Eur. Phys. J. C (2007) 52: 833-847
https://doi.org/10.1140/epjc/s10052-007-0440-2

Regular Article - Experimental Physics

Search for lepton flavour violation in ep collisions at HERA

¹ I. Physikalisches Institut der RWTH, Aachen, Germany
² Vinca Institute of Nuclear Sciences, Belgrade, Serbia
³ School of Physics and Astronomy, University of Birmingham, Birmingham, UK
⁴ Inter-University Institute for High Energies ULB-VUB, Brussels, Belgium
⁵ Universiteit Antwerpen, Antwerpen, Belgium
⁶ Rutherford Appleton Laboratory, Chilton, Didcot, UK
⁷ Institute for Nuclear Physics, Cracow, Poland
⁸ Institut für Physik, Universität Dortmund, Dortmund, Germany
⁹ Joint Institute for Nuclear Research, Dubna, Russia
¹⁰ CEA, DSM/DAPNIA, CE-Saclay, Gif-sur-Yvette, France
¹¹ DESY, Hamburg, Germany
¹² Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany
¹³ Max-Planck-Institut für Kernphysik, Heidelberg, Germany
¹⁴ Physikalisches Institut, Universität Heidelberg, Heidelberg, Germany
¹⁵ Kirchhoff-Institut für Physik, Universität Heidelberg, Heidelberg, Germany
¹⁶ Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovak Republic
¹⁷ Department of Physics, University of Lancaster, Lancaster, UK
¹⁸ Department of Physics, University of Liverpool, Liverpool, UK
¹⁹ Queen Mary and Westfield College, London, UK
²⁰ Physics Department, University of Lund, Lund, Sweden
²¹ CPPM, CNRS/IN2P3 – Univ. Mediterranee, Marseille, France
²² Departamento de Fisica Aplicada, CINVESTAV, Mérida, Yucatán, Mexico
²³ Departamento de Fisica, CINVESTAV, Mérida, Yucatán, Mexico
²⁴ Institute for Theoretical and Experimental Physics, Moscow, Russia
²⁵ Lebedev Physical Institute, Moscow, Russia
²⁶ Max-Planck-Institut für Physik, München, Germany
²⁷ LAL, Université de Paris-Sud 11, IN2P3-CNRS, Orsay, France
²⁸ LLR, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France
²⁹ LPNHE, Universités Paris VI and VII, IN2P3-CNRS, Paris, France
³⁰ Faculty of Science, University of Montenegro, Podgorica, Montenegro
³¹ Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic
³² Faculty of Mathematics and Physics, Charles University, Praha, Czech Republic
³³ Dipartimento di Fisica Università di Roma Tre and INFN Roma 3, Roma, Italy
³⁴ Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria
³⁵ Institute of Physics and Technology of the Mongolian Academy of Sciences, Ulaanbaatar, Mongolia
³⁶ Paul Scherrer Institut, Villigen, Switzerland
³⁷ Fachbereich C, Universität Wuppertal, Wuppertal, Germany
³⁸ Yerevan Physics Institute, Yerevan, Armenia
³⁹ DESY, Zeuthen, Germany
⁴⁰ Institut für Teilchenphysik, ETH, Zürich, Switzerland
⁴¹ Physik-Institut der Universität Zürich, Zürich, Switzerland
⁴² Physics Department, National Technical University, Zografou Campus, 15773, Athens, Greece
⁴³ Rechenzentrum, Universität Wuppertal, Wuppertal, Germany
⁴⁴ University of P.J. Šafárik, Košice, Slovak Republic
⁴⁵ CERN, Geneva, Switzerland
⁴⁶ Max-Planck-Institut für Physik, München, Germany
⁴⁷ Comenius University, Bratislava, Slovak Republic
⁴⁸ Helmholtz Humboldt Research Award, DESY and University Hamburg, Hamburg, Germany
⁴⁹ National Institute for Physics and Nuclear Engineering, Magurele, Bucharest, Romania

^* e-mail: diaconu@cppm.in2p3.fr

Received: 3 March 2007
Revised: 26 September 2007
Published online: 24 October 2007

Abstract

A search for the lepton flavour violating processes ep→μX and ep→τX is performed with the H1 experiment at HERA. Final states with a muon or tau and a hadronic jet are searched for in a data sample corresponding to an integrated luminosity of 66.5 pb^-1 for e⁺p collisions and 13.7 pb^-1 for e^-p collisions at a centre-of-mass energy of 319 GeV. No evidence for lepton flavour violation is found. Limits are derived on the mass and the couplings of leptoquarks inducing lepton flavour violation in an extension of the Buchmüller–Rückl–Wyler effective model. Leptoquarks produced in ep collisions with a coupling strength of λ=0.3 and decaying with the same coupling strength to a muon–quark pair or a tau–quark pair are excluded at 95% confidence level up to masses of 459 GeV and 379 GeV, respectively.