Flavor Anomalies in Heavy Quark Decays

Abstract

Recent measurements of $b$-hadron decays show a pattern of consistent tensions with the respective Standard Model (SM) predictions. These tensions appear both in the sector of rare flavour-changing neutral currents and in tree-level semileptonic $b$-hadron decays. Flavour-changing neutral-current decays are loop-suppressed in the SM and are thus very susceptible to contributions from new heavy particles and/or new interactions beyond the SM. In rare semileptonic decays tensions are observed in measurements of branching fractions and angular observables, as well as in lepton flavour universality tests. Lepton flavour universality is also tested by comparing tree-level $b\to c{\ell }^{-}{\bar{\nu }}_{\tau }$ processes involving third generation leptons $\ell =\tau$ to semileptonic decays with light leptons $\ell =e,\mu$ in the final state. These tests also show tensions between measurements and the SM prediction. Taken together, these tensions constitute the so-called flavour anomalies in $b$-hadron decays, and could be first signs of New Physics (NP) beyond the SM, if established beyond any reasonable doubt. This article reviews both the current experimental status of the flavour anomalies and developments for the relevant theoretical predictions. The review concludes with a discussion of future prospects for the field.

58 pages, 21 figures. Invited review for "Progress in Particle and Nuclear Physics". v1: matches accepted manuscript

References in corpus (29)

• Angular Distributions of B -> K ll Decays
• Lepton Flavor Violation in B Decays?
• $R(D^{\ast })$, $|V_{cb}|$, and the Heavy Quark Symmetry relations between form factors
• Measurement of the $\tau$ lepton polarization and $R(D^{\ast })$ in the decay $\bar{B}\to D^{\ast }{\tau }^{-}{\bar{\nu }}_{\tau }$ with one-prong hadronic $\tau$ decays at Belle
• On the impact of power corrections in the prediction of B->K*mu+mu- observables
• B->V gamma Beyond QCD Factorisation
• Extraction of $|V_{cb}|$ from $B\to D^{(\ast )}\ell {\nu }_{\ell }$ and the Standard Model predictions of $R(D^{(\ast )})$
• Leptoquark Flavor Patterns & B Decay Anomalies
• $B\to \pi \ell \nu$ and $B_s\to K\ell \nu$ form factors and $|V_{ub}|$ from 2+1-flavor lattice QCD with domain-wall light quarks and relativistic heavy quarks
• The B -> pi l nu semileptonic form factor from three-flavor lattice QCD: A model-independent determination of |V(ub)|
• $B_{(s)},D_{(s)}\to \pi ,K,\eta ,\rho ,K^{\ast },\omega ,\varphi$ Transition Form Factors and Decay Rates with Extraction of the CKM parameters $|V_{ub}|$, $|V_{cs}|$, $|V_{cd}|$
• $B_s\to K\ell \nu$ form factors from lattice QCD
• $B\to D^{(\ast )}$ Form Factors from QCD Light-Cone Sum Rules
• Exploiting the width difference in B_s -> phi gamma
• Precise predictions for ${\Lambda }_b\to {\Lambda }_c$ semileptonic decays
• Measurement of the phase difference between short- and long-distance amplitudes in the $B^{+}\to K^{+}{\mu }^{+}{\mu }^{-}$ decay
• Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) and the direct CP asymmetry in B0 -> K*0 gamma
• Time-Dependent CP Asymmetries in B0 -> Ks pi0 gamma transitions
• Measuring the Breaking of Lepton Flavour Universality in $B\to K^{\ast }{\ell }^{+}{\ell }^{-}$
• Measurement of the $B^{\pm }$ production cross-section in pp collisions at $\sqrt{s}=$ 7 and 13 TeV
• Time dependence in $B\to V\ell \ell$ decays
• Bayesian analysis of $b\to s{\mu }^{+}{\mu }^{-}$ Wilson coefficients using the full angular distribution of ${\Lambda }_b\to \Lambda (\to p{\pi }^{-}){\mu }^{+}{\mu }^{-}$ decays
• Evidence for Isospin Violation and Measurement of $CP$ Asymmetries in $B\to K^{\ast }(892)\gamma$
• Precise predictions for B -> Xc tau nu decay distributions
• Search for $B_s^0\to \gamma \gamma$ and a measurement of the branching fraction for $B_s^0\to \varphi \gamma$
• Photon helicity in Lambda_b --> p K gamma decays
• Direct determination of Wilson coefficients using $B^0\to K^{\ast 0}{\mu }^{+}{\mu }^{-}$ decays
• Differential branching fraction and angular moments analysis of the decay $B^0\to K^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-}$ in the $K_{0,2}^{\ast }(1430{)}^0$ region
• Tensor form factors of $B\to K_1$ transition from QCD light cone sum rules

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