Results For Form Factors Research Articles

Study of Bs→ϕ(ρ0,ω) decays in the standard model and a family nonuniversal Z′ model

Within the QCD factorization approach, we employ the new results of form factors of Bs→ϕ and calculate the branching fractions, CP asymmetries (CPAs) and polarization fractions of the decay modes Bs→ϕ(ρ0,ω) in both the standard model (SM) and the family nonuniversal Z′ model. We find that in SM the above observables are relate to two parameters, ρH and ϕH, which characterize the end-point divergence in the hard spectator-scattering amplitudes. When setting ρH=0.5 and ϕH∈[−180,180]°, the theoretical uncertainties are large. By combining the experimental data, our results can be used to constrain these two parameters. Supposing ρH=0, we study the effects of the Z′ boson on the concerned observables. With the available branching fraction of Bs→ϕρ0, the possible ranges of parameter spaces are obtained. Within the allowed parameter spaces, the branching fraction of Bs→ϕω can be enlarged remarkably. Furthermore, the new introduced weak phase plays important roles in significantly affecting the CPAs and polarization fractions, which are important observables for probing the effects of NP. If these decay modes were measured in the on-going LHC-b and Belle-II experiments in the future, the peculiar deviation from SM could provide a signal of the family nonuniversal Z′ model, which can also be used to constrain the mass of Z′ boson in turn. Published by the American Physical Society 2024

B(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_{(s)}$$\\end{document} to light 2--\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2^{--}$$\\end{document} tensor meson form factors via LCSR in HQEFT and relevant semileptonic decays

In this study, the form factors of B(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_{(s)}$$\\end{document} to light D-wave tensor mesons with JPC=2--\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J^{PC} = 2^{--}$$\\end{document} (ρ2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\rho _2$$\\end{document}, ω2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega _2$$\\end{document}, K2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K_2$$\\end{document} and ϕ2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi _2$$\\end{document}) are calculated via the light cone sum rules (LCSR) in the framework of heavy quark effective eld theory (HQEFT). Firstly, the expressions of form factors in terms of the light cone distribution amplitudes (LCDAs) of tensor mesons are derived via the LCSR at the leading order of heavy quark expansion. Similar to the case of 2++\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2^{++}$$\\end{document} tensor mesons, the penguin type form factors can be obtained directly from the corresponding semileptonic ones. Considering the light tensor meson LCDAs to twist-3 and quark mass corrections, we give the numerical results of form factors systematically. Based on the form factors given here, we investigate the branching ratios, longitudinal polarization fractions and forward-backward asymmetries of relevant charged current induced semileptonic decays. Our results may be tested by more precise experiments in the future.

Next-to-leading order QCD corrections to the form factors of B to scalar meson decays

We calculate the next-to-leading order QCD corrections to B to scalar meson form factors from QCD light-cone sum rules with B meson light-cone distribution amplitudes. We demonstrate that the B meson-to-vacuum correlation functions can be factorized into the convolution of short-distance coefficients and light-cone distribution amplitudes at the one-loop level and find that only ϕB+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\phi}_B^{+} $$\\end{document}(ω, μ) contributes to the form factors. We then employ the z-parameterization combined with constraints from strong coupling constants to reconstruct the q2 dependence of the form factors in the whole kinematic allowed regions. Due to the large cancellations between the hard functions and the jet functions, the next-to-leading order results show a modest increase of approximately 5% compared to the leading order results. Based on the results of form factors, we predict the branching ratios of semi-leptonic B → Sℓν¯ℓ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ S\\ell {\\overline{\ u}}_{\\ell } $$\\end{document} and B → Sνℓν¯ℓ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ S{\ u}_{\\ell }{\\overline{\ u}}_{\\ell } $$\\end{document} processes, as well as several angular observables, such as forward-backward asymmetries, “flat terms” and lepton polarization asymmetries. We compare these results with calculations from other methods. Experimental verification of these results is required in future experiments.

Weak decays of triply heavy baryons in light front approach

We analyze weak decays of triply heavy baryon Ωccc++ and calculate the form factors for Ωccc++→Ξcc++/Ωcc+ transitions in a light front quark model. The momentum distributions in form factors are accessed via the pole-model parametrization. Using the results for form factors, we predict decay branching fractions for semi-leptonic decays, and obtain B(Ωccc++→Ξcc+e+νe)=0.08%, B(Ωccc++→Ωcc+e+νe)=1.23%. Forward-backward asymmetry and angular distributions are then investigated in this work. We also estimate branching fractions for a few color-allowed processes and find that the Ωccc++→Ωcc+π+ has a sizable branching fraction: B(Ωccc++→Ωcc+π+)=1.82%. We point out that the Ωccc++→Ωcc+π+ is a golden channel for the discovery of the Ωccc++. This analysis can provide a useful reference for future experimental search in future.

D(s) to light tensor meson form factors and semileptonic decays via LCSR in HQEFT

In this paper, the form factors of D(s) to light tensor mesons a2(1320), [Formula: see text], [Formula: see text], [Formula: see text] and corresponding semileptonic decays are investigated through the method of light cone sum rules (LCSR) in the framework of heavy quark effective field theory (HQEFT). Considering the light cone distribution amplitudes (DAs) of tensor mesons to twist-3, we give numerical results of form factors systematically, which are necessary inputs for the analysis of relevant D(s) decays. Based on the form factor results, the relevant semileptonic decays induced by charged current (CC) as well as flavor changing neutral current (FCNC) are studied. Our predictions for the branching ratios, longitudinal polarization fractions and forward–backward asymmetries can be tested by more precise experiments such as LHCb, BESIII and BelleII in the future.

Λb→Λc*(2595,2625)ℓ−ν¯ form factors from lattice QCD

We present the first lattice-QCD determination of the form factors describing the semileptonic decays ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{*}(2595){\ensuremath{\ell}}^{\ensuremath{-}}\overline{\ensuremath{\nu}}$ and ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{*}(2625){\ensuremath{\ell}}^{\ensuremath{-}}\overline{\ensuremath{\nu}}$, where the ${\mathrm{\ensuremath{\Lambda}}}_{c}^{*}(2595)$ and ${\mathrm{\ensuremath{\Lambda}}}_{c}^{*}(2625)$ are the lightest charm baryons with ${J}^{P}={\frac{1}{2}}^{\ensuremath{-}}$ and ${J}^{P}={\frac{3}{2}}^{\ensuremath{-}}$, respectively. These decay modes provide new opportunities to test lepton flavor universality and also play an important role in global analyses of the strong interactions in $b\ensuremath{\rightarrow}c$ semileptonic decays. We determine the full set of vector, axial vector, and tensor form factors for both decays but only in a small kinematic region near the zero-recoil point. The lattice calculation uses three different ensembles of gauge-field configurations with $2+1$ flavors of domain-wall fermions, and we perform extrapolations of the form factors to the continuum limit and physical pion mass. We present Standard Model predictions for the differential decay rates and angular observables. In the kinematic region considered, the differential decay rate for the ${\frac{1}{2}}^{\ensuremath{-}}$ final state is found to be approximately 2.5 times larger than the rate for the ${\frac{3}{2}}^{\ensuremath{-}}$ final state. We also test the compatibility of our form-factor results with zero-recoil sum rules.

B_{(s)} to light tensor meson form factors via LCSR in HQEFT with applications to semileptonic decays

In the present work, the form factors of B_{(s)} to light P-wave tensor mesons (a_2(1320), K^*_2(1430), f_2(1270), f^prime _2(1525)) are calculated via the light cone sum rules (LCSR) in the framework of heavy quark effective field theory (HQEFT). Firstly, the expressions of form factors in terms of the light cone distribution amplitudes (DAs) of tensor mesons are derived via the LCSR at the leading order of heavy quark expansion. It is found that the penguin type form factors can be obtained directly from the corresponding semileptonic ones, which is similar to the case of S-wave mesons. Considering the light tensor meson DAs to twist-3, we give the numerical results of form factors systematically. As applications, we investigate the branching ratios, longitudinal polarization fractions and forward-backward asymmetries of relevant semileptonic decays induced by charged current and flavor changing neutral current (FCNC) separately. Our results may be tested by more precise experiments in the future.

Form factor ratios for Bs→Kℓν and Bs→Dsℓν semileptonic decays and |Vub/Vcb|

We present a lattice quantum chromodynamics determination of the ratio of the scalar and vector form factors for two semileptonic decays of the $B_s$ meson: $B_s \rightarrow K \ell \nu$ and $B_s \rightarrow D_s \ell \nu$. In conjunction with future experimental data, our results for these correlated form factors will provide a new method to extract $|V_{ub}/V_{cb}|$, which may elucidate the current tension between exclusive and inclusive determinations of these Cabibbo-Kobayashi-Maskawa mixing matrix parameters. In addition to the form factor results, we determine the ratio of the differential decay rates, and forward-backward and polarization asymmetries, for the two decays.

Weak decays of doubly heavy baryons: The FCNC processes

The discovery of doubly heavy baryon provides us with a new platform for precisely testing Standard Model and searching for new physics. As a continuation of our previous works, we investigate the FCNC processes of doubly heavy baryons. Light-front approach is adopted to extract the form factors, in which the two spectator quarks are viewed as a diquark. Results for form factors are then used to predict some phenomenological observables, such as the decay width and the forward-backward asymmetry. We find that most of the branching ratios for $b\to s$ processes are $10^{-8}\sim10^{-7}$ and those for $b\to d$ processes are $10^{-9}\sim10^{-8}$. The flavor SU(3) symmetry and symmetry breaking effects are explored. Parametric uncertainties are also investigated.

Weak decays of heavy baryons in the light-front approach**Supported by National Natural Science Foundation of China (11575110, 11655002, 11735010) and Natural Science Foundation of Shanghai (15DZ2272100)

In this work, we analyse semi-leptonic and non-leptonic weak decays of the heavy baryons: Λb, Ξb, Ωb and Λc, Ξc, Ωc. For non-leptonic decay modes, we study only the factorizable channels induced by the external W-emission. The two spectator quarks in the baryonic transitions are treated as a diquark and form factors are calculated in the light-front approach. Using the results for form factors, we also calculate some corresponding semi-leptonic and non-leptonic decay widths. We find that our results are comparable with the available experimental data and other theoretical predictions. Decay branching fractions for many channels are found to reach the level 10−3 ∼ 10−2, which is promising for discovery in future measurements at BESIII, LHCb and Belle II. The SU(3) symmetry in semi-leptonic decays is examined and sources of symmetry breaking are discussed.

B → πlv with Möbius Domain Wall Fermions

We report on the status of our calculation of the exclusive semileptonic decay, B → πlv; a key process in the determination of the CKM matrix element |Vub|. The Möbius domain wall action is used for both light and heavy quarks on gauge ensembles that include the effects of 2 + 1 flavours of quarks in the sea at three values of the lattice spacing: a ≈ 0.08 fm, a ≈ 0.055 fm, and a ≈ 0.044 fm. Pion masses go down to 300 MeV while heavy quarks masses are as large as 2.44mc. We present preliminary results of form factors from this process, showing dependence on momentum transfer, lattice spacing, and the heavy quark mass.

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.

|Vub|fromB→πℓνdecays and (2+1)-flavor lattice QCD

We present a lattice-QCD calculation of the $B\to\pi\ell\nu$ semileptonic form factors and a new determination of the CKM matrix element $|V_{ub}|$. We use the MILC asqtad 2+1-flavor lattice configurations at four lattice spacings and light-quark masses down to 1/20 of the physical strange-quark mass. We extrapolate the lattice form factors to the continuum using staggered chiral perturbation theory in the hard-pion and SU(2) limits. We employ a model-independent $z$ parameterization to extrapolate our lattice form factors from large-recoil momentum to the full kinematic range. We introduce a new functional method to propagate information from the chiral-continuum extrapolation to the $z$ expansion. We present our results together with a complete systematic error budget, including a covariance matrix to enable the combination of our form factors with other lattice-QCD and experimental results. To obtain $|V_{ub}|$, we simultaneously fit the experimental data for the $B\to\pi\ell\nu$ differential decay rate obtained by the BaBar and Belle collaborations together with our lattice form-factor results. We find $|V_{ub}|=(3.72\pm 0.16)\times 10^{-3}$ where the error is from the combined fit to lattice plus experiments and includes all sources of uncertainty. Our form-factor results bring the QCD error on $|V_{ub}|$ to the same level as the experimental error. We also provide results for the $B\to\pi\ell\nu$ vector and scalar form factors obtained from the combined lattice and experiment fit, which are more precisely-determined than from our lattice-QCD calculation alone. These results can be used in other phenomenological applications and to test other approaches to QCD.

Investigation of the $B_{c}\rightarrow\chi_{c2} l \overline {\nu} $ transition via QCD sum rules

We calculate the transition form factors of the semileptonic \(B_{c}\rightarrow\chi_{c2} l \overline{\nu} \) in the framework of QCD sum rules taking into account the two-gluon condensate corrections. Using the obtained results of form factors we estimate the decay widths and branching ratios related to this transition at all lepton channels. A comparison of the obtained results with the predictions of other non-perturbative approaches are also made. The orders of branching ratios for different lepton channels indicate that the \(B_{c}\rightarrow\chi_{c2} l \overline{\nu} \) transition can be studied at LHC using the collected or future data.

Exact form-factor results for the longitudinal structure factor of the massless XXZ model inzero field**Dedicated to Professor Michio Jimbo on his 60th birthday.

We consider the XXZ quantum spin chain in its massless, disordered regime at zero field.We derive an exact expression for the two-spinon form factor of by taking a limit of the massive XYZ form factors found by Lashkevichand by Lukyanov and Terras. This result is used to find the two-spinoncontribution to the spectral decomposition of the longitudinal structure factorSzz(k, w). We find that this contribution provides an accurate approximation to the full structurefactor over a wide range of the anisotropy parameter. The asymptotic behaviour ofSzz(k, w) is computed as the upperand lower w thresholdsof the two-spinon (w, k) band are approached, and an analysis of the region of validity of this threshold behaviour isperformed. Our results reproduce and refine existing threshold behaviour predictionsand extend these results to an accurate description throughout the two-spinoncontinuum.

SemileptonicBcto P-wave charmonia transitions within QCD sum rules

The form factors of the semileptonic ${B}_{c}\ensuremath{\rightarrow}S(AV)\ensuremath{\ell}\ensuremath{\nu}$ ($\ensuremath{\ell}=\ensuremath{\tau}$, $\ensuremath{\mu}$, $e$) transitions, where $S$ and $AV$ denote the scalar ${X}_{c0}$ and axial-vector $({X}_{c1},{h}_{c})$ mesons, are calculated within the framework of the three-point QCD sum rules. The heavy quark effective theory limit of the form factors is also obtained and compared with the values of the original transition form factors. The results of form factors are used to estimate the total decay widths and branching ratios of these transitions. A comparison of our results on branching ratios with the predictions of other approaches is also presented.

Ds→K,K*,ϕform factors in the Covariant Light-Front Approach and ExclusiveDsDecays

In the covariant light-front quark model, we investigate the form factors of D{sub s}{yields}K, K*, {phi} transitions and compare our results with the experimental data and the previous theoretical studies. The semileptonic D{sub s} decays are studied: our result for the branching ratio of D{sub s}{yields}{phi}l{sup +}{nu} is consistent with the data; while the other predictions, such as BR(D{sub s}{sup +}{yields}K{sup 0}l{sup +}{nu}), the branching ratio and the polarization of D{sub s}{yields}K*{sup 0}l{sup +}{nu}, will be tested at the future experiments. Utilizing the results for form factors, we then calculate the two-body nonleptonic D{sub s} decays and find: up to the leading power accuracy, theoretical predictions on branching ratios of nonleptonic D{sub s} decays are typically smaller than the experimental data by a factor of 1.5-2.0. Large contributions from weak annihilation diagrams, together with the s, t-channel final state interactions, are expected to resolve this problem. The D{sub s}{yields}K{sup +}K*{sup 0} decay, which can be easily measured in the K{sup +}K{sup +}{pi}{sup -} final state, can directly shed light on internal information of the doubly Cabibbo-suppressed decay amplitudes.

Deuteron form factors in chiral effective theory: Regulator-independent results and the role of two-pion exchange

We evaluate the deuteron charge, quadrupole, and magnetic form factors using wave functions obtained from chiral effective theory ($\chi$ET) when the potential includes one-pion exchange, chiral two-pion exchange, and genuine contact interactions. We study the manner in which the results for form factors behave as the regulator is removed from the $\chi$ET calculation, and compare co-ordinate- and momentum-space approaches. We show that, for both the LO and NNLO chiral potential, results obtained by imposing boundary conditions in co-ordinate space at $r=0$ are equivalent to the $\Lambda \to \infty$ limit of momentum-space calculations. The regulator-independent predictions for deuteron form factors that result from taking the $\Lambda \to \infty$ limit using the LO $\chi$ET potential are in reasonable agreement with data up to momentum transfers of order 600 MeV, provided that phenomenological information for nucleon structure is employed. In this range the use of the NNLO $\chi$ET potential results in only small changes to the LO predictions, and it improves the description of the zero of the charge form factor.

Analysis of semileptonicBdecays in the relativistic quark model

We present the new analysis of the semileptonic B decays in the framework of the relativistic quark model based on the quasipotential approach. Decays both to heavy D{sup (*)} and light {pi}({rho}) mesons are considered. All relativistic effects are systematically taken into account including contributions of the negative-energy states and the wave function transformation from the rest to moving reference frame. For heavy-to-heavy transitions the heavy quark expansion is applied. Leading and subleading Isgur-Wise functions are determined as the overlap integrals of initial and final meson wave functions. For heavy-to-light transitions the explicit relativistic expressions are used to determine the dependence of the form factors on the momentum transfer squared. Such treatment significantly reduces theoretical uncertainties and increases reliability of obtained predictions. All results for form factors, partial and total decay rates agree well with recent experimental data and unquenched lattice calculations. From this comparison we find the following values of the Cabibbo-Kobayashi-Maskawa matrix elements: |V{sub cb}|=(3.85{+-}0.15{+-}0.20)x10{sup -2} and |V{sub ub}|=(3.82{+-}0.20{+-}0.20)x10{sup -3}, where the first error is experimental and the second one is theoretical.

Semileptonic decays of D, B, K mesons and the full CKM matrix from unquenched lattice QCD

We use lattice QCD to fully determine the CKM matrix. |Vcd|, |Vcs|, |Vub|, |Vcb| and |Vus| are, respectively, directly determined with our lattice results for form factors of semileptonic D → πlν, D → Klν, B → πlν, B → Dlν and K → πlν decays. The accuracy is comparable to that of the Particle Data Group averages. In addition, |Vud|, |Vtb|, |Vts| and |Vtd| are determined by using unitarity of the CKM matrix and the experimental result for sin (2β). In this way, we obtain all 9 CKM matrix elements, where the only theoretical input is lattice QCD.