Motivated by more precise recent measurements of the $\textit{B}$ → $\textit{ηℓν}$ and $\textit{D}$ → $\textit{η}$ $\textit{ℓν}$ decays, we employ state-of-the-art parametrizations to describe the $\textit{B}$ , $\textit{D}$ → $\textit{η}$ form factors across the full $\textit{q}$ range, fitting them to the latest light-cone sum rule results. Using these results, we compute the branching ratios for all relevant decays and compare them with experimental data, finding good agreement. Additionally, we examine the validity and precision of the extracted $\textit{η}$-$\textit{η}$ mixing angle in the context of heavy meson decays. By combining our predictions for the $\textit{B}$, $\textit{D}$, $\textit{D}$ → $\textit{η}$ form factors with recent semileptonic decay measurements, we extract the CKM elements |$\textit{V}$ |, $\textit{V}$ , and $\textit{V}$ . We also provide tests of the lepton flavour universality in the $\textit{B}$, $\textit{D}$, $\textit{D}$ → $\textit{η}$ $\textit{ℓν}$ decays and present results for the forward-backwards asymmetries in these decays. Our findings indicate that the extracted values are becoming comparable in precision to those obtained from more conventional semileptonic decay analyses.

Croatia

Blaženka Melić

France

Méril Reboud

Form factors and phenomenology of $\textit{B}$

We fit the available data on exclusive semileptonic b → uℓ −   <math> <mover> <mi>ν</mi> <mo>¯</mo> </mover> </math>  $$ \overline{\nu} $$  decays within the Standard Model and in the Weak Effective Theory. Assuming Standard Model dynamics, we find   <math> <mfenced> <msub> <mi>V</mi> <mi>ub</mi> </msub> </mfenced> <mo>=</mo> <msubsup> <mn>3.59</mn> <mrow> <mo>−</mo> <mn>0.12</mn> </mrow> <mrow> <mo>+</mo> <mn>0.13</mn> </mrow> </msubsup> <mo>×</mo> <msup> <mn>10</mn> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> </math>  $$ \left|{V}_{ub}\right|={3.59}_{-0.12}^{+0.13}\times {10}^{-3} $$ . Lifting this assumption, we obtain stringent constraints on the coefficients of the ubℓν sector of the Weak Effective Theory. Performing a Bayesian model comparison, we find that a beyond the Standard Model interpretation is favoured over a Standard Model interpretation of the available data. We provide a Gaussian mixture model that enables the efficient use of our fit results in subsequent analyses beyond the Standard Model, within and beyond the framework of the Standard Model Effective Field Theory.

Domagoj Leljak

Germany

Filip Novak

United Kingdom

Danny Dyk

Toward a complete description of b → uℓ −   <math> <mover> <mi>ν</mi> <mo>¯</mo> </mover> </math>  $$ \overline{\nu} $$  within the Weak Effective Theory decays

We present updated predictions for lifetimes of doubly charmed baryons, within the heavy quark expansion, including available NLO α  s  contributions and newly-computed terms in the 1/m  c  series. Our improved results confirm the expected hierarchy  <math> <mi>τ</mi> <mfenced> <msubsup> <mi>Ξ</mi> <mi>cc</mi> <mo>+</mo> </msubsup> </mfenced> <mo>&lt;</mo> <mi>τ</mi> <mfenced> <msubsup> <mi>Ω</mi> <mi>cc</mi> <mo>+</mo> </msubsup> </mfenced> <mo>&lt;</mo> <mi>τ</mi> <mfenced> <msubsup> <mi>Ξ</mi> <mi>cc</mi> <mrow> <mo>+</mo> <mo>+</mo> </mrow> </msubsup> </mfenced> <mo>,</mo> </math>  $$ \tau \left({\Xi}_{cc}^{+}\right)&lt;\tau \left({\Omega}_{cc}^{+}\right)&lt;\tau \left({\Xi}_{cc}^{++}\right), $$

Lovro Dulibić

James Gratrex

Ivan Nišandžić

Revisiting lifetimes of doubly charmed baryons

In the 1990s, very low experimental values for the lifetime ratio τ(Λ b )/τ(B  d ) triggered a considerable amount of doubt in the applicability of the heavy quark expansion (HQE), which is based on the assumption of quark-hadron duality (QHD) for inclusive total decay rates. However, these low values turned out to be the result of purely experimental problems, and the current HFLAV average reads τ(Λ b )/τ(B  d ) = 0.969(6). In this work, we present the Standard Model predictions for the b-baryon lifetimes within the framework of the HQE. In particular, we include for the first time the contribution of the Darwin term and we update the estimates for the matrix elements of the dimension-six four-quark operators. Within experimental and theoretical uncertainties, we find excellent agreement between the data and the HQE predictions, and thus no indication for any visible violation of QHD. Our numerical results can be summarised by the ratios τ(Λ b )/τ(B  d ) = 0.955(14),   <math> <mi>τ</mi> <mfenced> <msubsup> <mi>Ω</mi> <mi>b</mi> <mo>−</mo> </msubsup> </mfenced> </math>  $$ \tau \left({\varOmega}_b^{-}\right) $$  /τ(B  d ) = 1.081(42), and   <math> <mi>τ</mi> <mfenced> <msubsup> <mi>Ξ</mi> <mi>b</mi> <mn>0</mn> </msubsup> </mfenced> <mo>/</mo> <mi>τ</mi> <mfenced> <msubsup> <mi>Ξ</mi> <mi>b</mi> <mo>−</mo> </msubsup> </mfenced> </math>  $$ \tau \left({\Xi}_b^0\right)/\tau \left({\Xi}_b^{-}\right) $$  = 0.929(28).

Alexander Lenz

Maria Piscopo

Aleksey Rusov

Quark-hadron duality at work: lifetimes of bottom baryons

We provide an extensive study of the lifetimes of singly charmed baryons and mesons, within the heavy quark expansion with all known corrections included. A special attention is devoted to the choice of the charm mass and wavefunctions of heavy baryons. We give our predictions for lifetimes, lifetime ratios, and semileptonic branching ratios of singly charmed baryons. Our results accommodate the experimentally-favoured hierarchy of singly charmed baryon lifetimes  <math> <mi>τ</mi> <mfenced> <msubsup> <mi>Ξ</mi> <mi>c</mi> <mn>0</mn> </msubsup> </mfenced> <mo>&lt;</mo> <mi>τ</mi> <mfenced> <msubsup> <mi>Λ</mi> <mi>c</mi> <mo>+</mo> </msubsup> </mfenced> <mo>&lt;</mo> <mi>τ</mi> <mfenced> <msubsup> <mi>Ω</mi> <mi>c</mi> <mn>0</mn> </msubsup> </mfenced> <mo>&lt;</mo> <mi>τ</mi> <mfenced> <msubsup> <mi>Ξ</mi> <mi>c</mi> <mo>+</mo> </msubsup> </mfenced> <mo>,</mo> </math>  $$ \tau \left({\Xi}_c^0\right)&lt;\tau \left({\Lambda}_c^{+}\right)&lt;\tau \left({\Omega}_c^0\right)&lt;\tau \left({\Xi}_c^{+}\right), $$

Lifetimes of singly charmed hadrons

We revisit light-cone sum rules with pion distribution amplitudes to determine the full set of local   <math> <mover> <mi>B</mi> <mo>¯</mo> </mover> </math>  $$ \overline{B} $$  → π form factors. To this end, we determine all duality threshold parameters from a Bayesian fit for the first time. Our results, obtained at small momentum transfer q 2, are extrapolated to large q 2 where they agree with precise lattice QCD results. We find that a modification to the commonly used BCL parametrization is crucial to interpolate the scalar form factor between the two q 2 regions. We provide numerical results for the form factor parameters — including their covariance — based on simultaneous fit of all three form factors to both the sum rule and lattice QCD results. Our predictions for the form factors agree well with measurements of the q 2 spectrum of the semileptonic decay   <math> <msup> <mover> <mi>B</mi> <mo>¯</mo> </mover> <mn>0</mn> </msup> <mo>→</mo> <msup> <mi>π</mi> <mo>+</mo> </msup> <msup> <mi>ℓ</mi> <mo>−</mo> </msup> <msub> <mover> <mi>ν</mi> <mo>¯</mo> </mover> <mi>ℓ</mi> </msub> </math>  $$ {\overline{B}}^0\to {\pi}^{+}{\mathrm{\ell}}^{-}{\overline{\nu}}_{\mathrm{\ell}} $$ . From the world average of the latter we obtain |V  ub | = (3.77 ± 0.15) · 10 −3, which is in agreement with the most recent inclusive determination at the 1 σ level.

The   <math> <mover> <mi>B</mi> <mo>¯</mo> </mover> </math>  $$ \overline{B} $$  → π form factors from QCD and their impact on |V  ub  |

We revisit the calculation of the strong couplings D ∗ Dπ and B ∗ Bπ from the QCD light-cone sum rules using the pion light-cone distribution amplitudes. The accuracy of the correlation function, calculated from the operator product expansion near the light-cone, is upgraded by taking into account the gluon radiative corrections to the twist-3 terms. The double spectral density of the correlation function, including the twist-2, 3 terms at   <math> <mi>O</mi> <mfenced> <msub> <mi>α</mi> <mi>s</mi> </msub> </mfenced> </math>  $$ \mathcal{O}\left({\alpha}_s\right) $$  and the twist-4 LO terms, is presented in an analytical form for the first time. This form allows us to use various versions of the quark-hadron duality regions in the double dispersion relation underlying the sum rules. We predict   <math> <msub> <mi>g</mi> <mrow> <msup> <mi>D</mi> <mo>∗</mo> </msup> <mi>Dπ</mi> </mrow> </msub> <mo>=</mo> <msubsup> <mn>14.1</mn> <mrow> <mo>−</mo> <mn>1.2</mn> </mrow> <mrow> <mo>+</mo> <mn>1.3</mn> </mrow> </msubsup> </math>  $$ {g}_{D^{\ast } D\pi}={14.1}_{-1.2}^{+1.3} $$  and   <math> <msub> <mi>g</mi> <mrow> <msup> <mi>B</mi> <mo>∗</mo> </msup> <mi>Bπ</mi> </mrow> </msub> <mo>=</mo> <msubsup> <mn>30.0</mn> <mrow> <mo>−</mo> <mn>2.4</mn> </mrow> <mrow> <mo>+</mo> <mn>2.6</mn> </mrow> </msubsup> </math>  $$ {g}_{B^{\ast } B\pi}={30.0}_{-2.4}^{+2.6} $$  when the decay constants of heavy mesons entering the light-cone sum rule are taken from lattice QCD results. We compare our results with the experimental value for the charmed meson coupling and with the lattice QCD calculations.

Alexander Khodjamirian

China

Yu-Ming Wang

Yan-Bing Wei

The D ∗ Dπ and B ∗ Bπ couplings from light-cone sum rules

In light of prospects for measurements of B  c  → D (∗) lv decays in the upcoming Upgrade II of the LHC, we show that by using calculated B  c  → D (∗) form factors a competitive extraction of the |V  ub | CKM matrix element from the   <math> <msub> <mi>B</mi> <mi>c</mi> </msub> <mo>→</mo> <mi>Dμ</mi> <msub> <mover> <mi>v</mi> <mo>¯</mo> </mover> <mi>μ</mi> </msub> </math>  $$ {B}_c\to D\mu {\overline{v}}_{\mu } $$  decay might be possible. To minimize experimental and theoretical uncertainties we provide the ratio |V  ub |/|V  cb | by normalizing the   <math> <msub> <mi>B</mi> <mi>c</mi> </msub> <mo>→</mo> <msup> <mi>D</mi> <mfenced> <mo>∗</mo> </mfenced> </msup> <mi>μ</mi> <msub> <mover> <mi>v</mi> <mo>¯</mo> </mover> <mi>μ</mi> </msub> </math>  $$ {B}_c\to {D}^{\left(\ast \right)}\mu {\overline{v}}_{\mu } $$  to   <math> <msub> <mi>B</mi> <mi>c</mi> </msub> <mo>→</mo> <mi>J</mi> <mo>/</mo> <mi>ψμ</mi> <msub> <mover> <mi>v</mi> <mo>¯</mo> </mover> <mi>μ</mi> </msub> </math>  $$ {B}_c\to J/\psi \mu {\overline{v}}_{\mu } $$  decay. We also briefly examine the suggestion to extract |V  ub |/|V  cs | from the theoretically interesting ratio of   <math> <msub> <mi>B</mi> <mi>c</mi> </msub> <mo>→</mo> <msup> <mi>D</mi> <mn>0</mn> </msup> <mi>e</mi> <msub> <mover> <mi>v</mi> <mo>¯</mo> </mover> <mi>e</mi> </msub> </math>  $$ {B}_c\to {D}^0e{\overline{v}}_e $$  and   <math> <msub> <mi>B</mi> <mi>c</mi> </msub> <mo>→</mo> <msub> <mi>B</mi> <mi>s</mi> </msub> <mi>e</mi> <msub> <mover> <mi>v</mi> <mo>¯</mo> </mover> <mi>e</mi> </msub> </math>  $$ {B}_c\to {B}_se{\overline{v}}_e $$  decay rates in the zero-recoil limit. With the present average value of |V  ub |, the predicted branching ratios are estimated to be   <math> <mi>BR</mi> <mfenced> <mrow> <msub> <mi>B</mi> <mi>c</mi> </msub> <mo>→</mo> <msup> <mi>D</mi> <mn>0</mn> </msup> <mi>μ</mi> <msub> <mover> <mi>ν</mi> <mo>¯</mo> </mover> <mi>μ</mi> </msub> </mrow> </mfenced> <mo>=</mo> <mfenced> <mrow> <mn>2.4</mn> <mo>±</mo> <mn>0.4</mn> </mrow> </mfenced> <mo>·</mo> <msup> <mn>10</mn> <mrow> <mo>−</mo> <mn>5</mn> </mrow> </msup> </math>  $$ BR\left({B}_c\to {D}^0\mu {\overline{\nu}}_{\mu}\right)=\left(2.4\pm 0.4\right)\cdotp {10}^{-5} $$  and   <math> <mi>BR</mi> <mfenced> <mrow> <msub> <mi>B</mi> <mi>c</mi> </msub> <mo>→</mo> <msup> <mi>D</mi> <mo>∗</mo> </msup> <mi>μ</mi> <msub> <mover> <mi>ν</mi> <mo>¯</mo> </mover> <mi>μ</mi> </msub> </mrow> </mfenced> <mo>=</mo> <mfenced> <mrow> <mn>7</mn> <mo>±</mo> <mn>3</mn> </mrow> </mfenced> <mo>·</mo> <msup> <mn>10</mn> <mrow> <mo>−</mo> <mn>5</mn> </mrow> </msup> <mo>,</mo> </math>  $$ BR\left({B}_c\to {D}^{\ast}\mu {\overline{\nu}}_{\mu}\right)=\left(7\pm 3\right)\cdotp {10}^{-5}, $$  and the semileptonic ratios for testing the lepton flavour universality in these B  c  decays are R  c (D 0) = 0.64 ± 0.05 and R  c (D  ∗ ) = 0.55 ± 0.05. We also provide q 2 distributions and various angular observables of B  c  → D (∗) lν decays.

|Vub| determination and testing of lepton flavour universality in semileptonic Bc → D(∗) decays

We elaborate on the dichotomy between the description of the semileptonic decays of heavy hadrons on the one hand and the semileptonic decays of light hadrons such as neutron $$\beta $$ <math><mi>β</mi></math>  decays on the other hand. For example, almost without exception the semileptonic decays of heavy baryons are described in cascade fashion as a sequence of two two-body decays $$B_1 \rightarrow B_2 + W_\mathrm{off-shell}$$ <math><mrow><msub><mi>B</mi><mn>1</mn></msub><mo>→</mo><msub><mi>B</mi><mn>2</mn></msub><mo>+</mo><msub><mi>W</mi><mrow><mi>off</mi><mo>-</mo><mi>shell</mi></mrow></msub></mrow></math>  and $$W_{\mathrm{off-shell}} \rightarrow \ell + \nu _\ell $$ <math><mrow><msub><mi>W</mi><mrow><mi>off</mi><mo>-</mo><mi>shell</mi></mrow></msub><mo>→</mo><mi>ℓ</mi><mo>+</mo><msub><mi>ν</mi><mi>ℓ</mi></msub></mrow></math>  whereas neutron $$\beta $$ <math><mi>β</mi></math>  decays are analyzed as true three-body decays $$n \rightarrow p + e^- +{\bar{\nu }}_e$$ <math><mrow><mi>n</mi><mo>→</mo><mi>p</mi><mo>+</mo><msup><mi>e</mi><mo>-</mo></msup><mo>+</mo><msub><mover><mrow><mi>ν</mi></mrow><mrow><mo>¯</mo></mrow></mover><mi>e</mi></msub></mrow></math> . Within the cascade approach it is possible to define a set of seven angular observables for polarized neutron $$\beta $$ <math><mi>β</mi></math>  decays as well as the longitudinal, transverse and normal polarization of the decay electron. We determine the dependence of the observables on the usual vector and axial vector form factors. In order to be able to assess the importance of recoil corrections we expand the rate and the $$q^2$$ <math><msup><mi>q</mi><mn>2</mn></msup></math>  averages of the observables up to NLO and NNLO in the recoil parameter $$\delta =(M_n-M_p)/(M_n+M_p)= 0.689\cdot 10^{-3}$$ <math><mrow><mi>δ</mi><mo>=</mo><mrow><mo>(</mo><msub><mi>M</mi><mi>n</mi></msub><mo>-</mo><msub><mi>M</mi><mi>p</mi></msub><mo>)</mo></mrow><mo>/</mo><mrow><mo>(</mo><msub><mi>M</mi><mi>n</mi></msub><mo>+</mo><msub><mi>M</mi><mi>p</mi></msub><mo>)</mo></mrow><mo>=</mo><mn>0.689</mn><mo>·</mo><msup><mn>10</mn><mrow><mo>-</mo><mn>3</mn></mrow></msup></mrow></math> . Remarkably, we find that the rate and three of the four parity conserving polarization observables that we analyze are protected from NLO recoil corrections when the second class current contributions are set to zero.

Estonia

Stefan Groote

Jürgen Körner

A new angle on an old problem: helicity approach to neutron beta decay in the Standard Model

We discuss B  c  → η  c  and B  c  → J/ψ semileptonic decays within the Standard Model (SM) and beyond. The relevant transition form factors, being the main source of theoretical uncertainties, are calculated in the sum rule approach and are provided in a full q 2 range. We calculate the semileptonic branching fractions and find for the ratios,   <math> <mfenced> <msub> <mi>R</mi> <msub> <mi>η</mi> <mi>c</mi> </msub> </msub> </mfenced> <mi>S</mi> <mi>M</mi> <mo>=</mo> <mn>0.32</mn> <mo>±</mo> <mn>0.02</mn> </math>  $$ \left.{R}_{\eta_c}\right|\mathrm{S}\mathrm{M}=0.32\pm 0.02 $$ , R  J/ψ  |SM = 0.23 ± 0.01. Both predictions are in agreement with other existing calculations and support the current tension in R  J/ψ  at 2σ level with the experiment. To extend the potential of testing the SM in the semileptonic B  c  decays, we consider the forward-backward asymmetry and polarization observables. We also study the 4-fold differential distributions of   <math> <msub> <mi>B</mi> <mi>c</mi> </msub> <mo>→</mo> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> <mfenced> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> <mo>→</mo> <msup> <mover> <mi>ℓ</mi> <mo>˜</mo> </mover> <mo>−</mo> </msup> <msup> <mover> <mi>ℓ</mi> <mo>˜</mo> </mover> <mo>+</mo> </msup> </mrow> </mfenced> <msup> <mi>ℓ</mi> <mo>−</mo> </msup> <msub> <mover> <mi>ν</mi> <mo>¯</mo> </mover> <mi>ℓ</mi> </msub> </math>  $$ {B}_c\to J/\psi \left(J/\psi \to {\tilde{\ell}}^{-}{\tilde{\ell}}^{+}\right){\ell}^{-}{\overline{\nu}}_{\ell } $$ , where   <math> <mover> <mi>ℓ</mi> <mo>˜</mo> </mover> <mspace width="0.25em"></mspace> <mo>=</mo> <mi>e</mi> <mo>,</mo> <mi>μ</mi> </math>  $$ \tilde{\ell} = e,\mu $$ , in the presence of different new physics scenarios and find that the new physics effects can significantly modify the angular observables and can also produce effects which do not exist in the SM. Using the constraints on the new physics couplings from the recent combined analysis of BaBar, Belle and LHCb data on semileptonic B → D (∗) decays, where the effects of new physics could be visible, we find that these different new physics scenarios are not able to simultaneously explain the current experimental value of R  J/ψ .