Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement

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We confront the indications of lepton flavor universality (LFU) violation observed in semi-tauonic B meson decays with new physics (NP) searches using high pT tau leptons at the LHC. Using effective field theory arguments we correlate possible non-standard contributions to semi-tauonic charged currents with the τ + τ − signature at high energy hadron colliders. Several representative standard model extensions put forward to explain the anomaly are examined in detail: (i) weak triplet of color-neutral vector resonances, (ii) second Higgs doublet and (iii) scalar or (iv) vector leptoquark. We find that, in general, τ + τ − searches pose a serious challenge to NP explanations of the LFU anomaly. Recasting existing 8 TeV and 13 TeV LHC analyses, stringent limits are set on all considered simplified models. Future projections of the τ + τ − constraints as well as caveats in interpreting them within more elaborate models are also discussed.

We examine various scenarios in which the Standard Model is extended by a light leptoquark state to explain one or both B-physics anomalies. Combining low-energy constraints and direct searches at the LHC, we confirm that the only single leptoquark model that can explain both anomalies at the same time is a vector leptoquark, known as U1. Focusing on U1, we highlight the complementarity between LHC and low-energy constraints, and argue that improving the experimental bound on B(B → Kµτ ) by two orders of magnitude could compromise its viability as a solution to the B-physics anomalies.