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 $$pp \rightarrow \ell _k \ell _l$$pp→ℓkℓl (with $$k\ne l$$k≠l). The current (projected) limits derived in this paper from LHC data with $$36~\mathrm {fb}^{-1}$$36fb-1 ($$3~\mathrm {ab}^{-1}$$3ab-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 $$b\rightarrow d$$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 $$K\rightarrow \pi \ell ^{\pm }_k \ell ^{{\mp }}_l$$K→πℓk±ℓl∓, $$B\rightarrow \pi \ell ^{\pm }_k \ell ^{{\mp }}_l$$B→πℓk±ℓl∓ and $$B\rightarrow K^{(*)} \ell ^{\pm }_k \ell ^{{\mp }}_l$$B→K(∗)ℓk±ℓl∓.