Di-jet production in γ γ collisions at LEP2

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; 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; S. Nemecek; 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; D. Radojicic; 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; 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; Yu. L. Vertogradova; 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/s10052-008-0777-1

2022 Impact factor 4.4

Particles and Fields

Open Access

Eur. Phys. J. C (2008) 58: 531-541
https://doi.org/10.1140/epjc/s10052-008-0777-1

Regular Article - Experimental Physics

Di-jet production in γ γ collisions at LEP2

J. Abdallah²⁷, P. Abreu²⁴, W. Adam⁵⁶, P. Adzic¹³, T. Albrecht¹⁹, R. Alemany-Fernandez¹⁰, T. Allmendinger¹⁹, P. P. Allport²⁵, U. Amaldi³¹, N. Amapane⁴⁹, S. Amato⁵³, E. Anashkin³⁸, A. Andreazza³⁰, S. Andringa²⁴, N. Anjos²⁴, P. Antilogus²⁷, W-D. Apel¹⁹, Y. Arnoud¹⁶, S. Ask¹⁰, B. Asman⁴⁸, J. E. Augustin²⁷, A. Augustinus¹⁰, P. Baillon¹⁰, A. Ballestrero⁵⁰, P. Bambade²², R. Barbier²⁹, D. Bardin¹⁸, G. J. Barker⁵⁸, A. Baroncelli⁴¹, M. Battaglia¹⁰, M. Baubillier²⁷, K-H. Becks⁵⁹, M. Begalli⁸, A. Behrmann⁵⁹, E. Ben-Haim²², N. Benekos³⁴, A. Benvenuti⁶, C. Berat¹⁶, M. Berggren²⁷, D. Bertrand³, M. Besancon⁴², N. Besson⁴², D. Bloch¹¹, M. Blom³³, M. Bluj⁵⁷, M. Bonesini³¹, M. Boonekamp⁴², P. S. L. Booth²⁵, G. Borisov²³, O. Botner⁵⁴, B. Bouquet²², T. J. V. Bowcock²⁵, I. Boyko¹⁸, M. Bracko⁴⁵, R. Brenner⁵⁴, E. Brodet³⁷, P. Bruckman²⁰, J. M. Brunet⁹, B. Buschbeck⁵⁶, P. Buschmann⁵⁹, M. Calvi³¹, T. Camporesi¹⁰, V. Canale⁴⁰, F. Carena¹⁰, N. Castro²⁴, F. Cavallo⁶, M. Chapkin⁴⁴, Ph. Charpentier¹⁰, P. Checchia³⁸, R. Chierici¹⁰, P. Chliapnikov⁴⁴, J. Chudoba¹⁰, S. U. Chung¹⁰, K. Cieslik²⁰, P. Collins¹⁰, R. Contri¹⁵, G. Cosme²², F. Cossutti⁵¹, M. J. Costa⁵⁵, D. Crennell³⁹, J. Cuevas³⁶, J. D’Hondt³, T. da Silva⁵³, W. Da Silva²⁷, G. Della Ricca⁵¹, A. De Angelis⁵², W. De Boer¹⁹, C. De Clercq³, B. De Lotto⁵², N. De Maria⁴⁹, A. De Min³⁸, L. de Paula⁵³, L. Di Ciaccio⁴⁰, A. Di Simone⁴¹, K. Doroba⁵⁷, J. Drees¹⁰^,59, G. Eigen⁵, T. Ekelof⁵⁴, M. Ellert⁵⁴, M. Elsing¹⁰, M. C. Espirito Santo²⁴, G. Fanourakis¹³, D. Fassouliotis⁴^,13, M. Feindt¹⁹, J. Fernandez⁴³, A. Ferrer⁵⁵, F. Ferro¹⁵, U. Flagmeyer⁵⁹, H. Foeth¹⁰, E. Fokitis³⁴, F. Fulda-Quenzer²², J. Fuster⁵⁵, M. Gandelman⁵³, C. Garcia⁵⁵, Ph. Gavillet¹⁰, E. Gazis³⁴, R. Gokieli¹⁰^,57, B. Golob⁴⁵^,47, G. Gomez-Ceballos⁴³, P. Goncalves²⁴, E. Graziani⁴¹, G. Grosdidier²², K. Grzelak⁵⁷, J. Guy³⁹, C. Haag¹⁹, A. Hallgren⁵⁴, K. Hamacher⁵⁹, K. Hamilton³⁷, S. Haug³⁵, F. Hauler¹⁹, V. Hedberg²⁸, M. Hennecke¹⁹, J. Hoffman⁵⁷, S-O. Holmgren⁴⁸, P. J. Holt¹⁰, M. A. Houlden²⁵, J. N. Jackson²⁵, G. Jarlskog²⁸, P. Jarry⁴², D. Jeans³⁷, E. K. Johansson⁴⁸, P. Jonsson²⁹, C. Joram¹⁰, L. Jungermann¹⁹, F. Kapusta²⁷, S. Katsanevas²⁹, E. Katsoufis³⁴, G. Kernel⁴⁵, B. P. Kersevan⁴⁵^,47, U. Kerzel¹⁹, B. T. King²⁵, N. J. Kjaer¹⁰, P. Kluit³³, P. Kokkinias¹³, C. Kourkoumelis⁴, O. Kouznetsov¹⁸, Z. Krumstein¹⁸, M. Kucharczyk²⁰, J. Lamsa¹, G. Leder⁵⁶, F. Ledroit¹⁶, L. Leinonen⁴⁸, R. Leitner³², J. Lemonne³, V. Lepeltier²², T. Lesiak²⁰, W. Liebig⁵⁹, D. Liko⁵⁶, A. Lipniacka⁴⁸, J. H. Lopes⁵³, J. M. Lopez³⁶, D. Loukas¹³, P. Lutz⁴², L. Lyons³⁷, J. MacNaughton⁵⁶, A. Malek⁵⁹, S. Maltezos³⁴, F. Mandl⁵⁶, J. Marco⁴³, R. Marco⁴³, B. Marechal⁵³, M. Margoni³⁸, J-C. Marin¹⁰, C. Mariotti¹⁰, A. Markou¹³, C. Martinez-Rivero⁴³, J. Masik¹⁴, N. Mastroyiannopoulos¹³, F. Matorras⁴³, C. Matteuzzi³¹, F. Mazzucato³⁸, M. Mazzucato³⁸, R. Mc Nulty²⁵, C. Meroni³⁰, E. Migliore⁴⁹, W. Mitaroff⁵⁶, U. Mjoernmark²⁸, T. Moa⁴⁸, M. Moch¹⁹, K. Moenig¹⁰^,12, R. Monge¹⁵, J. Montenegro³³, D. Moraes⁵³, S. Moreno²⁴, P. Morettini¹⁵, U. Mueller⁵⁹, K. Muenich⁵⁹, M. Mulders³³, L. Mundim⁸, W. Murray³⁹, B. Muryn²¹, G. Myatt³⁷, T. Myklebust³⁵, M. Nassiakou¹³, F. Navarria⁶, K. Nawrocki⁵⁷, S. Nemecek¹⁴, R. Nicolaidou⁴², M. Nikolenko¹¹^,18, A. Oblakowska-Mucha²¹, V. Obraztsov⁴⁴, A. Olshevski¹⁸, A. Onofre²⁴, R. Orava¹⁷, K. Osterberg¹⁷, A. Ouraou⁴², A. Oyanguren⁵⁵, M. Paganoni³¹, S. Paiano⁶, J. P. Palacios²⁵, H. Palka²⁰, Th. D. Papadopoulou³⁴, L. Pape¹⁰, C. Parkes²⁶, F. Parodi¹⁵, U. Parzefall¹⁰, A. Passeri⁴¹, O. Passon⁵⁹, L. Peralta²⁴, V. Perepelitsa⁵⁵, A. Perrotta⁶, A. Petrolini¹⁵, J. Piedra⁴³, L. Pieri⁴¹, F. Pierre⁴², M. Pimenta²⁴, E. Piotto¹⁰, T. Podobnik⁴⁵^,47, V. Poireau¹⁰, M. E. Pol⁷, G. Polok²⁰, V. Pozdniakov¹⁸, N. Pukhaeva¹⁸, A. Pullia³¹, D. Radojicic³⁷, P. Rebecchi¹⁰, J. Rehn¹⁹, D. Reid³³, R. Reinhardt⁵⁹, P. Renton³⁷, F. Richard²², J. Ridky¹⁴, M. Rivero⁴³, D. Rodriguez⁴³, A. Romero⁴⁹, P. Ronchese³⁸, P. Roudeau²², T. Rovelli⁶, V. Ruhlmann-Kleider⁴², D. Ryabtchikov⁴⁴, A. Sadovsky¹⁸, L. Salmi¹⁷, J. Salt⁵⁵, C. Sander¹⁹, A. Savoy-Navarro²⁷, U. Schwickerath¹⁰, R. Sekulin³⁹, M. Siebel⁵⁹, A. Sisakian¹⁸, G. Smadja²⁹, O. Smirnova²⁸, A. Sokolov⁴⁴, A. Sopczak²³, R. Sosnowski⁵⁷, T. Spassov¹⁰, M. Stanitzki¹⁹, A. Stocchi²², J. Strauss⁵⁶, B. Stugu⁵, M. Szczekowski⁵⁷, M. Szeptycka⁵⁷, T. Szumlak²¹, T. Tabarelli³¹, F. Tegenfeldt⁵⁴, J. Timmermans³³^*, L. Tkatchev¹⁸, M. Tobin²⁵, S. Todorovova¹⁴, B. Tome²⁴, A. Tonazzo³¹, P. Tortosa⁵⁵, P. Travnicek¹⁴, D. Treille¹⁰, G. Tristram⁹, M. Trochimczuk⁵⁷, C. Troncon³⁰, M-L. Turluer⁴², I. A. Tyapkin¹⁸, S. Tzamarias¹³, V. Uvarov⁴⁴, G. Valenti⁶, P. Van Dam³³, J. Van Eldik¹⁰, N. van Remortel², I. Van Vulpen¹⁰, G. Vegni³⁰, F. Veloso²⁴, W. Venus³⁹, P. Verdier²⁹, Yu. L. Vertogradova¹⁸, V. Verzi⁴⁰, D. Vilanova⁴², L. Vitale⁵¹, V. Vrba¹⁴, H. Wahlen⁵⁹, A. J. Washbrook²⁵, C. Weiser¹⁹, D. Wicke¹⁰, J. Wickens³, G. Wilkinson³⁷, M. Winter¹¹, M. Witek²⁰, O. Yushchenko⁴⁴, A. Zalewska²⁰, P. Zalewski⁵⁷, D. Zavrtanik⁴⁶, V. Zhuravlov¹⁸, N. I. Zimin¹⁸, A. Zintchenko¹⁸, M. Zupan¹³ and DELPHI Collaboration

¹ Department of Physics and Astronomy, Iowa State University, Ames IA, 50011-3160, USA
² Physics Department, Universiteit Antwerpen, Universiteitsplein 1, 2610, Antwerpen, Belgium
³ IIHE, ULB-VUB, Pleinlaan 2, 1050, Brussels, Belgium
⁴ Physics Laboratory, University of Athens, Solonos Str. 104, 10680, Athens, Greece
⁵ Department of Physics, University of Bergen, Allégaten 55, 5007, Bergen, Norway
⁶ Dipartimento di Fisica, Università di Bologna and INFN, Via Irnerio 46, 40126, Bologna, Italy
⁷ Centro Brasileiro de Pesquisas Físicas, rua Xavier Sigaud 150, 22290, Rio de Janeiro, Brazil
⁸ Inst. de Física, Univ. Estadual do Rio de Janeiro, rua São Francisco Xavier 524, Rio de Janeiro, Brazil
⁹ Collège de France, Lab. de Physique Corpusculaire, IN2P3-CNRS, 75231, Paris Cedex 05, France
¹⁰ CERN, 1211, Geneva 23, Switzerland
¹¹ Institut de Recherches Subatomiques, IN2P3-CNRS/ULP-BP20, 67037, Strasbourg Cedex, France
¹² DESY-Zeuthen, Platanenallee 6, 15735, Zeuthen, Germany
¹³ Institute of Nuclear Physics, N.C.S.R. Demokritos, P.O. Box 60228, 15310, Athens, Greece
¹⁴ FZU, Inst. of Phys. of the C.A.S. High Energy Physics Division, Na Slovance 2, 182 21, Praha 8, Czech Republic
¹⁵ Dipartimento di Fisica, Università di Genova and INFN, Via Dodecaneso 33, 16146, Genova, Italy
¹⁶ Institut des Sciences Nucléaires, IN2P3-CNRS, Université de Grenoble 1, 38026, Grenoble Cedex, France
¹⁷ Helsinki Institute of Physics and Department of Physical Sciences, P.O. Box 64, 00014, Helsinki, Finland
¹⁸ Joint Institute for Nuclear Research, Dubna, Head Post Office, P.O. Box 79, 101 000, Moscow, Russian Federation
¹⁹ Institut für Experimentelle Kernphysik, Universität Karlsruhe, Postfach 6980, 76128, Karlsruhe, Germany
²⁰ Institute of Nuclear Physics PAN, Ul, Radzikowskiego 152, 31142, Krakow, Poland
²¹ Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy, 30055, Krakow, Poland
²² LAL, Univ Paris-Sud, CNRS/IN2P3, Orsay, France
²³ School of Physics and Chemistry, University of Lancaster, Lancaster, LA1 4YB, UK
²⁴ LIP, IST, FCUL, Av. Elias Garcia, 14-1º, 1000, Lisboa Codex, Portugal
²⁵ Department of Physics, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, UK
²⁶ Dept. of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow, G12 8QQ, UK
²⁷ LPNHE, IN2P3-CNRS, Univ. Paris VI et VII, Tour 33 (RdC), 4 place Jussieu, 75252, Paris Cedex 05, France
²⁸ Department of Physics, University of Lund, Sölvegatan 14, 223 63, Lund, Sweden
²⁹ Université Claude Bernard de Lyon, IPNL, IN2P3-CNRS, 69622, Villeurbanne Cedex, France
³⁰ Dipartimento di Fisica, Università di Milano and INFN-MILANO, Via Celoria 16, 20133, Milan, Italy
³¹ Dipartimento di Fisica, Univ. di Milano-Bicocca and INFN-MILANO, Piazza della Scienza 3, 20126, Milan, Italy
³² IPNP of MFF, Charles Univ., Areal MFF, V Holesovickach 2, 180 00, Praha 8, Czech Republic
³³ NIKHEF, Postbus 41882, 1009, DB Amsterdam, The Netherlands
³⁴ Physics Department, National Technical University, Zografou Campus, 15773, Athens, Greece
³⁵ Physics Department, University of Oslo, Blindern, 0316, Oslo, Norway
³⁶ Dpto. Fisica, Univ. Oviedo, Avda. Calvo Sotelo s/n, 33007, Oviedo, Spain
³⁷ Department of Physics, University of Oxford, Keble Road, Oxford, OX1 3RH, UK
³⁸ Dipartimento di Fisica, Università di Padova and INFN, Via Marzolo 8, 35131, Padua, Italy
³⁹ Rutherford Appleton Laboratory, Chilton, Didcot, OX11 OQX, UK
⁴⁰ Dipartimento di Fisica, Università di Roma II and INFN, Tor Vergata, 00173, Rome, Italy
⁴¹ Dipartimento di Fisica, Università di Roma III and INFN, Via della Vasca Navale 84, 00146, Rome, Italy
⁴² DAPNIA/Service de Physique des Particules, CEA-Saclay, 91191, Gif-sur-Yvette Cedex, France
⁴³ Instituto de Fisica de Cantabria (CSIC-UC), Avda. los Castros s/n, 39006, Santander, Spain
⁴⁴ Inst. for High Energy Physics, Serpukov, P.O. Box 35, Protvino, (Moscow Region), Russian Federation
⁴⁵ J. Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
⁴⁶ Laboratory for Astroparticle Physics, University of Nova Gorica, Kostanjeviska 16a, 5000, Nova Gorica, Slovenia
⁴⁷ Department of Physics, University of Ljubljana, 1000, Ljubljana, Slovenia
⁴⁸ Fysikum, Stockholm University, Box 6730, 113 85, Stockholm, Sweden
⁴⁹ Dipartimento di Fisica Sperimentale, Università di Torino and INFN, Via P. Giuria 1, 10125, Turin, Italy
⁵⁰ INFN, Sezione di Torino and Dipartimento di Fisica Teorica, Università di Torino, Via Giuria 1, 10125, Turin, Italy
⁵¹ Dipartimento di Fisica, Università di Trieste and INFN, Via A. Valerio 2, 34127, Trieste, Italy
⁵² Istituto di Fisica, Università di Udine and INFN, 33100, Udine, Italy
⁵³ Univ. Federal do Rio de Janeiro, C.P. 68528 Cidade Univ., Ilha do Fundão, 21945-970, Rio de Janeiro, Brazil
⁵⁴ Department of Radiation Sciences, University of Uppsala, P.O. Box 535, 751 21, Uppsala, Sweden
⁵⁵ IFIC, Valencia-CSIC, and D.F.A.M.N., U. de Valencia, Avda. Dr. Moliner 50, 46100, Burjassot (Valencia), Spain
⁵⁶ Institut für Hochenergiephysik, Österr. Akad. d. Wissensch., Nikolsdorfergasse 18, 1050, Vienna, Austria
⁵⁷ Inst. 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: 5 August 2008
Revised: 27 September 2008
Published online: 19 November 2008

Abstract

The production of two high-p _T jets in the interactions of quasi-real photons in e ⁺ e ⁻ collisions at from 189 GeV to 209 GeV is studied with data corresponding to an integrated e ⁺ e ⁻ luminosity of 550 pb⁻¹. The jets reconstructed by the k _⊥-cluster algorithm are defined within the pseudo-rapidity range −1<η<1 and with jet transverse momentum, p _T, above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum of the jets and is compared to perturbative QCD calculations.