#Lepton flavors update

We update and extend these analyses by considering the most recent LHC data, as well by accounting for the most general effective operators. Previous phenomenological analyses have considered effective operators with particular Lorentz and/or flavor structures.

To this purpose, we formulate an EFT with generic semileptonic dimension-6 operators and we study their impact onto the LFV dilepton tails at the LHC. In this paper, we derive constraints on four-fermion LFV operators by using LHC data. The main focus of this study is to perform an analogous analysis of the LFV processes p p → ℓ k ℓ l (with k ≠ l) at the LHC, which have not been thoroughly explored thus far, and which can also provide complementary information to low-energy observables. These constraints turn out to be complementary to the ones coming from flavor physics observables and, in particular, they have been useful to identify the viable solutions of the LFUV anomalies observed in B-meson decays. In particular, recasts of resonant searches in the invariant mass tails of the p p → ℓ - ℓ + and p p → ℓ ± ν ℓ processes have been used to derive stringent limits on various new physics models. In recent years, the large luminosity accumulated at the LHC has offered many opportunities to indirectly test flavor-physics scenarios at high- p T. Notably, several BSM resolutions of these discrepancies predict sizeable LFV effects in semi-leptonic operators, see e.g. for a recent review), which have attracted a lot of attention in the particle physics community. While up to date there is no evidence for charged LFV, there are hints of Lepton Flavor Universality Violation (LFUV) in B-meson semi-leptonic decays (see e.g. Ref. The current sensitivity will be significantly improved in the coming years by the ongoing effort at the present NA62, LHCb and Belle-II, as well as at the future Mu2E, Mu3E and COMET experiments. On the experimental side, there is a rich flavor-physics program dedicated to LFV in both lepton and meson decays. Under the assumption of heavy new physics states, the low-energy LFV data can be described by means of an Effective Field Theory (EFT), with the information on the underlying dynamics encoded in effective coefficients that can be probed experimentally. This makes charged Lepton Flavor Violation (LFV) an appealing target for experimental searches beyond the SM (BSM), as its observation would clearly point to the existence of new phenomena.įrom a theoretical perspective, LFV is predicted in various BSM scenarios, such as the ones involving sterile neutrinos, extended Higgs sectors, Z ′ bosons and leptoquarks. Neutrino masses are also responsible for flavor violation in the charged-lepton sector, with unobservable rates suppressed by ( m ν / m W ) 4 ≈ 10 - 48. Lepton flavor symmetry is accidental in the SM and it is known to be explicitly broken by the nonzero neutrino masses and mixing, as established by neutrino oscillation experiments. 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 ∓. 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. 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. 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. 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.

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).

Lepton flavors