derive a lower limit of 69.4 GeV for the mass of the Standard Model Higgs boson at the 95% confidence level.

Events with four distinct jets from e(+)e(-) collisions, collected by the OPAL detector at centre-of-mass energies between 130 and 184 GeV, are analysed for a peak in the sum of dijet masses. This search is motivated by the ALEPH Collaboration's observation of a clear excess of events with dijet mass sums close to 105 GeV in data taken at centre-of-mass energies of 130 and 136 GeV in 1995. We have observed no significant excess of four-jet events compared to the Standard Model expectation for any dijet mass sum at any energy. Our observation is inconsistent with the excess observed by ALEPH in 1995. Upper limits are determined on the production cross-section as a function of the dijet mass sum. (C) 1998 Elsevier Science B.V. All rights reserved.

Using radiative Z(0) --> tau(+) tau(-) gamma events collected with the OPAL detector at LEP at root(s) = M-Z during 1990-95, a direct study of the electromagnetic current at the tau gamma vertex has been performed in terms of the anomalous magnetic form factor F-2 of the tau lepton. The analysis is based on a data sample of 1429 e(+)e(-) --> tau(+)tau(-) gamma events which are examined for a deviation from the expectation with F-2 = 0. From the non-observation of anomalous tau(+)tau(-) gamma production a limit of -0.068 < F-2 < 0.065 is obtained. This can also be interpreted as a limit on the electric dipole form factor F-3 as \eF(3)\ < 3.7 x 10(-16) e cm.The above ranges are valid at the 95% confidence level. (C) 1998 Elsevier Science B.V. All rights reserved.