Decay Form Factors Research Articles

Two body non-leptonic D0 decays from LCSR and implications for\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\Delta a}_{{\ ext{CP}}}^{{\ ext{dir}}}$$\\end{document}

Motivated by the recent measurements of CP violating effects in singly Cabibbo suppressed D0 decays, we revisit the theoretical predictions of these channels. Using up-to-date values for the decay constants and form factors, we find already within naive QCD factorisation, surprisingly good agreement between the central values of the branching ratios and the corresponding experimental data. We further extend the study of these modes by employing the method of light-cone sum rules (LCSR) with light-meson light-cone distribution amplitudes. Using for the first time this framework to compute the leading contribution to the decay amplitude, we can again describe well the experimental branching ratios for the modes D0 → π+K−, D0 → K+K−, D0 → π+π− and D0 → K+π−. The combination of our results with known predictions for the penguin contributions obtained with LCSR, leads to an upper bound for the value of direct CP violation expected in the Standard Model of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left|{\\Delta a}_{{\ ext{CP}}}^{{\ ext{dir}}}\\right|\\le 2.4\ imes {10}^{-4}$$\\end{document}, which is approximately a factor six smaller than the current measurement.

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|.

Recent results from the NA62 experiment at CERN

The NA62 experiment at CERN collected the world's largest data set of charged kaon decays in 2016-2018, leading to the most precise measurement of the branching fraction of the ultra-rare K+→π+νν‾ decay, based on 20 candidates. This provides evidence for the observation of the K+→π+νν‾ decay with a significance of 3.4σ. This measurement is also used to set limits on B(K+→π+X), where X is a scalar or pseudo-scalar particle. The analysis of the full 2016-2018 data sample is reviewed. More recent results from NA62 analyses of K+→π0e+νγ, K+→π+μ+μ− and K+→π+γγ decays, using data samples recorded in 2017–2018, are also reported. The radiative kaon decay K+→π0e+νγ (Ke3γ) is studied with a data sample of O(100k) Ke3γ candidates with sub-percent background contamination. Final results of the most precise measurements of the Ke3γ branching ratios and T-asymmetry are presented. The K+→π+μ+μ− sample comprises about 27k signal events with negligible background contamination, and the results presented include the most precise determination of the branching fraction and the decay form factor. The K+→π+γγ sample contains about 4k signal events with 10% background contamination, and the preliminary analysis results improve the precision of the branching fraction measurement by a factor of 3 with respect to previous measurements. An overview of the latest NA62 results and future prospects for the experiment is presented.

Analysis of the decay constants and form factors of pseudoscalar mesons in a dirac formalism

We investigate the weak leptonic and semileptonic decay widths of pseudoscalar light and heavy mesons in a Dirac formalism. We take relativistic-independent quark model of the form [Formula: see text], where [Formula: see text]. This is computed using the binding quark eigenfunction and taking the assumptions of a significant relationship between the quark and antiquark momenta inside the decaying meson in the rest frame. To calculate the decay constant [Formula: see text], decay width and branching fractions of pseudoscalar mesons, we employ the model parameters that we used earlier. The experimental findings and various similar models are in good agreement with our predictions such as [Formula: see text] and [Formula: see text]”. Finally, we calculate the form factors and branching fractions for the semileptonic [Formula: see text] decays [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]” and find reasonable agreement with the experimental results.

Recent Progress in Leptonic and Semileptonic Decays of Charmed Hadrons

We present a comprehensive review of purely leptonic and semileptonic decays of D0(+), [Formula: see text], and charmed baryons (including [Formula: see text], Ξ c, and Ω c). The precise studies of these decays help deepen our understanding and knowledge of quantum chromodynamics via measuring decay constants and form factors, and test the Standard Model through examining the unitarity of the Cabibbo–Kobayashi–Maskawa matrix and lepton flavor universality. We give an overview of the theoretical and experimental tools before discussing the recent progress. The data sets collected by the Beijing Spectrometer III (BESIII) near the production thresholds of [Formula: see text], [Formula: see text], and [Formula: see text] offer important opportunities for studies of charm physics.

Form factors in HQEFT and model independent analysis of relevant semileptonic decays with NP effects* *Supported in part by the National Natural Science Foundation of China (12147214)

The form factors of decays into P-wave excited charmed mesons (including , , , and their strange counterparts, denoted generically as ) are systematically calculated via QCD sum rules in the framework of heavy quark effective field theory (HQEFT). We consider contributions up to the next leading order of heavy quark expansion and give all the relevant form factors, including the scalar and tensor ones only relevant for possible new physics effects. The expressions for the form factors in terms of several universal wave functions are derived via heavy quark expansion. These universal functions can be evaluated through QCD sum rules. Then, the numerical results of the form factors are presented. With the form factors given here, a model independent analysis of relevant semileptonic decays is performed, including the contributions from possible new physics effects. Our predictions for the differential decay widths, branching fractions, and ratios of branching fractions may be tested in more precise experiments in the future.

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.

D -meson semileptonic decays to pseudoscalars from four-flavor lattice QCD

We present lattice-QCD calculations of the hadronic form factors for the semileptonic decays $D\to\pi\ell\nu$, $D\to K\ell\nu$, and $D_s\to K\ell\nu$. Our calculation uses the highly improved staggered quark (HISQ) action for all valence and sea quarks and includes $N_f=2+1+1$ MILC ensembles with lattice spacings ranging from $a\approx0.12$ fm down to $0.042$ fm. At most lattice spacings, an ensemble with physical-mass light quarks is included. The HISQ action allows all the quarks to be treated with the same relativistic light-quark action, allowing for nonperturbative renormalization using partial conservation of the vector current. We combine our results with experimental measurements of the differential decay rates to determine $|V_{cd}|^{D\to\pi}=0.2238(11)^{\rm Expt}(15)^{\rm QCD}(04)^{\rm EW}(02)^{\rm SIB}[22]^{\rm QED}$ and $|V_{cs}|^{D\to K}=0.9589(23)^{\rm Expt}(40)^{\rm QCD}(15)^{\rm EW}(05)^{\rm SIB}[95]^{\rm QED}$ This result for $|V_{cd}|$ is the most precise to date, with a lattice-QCD error that is, for the first time for the semileptonic extraction, at the same level as the experimental error. Using recent measurements from BES III, we also give the first-ever determination of $|V_{cd}|^{D_s\to K}=0.258(15)^{\rm Expt}(01)^{\rm QCD}[03]^{\rm QED}$ from $D_s\to K \ell\nu$. Our results also furnish new Standard Model calculations of the lepton flavor universality ratios $R^{D\to\pi}=0.98671(17)^{\rm QCD}[500]^{\rm QED}$, $R^{D\to K}=0.97606(16)^{\rm QCD}[500]^{\rm QED}$, and $R^{D_s\to K}=0.98099(10)^{\rm QCD}[500]^{\rm QED}$, which are consistent within $2\sigma$ with experimental measurements. Our extractions of $|V_{cd}|$ and $|V_{cs}|$, when combined with a value for $|V_{cb}|$, provide the most precise test of second-row CKM unitarity, finding agreement with unitarity at the level of one standard deviation.

Methods for high-precision determinations of radiative-leptonic decay form factors using lattice QCD

We present a study of lattice-QCD methods to determine the relevant hadronic form factors for radiative-leptonic decays of pseudoscalar mesons. We provide numerical results for ${D}_{s}^{+}\ensuremath{\rightarrow}{\ensuremath{\ell}}^{+}\ensuremath{\nu}\ensuremath{\gamma}$. Our calculation is performed using a domain-wall action for all quark flavors and on a single RBC/UKQCD lattice gauge-field ensemble. The first part of the study is how to best control two sources of systematic error inherent in the calculation, specifically the unwanted excited states created by the meson interpolating field and unwanted exponentials in the sum over intermediate states. Using a 3D sequential propagator allows for better control over unwanted exponentials from intermediate states, while using a 4D sequential propagator allows for better control over excited states. We perform individual analyses of the 3D and 4D methods, as well as a combined analysis using both methods, and find that the 3D sequential propagator offers good control over both sources of systematic uncertainties for the smallest number of propagator solves. From there, we further improve the use of a 3D sequential propagator by employing an infinite-volume approximation method, which allows us to calculate the relevant form factors over the entire allowed range of photon energies. We then study improvements gained by performing the calculation using a different three-point function, using ratios of three-point functions, averaging over positive and negative photon momentum, and using an improved method for extracting the structure-dependent part of the axial form factor. The optimal combination of methods yields results for the ${D}_{s}^{+}\ensuremath{\rightarrow}{\ensuremath{\ell}}^{+}\ensuremath{\nu}\ensuremath{\gamma}$ structure-dependent vector and axial form factors in the entire kinematic range with statistical plus fitting uncertainties of order 5%, using 25 gauge configurations with 64 samples per configuration.

Precision calculations of Bd,s → π, K decay form factors in soft-collinear effective theory

We improve QCD calculations of the semileptonic Bd,s→ π, K decay form factors at large hadronic recoil by implementing the next-to-leading-logarithmic resummation for the obtained leading-power light-cone sum rules in the soft-collinear effective theory (SCET) framework and by computing for the first time the non-vanishing spectator-quark mass correction dictating the SU(3)-flavour symmetry breaking effects between these fundamental quantities at the one-loop accuracy. Additionally, we endeavour to investigate a variety of the subleading-power contributions to these heavy-to-light form factors at mathcal{O}left({alpha}_s^0right) with the same methodology, by including the higher-order terms in the heavy-quark expansion of the hard-collinear quark propagator, by evaluating the desired effective matrix element of the next-to-leading-order term in the SCETI representation of the weak transition current, by taking into account the off-light-cone contributions of the two-body heavy-quark effective theory (HQET) matrix elements as well as the three-particle higher-twist corrections from the subleading bottom-meson light-cone distribution amplitudes (LCDAs), and by computing the twist-five and twist-six four-body higher-twist effects with the aid of the factorization approximation. Having at our disposal the SCET sum rules for the exclusive B-meson decay form factors under discussion, we further explore in detail numerical implications of the newly computed subleading-power corrections by employing the three-parameter model for both the leading-twist and higher-twist B-meson distribution amplitudes. Taking advantage of the customary Bourrely-Caprini-Lellouch (BCL) parametrization for the complete set of the semileptonic Bd,s→ π, K form factors, we then determine the correlated numerical results for the interesting series coefficients, by carrying out the simultaneous fit of the exclusive B-meson decay form factors to both the achieved SCET sum rule predictions at small momentum transfer (q2) and the available lattice QCD results at large momentum transfer. Subsequently, we perform a comprehensive phenomenological analysis of the full angular observables, the lepton-flavour university ratios and the lepton polarization asymmetries for the flavour-changing charged- current Bto pi ell {overline{nu}}_{ell } and {B}_sto Kell {overline{nu}}_{ell } decays (with ℓ = μ, τ) together with the differential q2-distribution for the exclusive rare Bto K{nu}_{ell }{overline{nu}}_{ell } decays in the Standard Model.

Investigations of the semileptonic decays of D and $$D_s$$ into a pseudoscalar meson using the Isgur-Wise functions

The branching ratios of the semileptonic decay widths of the charm mesons are analyzed, using three different models for the Isgur-Wise functions, such as \({D^0} \rightarrow {K^ - }{l^ + }\upsilon\), \({D^0} \rightarrow {\pi ^ - }{l^ + }\nu\), \({D_s} \rightarrow {K^0}{l^ + }\nu\) and \({D_s} \rightarrow \eta {l^ + }\nu\), where the form factors of these decays are discussed. The mass spectra of the charm mesons are obtained. We use a potential quark model and consider the non-relativistic Hamiltonian of the charm meson as a bound state of the quark-antiquark system. We take into account the harmonic-type confinement and also Hellmann potential, which is a superposition of the Coulomb and the Yukawa potential. Using the variational approach along with the harmonic oscillator wave functions, we evaluate the mass spectra of the charm mesons, the form factors and the semileptonic decay widths of \(D_{(s)}\). We present our results for masses of \(D, D_s\) and \(\eta\), the Isgur-Wise functions, the form factors of the semileptonic decays, and the branching fractions of the semileptonic decays of D and \(D_s\). Our results are motivating.

Study of the Semileptonic Decay Λ_{c}^{+}→Λe^{+}ν_{e}.

The study of the Cabibbo-favored semileptonic decay Λ_{c}^{+}→Λe^{+}ν_{e} is reported using a 4.5 fb^{-1} data sample of e^{+}e^{-} annihilations collected at center-of-mass energies ranging from 4.600GeV to 4.699GeV with the BESIII detector at the BEPCII collider. The branching fraction of the decay is measured to be B(Λ_{c}^{+}→Λe^{+}ν_{e})=(3.56±0.11_{stat}±0.07_{syst})%, which is the most precise measurement to date. Furthermore, we perform an investigation of the internal dynamics in Λ_{c}^{+}→Λe^{+}ν_{e}. We provide the first direct comparisons of the differential decay rate and form factors with those predicted from lattice quantum chromodynamics (LQCD) calculations. Combining the measured branching fraction with a q^{2}-integrated rate predicted by LQCD, we determine |V_{cs}|=0.936±0.017_{B}±0.024_{LQCD}±0.007_{τ_{Λ_{c}}}.

A measurement of the K+→ π+μ+μ− decay

A sample of 2.8 × 104K+ → π+μ+μ− candidates with negligible background was collected by the NA62 experiment at the CERN SPS in 2017–2018. The model-independent branching fraction is measured to be (9.15 ± 0.08) × 10−8, a factor three more precise than previous measurements. The decay form factor is presented as a function of the squared dimuon mass. A measurement of the form factor parameters and their uncertainties is performed using a description based on Chiral Perturbation Theory at mathcal{O} (p6).

Form factors of B→πℓν and a determination of |Vub| with Möbius domain-wall fermions

Using a fully relativistic lattice fermion action, we compute the form factors of the semileptonic decay $B\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\ell}\ensuremath{\nu}$, which is required for the determination of the Cabibbo-Kobayashi-Maskawa matrix element $|{V}_{ub}|$. We employ the M\"obius domain-wall fermion formalism for the generation of lattice ensembles with $2+1$ sea quark flavors as well as for the valence heavy and light quarks. We compute the form factors at various values of the lattice spacing and multiple light and heavy quark masses, and extrapolate the results to the physical point. We combine our lattice results with the available experimental data to obtain $|{V}_{ub}|=(3.93\ifmmode\pm\else\textpm\fi{}0.41)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$.

Rare radiative Ξb−→ Ξ−γ decay in the relativistic quark model

Recently, the LHCb collaboration put the upper limit on the [Formula: see text] decay branching ratio [Formula: see text]. The measured value is below the light-cone sum rule prediction. In this paper, the rare radiative decay of the [Formula: see text] baryon is studied in the framework of the relativistic quark model based on the quasipotential approach and QCD. The decay form factors are calculated with the comprehensive account of the relativistic effects. The obtained result for the branching ratio is found to be below the upper limit set by LHCb and is consistent with theoretical predictions based on the SU(3) flavor-symmetry, light-front quark model and light-cone QCD sum rules in full theory within theoretical uncertainties.

Forward-backward asymmetries in in the Bethe-Salpeter equation approach * *Supported by National Natural Science Foundation of China (11905117, 11775024)

Using the Bethe-Salpeter equation (BSE), we investigate the forward-backward asymmetries in in the quark-diquark model. This approach provides precise form factors that are different from those of quantum chromodynamics (QCD) sum rules. We calculate the rare decay form factors for b and investigate the (integrated) forward-backward asymmetries in these decay channels. We observe the integrated , , , and ; the hadron side asymmetries ; the lepton-hadron side asymmetries ; and the longitudinal polarization fractions .

B → D1(2420) and B → {mathrm{D}}_1^{prime } (2430) form factors from QCD light-cone sum rules

We perform the first calculation of form factors in the semileptonic decays B → D1(2420)ℓνℓ and B → {D}_1^{prime } (2430)ℓνℓ using QCD light-cone sum rules (LCSRs) with B-meson distribution amplitudes. In this calculation the c-quark mass is finite. Analytical expressions for two-particle contributions up to twist four are obtained. To disentangle the D1 and {D}_1^{prime } contributions in the LCSRs, we suggest a novel approach that introduces a combination of two interpolating currents for these charmed mesons. To fix all the parameters in the LCSRs, we use the two-point QCD sum rules for the decay constants of D1 and {D}_1^{prime } mesons augmented by a single experimental input, that is the B → D1(2420)ℓνℓ decay width. We provide numerical results for all B → D1 and B → {D}_1^{prime } form factors. As a byproduct, we also obtain the D1- and {D}_1^{prime } -meson decay constants and predict the lepton-flavour universality ratios R(D1) and R( {D}_1^{prime } ).

New measurement of the K+ → π+μ+μ− decay

The flavor-changing neutral current decay [Formula: see text] ([Formula: see text]) is well suited to explore the Standard Model structure. A new measurement of this decay branching fraction and form factor has been performed by the NA62 experiment at CERN based on data collected in 2017–2018. From the selected sample of 28011 [Formula: see text] event candidates with a negligible background, the decay form factor parameters [Formula: see text] and [Formula: see text], as well as the branching fraction [Formula: see text] have been measured.

Radiative semileptonic overline{B} decays

We consider the form factors for the radiative semileptonic decays overline{B} (v) → D(*)(v′)ℓ overline{nu} ℓγ in the kinematic region where the photon momentum, k, is small enough that heavy quark symmetry (HQS) can be applied without the radiated photon changing the heavy quark velocity (i.e., v(′) ∙ k < m(b,c)). We find that HQS is remarkably powerful, leaving only four new undetermined form factors at leading order in 1/m(b,c). In addition, one of them is fixed in terms of the leading order Isgur-Wise function in the kinematic region, v(′) ∙ k < ΛQCD.

Hadronic currents and form factors in three-body semileptonic tau decays

Three-body semileptonic tau -decays offer a path to understand the properties of light hadronic systems and CP symmetry violations through searches for electric dipole moments. In studies of electro-weak physics, the hadronic part of the final states has traditionally been described using the language of form factors. Spectroscopic information, resolved in terms of orbital angular momentum quantum-numbers, is best being derived from an explicit decomposition of the hadronic current in the orbital angular momentum basis. Motivated by the upcoming large data samples from mathrm {B} factories, we present the full description of the hadronic currents decomposed into quantum numbers of the hadronic final state using the isobar picture. We present formulas for orbital angular momenta up to three and apply the rules derived from hadron spectroscopy to formulate the decay chain of hadronic three-body systems of arbitrary mass. We also translate this formalism to the language of form factors and thereby correct insufficiencies found in previous analyses of three-body hadronic final states.