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 $pp\to {\ell }_k{\ell }_l$ (with $k\ne l$ ). The current (projected) limits derived in this paper from LHC data with $36{\mathrm{fb}}^{-1}$ ( $3{\mathrm{ab}}^{-1}$ ) 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 $b\to d$ 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 $K\to \pi {\ell }_k^{\pm }{\ell }_l^{\mp }$ , $B\to \pi {\ell }_k^{\pm }{\ell }_l^{\mp }$ and $B\to K^{(\ast )}{\ell }_k^{\pm }{\ell }_l^{\mp }$ .