Abstract
Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and ℓ-τ conversion in nuclei, with ℓ = e, μ. Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. Our work paves the way to extract the related information from Belle II and foreseen future experiments.
Highlights
Both light quark and lepton families are triple replicated in nature, their description in the Standard Model (SM) of particles has a significative difference: while quark families mix, giving a rich flavour-physics phenomenology, lepton families do not
All these effects are included in the nuclear parton distribution functions, which we find more suitable to describe the -τ conversion in nuclei: we use the nCTEQ15-np fit of the nPDFs provided by the group around the nCTEQ15 project [62], incorporated within the ManeParse Mathematica package [63]
We address the case of hadronic τ decays both for the existing Belle and expected Belle II limits
Summary
Both light quark and lepton families are triple replicated in nature, their description in the Standard Model (SM) of particles has a significative difference: while quark families mix, giving a rich flavour-physics phenomenology, lepton families do not This fact is due to the neutrino-mass degeneracy (they are all massless in the SM), that produces a set of conservation laws for the lepton flavours, namely, the Lagrangian is invariant under global L ≡ U(1)e × U(1)μ × U(1)τ rotations of the lepton fields. Similar hints appeared in W → ν [17], this tension seems to have been released by a recent experimental determination by ATLAS [18]
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