Semileptonic Decay Processes Research Articles

Decay process within the QCDSR approach* *Supported in part by the National Natural Science Foundation of China (12265010, 12265009) and the Project of Guizhou Provincial Department of Science and Technology (ZK[2021]024, ZK[2023]142)

In this paper, we investigate the charmed meson rare decay process using an approach based on QCD sum rules. First, the pion twist-2, 3 distribution amplitude (DA) moments and are calculated up to the tenth and fourth orders, respectively, in the QCD sum rules according to the background field theory. After constructing the light-cone harmonic oscillator model for the pion twist-2, 3 DAs, we obtain their behaviors by matching the calculated ξ-moments. Then, the transition form factors (TFFs) are calculated using an approach based on QCD light-cone sum rules. The vector form factor at the large recoil region is . Using the rapidly converging simplified series expansion of , we present the TFFs and corresponding angular coefficients in the whole squared momentum transfer physical region. Based on non-standard neutrino interactions, the decay can be related to the decay indirectly. Thus, we first describe the semileptonic decay process , differential decay widths, and branching fraction with . The differential/total predictions for forward-backward asymmetry, -differential flat terms, and lepton polarization asymmetry are also reported. The prediction for the branching fraction is .

D(s)− mesons semileptonic form factors in four-flavor holographic QCD

We investigate semileptonic form factors of a D(s) meson from a modified soft-wall 4-flavor holographic model. The model successfully reproduces the masses and decay constants of various mesons, including ρ, K*, D*, Ds*, a1, K1, f1, D1, Ds1, π, K, η, D, and Ds. Moreover, we study the semileptonic decay processes D+→(π,K,η)l+νl and Ds+→(K,η)l+νl, associated with the vector meson exchange, as well as D(s)+→Kl+νl, associated with the vector and axial vector meson exchange. The form factors f+(q2) for D→π and D(s)→K decays agree excellently with experimental and lattice data, outperforming other theoretical approaches. The f+(q2) form factor for D+→η is compatible with experimental data, while a slight discrepancy is observed for Ds+→η at large q2. Additionally, we predict the vector form factors V(q2) and A1(q2) for D→K and Ds→K decays, respectively. The results agree well with other approaches and lattice data at maximum recoil (q2=0). Published by the American Physical Society 2024

Semileptonic decay of Ξc→Ξℓ+νℓ from light-cone QCD sum rules

Semileptonic decay processes of $\Xi_c \to \Xi\ell\nu_\ell$ are studied by light-cone QCD sum rules in this paper. The six form factors of $\Xi_c \to \Xi$ semileptonic transition matrix elements are calculated by this method with the light-cone distribution amplitudes of $\Xi$ baryon up to twist six. With the six form factors, the absolute branching ratios of $\Xi_c^0 \to \Xi^- \ell^+ \nu_\ell$ and $\Xi_c^+ \to \Xi^0 \ell^+ \nu_\ell$ are calculated by the helicity amplitudes formalism of semileptonic differential decay widths. The ratios of absolute branching ratios of electron and muon final states processes give the proof of lepton flavor universality. Our results are in accordance with the recent experimental and theoretical reports.

Light-cone sum rule analysis of semileptonic decays varLambda _b^0 rightarrow varLambda _c^+ ell ^- {overline{nu }}_ell

In this work, we analyze the semileptonic decay processes of varLambda _b rightarrow varLambda _c in the light-cone sum rule approach. In order to calculate the form factors of the varLambda _b baryon transition matrix element, we use the light-cone distribution amplitudes of varLambda _b obtained from the QCD sum rule in the heavy quark effective field theory framework. With the calculation of the six form factors of the varLambda _b rightarrow varLambda _c transition matrix element, the differential decay widths of varLambda _b^0 rightarrow varLambda _c^+ ell ^- {overline{nu }}_ell (ell = e, ~mu , ~tau ) and their absolute branching fractions are obtained. Additionally, the ratio of R(varLambda _c^+) equiv {mathcal {B}}r(varLambda _b^0 rightarrow varLambda _c^+ tau ^- {overline{nu }}_tau )/{mathcal {B}}r(varLambda _b^0 rightarrow varLambda _c^+ mu ^- {overline{nu }}_mu ) is also obtained in this work. Our results are in accord with the newest experimental result and other theoretical calculations and predictions.

Using Deep Learning Algorithms to Improve Energy Resolution in the Semileptonic Decays

The neutrino closure method can be used to obtain the decay kinematics with one missing final state particle (ν) in semileptonic decays. Its solution should give the square of the invariant mass of the lv system (q2) and momentum (P) of the decayed mother particle in semileptonic decay process. However, the resolution obtained by solving two-solution problems with existing algorithms is limited. We propose a new method based on deep learning to improve the resolution of the two key physical quantities when processing Large Hadron Collider beauty (LHCb) experimental data. Resolution of q2 (P) can be improved evenly 1.7% (8.2%) by regression algorithm and 2.7% (9.6%) by classification algorithm compared to linear regression algorithm. The resolution improvements using the new method will benefit the studies on semileptonic decays in hardon collider experiments. Moreover, the new method can be applied to other decays with a missing particle in the final state.

Radiative Corrections to Semileptonic Beta Decays: Progress and Challenges

We review some recent progress in the theory of electroweak radiative corrections in semileptonic decay processes. The resurrection of the so-called Sirlin’s representation based on current algebra relations permits a clear separation between the perturbatively-calculable and incalculable pieces in the O(GFα) radiative corrections. The latter are expressed as compact hadronic matrix elements that allow systematic non-perturbative analysis such as dispersion relation and lattice QCD. This brings substantial improvements to the precision of the electroweak radiative corrections in semileptonic decays of pion, kaon, free neutron and JP=0+ nuclei that are important theory inputs in precision tests of the Standard Model. Unresolved issues and future prospects are discussed.

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

In the semileptonic decays of heavy mesons and baryons, the lepton-mass dependence factors out in the quadratic ${\mathrm{cos}}^{2}\ensuremath{\theta}$ coefficient of the differential $\mathrm{cos}\ensuremath{\theta}$ 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 $\ensuremath{\tau}$ lepton phase space, one can define optimized partial rates which, in the Standard Model, are the same for all three $(e,\ensuremath{\mu},\ensuremath{\tau})$ 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 ${\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{(*)+}{\ensuremath{\ell}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ and ${B}_{c}^{\ensuremath{-}}\ensuremath{\rightarrow}J/\ensuremath{\psi}({\ensuremath{\eta}}_{c}){\ensuremath{\ell}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ and semileptonic heavy baryon decays such as ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}{\ensuremath{\ell}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ for each $\ensuremath{\ell}=e$, $\ensuremath{\mu}$, $\ensuremath{\tau}$.

D → P(π, K) helicity form factors within light-cone sum rule approach * * Supported in part by the National Science Foundation of China (11765007), the National Natural Science Foundation of China (11947302), the Project of Guizhou Provincial Department of Science and Technology (KY[2017]1089, No.KY[2019]1171) and the China Postdoctoral Science Foundation (2019TQ0329)

In this study, helicity form factors (HFFs) are investigated by applying the QCD light-cone sum rule (LCSR) approach. The calculation accuracy is up to the next-to-leading order (NLO) gluon radiation correction of twist-(2,3) distribution amplitude. The resultant HFFs at a large recoil point are and , in which the contributions from the three particles of the leading order (LO) are so small that they can be safely neglected. The maximal contribution of the NLO gluon radiation correction for is less than 3%. After extrapolating the LCSR predictions for these HFFs to the whole -region, we obtain the decay widths for semileptonic decay processes , which are consistent with the BES-III collaboration predictions within error limits. After considering the -meson lifetime, we give the branching fractions of with ; our predictions also agree with the BES-III collaboration results within error limits, especially for the decay process. Finally, we present the forward-backward asymmetry and lepton convexity parameter , and further calculate the mean value of these two observations, and , which may provide a way to test those HFFs in future experiments.

B→Kl+l−decay form factors from three-flavor lattice QCD

We compute the form factors for the $B \to Kl^+l^-$ semileptonic decay process in lattice QCD using gauge-field ensembles with 2+1 flavors of sea quark, generated by the MILC Collaboration. The ensembles span lattice spacings from 0.12 to 0.045 fm and have multiple sea-quark masses to help control the chiral extrapolation. The asqtad improved staggered action is used for the light valence and sea quarks, and the clover action with the Fermilab interpretation is used for the heavy $b$ quark. We present results for the form factors $f_+(q^2)$, $f_0(q^2)$, and $f_T(q^2)$, where $q^2$ is the momentum transfer, together with a comprehensive examination of systematic errors. Lattice QCD determines the form factors for a limited range of $q^2$, and we use the model-independent $z$ expansion to cover the whole kinematically allowed range. We present our final form-factor results as coefficients of the $z$ expansion and the correlations between them, where the errors on the coefficients include statistical and all systematic uncertainties. We use this complete description of the form factors to test QCD predictions of the form factors at high and low $q^2$. We also compare a Standard-Model calculation of the branching ratio for $B \to Kl^+l^-$ with experimental data.

A light-cone QCD sum rule approach for the Ξ baryon electromagnetic form factors and the semileptonic decay Ξc → Ξe+νe

The electromagnetic form factors of the Ξ baryons and the semileptonic decay process Ξc → Ξe+νe are investigated in the frame work of the light-cone QCD sum rule method with Ioffe-type interpolating currents. Our estimates on the magnetic moments are and . The decay width of the semileptonic process is expected to be Γ(Ξc → Ξe+νe) = (6.17+2.24− 2.48) × 10−14 GeV. The results show that the adoption of this type of interpolating current improves the calculations of the magnetic form factors and gives more reliable prediction for the analysis of the semileptonic decay process.

Rare semileptonic decays of heavy mesons in the heavy quark limit

We study the branching ratios of D+ → D0e+ν, DS+ → D0e+ν, BS0 → B+e−ν̄, DS+ → D+e−e+ and BS0 → B0e−e+ rare semileptonic decay processes, which are induced by decays of light quarks, the heavy quarks remain unchanged. The branching ratios of these decay processes are estimated in the heavy quark limit and with SU (3) flavor symmetry. We find that the decay rates are very tiny in the framework of the Standard Model. We also estimate the sensitivities of the measurements of these rare decays at the future experiments, such as BES-III, super-B and LHC-b. Observations of these decays may shed some light on new physics beyond the standard model.

Rare semileptonic decays of heavy mesons with flavor SU(3) symmetry

In this paper, we calculate the decay rates of $D^+ \to D^0 e^+ \nu$, $D^+_S \to D^0 e^+ \nu$, $B^0_S \to B^+ e^- \bar{\nu}$, $D^+_S \to D^+ e^- e^+$ and $B^0_S \to B^0 e^-e^+$ semileptonic decay processes, in which only the light quarks decay, while the heavy flavors remain unchanged. The branching ratios of these decay processes are calculated with the flavor SU(3) symmetry. The uncertainties are estimated by considering the SU(3) breaking effect. We find that the decay rates are very tiny in the framework of the Standard Model. We also estimate the sensitivities of the measurements of these rare decays at the future experiments, such as BES-III, super-$B$ and LHC-$b$.

One-gluon-exchange effects on semileptonic decay of baryon octet

We study one-gluon-exchange (OGE) effects ongA/gV of weak semileptonic decay processes of theSU(3) baryon octet. We especially investigate the systematic behavior of OGE effects on all the possible decay processes and search for better overall agreements between theory and experiment. We adopt the MIT bag model to describe quarks confined in a baryon. We also use a formulation of the perturbative QCD in which gluon field is also confined in the bag. Our calculations respect the boundary conditions which achieve the confinement of each field within the bag. The magnitudes of our corrections togA/gV have a variation of 1 ∼30% depending on the decay, processes. They have process-dependence quite different from that of the uncorrected values ofgA/gV primarily governed by theSU(6) symmetry. These OGE effects ongA/gV reflectSU(6) asymmetric spin-spin correlation between quarks due to the color magnetic interactions. Especially, the OGE corrections togA/gV are very important in the processes,\(\Sigma ^ - \to n + l^ - + \bar v_l ,\Sigma ^ - \to p + l^ - + \bar v_l \) and\(\Xi ^ - \to \Xi ^0 + e^ - + \bar v_e \). Consequently, we clarify that the OGE effects can sizably improve theoretical values ofgA/gV in favor of overall agreements with the present experimental data of semileptonic decays of the baryon octet, at least, in the MIT bag model.

Semileptonic Decays of Mesons in Relativistic Harmonic Oscillator Model

We give meson weak currents in the relativistic harmonic oscillator model with generalizing the replacement p2→\notp2 by Feynman, Kislinger and Ravndal. Semileptonic decay processes of mesons are studied with discussing flavor dependence of the replacement. The ratio Γ(B→Deν)/Γ(B→D*eν) is predicted to be 4.3.

Semileptonic decays of heavy quarks in quantum chromodynamics

We investigate the semileptonic decays of heavy quarks in the leading non-trivial order in quantum chromodynamics. Effects of gluon corrections and the initial quark Fermi motion on the semileptonic rates and decay distributions are calculated. The resulting lepton energy spectrum for the charm semileptonic decay is compared with data to extract the mass of the charm quark. This is combined with the semileptonic branching ratio to predict the charm-quark lifetime. We find the lepton energy spectrum very stable with respect to gluon corrections. Expected spectra from the semileptonic decays of bottom and top quarks are presented. We also study the semileptonic decay process Q → qℓ v ℓ + G, involving the emission of a single hard non-collinear gluon. This process should be observable with a branching ratio of a few percent in the decays of top (and heavier) quarks.