Pair production of scalar leptoquarks at the Tevatron

We present the cross section for pair production of scalar leptoquarks LQ in p¯ p collisions, p + ¯ p → LQ + LQ + X, at the Fermilab Tevatron in next-to-leading order QCD. Including the higher-order corrections stabilizes the theoretical prediction and increases the size of the cross section for renormalization/factorization scales close to the mass of the leptoquarks. This leads to an increase of the lower bound on the mass of scalar leptoquarks by up to 15 GeV with respect to earlier analyses. 1. Theoretical speculations have focussed on two different elements to explain the recently observed surplus of DIS e + p events at HERA [1]: contact interactions at an effective scale Λ eq ∼ > 1.5 TeV, and narrow resonance formation at a mass scale M ∼ 200 GeV. The resonance interpretation is based in particular on the H1 data which appear to cluster in a narrow range at invariant (eq) masses of about 200 GeV. Such resonances [2– 7] can be identified with scalar squarks in supersymmetric theories with R-Parity breaking or with leptoquarks in general. Leptoquarks encompass a large variety of particles which can be classified in multiplets according to spin, isospin and hypercharge [8]. The production of leptoquarks in positron collisions with sea quarks requires large Yukawa couplings, which can in general not be reconciled with bounds from rare decay processes, nor with the early e − p scattering data from HERA. However, the Yukawa couplings in positron collisions with valence quarks, λ ∼ 1/30, are so small that they are not in conflict with any such bounds. Moreover, they cannot be ruled out by present limits on eeqq contact interactions from LEP [9] or from the Tevatron [10]. The most powerful competitor in this scenario is the pair production of leptoquarks [11] at the Tevatron 1 p + ¯ p → LQ + LQ + X (1) Mass bounds on vector leptoquarks, which decay solely into charged leptons and quarks, appear significantly above 200 GeV in the analyses of Refs.[12,13]. Even if the unknown anomalous couplings of vector leptoquarks are chosen such as to minimize the cross section , the minimum mass is 210 GeV, see [3,6]. The present limits for scalar leptoquarks are near 200 GeV [12]. The experimental bounds will be refined further by the two Teva-tron experiments in the near future. The limits for scalar leptoquarks are particularly important …