Observation of the muon inner bremsstrahlung at LEP1

J. Abdallah; P. Abreu; W. Adam; P. Adzic; T. Albrecht; R. Alemany-Fernandez; T. Allmendinger; P. P. Allport; U. Amaldi; N. Amapane; S. Amato; E. Anashkin; A. Andreazza; S. Andringa; N. Anjos; P. Antilogus; W-D. Apel; Y. Arnoud; S. Ask; B. Asman; J. E. Augustin; A. Augustinus; P. Baillon; A. Ballestrero; P. Bambade; R. Barbier; D. Bardin; G. J. Barker; A. Baroncelli; M. Battaglia; M. Baubillier; K-H. Becks; M. Begalli; A. Behrmann; E. Ben-Haim; N. Benekos; A. Benvenuti; C. Berat; M. Berggren; D. Bertrand; M. Besancon; N. Besson; D. Bloch; M. Blom; M. Bluj; M. Bonesini; M. Boonekamp; P. S. L. Booth; G. Borisov; O. Botner; B. Bouquet; T. J. V. Bowcock; I. Boyko; M. Bracko; R. Brenner; E. Brodet; P. Bruckman; J. M. Brunet; B. Buschbeck; P. Buschmann; M. Calvi; T. Camporesi; V. Canale; F. Carena; N. Castro; F. Cavallo; M. Chapkin; Ph. Charpentier; P. Checchia; R. Chierici; P. Chliapnikov; J. Chudoba; S. U. Chung; K. Cieslik; P. Collins; R. Contri; G. Cosme; F. Cossutti; M. J. Costa; D. Crennell; J. Cuevas; J. D’Hondt; T. da Silva; W. Da Silva; G. Della Ricca; A. De Angelis; W. De Boer; C. De Clercq; B. De Lotto; N. De Maria; A. De Min; L. de Paula; L. Di Ciaccio; A. Di Simone; K. Doroba; J. Drees; G. Eigen; T. Ekelof; M. Ellert; M. Elsing; M. C. Espirito Santo; G. Fanourakis; D. Fassouliotis; M. Feindt; J. Fernandez; A. Ferrer; F. Ferro; U. Flagmeyer; H. Foeth; E. Fokitis; F. Fulda-Quenzer; J. Fuster; M. Gandelman; C. Garcia; Ph. Gavillet; E. Gazis; R. Gokieli; B. Golob; G. Gomez-Ceballos; P. Goncalves; E. Graziani; G. Grosdidier; K. Grzelak; J. Guy; C. Haag; A. Hallgren; K. Hamacher; K. Hamilton; S. Haug; F. Hauler; V. Hedberg; M. Hennecke; H. Herr; J. Hoffman; S-O. Holmgren; P. J. Holt; M. A. Houlden; J. N. Jackson; G. Jarlskog; P. Jarry; D. Jeans; E. K. Johansson; P. Jonsson; C. Joram; L. Jungermann; F. Kapusta; S. Katsanevas; E. Katsoufis; G. Kernel; B. P. Kersevan; U. Kerzel; B. T. King; N. J. Kjaer; P. Kluit; P. Kokkinias; C. Kourkoumelis; O. Kouznetsov; Z. Krumstein; M. Kucharczyk; J. Lamsa; G. Leder; F. Ledroit; L. Leinonen; R. Leitner; J. Lemonne; V. Lepeltier; T. Lesiak; W. Liebig; D. Liko; A. Lipniacka; J. H. Lopes; J. M. Lopez; D. Loukas; P. Lutz; L. Lyons; J. MacNaughton; A. Malek; S. Maltezos; F. Mandl; J. Marco; R. Marco; B. Marechal; M. Margoni; J-C. Marin; C. Mariotti; A. Markou; C. Martinez-Rivero; J. Masik; N. Mastroyiannopoulos; F. Matorras; C. Matteuzzi; F. Mazzucato; M. Mazzucato; R. Mc Nulty; C. Meroni; E. Migliore; W. Mitaroff; U. Mjoernmark; T. Moa; M. Moch; K. Moenig; R. Monge; J. Montenegro; D. Moraes; S. Moreno; P. Morettini; U. Mueller; K. Muenich; M. Mulders; L. Mundim; W. Murray; B. Muryn; G. Myatt; T. Myklebust; M. Nassiakou; F. Navarria; K. Nawrocki; R. Nicolaidou; M. Nikolenko; A. Oblakowska-Mucha; V. Obraztsov; A. Olshevski; A. Onofre; R. Orava; K. Osterberg; A. Ouraou; A. Oyanguren; M. Paganoni; S. Paiano; J. P. Palacios; H. Palka; Th. D. Papadopoulou; L. Pape; C. Parkes; F. Parodi; U. Parzefall; A. Passeri; O. Passon; L. Peralta; V. Perepelitsa; A. Perrotta; A. Petrolini; J. Piedra; L. Pieri; F. Pierre; M. Pimenta; E. Piotto; T. Podobnik; V. Poireau; M. E. Pol; G. Polok; V. Pozdniakov; N. Pukhaeva; A. Pullia; J. Rames; A. Read; P. Rebecchi; J. Rehn; D. Reid; R. Reinhardt; P. Renton; F. Richard; J. Ridky; M. Rivero; D. Rodriguez; A. Romero; P. Ronchese; P. Roudeau; T. Rovelli; V. Ruhlmann-Kleider; D. Ryabtchikov; A. Sadovsky; L. Salmi; J. Salt; C. Sander; A. Savoy-Navarro; U. Schwickerath; R. Sekulin; M. Siebel; A. Sisakian; G. Smadja; O. Smirnova; A. Sokolov; A. Sopczak; R. Sosnowski; T. Spassov; M. Stanitzki; A. Stocchi; J. Strauss; B. Stugu; M. Szczekowski; M. Szeptycka; T. Szumlak; T. Tabarelli; F. Tegenfeldt; J. Timmermans; L. Tkatchev; M. Tobin; S. Todorovova; B. Tome; A. Tonazzo; P. Tortosa; P. Travnicek; D. Treille; G. Tristram; M. Trochimczuk; C. Troncon; M-L. Turluer; I. A. Tyapkin; P. Tyapkin; S. Tzamarias; V. Uvarov; G. Valenti; P. Van Dam; J. Van Eldik; N. van Remortel; I. Van Vulpen; G. Vegni; F. Veloso; W. Venus; P. Verdier; V. Verzi; D. Vilanova; L. Vitale; V. Vrba; H. Wahlen; A. J. Washbrook; C. Weiser; D. Wicke; J. Wickens; G. Wilkinson; M. Winter; M. Witek; O. Yushchenko; A. Zalewska; P. Zalewski; D. Zavrtanik; V. Zhuravlov; N. I. Zimin; A. Zintchenko; M. Zupan

doi:10.1140/epjc/s10052-008-0779-z

2022 Impact factor 4.4

Particles and Fields

Open Access

Eur. Phys. J. C (2008) 57: 499-514
https://doi.org/10.1140/epjc/s10052-008-0779-z

Regular Article - Experimental Physics

Observation of the muon inner bremsstrahlung at LEP1

J. Abdallah²⁶, P. Abreu²³, W. Adam⁵⁶, P. Adzic¹², T. Albrecht¹⁸, R. Alemany-Fernandez⁹, T. Allmendinger¹⁸, P. P. Allport²⁴, U. Amaldi³⁰, N. Amapane⁴⁸, S. Amato⁵², E. Anashkin³⁷, A. Andreazza²⁹, S. Andringa²³, N. Anjos²³, P. Antilogus²⁶, W-D. Apel¹⁸, Y. Arnoud¹⁵, S. Ask⁹, B. Asman⁴⁷, J. E. Augustin²⁶, A. Augustinus⁹, P. Baillon⁹, A. Ballestrero⁴⁹, P. Bambade²¹, R. Barbier²⁸, D. Bardin¹⁷, G. J. Barker⁵⁸, A. Baroncelli⁴⁰, M. Battaglia⁹, M. Baubillier²⁶, K-H. Becks⁵⁹, M. Begalli⁷, A. Behrmann⁵⁹, E. Ben-Haim²¹, N. Benekos³³, A. Benvenuti⁵, C. Berat¹⁵, M. Berggren²⁶, D. Bertrand², M. Besancon⁴¹, N. Besson⁴¹, D. Bloch¹⁰, M. Blom³², M. Bluj⁵⁷, M. Bonesini³⁰, M. Boonekamp⁴¹, P. S. L. Booth²⁴, G. Borisov²², O. Botner⁵³, B. Bouquet²¹, T. J. V. Bowcock²⁴, I. Boyko¹⁷, M. Bracko⁴⁴, R. Brenner⁵³, E. Brodet³⁶, P. Bruckman¹⁹, J. M. Brunet⁸, B. Buschbeck⁵⁶, P. Buschmann⁵⁹, M. Calvi³⁰, T. Camporesi⁹, V. Canale³⁹, F. Carena⁹, N. Castro²³, F. Cavallo⁵, M. Chapkin⁴³, Ph. Charpentier⁹, P. Checchia³⁷, R. Chierici⁹, P. Chliapnikov⁴³, J. Chudoba⁹, S. U. Chung⁹, K. Cieslik¹⁹, P. Collins⁹, R. Contri¹⁴, G. Cosme²¹, F. Cossutti⁵⁰, M. J. Costa⁵⁴, D. Crennell³⁸, J. Cuevas³⁵, J. D’Hondt², T. da Silva⁵², W. Da Silva²⁶, G. Della Ricca⁵⁰, A. De Angelis⁵¹, W. De Boer¹⁸, C. De Clercq², B. De Lotto⁵¹, N. De Maria⁴⁸, A. De Min³⁷, L. de Paula⁵², L. Di Ciaccio³⁹, A. Di Simone⁴⁰, K. Doroba⁵⁷, J. Drees⁹^,59, G. Eigen⁴, T. Ekelof⁵³, M. Ellert⁵³, M. Elsing⁹, M. C. Espirito Santo²³, G. Fanourakis¹², D. Fassouliotis³^,12, M. Feindt¹⁸, J. Fernandez⁴², A. Ferrer⁵⁴, F. Ferro¹⁴, U. Flagmeyer⁵⁹, H. Foeth⁹, E. Fokitis³³, F. Fulda-Quenzer²¹, J. Fuster⁵⁴, M. Gandelman⁵², C. Garcia⁵⁴, Ph. Gavillet⁹, E. Gazis³³, R. Gokieli⁹^,57, B. Golob⁴⁴^,46, G. Gomez-Ceballos⁴², P. Goncalves²³, E. Graziani⁴⁰, G. Grosdidier²¹, K. Grzelak⁵⁷, J. Guy³⁸, C. Haag¹⁸, A. Hallgren⁵³, K. Hamacher⁵⁹, K. Hamilton³⁶, S. Haug³⁴, F. Hauler¹⁸, V. Hedberg²⁷, M. Hennecke¹⁸, H. Herr⁹, J. Hoffman⁵⁷, S-O. Holmgren⁴⁷, P. J. Holt⁹, M. A. Houlden²⁴, J. N. Jackson²⁴, G. Jarlskog²⁷, P. Jarry⁴¹, D. Jeans³⁶, E. K. Johansson⁴⁷, P. Jonsson²⁸, C. Joram⁹, L. Jungermann¹⁸, F. Kapusta²⁶, S. Katsanevas²⁸, E. Katsoufis³³, G. Kernel⁴⁴, B. P. Kersevan⁴⁴^,46, U. Kerzel¹⁸, B. T. King²⁴, N. J. Kjaer⁹, P. Kluit³², P. Kokkinias¹², C. Kourkoumelis³, O. Kouznetsov¹⁷, Z. Krumstein¹⁷, M. Kucharczyk¹⁹, J. Lamsa¹, G. Leder⁵⁶, F. Ledroit¹⁵, L. Leinonen⁴⁷, R. Leitner³¹, J. Lemonne², V. Lepeltier²¹, T. Lesiak¹⁹, W. Liebig⁵⁹, D. Liko⁵⁶, A. Lipniacka⁴⁷, J. H. Lopes⁵², J. M. Lopez³⁵, D. Loukas¹², P. Lutz⁴¹, L. Lyons³⁶, J. MacNaughton⁵⁶, A. Malek⁵⁹, S. Maltezos³³, F. Mandl⁵⁶, J. Marco⁴², R. Marco⁴², B. Marechal⁵², M. Margoni³⁷, J-C. Marin⁹, C. Mariotti⁹, A. Markou¹², C. Martinez-Rivero⁴², J. Masik¹³, N. Mastroyiannopoulos¹², F. Matorras⁴², C. Matteuzzi³⁰, F. Mazzucato³⁷, M. Mazzucato³⁷, R. Mc Nulty²⁴, C. Meroni²⁹, E. Migliore⁴⁸, W. Mitaroff⁵⁶, U. Mjoernmark²⁷, T. Moa⁴⁷, M. Moch¹⁸, K. Moenig⁹^,11, R. Monge¹⁴, J. Montenegro³², D. Moraes⁵², S. Moreno²³, P. Morettini¹⁴, U. Mueller⁵⁹, K. Muenich⁵⁹, M. Mulders³², L. Mundim⁷, W. Murray³⁸, B. Muryn²⁰, G. Myatt³⁶, T. Myklebust³⁴, M. Nassiakou¹², F. Navarria⁵, K. Nawrocki⁵⁷, R. Nicolaidou⁴¹, M. Nikolenko¹⁰^,17, A. Oblakowska-Mucha²⁰, V. Obraztsov⁴³, A. Olshevski¹⁷, A. Onofre²³, R. Orava¹⁶, K. Osterberg¹⁶, A. Ouraou⁴¹, A. Oyanguren⁵⁴, M. Paganoni³⁰, S. Paiano⁵, J. P. Palacios²⁴, H. Palka¹⁹, Th. D. Papadopoulou³³, L. Pape⁹, C. Parkes²⁵, F. Parodi¹⁴, U. Parzefall⁹, A. Passeri⁴⁰, O. Passon⁵⁹, L. Peralta²³, V. Perepelitsa⁵⁵^,54, A. Perrotta⁵, A. Petrolini¹⁴, J. Piedra⁴², L. Pieri⁴⁰, F. Pierre⁴¹, M. Pimenta²³, E. Piotto⁹, T. Podobnik⁴⁴^,46, V. Poireau⁹, M. E. Pol⁶, G. Polok¹⁹, V. Pozdniakov¹⁷, N. Pukhaeva¹⁷, A. Pullia³⁰, J. Rames¹³, A. Read³⁴, P. Rebecchi⁹, J. Rehn¹⁸, D. Reid³², R. Reinhardt⁵⁹, P. Renton³⁶, F. Richard²¹, J. Ridky¹³, M. Rivero⁴², D. Rodriguez⁴², A. Romero⁴⁸, P. Ronchese³⁷, P. Roudeau²¹, T. Rovelli⁵, V. Ruhlmann-Kleider⁴¹, D. Ryabtchikov⁴³, A. Sadovsky¹⁷, L. Salmi¹⁶, J. Salt⁵⁴, C. Sander¹⁸, A. Savoy-Navarro²⁶, U. Schwickerath⁹, R. Sekulin³⁸, M. Siebel⁵⁹, A. Sisakian¹⁷, G. Smadja²⁸, O. Smirnova²⁷, A. Sokolov⁴³, A. Sopczak²², R. Sosnowski⁵⁷, T. Spassov⁹, M. Stanitzki¹⁸, A. Stocchi²¹, J. Strauss⁵⁶, B. Stugu⁴, M. Szczekowski⁵⁷, M. Szeptycka⁵⁷, T. Szumlak²⁰, T. Tabarelli³⁰, F. Tegenfeldt⁵³, J. Timmermans³²^*, L. Tkatchev¹⁷, M. Tobin²⁴, S. Todorovova¹³, B. Tome²³, A. Tonazzo³⁰, P. Tortosa⁵⁴, P. Travnicek¹³, D. Treille⁹, G. Tristram⁸, M. Trochimczuk⁵⁷, C. Troncon²⁹, M-L. Turluer⁴¹, I. A. Tyapkin¹⁷, P. Tyapkin¹⁷, S. Tzamarias¹², V. Uvarov⁴³, G. Valenti⁵, P. Van Dam³², J. Van Eldik⁹, N. van Remortel¹⁶, I. Van Vulpen⁹, G. Vegni²⁹, F. Veloso²³, W. Venus³⁸, P. Verdier²⁸, V. Verzi³⁹, D. Vilanova⁴¹, L. Vitale⁵⁰, V. Vrba¹³, H. Wahlen⁵⁹, A. J. Washbrook²⁴, C. Weiser¹⁸, D. Wicke⁹, J. Wickens², G. Wilkinson³⁶, M. Winter¹⁰, M. Witek¹⁹, O. Yushchenko⁴³, A. Zalewska¹⁹, P. Zalewski⁵⁷, D. Zavrtanik⁴⁵, V. Zhuravlov¹⁷, N. I. Zimin¹⁷, A. Zintchenko¹⁷, M. Zupan¹² and DELPHI Collaboration

¹ Department of Physics and Astronomy, Iowa State University, Ames, IA, 50011-3160, USA
² IIHE, ULB-VUB, Pleinlaan 2, 1050, Brussels, Belgium
³ Physics Laboratory, University of Athens, Solonos Str. 104, 10680, Athens, Greece
⁴ Department of Physics, University of Bergen, Allégaten 55, 5007, Bergen, Norway
⁵ Dipartimento di Fisica, Università di Bologna and INFN, Via Irnerio 46, 40126, Bologna, Italy
⁶ Centro Brasileiro de Pesquisas Físicas, rua Xavier Sigaud 150, 22290, Rio de Janeiro, Brazil
⁷ Inst. de Física, Univ. Estadual do Rio de Janeiro, rua São Francisco Xavier 524, Rio de Janeiro, Brazil
⁸ Collège de France, Lab. de Physique Corpusculaire, IN2P3-CNRS, 75231, Paris Cedex 05, France
⁹ CERN, 1211, Geneva 23, Switzerland
¹⁰ Institut de Recherches Subatomiques, IN2P3-CNRS/ULP-BP20, 67037, Strasbourg Cedex, France
¹¹ DESY-Zeuthen, Platanenallee 6, 15735, Zeuthen, Germany
¹² Institute of Nuclear Physics, N.C.S.R. Demokritos, P.O. Box 60228, 15310, Athens, Greece
¹³ FZU, Inst. of Phys. of the C.A.S. High Energy Physics Division, Na Slovance 2, 182 21, Prague 8, Czech Republic
¹⁴ Dipartimento di Fisica, Università di Genova and INFN, Via Dodecaneso 33, 16146, Genova, Italy
¹⁵ Institut des Sciences Nucléaires, IN2P3-CNRS, Université de Grenoble 1, 38026, Grenoble Cedex, France
¹⁶ Helsinki Institute of Physics and Department of Physical Sciences, P.O. Box 64, 00014, University of Helsinki, Finland
¹⁷ Joint Institute for Nuclear Research, Dubna, Head Post Office, P.O. Box 79, 101 000, Moscow, Russian Federation
¹⁸ Institut für Experimentelle Kernphysik, Universität Karlsruhe, Postfach 6980, 76128, Karlsruhe, Germany
¹⁹ Institute of Nuclear Physics PAN, Ul. Radzikowskiego 152, 31142, Krakow, Poland
²⁰ Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy, 30055, Krakow, Poland
²¹ Université de Paris-Sud, Lab. de l’Accélérateur Linéaire, IN2P3-CNRS, Bât. 200, 91405, Orsay Cedex, France
²² School of Physics and Chemistry, University of Lancaster, Lancaster, LA1 4YB, UK
²³ LIP, IST, FCUL Av. Elias Garcia, 14-1, 1000, Lisboa Codex, Portugal
²⁴ Department of Physics, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, UK
²⁵ Department of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow, G12 8QQ, UK
²⁶ LPNHE, IN2P3-CNRS, Univ. Paris VI et VII, Tour 33 (RdC), 4 place Jussieu, 75252, Paris Cedex 05, France
²⁷ Department of Physics, University of Lund, Sölvegatan 14, 223 63, Lund, Sweden
²⁸ Université Claude Bernard de Lyon, IPNL, IN2P3-CNRS, 69622, Villeurbanne Cedex, France
²⁹ Dipartimento di Fisica, Università di Milano and INFN-MILANO, Via Celoria 16, 20133, Milan, Italy
³⁰ Dipartimento di Fisica, Università di Milano-Bicocca and INFN-MILANO, Piazza della Scienza 3, 20126, Milan, Italy
³¹ IPNP of MFF, Charles University, Areal MFF, V Holesovickach 2, 180 00, Prague 8, Czech Republic
³² NIKHEF, Postbus 41882, 1009 DB, Amsterdam, The Netherlands
³³ Physics Department, National Technical University, Zografou Campus, 15773, Athens, Greece
³⁴ Physics Department, University of Oslo, Blindern, 0316, Oslo, Norway
³⁵ Departamento de la Fisica, Universidad Oviedo, Avda. Calvo Sotelo s/n, 33007, Oviedo, Spain
³⁶ Department of Physics, University of Oxford, Keble Road, Oxford, OX1 3RH, UK
³⁷ Dipartimento di Fisica, Università di Padova and INFN, Via Marzolo 8, 35131, Padua, Italy
³⁸ Rutherford Appleton Laboratory, Chilton, Didcot, OX11 OQX, UK
³⁹ Dipartimento di Fisica, Università di Roma II and INFN, Tor Vergata, 00173, Rome, Italy
⁴⁰ Dipartimento di Fisica, Università di Roma III and INFN, Via della Vasca Navale 84, 00146, Rome, Italy
⁴¹ DAPNIA/Service de Physique des Particules, CEA-Saclay, 91191, Gif-sur-Yvette Cedex, France
⁴² Instituto de Fisica de Cantabria (CSIC-UC), Avda. los Castros s/n, 39006, Santander, Spain
⁴³ Institute for High Energy Physics, Serpukov P.O. Box 35, Protvino, Moscow Region, Russian Federation
⁴⁴ J. Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
⁴⁵ Laboratory for Astroparticle Physics, University of Nova Gorica, Kostanjeviska 16a, 5000, Nova Gorica, Slovenia
⁴⁶ Department of Physics, University of Ljubljana, 1000, Ljubljana, Slovenia
⁴⁷ Fysikum, Stockholm University, Box 6730, 113 85, Stockholm, Sweden
⁴⁸ Dipartimento di Fisica Sperimentale, Università di Torino and INFN, Via P. Giuria 1, 10125, Turin, Italy
⁴⁹ INFN, Sezione di Torino and Dipartimento di Fisica Teorica, Università di Torino, Via Giuria 1, 10125, Turin, Italy
⁵⁰ Dipartimento di Fisica, Università di Trieste and INFN, Via A. Valerio 2, 34127, Trieste, Italy
⁵¹ Istituto di Fisica, Università di Udine and INFN, 33100, Udine, Italy
⁵² Univ. Federal do Rio de Janeiro, C.P. 68528 Cidade Univ., Ilha do Fundão, 21945-970, Rio de Janeiro, Brazil
⁵³ Department of Radiation Sciences, University of Uppsala, P.O. Box 535, 751 21, Uppsala, Sweden
⁵⁴ IFIC, Valencia-CSIC, and D.F.A.M.N., U. de Valencia, Avda. Dr. Moliner 50, 46100, Burjassot (Valencia), Spain
⁵⁵ ITEP, 117259, Moscow, Russian Federation
⁵⁶ Institut für Hochenergiephysik, Österr. Akad. d. Wissensch., Nikolsdorfergasse 18, 1050, Vienna, Austria
⁵⁷ Institute Nuclear Studies and University of Warsaw, Ul. Hoza 69, 00681, Warsaw, Poland
⁵⁸ University of Warwick, Coventry, CV4 7AL, UK
⁵⁹ Fachbereich Physik, University of Wuppertal, Postfach 100 127, 42097, Wuppertal, Germany

^* e-mail: jan.timmermans@cern.ch

Received: 24 June 2007
Revised: 5 June 2008
Published online: 11 November 2008

Abstract

Muon bremsstrahlung photons converted in front of the DELPHI main tracker (TPC) in dimuon events at LEP1 were studied in two photon kinematic ranges: 0.2<E _γ≤1 GeV and transverse momentum with respect to the parent muon p _T<40 MeV/c, and 1<E _γ≤10 GeV and p _T<80 MeV/c. A good agreement of the observed photon rate with predictions from QED for the muon inner bremsstrahlung was found, contrary to the anomalous soft photon excess that has been observed recently in hadronic Z ⁰ decays. The obtained ratios of the observed signal to the predicted level of the muon bremsstrahlung are 1.06±0.12±0.07 in the photon energy range 0.2<E _γ≤1 GeV and 1.04±0.09±0.12 in the photon energy range 1<E _γ≤10 GeV. The bremsstrahlung dead cone is observed for the first time in the direct photon production at LEP.