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We compute the isospin asymmetries in B → (K * , ρ)γ and B → (K, K * , ρ)l + l − for low lepton pair invariant mass q 2 , within the Standard Model (SM) and beyond the SM (BSM) in a generic dimension six operator basis. Within the SM the CPaveraged isospin asymmetries for B → (K, K * , ρ)ll, between 1 GeV 2 ≤ q 2 ≤ 4m 2 c , are predicted to be small (below 1.5%) though with significant cancellation. In the SM the non-CP averaged asymmetries for B → ρll deviate by ≈ ±5% from the CP-averaged ones. We provide physical arguments, based on resonances, of why isospin asymmetries have to decrease for large q 2 (towards the endpoint). Two types of isospin violating effects are computed: ultraviolet (UV) isospin violation due to differences between operators coupling to up and down quarks, and infrared (IR) isospin violation where a photon is emitted from the spectator quark and is hence proportional to the difference between the up-and down-quark charges. These isospin violating processes may be subdivided into weak annihilation (WA), quark loop spectator scattering (QLSS) and a chromomagnetic contribution. Furthermore we discuss generic selection rules based on parity and angular momentum for the B → Kll transition as well as specific selection rules valid for WA at leading order in the strong coupling constant. We clarify that the relation between the K and the longitudinal part of the K * only holds for leading twist and for left-handed currents. In general the B → ρll and B → K * ll isospin asymmetries are structurally different yet the closeness of α CKM to ninety degrees allows us to construct a (quasi) null test for the SM out of the respective isospin symmetries. We provide and discuss an update on B(B 0 → K * 0 γ)/B(B s → φγ) which is sensitive to WA.

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“…The LHCb collaboration has recently measured [61] the ratio of branching fractions of B 0 → K * 0 γ to B s → φγ to be…”

Section: Resultsmentioning

confidence: 99%

Isospin asymmetries inB→(K*,ρ)γ/l+l−<

Lyon

Zwicky

2013

Phys. Rev. D

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“…4.33 ± 0.77 3.5 ± 0.4 [54,55] for this region is challenging. Hence, we do not include the R K * data from the low-recoil region provided by the recent Belle measurement from [12].…”

Section: A Experimentalmentioning

confidence: 98%

Exhaustive model selection in b→sℓℓ decays: Pitting cross-validation against the Akaike information criterion

et al. 2020

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In the light of recent data, we study the new physics effects in the exclusive b → s + − decays from a model independent perspective. Different combinations of the dimension six effective operators along with their respective Wilson coefficients are chosen for the analysis. To find out the operator or sets of operators that can best explain the available data in this channel, we simultaneously apply popular model selection tools like cross-validation and the information theoretic approach like Akaike Information Criterion (AIC). There are one, two, and three-operator scenarios which survive the test and a left-handed quark current with vector muon coupling is common among them. This is also the only surviving one-operator scenario. Best-fit values and correlations of the new Wilson coefficients are supplied for all the selected scenarios. We find that the angular observables play the dominant role in the model selection procedure. We also note that while a left-handed quark current with axial-vector muon coupling is the only one-operator scenario able to explain the ratios R K ( * ) (RK * for q 2 ∈ [0.045, 1.1]GeV 2 in particular), there are also a couple of two operator scenarios that can simultaneously explain the measured R K ( * ) .

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“…to a plethora of b → s + − observables. The corresponding measurements include total branching ratios of B s → + −[11], of the exclusive decays B → K * γ[11], B → φγ[116], the inclusive decay B → X s γ[11], the angular analyses of B → K ( * ) + −[117- 123] (proposed in Refs [124][125][126][127], and also the ratios R K [9] and R K *[10,128] measuring lepton flavour universality violation.First of all, the contributions of scalar operators are helicity-enhanced in the B s → µ + µ − branching ratio with respect to the O 10 contribution of the SM.…”

mentioning

confidence: 99%

Generic loop effects of new scalars and fermions in b → sℓ+ℓ− and a vector-like 4th generation

Arnan¹,

Crivellin²,

Fedele³

et al. 2019

J. High Energ. Phys.

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In this article we investigate in detail the possibility of accounting for the b → s + − anomalies via box contributions involving with new scalars and fermions. For this purpose, we first write down the most general Lagrangian which can generate the desired effects and then calculate the generic expressions for all relevant b → s Wilson coefficients. Here we extend previous analysis by allowing that the new particles can also couple to right-handed Standard Model (SM) fermions as preferred by recent b → s + − data and the anomalous magnetic moment of the muon. In the second part of this article we illustrate this generic approach for a UV complete model in which we supplement the Standard Model by a 4 th generation of vector-like fermions and a real scalar field. This model allows one to coherently address the observed anomalies in b → s + − transitions and in a µ without violating the bounds from other observables (in particular B s −B s mixing) or LHC searches. In fact, we find that our global fit to this model, after the recent experimental updates, is very good and prefers couplings to right-handed SM fermions, showing the importance of our generic setup and calculation performed in the first part of the article.

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Measurement of the ratio of branching fractions B(B0→K⁎0γ)

Cited by 43 publications

References 26 publications

Isospin asymmetries inB→(K*,ρ)γ/l+l−<

Isospin asymmetries inB→(K*,ρ)γ/l+l−<

Exhaustive model selection in b→sℓℓ decays: Pitting cross-validation against the Akaike information criterion

Generic loop effects of new scalars and fermions in b → sℓ+ℓ− and a vector-like 4th generation

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