CKM Matrix Element Research Articles

Searching for |Vcd| through the exclusive decay [formula omitted] within QCD sum rules

In this paper, we carry out an investigation into the semileptonic decays Ds+→K0ℓ+νℓ with ℓ=(e,μ) by employing the QCD light-cone sum rules approach. The vector transition form factor (TFF) f+Ds+K0(q2) for Ds+→K0 decay is calculated while considering its next-to-leading order contribution. Subsequently, we briefly introduce the twist-2, 3 kaon distribution amplitudes, which are calculated by using QCD sum rules within the framework of the background field theory. At the large recoil point, the TFF has f+Ds+K0(0)=0.692−0.026+0.027. Then, we extrapolate f+Ds+K0(q2) to the whole physical q2-region via the simplified z(q2,t)-series expansion, and the behavior of TFF f+Ds+K0(q2) is exhibited in the numerical results part, including the theoretical and experimental predictions for comparison. In addition, we compute the differential branching fraction B(Ds+→K0ℓ+νℓ) with the electron and muon channels, which are expected to be B(Ds+→K0e+νe)=3.379−0.275+0.301×10−3 and B(Ds+→K0μ+νμ)=3.351−0.273+0.299×10−3 as well as contained other results for comparison. Our results show good agreement with the BESIII measurements and theoretical predictions. Furthermore, we present our prediction with respect to the CKM matrix element |Vcd| by using the B(Ds+→K0e+νe) result from BESIII Collaboration, yielding |Vcd|=0.221−0.010+0.008. Finally, we provide the ratio between Ds+→K0e+νe and Ds+→ηe+νe channels, i.e.RK0/ηe=0.144−0.020+0.028.

Model-independent extraction of form factors and |Vcb| in B¯→Dℓ−ν¯ℓ with hadronic tagging at BABAR

Using the entire ϒ(4S) dataset, the first two-dimensional unbinned angular analysis of the semileptonic decay B¯→Dℓ−ν¯ℓ is performed, employing hadronic reconstruction of the tag-side B meson from ϒ(4S)→BB¯. Here, ℓ denotes the light charged leptons e and μ. A novel data-driven signal-background separation procedure with minimal dependence on simulation is developed. This procedure preserves all multidimensional correlations present in the data. The expected sin2θℓ dependence of the differential decay rate in the Standard Model is demonstrated, where θℓ is the lepton helicity angle. Including input from the latest lattice QCD calculations and previously available experimental data, the underlying form factors are extracted using both model-independent (BGL) and dependent (CLN) methods. Comparisons with lattice calculations show flavor SU(3) symmetry to be a good approximation in the B(s)→D(s) sector. Using the BGL results, the CKM matrix element |Vcb|=(41.09±1.16)×10−3 and the Standard Model prediction of the lepton-flavor universality violation variable R(D)=0.300±0.004, are extracted. The value of |Vcb| from B¯→Dℓ−ν¯ℓ tends to be higher than that extracted using B¯→D*ℓ−ν¯ℓ. The Standard Model R(D) calculation is at a 1.97σ tension with the latest HFLAV experimental average. Published by the American Physical Society 2024

Measurement of t-channel production of single top quarks and antiquarks in pp collisions at 13 TeV using the full ATLAS Run 2 data sample

The production of single top quarks and top antiquarks via the t-channel exchange of a virtual W boson is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV at the LHC using 140 fb−1 of ATLAS data. The total cross-sections are determined to be σtq=137−8+8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sigma (tq)={137}_{-8}^{+8} $$\\end{document} pb and σt¯q=84−5+6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sigma \\left(\\overline{t}q\\right)={84}_{-5}^{+6} $$\\end{document} pb for top-quark and top-antiquark production, respectively. The combined cross-section is found to be σtq+t¯q=221−13+13\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sigma \\left( tq+\\overline{t}q\\right)={221}_{-13}^{+13} $$\\end{document} pb and the cross-section ratio is Rt=σtq/σt¯q=1.636−0.034+0.036\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {R}_t=\\sigma (tq)/\\sigma \\left(\\overline{t}q\\right)={1.636}_{-0.034}^{+0.036} $$\\end{document}. The predictions at next-to-next-to-leading-order in quantum chromodynamics are in good agreement with these measurements. The predicted value of Rt using different sets of parton distribution functions is compared with the measured value, demonstrating the potential to further constrain the functions when using this result in global fits. The measured cross-sections are interpreted in an effective field theory approach, setting limits at the 95% confidence level on the strength of a four-quark operator and an operator coupling the third quark generation to the Higgs boson doublet: −0.37<CQq3,1/Λ2<0.06\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ -0.37<{C}_{Qq}^{3,1}/{\\Lambda}^2<0.06 $$\\end{document} and −0.87<CϕQ3/Λ2<1.42\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ -0.87<{C}_{\\phi Q}^3/{\\Lambda}^2<1.42 $$\\end{document}. The constraint |Vtb| > 0.95 at the 95% confidence level is derived from the measured value of σtq+t¯q\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sigma \\left( tq+\\overline{t}q\\right) $$\\end{document}, assuming that the Wtb interaction is a left-handed weak coupling and that |Vtb| ≫ |Vtd|, |Vts|. In a more general approach, pairs of CKM matrix elements involving top quarks are simultaneously constrained, leading to confidence contours in the corresponding two-dimensional parameter spaces.

On the Magnitudes of some CKM Matrix Elements

Abstract This write-up follows the presentation at the symposium, with emphasis on topics and ideas discussed there. It is purposefully informal, not a review of the field, and neither does it include a complete list of references. However, I hope that readers might find somwe comments useful or amusing, and may appreciate the challenges and reasons for excitement about recent progress and future opportunities in flavor physics.

Analytic third-order QCD corrections to top-quark and semileptonic b→u decays

We present the first analytic results of next-to-next-to-next-to-leading-order (N3LO) QCD corrections to the top-quark decay width. We focus on the dominant leading color contribution, which includes light-quark loops. At next-to-next-to-leading order (NNLO), this dominant contribution accounts for 95% of the total correction. By utilizing the optical theorem, the N3LO corrections are related to the imaginary parts of the four-loop self-energy Feynman diagrams, which are calculated with differential equations. The results are expressed in terms of harmonic polylogarithms, enabling fast and accurate evaluation. The third-order QCD corrections decrease the leading-order decay width by 0.667%, and the scale uncertainty is reduced by half compared to the NNLO result. The most precise prediction for the top-quark width is now 1.321 GeV for mt=172.69 GeV. Additionally, we obtain the third-order QCD corrections to the dilepton invariant mass spectrum and decay width in the semileptonic b→u transition. The perturbative series in the on-shell mass scheme exhibits poor convergence behavior. In the MS¯ mass scheme, the scale dependence is greatly improved. A more precise determination of the CKM matrix element Vub could be obtained with such higher-order corrections. Published by the American Physical Society 2024

Properties of the ηq\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta _q$$\\end{document} leading-twist distribution amplitude and its effects to the B/D+→η(′)ℓ+νℓ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B/D^+ \\rightarrow \\eta ^{(\\prime )}\\ell ^+ \ u _\\ell $$\\end{document} decays

The η(′)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta ^{(\\prime )}$$\\end{document}-mesons in the quark-flavor basis are mixtures of two mesonic states |ηq⟩=|u¯u+d¯d⟩/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$|\\eta _{q}\\rangle =|{\\bar{u}} u+{\\bar{d}} d\\rangle /\\sqrt{2}$$\\end{document} and |ηs⟩=|s¯s⟩.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$|\\eta _{s}\\rangle =|{\\bar{s}} s\\rangle .$$\\end{document} In previous work, we have made a detailed study on the ηs\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta _{s}$$\\end{document} leading-twist distribution amplitude by using the Ds+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D^+_s$$\\end{document} meson semileptonic decays. As a sequential work, in the present paper, we fix the ηq\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta _q$$\\end{document} leading-twist distribution amplitude by using the light-cone harmonic oscillator model for its wave function and by using the QCD sum rules within the QCD background field to calculate its moments. The input parameters of ηq\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta _q$$\\end{document} leading-twist distribution amplitude ϕ2;ηq\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi _{2;\\eta _q}$$\\end{document} at the initial scale μ0∼1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu _0\\sim 1$$\\end{document} GeV are fixed by using those moments. The QCD sum rules for the 0th\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0_{\ extrm{th}}$$\\end{document}-order moment can also be used to fix the magnitude of ηq\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta _q$$\\end{document} decay constant, giving fηq=0.141±0.005\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_{\\eta _q}=0.141\\pm 0.005$$\\end{document} GeV. As an application of ϕ2;ηq,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi _{2;\\eta _q},$$\\end{document} we calculate the transition form factors B(D)+→η(′)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B(D)^+ \\rightarrow \\eta ^{(\\prime )}$$\\end{document} by using the QCD light-cone sum rules up to twist-4 accuracy and by including the next-to-leading order QCD corrections to the leading-twist part, and then fix the related CKM matrix element and the decay width for the semi-leptonic decays B(D)+→η(′)ℓ+νℓ.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B(D)^+ \\rightarrow \\eta ^{(\\prime )}\\ell ^+ \ u _\\ell .$$\\end{document}

Bayesian inference for form-factor fits regulated by unitarity and analyticity

We propose a model-independent framework for fitting hadronic form-factor data, which is often only available at discrete kinematical points, using parameterisations based on to unitarity and analyticity. In this novel approach the latter two properties of quantum-field theory regulate the ill-posed fitting problem and allow model-independent predictions over the entire physical range. Kinematical constraints, for example for the vector and scalar form factors in semileptonic meson decays, can be imposed exactly. The core formulae are straight-forward to implement with standard math libraries. We take account of a generalisation of the original Boyd Grinstein Lebed (BGL) unitarity constraint for form factors and demonstrate our method for the exclusive semileptonic decay Bs→ Kℓν, for which we make a number of phenomenologically relevant predictions, including the CKM matrix element |Vub|.

Exclusive semileptonic Bs→Kℓν decays on the lattice

Semileptonic $B_s \to K \ell \nu$ decays provide an alternative $b$-decay channel to determine the CKM matrix element $|V_{ub}|$, and to obtain a $R$-ratio to investigate lepton-flavor-universality violations. Results for the CKM matrix element may also shed light on the discrepancies seen between analyses of inclusive or exclusive decays. We calculate the decay form factors using lattice QCD with domain-wall light quarks and a relativistic $b$-quark. We analyze data at three lattice spacings with unitary pion masses down to $268\,\mathrm{MeV}$. Our numerical results are interpolated/extrapolated to physical quark masses and to the continuum to obtain the vector and scalar form factors $f_+(q^2)$ and $f_0(q^2)$ with full error budgets at $q^2$ values spanning the range accessible in our simulations. We provide a possible explanation of tensions found between results for the form factor from different lattice collaborations. Model- and truncation-independent $z$-parameterization fits following a recently proposed Bayesian-inference approach extend our results to the entire allowed kinematic range. Our results can be combined with experimental measurements of $B_s \to D_s$ and $B_s\to K$ semileptonic decays to determine $|V_{ub}|=3.8(6)\times 10^{-3}$. The error is currently dominated by experiment. We compute differential branching fractions and two types of $R$ ratios, the one commonly used as well as a variant better suited to test lepton-flavor universality.

An SU(5) × U(1)′ SUSY GUT with a “vector-like chiral” fourth family to fit all low energy data, including the muon g − 2

An additional generation of quarks and leptons and their SUSY counterparts, which are vector-like under the Standard Model gauge group but are chiral with respect to the new U(1)3−4 gauge symmetry, are added to the Minimal Supersymmetric Standard Model (MSSM). We show that this model is a GUT and unifies the three SM gauge couplings and also the additional U(1)3−4 coupling at a GUT scale of ≈ 5 × 1016 GeV and explains the experimentally observed deviation of the muon g – 2. We also fit the quark flavor changing processes consistent with the latest experimental data and look at the effect of the new particles on the W boson mass without obviously conflicting with the observed masses of particles, CKM matrix elements, neutrino mixing angles, their mass differences, and the lepton-flavor violating bounds. This model predicts sparticle masses less than 25 TeV, with a gluino mass ≈ 2.3 – 3 TeV consistent with constraints, and one of the neutralinos as the LSP with a mass of ≈ 480 – 580 GeV, which is a potential dark matter candidate. The model is string theory motivated and predicts the VL quarks, leptons, a massive Z′ and two Dirac neutrinos at the TeV scale and the branching ratios of μ ⟶ eγ, τ ⟶ μγ and τ ⟶ 3μ with BR(μ ⟶ eγ) within reach of future experiments.

Strong Interaction Dynamics and Fermi β Decay in the Nucleon and the Nucleus

Nuclear super-allowed β decay has been used to obtain tight limits on the value of the CKM matrix element Vud that is important for unitarity tests and, therefore, for tests of the standard model. Current requirements on precision are so intense that effects formerly thought too small to matter are now considered relevant. This article is a brief review of personal efforts to include the effects of strong interactions on Fermi β decay. First, I examine the role of isospin violation in the decay of the neutron. The size of the necessary correction depends upon detailed strong-interaction dynamics. The isospin violating parts of the nucleon wave function, important at the low energy of β decay, can be constrained by data taken at much higher energies, via measurements, for example, of ed→e′π±+X reactions at Jefferson Laboratory. The next point of focus is on the role of nuclear short-ranged correlations, which affect the value of the correction needed to account for isospin violation in extracting the value of Vud. The net result is that effects previously considered as irrelevant are now considered relevant for both neutron and nuclear β decay.

New physics in B q 0– mixing: present challenges, prospects, and implications for

The phenomenon of B0 q – mixing (q = d, s) provides a sensitive probe for physics beyond the Standard Model (SM). We explore the corresponding space for New Physics left through the current data, having a careful look at analyses of the Unitarity Triangle that are needed for the SM predictions of the B q mixing parameters. In particular, we explore the impact of tensions between inclusive and exclusive determinations of the CKM matrix elements ∣V ub ∣ and ∣V cb ∣. Moreover, we focus on the angle γ of the Unitarity Triangle, comparing measurements from B → DK and B → π π, ρ π, ρ ρ decays, where the latter are typically interpreted in terms of the angle α. We discuss various scenarios and present the corresponding state-of-the-art constraints on the New Physics parameters of B q 0– mixing. We point out that these results have an interesting application in the analysis of rare decays, allowing us to minimise the impact of CKM parameters in the search for New Physics. In view of the high-precision era, we make future projections. Interestingly, we find that for the extraction of the New Physics parameters in the B d system the determination of the apex of the Unitarity Triangle results in a key limiting factor. By contrast, the corresponding impact is negligible for the B s system, making it a promising candidate to reveal sources of New Physics.

A precision relation between Γ(K → μ+μ−)(t) and mathcal{B}left({K}_Lto {mu}^{+}{mu}^{-}right)/mathcal{B}left({K}_Lto gamma gamma right)

We find that the phase appearing in the unitarity relation between mathcal{B}left({K}_Lto {mu}^{+}{mu}^{-}right) and mathcal{B}left({K}_Lto gamma gamma right) is equal to the phase shift in the interference term of the time- dependent K → μ+μ− decay. A probe of this relation at future kaon facilities constitutes a Standard Model test with a theory precision of about 2%. The phase has further importance for sensitivity studies regarding the measurement of the time-dependent K → μ+μ− decay rate to extract the CKM matrix element combination mid {V}_{ts}{V}_{td}sin left(beta +{beta}_sright)mid approx {A}^2{lambda}^5overline{eta} . We find a model-independent theoretically clean prediction, cos2φ0 = 0.96 ± 0.03. The quoted error is a combination of the theoretical and experimental errors, and both of them are expected to shrink in the future. Using input from the large-NC limit within chiral perturbation theory, we find a theory preference towards solutions with negative cos φ0, reducing a four-fold ambiguity in the angle φ0 to a two-fold one.

Isospin-breaking corrections to light-meson leptonic decays from lattice simulations at physical quark masses

The decreasing uncertainties in theoretical predictions and experimental measurements of several hadronic observables related to weak processes, which in many cases are now smaller than O(1%), require theoretical calculations to include subleading corrections that were neglected so far. Precise determinations of leptonic and semi-leptonic decay rates, including QED and strong isospin-breaking effects, can play a central role in solving the current tensions in the first-row unitarity of the CKM matrix. In this work we present the first RBC/UKQCD lattice calculation of the isospin-breaking corrections to the ratio of leptonic decay rates of kaons and pions into muons and neutrinos. The calculation is performed at fixed lattice spacing (a−1 ≃ 1.730 GeV) on a 483× 96 volume with Nf = 2 + 1 dynamical quarks close to the physical point and domain wall fermions in the Möbius formulation are employed. Long-distance QED interactions are included according to the QEDL prescription and the crucial role of finite-volume electromagnetic corrections in the determination of leptonic decay rates, which produce a large systematic uncertainty, is extensively discussed. Finally, we study the different sources of uncertainty on |Vus|/|Vud| and observe that, if finite-volume systematics can be reduced, the error from isospin-breaking corrections is potentially sub-dominant in the final precision of the ratio of the CKM matrix elements.

Semileptonic form factors for Brightarrow D^*ell nu at nonzero recoil from 2+1-flavor lattice QCD

We present the first unquenched lattice-QCD calculation of the form factors for the decay Brightarrow D^*ell nu at nonzero recoil. Our analysis includes 15 MILC ensembles with N_f=2+1 flavors of asqtad sea quarks, with a strange quark mass close to its physical mass. The lattice spacings range from aapprox 0.15 fm down to 0.045 fm, while the ratio between the light- and the strange-quark masses ranges from 0.05 to 0.4. The valence b and c quarks are treated using the Wilson-clover action with the Fermilab interpretation, whereas the light sector employs asqtad staggered fermions. We extrapolate our results to the physical point in the continuum limit using rooted staggered heavy-light meson chiral perturbation theory. Then we apply a model-independent parametrization to extend the form factors to the full kinematic range. With this parametrization we perform a joint lattice-QCD/experiment fit using several experimental datasets to determine the CKM matrix element |V_{cb}|. We obtain left| V_{cb}right| = (38.40 pm 0.68_{text {th}} pm 0.34_{text {exp}} pm 0.18_{text {EM}})times 10^{-3}. The first error is theoretical, the second comes from experiment and the last one includes electromagnetic and electroweak uncertainties, with an overall chi ^2text {/dof} = 126/84, which illustrates the tensions between the experimental data sets, and between theory and experiment. This result is in agreement with previous exclusive determinations, but the tension with the inclusive determination remains. Finally, we integrate the differential decay rate obtained solely from lattice data to predict R(D^*) = 0.265 pm 0.013, which confirms the current tension between theory and experiment.

(Semi-) leptonic D(s) decays at BESIII

BESIII has collected 2.93fb−1 and 6.32fb−1 of e+e− collision data samples at the center-of-mass energies 3.773 and 4.178–4.226 GeV, respectively. We report recent measurements of the (semi-) leptonic decays Ds→ℓ+νℓ (ℓ=μ,τ) and D(s)→Xℓ+νℓ [X=η,K1(1270) or denotes generic decays, and ℓ=e,μ]. The decay constant fDs+, the semileptonic form factor f+η(0) and the CKM matrix elements |Vcd(s)| are determined precisely. These results are important to verify the theoretical calculations of fDs+ and f+η(0), and the unitarity of the CKM matrix. Precision tests of lepton-flavor universality with (semi-) leptonic D(s) decays are also performed.

CKM substructure from the weak to the Planck scale

We look for relations among CKM matrix elements that are not consequences of the Wolfenstein parametrization. In particular, we search for products of CKM elements raised to integer powers that approximately equal 1. We study the running of the CKM matrix elements and resolve an apparent discrepancy in the literature. To a good approximation only A runs, among the Wolfenstein parameters. Using the Standard Model renormalization group we look for CKM relations at energy scales ranging from the electroweak scale to the Planck scale, and we find 19 such relations. These relations could point to structure in the UV, or be numerical accidents. For example, we find that |VtdVus| = | {V}_{cb}^2 |, within 2% accuracy, in the 109–1015 GeV range. We discuss the implications of this CKM relation for a Yukawa texture in the UV.

Feasibility study of D_s^+ rightarrow tau ^+ nu _{tau } decay and test of lepton flavor universality with leptonic D_s^+ decays at STCF

We report a sensitive study of D_s^+ rightarrow tau ^+ nu _{tau } decay via tau ^+ rightarrow e^+ nu _e bar{nu }_{tau } with an integrated luminosity of 1 ab^{-1} at the center-of-mass energy of 4.009 GeV at a future Super Tau Charm Facility (STCF). Under the help of the fast simulation software package, the statistical sensitivity for the absolute branching fraction of D_s^+ rightarrow tau ^+ nu _{tau } is determined to be 2times 10^{-4}. Combining with our previous prospect of D_s^+ rightarrow mu ^+ nu _{mu }, the ratio of the branching fractions for D_s^+ rightarrow tau ^+ nu _{tau } over D_s^+ rightarrow mu ^+ nu _{mu } can achieve a relative statistical precision of 0.5%, which will provide the most stringent test of the tau -mu lepton flavor universality in heavy quark decays. Taking the decay constant f_{D_s^+} from lattice QCD calculations or the CKM matrix element |V_{cs}| from the CKMfitter group as an input, the relative statistical uncertainties for |V_{cs}| and f_{D_s^+} are estimated to be 0.3% and 0.2%, respectively.

W + charm production with massive c quarks in PowHel

The hadroproduction of a W boson in association with a charm quark at the Large Hadron Collider is at the centre of current investigations due to its potential to probe the strangeness content of the proton. In this paper we present an implementation of the W + c production process in the PowHel event generator matched to the PYTHIA8 parton shower approach, allowing to obtain predictions for differential cross-sections with NLO QCD accuracy matched to the accuracy of the Shower Monte Carlo event generator. Effects of non-diagonal CKM matrix elements, finite charm quark mass and off-shell W decays including spin correlations are taken into account. We investigate the production of a leptonically decaying W boson in association with either a charmed meson (W± + D∗∓) or a charmed jet (W± + jc) and compare our predictions with particle-level measurements by the ATLAS and CMS collaborations at sqrt{s} = 7 and 13 TeV. The role of the so-called “opposite sign” and “same sign” contributions to the theoretical cross-sections is presented and discussed, pointing out the importance of including parton shower effects for a reliable estimate of the latter and a faithful comparison with experimental data.

Helicity form factors and the decays * *Supported in part by the National Natural Science Foundation of China (11765007, 11625520, 11947406, 12047564), the Project of Guizhou Provincial Department of Science and Technology (KY[2019]1171), the Project of Guizhou Provincial Department of Education (KY[2021]030), the China Postdoctoral Science Foundation (2019TQ0329, 2020M670476), the Chongqing Graduate Research and Innovation Foundation (ydstd1912), the Fundamental Research

In this paper, we calculate the helicity form factors (HFFs) up to twist-4 accuracy by using the light-cone sum rules (LCSR) approach. After extrapolating those HFFs to the physically allowable region, we investigate the -meson two-body decays and semi-leptonic decays , where stand for light pseudoscalar and vector mesons, respectively. The branching fractions can be derived using the CKM matrix element and the lifetime from the Particle Data Group, and we obtain , , , , and . We then obtain and , which agree with the LHCb measured value within -error. We also obtain , which like other theoretical predictions, is consistent with the LHCb measured value within -error. These imply that the HFFs under the LCSR approach are also applicable to the meson two-body decays and semi-leptonic decays , and the HFFs obtained using LCSR in a new way implies that there may be new physics in the semi-leptonic decays.

Diluting quark flavor hierarchies using dihedral symmetry

We present a D_4 flavored extension of the SM which provides an intuitive reasoning for the masses and mixing patterns in the quark sector. In our model, the Cabibbo mixing angle becomes related to the ratio of two vacuum expectation values. In fact, the orders of magnitude of the CKM matrix elements are readily obtained from the hierarchical nature of the vacuum expectation values. Moreover, we also show that the smallness of the off-Cabibbo elements in the CKM matrix is strongly connected to the heaviness of the third generation of quarks.