With or without U(2)? Probing non-standard flavor and helicity structures in semileptonic B decays

Extending the Standard Model with higher-dimensional operators in an effective-fieldtheory (EFT) approach provides a systematic framework to study new-physics (NP) effects from a bottom-up perspective, as long as the NP scale is sufficiently large compared to the energies probed in the experimental observables. However, when taking into account the different quark and lepton flavours, the number of free parameters increases dramatically, which makes generic studies of the NP flavour structure infeasible. In this paper, we address this issue in view of the recently observed "flavour anomalies" in B-meson decays, which we take as a motivation to develop a general framework that allows us to systematically reduce the number of flavour parameters in the EFT. This framework can be easily used in global fits to flavour observables at Belle II and LHCb as well as in analyses of flavour-dependent collider signatures at the LHC. Our formalism represents an extension of the well-known minimal-flavour-violation approach, and uses Froggatt-Nielsen charges to define the flavour power-counting. As a relevant illustration of the formalism, we apply it to the flavour structures which could be induced by a U 1 vector leptoquark, which represents one of the possible explanations for the recent hints of flavour non-universality in semileptonic B-decays. We study the phenomenological viability of this specific framework performing a fit to low-energy flavour observables.

Section: Constraints On Fn Chargesmentioning

confidence: 99%

Effective theory approach to new physics with flavour: general framework and a leptoquark example

Bordone

Catà

Feldmann

2020

“…Both the experimental signature of the decays and the large data sample available motivate the choice of Λ 0 b → pK − + − decays for this study. Similarly to other R H ratios, R pK is expected to be close to unity in the SM [24].…”

Section: Jhep05(2020)040mentioning

confidence: 75%

Test of lepton universality with $$ {\Lambda}_b^0\to {pK}^{-}{\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-} $$ decays

Aaij¹,

Beteta²,

Ackernley³

et al. 2020

The ratio of branching fractions of the decays Λ 0 b → pK − e + e − and Λ 0 b → pK − µ + µ − , R −1 pK , is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb −1 recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range 0.1 < q 2 < 6.0 GeV 2 /c 4 and the pK − mass range m(pK −) < 2600 MeV/c 2 , the ratio of branching fractions is measured to be R −1 pK = 1.17 +0.18 −0.16 ± 0.07, where the first uncertainty is statistical and the second systematic. This is the first test of lepton universality with b baryons and the first observation of the decay Λ 0 b → pK − e + e − .

“…u ≡ φ q , while all leptonic phases can be set to zero. With these settings, neglecting tiny subleading terms, we get [34]…”

Section: Jhep08(2020)166mentioning

confidence: 99%

“…Following ref. [34], the left handed matrices L f are JHEP08(2020)166 Table 9. Number of independent operators in the SMEFT for the MFV scenario with insertions of different combinations of spurion.…”

Section: Jhep08(2020)166mentioning

confidence: 99%

Flavour symmetries in the SMEFT

Faroughy

Isidori

Wilsch

et al. 2020

Self Cite

We analyse how U(3) 5 and U(2) 5 flavour symmetries act on the Standard Model Effective Field Theory, providing an organising principle to classify the large number of dimension-six operators involving fermion fields. A detailed counting of such operators, at different order in the breaking terms of both these symmetries, is presented. A brief discussion about possible deviations from these two reference cases, and a simple example of the usefulness of this classification scheme for high-p T analyses at the LHC, are also presented.