Leptoquark production at LEP2

We study the production of scalar and vector leptoquarks at LEP2. All leptoquark contributions into semileptonic four-fermion final states have been calculated and incorporated in the Monte Carlo event generator ERATO. Taking into account the irreducible Standard Model backgrounds we find that, at √ s = 192 GeV and with an integrated luminosity L = 500 pb, first generation leptoquarks in the mass range of 150-180 GeV and with a Yukawa coupling in the range 0.03 to 0.3 can give detectable contributions. E-mail: [email protected]. The reported excess of high Q events at HERA by the H1 [1] and ZEUS [2] collaborations stimulated a substantial research interest on the possible existence of new particles of leptoquark type. Such particles emerge in several contexts, including the Pati-Salam model [3] and the grand-unified supersymmetric theories [4]. Leptoquark-type interactions, described by higher-dimensional contact terms, are naturally incorporated within the idea of compositeness of quarks and leptons [5]. Although the current HERA data are not yet conclusive [1, 2] and no unambiguous interpretation exists [7, 8, 9, 10], it is rather important to ask the question whether LEP2 will be able to sed some light on this issue. In this paper we present results concerning the contribution of leptoquark states in twoand four-fermion production processes at LEP2. We start the presentation with the most general effective Lagrangian [11], which is SU(3)×SU(2)×U(1) invariant, baryonand lepton-number conserving as well as family diagonal, in order to avoid the most severe constraints from low-energy considerations [12]. It can be written as LF=−2 = (g0L q̄ Liτ2lL + g0R ūcReR)S0 + g̃0R d̄cReRS̃0 + g1L q̄ Liτ2~τ lL~ S1 + ( g 1 2 L d̄ c Lγ lL + g 1 2 R q̄ c Lγ eR ) V 1 2 μ + g̃ 1 2 L ū c Rγ lLṼ 1 2 μ + cc (1)