Abstract

A search for the lepton flavour violating processes ep->mu X and ep -> tau X 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 Buchm"uller-R"uckl-Wyler effective model. Leptoquarks produced in ep collisions with a coupling strength of lambda=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.

Highlights

  • In the Standard Model (SM) the particle interactions conserve lepton flavour, there is no underlying symmetry supporting this feature

  • To account for possible effects due to different muon kinematics resulting from a tau decay, the selection efficiency was studied in detail with a lepton flavour violation (LFV) Monte Carlo (MC) signal sample with a τ X final state and a subsequent muonic tau decay

  • The energy of electrons is measured with a systematic uncertainty in the range from 0.7% to 3% depending on the polar angle

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Summary

Introduction

In the Standard Model (SM) the particle interactions conserve lepton flavour, there is no underlying symmetry supporting this feature. Experimental evidence for lepton flavour violation (LFV) in solar and atmospheric neutrino oscillations has been reported [1, 2]. The experimental upper bounds on neutrino masses imply very small LFV effects in the charged lepton sector. The observation of such effects would clearly indicate new phenomena beyond the SM. The LFV process can proceed via the exchange of a leptoquark (LQ), a boson with both lepton and baryon quantum number which appears naturally as a colour triplet scalar or vector boson in many extensions of the SM such as grand unified theories [3], supersymmetry [4], compositeness [5] and technicolor [6]. In this paper a search for LFV phenomena is performed in ep collision data recorded during the years 1998-2000 by the H1 experiment, corresponding to an integrated luminosity.

Experimental conditions
LFV phenomenology and SM background processes
High PT Muon Signatures
Electronic tau decays
Muonic tau decays
Hadronic tau decays
Systematic Uncertainties
Results
Limits
Conclusion
Channel
Full Text
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