A case study of the sensitivity to LFV operators with precision measurements and the LHC

Abstract

Abstract:We compare the sensitivity of precision measurements of lepton flavour observables to the reach of the LHC in a case study of lepton-flavour violating operators of dimension six with two leptons and two quarks. For light quarks precision measurements always yield the more stringent constraints. The LHC complements precision measurements for operators with heavier quarks. Competitive limits can already be set on the cutoff scale Λ > 600-800 GeV for operators with right-handed τ leptons using the LHC run 1 data.

Charged-lepton-flavor violation in |ΔS| = 1 hyperon decays

“…For this reason, processes manifesting LFV provide an ideal window to new physics (NP), and hence quests for them are of tremendous importance. Many extensions of the SM do not preserve lepton-flavor number, and the corresponding parameters have been tightly restricted by the negative outcomes of the various searches conducted so far in the decays of kaons, B mesons, and charged leptons, among others [1][2][3][4][5][6][7][8][9][10][11]. The most common examples of NP exhibiting LFV include leptoquarks [12][13][14][15][16][17][18][19][20][21][22], heavy neutrinos [23][24][25][26][27][28][29][30][31][32], gauged U(1) extensions of the SM with their associated Z gauge bosons [33][34][35][36][37][38][39][40][41], and multi-Higgs models [42][43][44][45]…”

Constraints on 2ℓ2q operators from μ↔e flavor-changing meson decays

“…are the 4 × 4 and 6 × 6 matrices defined in appendix D we inverted to obtain the bounds at Λ exp (see section 4) and R has the form of the matrices defined in eqn. (28), (29) and (30). Finally, eqn.…”

“…All bounds apply under permutation of the lepton and/or quark indices. In the leptonic decays, the evolution of the bounds on the pseudoscalar coefficients between Λ exp and Λ W is the most important effect of the RGEs as shown in the first two columns of the left panel (29) or (30), the running of the (pseudo)scalar coefficients is ∼ 1.6(1.4), which means that if we neglect the mixing of the tensor into (pseudo)scalar coefficients, the bounds on S and P will be better at Λ W for all the decays we considered. However, the large mixing of the tensor coefficients into the (pseudo)scalar ones (see eqn.…”

“…The experimental sensitivity to the coefficients of four-fermion operators (sometimes refered to as one-operator-at-a-time bounds), evaluated at the experimental scale, has been compiled by various authors [26,27,28]. Reference [29] compared the sensitivities of the LHC vs low-energy processes, to quark flavour-diagonal scalar operators. The constraints on combinations of lepton-flavour-changing operator coefficients, which can be obtained from the decays of same-flavour mesons, were studied in [30], and the radiative decays of B, D and K mesons were discussed in [31].…”

Studies of lepton flavor violation at the LHC

“…The operators in Eq. (1) can be probed in a variety of ways, both at high [29][30][31][32] and low energies [33][34][35][36][37][38][39][40][41]. 1 The large parton luminosity for gluon-gluon interactions at high-energy pp colliders, such as the LHC, implies that gluon-initiated processes might be prevalent there.…”