Mono-τ Signatures at the LHC Constrain Explanations of B-decay Anomalies

Lepton flavor violation and dilepton tails at the LHC

Starting from a general effective Lagrangian for lepton flavor violation (LFV) in quark-lepton transitions, we derive constraints on the effective coefficients from the high-mass tails of the dilepton processes p p → ℓ k ℓ l (with k ≠ l ). The current (projected) limits derived in this paper from LHC data with 36 fb - 1 ( 3 ab - 1 ) can be applied to generic new physics scenarios, including the ones with scalar, vector and tensor effective operators. For purely left-handed operators, we explicitly compare these LHC constraints with the ones derived from flavor-physics observables, illustrating the complementarity of these different probes. While flavor physics is typically more constraining for quark-flavor violating operators, we find that LHC provides the most stringent limits on several flavor-conserving ones. Furthermore, we show that dilepton tails offer the best probes for charm-quark transitions at current luminosities and that they provide competitive limits for tauonic b → d transitions at the high-luminosity LHC phase. As a by-product, we also provide general numerical expressions for several low-energy LFV processes, such as the semi-leptonic decays K → π ℓ k ± ℓ l ∓ , B → π ℓ k ± ℓ l ∓ and B → K ( ∗ ) ℓ k ± ℓ l ∓ .