Form-factor-independent test of lepton universality in semileptonic heavy meson and baryon decays

Abstract

In the semileptonic decays of heavy mesons and baryons the lepton-mass dependence factors out in the quadratic ${\cos }^2\theta$ coefficient of the differential $\cos \theta$ distribution. We call the corresponding normalized coefficient the convexity parameter. This observation opens the path to a test of lepton universality in semileptonic heavy meson and baryon decays that is independent of form-factor effects. By projecting out the quadratic rate coefficient, dividing out the lepton-mass-dependent factor and restricting the phase space integration to the $\tau$ lepton phase space, one can define optimized partial rates which, in the Standard Model, are the same for all three $(e,\mu ,\tau )$ modes in a given semileptonic decay process. We discuss how the identity is spoiled by New Physics effects. We discuss semileptonic heavy meson decays such as ${\bar{B}}^0\to D^{(\ast )+}{\ell }^{-}{\bar{\nu }}_{\ell }$ and $B_c^{-}\to J/\psi ({\eta }_c){\ell }^{-}{\bar{\nu }}_{\ell }$, and semileptonic heavy baryon decays such as ${\Lambda }_b\to {\Lambda }_c{\ell }^{-}{\bar{\nu }}_{\ell }$ for each $\ell =e,\mu ,\tau$.

arXiv comment14 pages, 4 figures, 3 tables. Some discussion and references added. Will be published in PRD

References in corpus (36)

• Evidence for an excess of B -> D(*) Tau Nu decays
• Measurement of an Excess of B -> D(*) Tau Nu Decays and Implications for Charged Higgs Bosons
• Measurement of the branching ratio of $\bar{B}\to D^{(\ast )}{\tau }^{-}{\bar{\nu }}_{\tau }$ relative to $\bar{B}\to D^{(\ast )}{\ell }^{-}{\bar{\nu }}_{\ell }$ decays with hadronic tagging at Belle
• Measurement of the ratio of branching fractions $\mathcal{B}({\overline{B}}^0\to D^{\ast +}{\tau }^{-}{\overline{\nu }}_{\tau })/\mathcal{B}({\overline{B}}^0\to D^{\ast +}{\mu }^{-}{\overline{\nu }}_{\mu })$
• Measurement of the $\tau$ lepton polarization and $R(D^{\ast })$ in the decay $\bar{B}\to D^{\ast }{\tau }^{-}{\bar{\nu }}_{\tau }$
• Measurement of the branching ratio of ${\bar{B}}^0\to D^{\ast +}{\tau }^{-}{\bar{\nu }}_{\tau }$ relative to ${\bar{B}}^0\to D^{\ast +}{\ell }^{-}{\bar{\nu }}_{\ell }$ decays with a semileptonic tagging method
• Combined analysis of semileptonic $B$ decays to $D$ and $D^{\ast }$: $R(D^{(\ast )})$, $|V_{cb}|$, and new physics
• The $B\to D\ell \nu$ form factors at nonzero recoil and $|V_{cb}|$ from $2+1$-flavor lattice QCD
• Flavor models for $\bar{B}\to D^{(\ast )}\tau \bar{\nu }$
• $B\to Dl\nu$ Form Factors at Non-Zero Recoil and Extraction of $|V_{cb}|$
• Revisiting $B\to D\ell \nu$
• ${\Lambda }_b\to p{\ell }^{-}{\bar{\nu }}_{\ell }$ and ${\Lambda }_b\to {\Lambda }_c{\ell }^{-}{\bar{\nu }}_{\ell }$ form factors from lattice QCD with relativistic heavy quarks
• The $V_{cb}$ puzzle: an update
• Update of $|V_{cb}|$ from the $\bar{B}\to D^{\ast }\ell \bar{\nu }$ form factor at zero recoil with three-flavor lattice QCD
• The semileptonic decay Lambda_b -> Lambda_c + tau(-) + antinu_tau in the covariant confined quark model
• Observation of B+ -> Dbar*0 tau+ nu_tau and Evidence for B+ -> Dbar^0 tau+ nu_tau at Belle
• Phenomenology of ${\Lambda }_b\to {\Lambda }_c\tau {\bar{\nu }}_{\tau }$ using lattice QCD calculations
• Theory determination of $\bar{B}\to D^{(\ast )}{\ell }^{-}\bar{\nu }$ form factors at $\mathcal{O}(1/m_c^2)$
• Implications of new physics in the decays $B_c\to (J/\psi ,{\eta }_c)\tau \nu$
• Analyzing new physics in the decays ${\bar{B}}^0\to D^{(\ast )}{\tau }^{-}{\bar{\nu }}_{\tau }$ with form factors obtained from the covariant quark model
• A Challenge to Lepton Universality in B Meson Decays
• Complete angular analysis of polarized top decay at O(alpha_s)
• Helicity Analysis of Semileptonic Hyperon Decays Including Lepton Mass Effects
• Exclusive decays $B\to {\ell }^{-}\bar{\nu }$ and $B\to D^{(\ast )}{\ell }^{-}\bar{\nu }$ in the covariant quark model
• Semileptonic $B_{(s)}$ decays to excited charmed mesons with $e,\mu ,\tau$ and searching for new physics with $R(D^{\ast \ast })$
• Revisit to the $b\to c\tau \nu$ transition: in and beyond the SM
• Precision Model-Independent Bounds from Global Analysis of $b\to c\ell \nu$ Form Factors
• Further tests of lepton flavour universality from the charged lepton energy distribution in $b\to c$ semileptonic decays: The case of ${\Lambda }_b\to {\Lambda }_c\ell {\bar{\nu }}_{\ell }$
• Angular distributions of $\bar{B}\to D^{(\ast )}\ell {\bar{\nu }}_{\ell }$ decays and search of New Physics
• Hadron and lepton tensors in semileptonic decays including new physics
• Optimized Lepton Universality Tests in $B\to V\ell \bar{\nu }$ decays
• Detailed Study of the Decay Lambda_b --> Lambda_c tau {\bar ν}_τ
• ${\bar{B}}_c\to {\eta }_c$, ${\bar{B}}_c\to J/\psi$ and $\bar{B}\to D^{(\ast )}$ semileptonic decays including new physics
• A new angle on an old problem: Helicity approach to neutron beta decay in the Standard Model
• Angular distribution as an effective probe of new physics in semi-hadronic three-body meson decays
• Analyzing New Physics in ${\bar{B}}^0\to D^{(\ast )}{\tau }^{-}{\bar{\nu }}_{\tau }$

Cited by in corpus (5)

• Radiative decays $D^*_{(s)}\to D_{(s)}γ$ in covariant confined quark model
• Heavy quark symmetry of ${\Lambda }_b^0$ decays in quark models
• Polarization observables in semileptonic $V\to P$ decays of quarkonia
• Probing the ATOMKI X17 vector boson using Dalitz decays $V\to P{e}^{+}{e}^{-}$
• Radiative and Dalitz decays of ${\rm Y}(1S)$ in the light of the ATOMKI X17 anomaly