The Forward-Backward Asymmetry in B→ D^*ℓν: One more hint for Scalar Leptoquarks?

2021/06/30 by Alexandre Carvunis, Andreas Crivellin, Diego Guadagnoli +1 · 28 citations
Computer Science · Mathematics · Physics and Astronomy · #Anomalous magnetic dipole moment #Asymmetry #Combinatorics #Computational Physics and Python Applications #Dark Matter and Cosmic Phenomena #Electron #Hadron #Lepton #Mathematics #Muon #Nuclear physics #Observable #Particle physics #Particle physics theoretical and experimental studies #Physics #Physics beyond the Standard Model #Quantum mechanics #hep-ex #hep-lat #hep-ph

paper · pdf · open access · doi:10.1103/physrevd.105.l031701

published in Physical review. D/Physical review. D. 105(3) (American Physical Society) · 7 pages, 3 figures, 1 table, matches journal version

openalex publication_date 2022/02/23 · openalex created_date 2022/02/24 · arxiv created 2022/03/08 · arxiv updated 2022/03/14 · openalex updated_date 2026/08/06

Abstract

Experimental data have provided intriguing hints for the violation of lepton flavour universality (LFU), including B→ D^(*)τν/B→ D^(*)ℓν, the anomalous magnetic moment of the muon and b → sℓ⁺ℓ^- with a significance of >3 σ, > 4 σ and > 5 σ, respectively. Furthermore, in a recent re-analysis of 2018 Belle data, it was found that the forward-backward asymmetry (ΔA_{\rm FB}) of B → D^*μ ν vs B→ D^*e ν disagrees with the SM prediction by ≈ 4 σ, providing an additional sign of LFU violation. We show that a tensor operator is necessary to significantly improve the agreement with data in ΔA_{\rm FB} while respecting the bounds from other b→ cℓν observables. Importantly, this tensor operator can only be induced (at tree-level within renormalizable models) by a scalar leptoquark. Furthermore, among the two possible representations, the SU(2)_L-singlet S₁ and the doublet S₂, which can interestingly both also account for the anomalous magnetic moment of the muon, only S₁ can provide a good fit. Even though the constraints from (differences of) other angular observables prefer a smaller value of ΔA_{\rm FB} than the current central one, this scenario is significantly preferred (nearly 4 σ) over the SM hypothesis, and is compatible with constraints such as B→ K^*νν and electroweak precision bounds. Therefore, if the ΔA_{\rm FB} anomaly is confirmed, it would provide circumstantial evidence for scalar leptoquarks and pave the way for a natural connection with all other anomalies pointing towards LFU violation.

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