Light-cone Sum Rules Research Articles

New scalar resonance X 0(2900) as a molecule: mass and width

We explore features of the scalar structure X 0(2900), which is one of the two resonances discovered recently by LHCb in the D − K + invariant mass distribution in the decay B + → D + D − K +. We treat X 0(2900) as a hadronic molecule composed of the conventional mesons and K ∗0 and calculate its mass, coupling and width. The mass and coupling of X 0(2900) are determined using the QCD two-point sum rule method by taking into account quark, gluon, and mixing vacuum condensates up to dimension 15. The decay of this structure to final state D − K + is investigated in the context of the light-cone sum rule approach supported by a soft-meson technique. To this end, we evaluate strong coupling G corresponding to vertex X 0 D − K +, which allows us to find width of the decay X 0(2900) → D − K +. Obtained predictions for the mass of the hadronic molecule and for its width Γ = (49.6 ± 9.3) MeV can be considered as arguments in favor of molecule interpretation of X 0(2900).

Implications of new physics in B → K 1 μ + μ − decay processes

Recently, several discrepancies at the level of (2–3)σ have been observed in the decay processes mediated by flavour changing neutral current (FCNC) transitions b → sℓ + ℓ −, which may be considered as the smoking-gun signal of new physics (NP). These intriguing hints of NP have attracted a lot of attention and many attempts are being made to find the possible NP signature in other related processes, which are mediated through the same quark-level transitions. In this work, we perform a comprehensive analysis of the FCNC decays of the B meson to axial vector mesons K 1(1270) and K 1(1400), which are an admixture of the 13 P 1 and 11 P 1 states K 1A and K 1B , in a model independent framework. Using the B → K 1 form factors evaluated in the light cone sum rule approach, we investigate the rare exclusive semileptonic decays B → K 1(1270)μ + μ − and B → K 1(1400)μ + μ −. Considering all the possible relevant operators for b → sℓ + ℓ − transitions, we study their effects on various observables such as branching fractions, the lepton flavor universality violating ratio , forward–backward asymmetries, and lepton polarization asymmetries of these processes. These results will not only enhance the theoretical understanding of the mixing angle but also serve as a good tool for probing NP.

A closer look at the extraction of |Vub| from B \u2192 \u03c0\u2113\u03bd

To extract the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |Vub|, we have re-analyzed all the available inputs (data and theory) on the B → πℓν decays including the newly available inputs on the form-factors from light cone sum rule (LCSR) approach. We have reproduced and compared the results with the procedure taken up by the Heavy Flavor Averaging Group (HFLAV), while commenting on the effect of outliers on the fits. After removing the outliers and creating a comparable group of data-sets, we mention a few scenarios in the extraction of |Vub|. In all those scenarios, the extracted values of |Vub| are higher than that obtained by HFLAV. Our best results for |Vub|exc. are (3.94 ± 0.14) × 10−3 and left({3.93}_{-0.15}^{+0.14}right) × 10−3 in frequentist and Bayesian approaches, respectively, which are consistent with that extracted from inclusive decays |Vub|inc. within 1 σ confidence interval.

The overline{B} \u2192 \u03c0 form factors from QCD and their impact on |Vub|

We revisit light-cone sum rules with pion distribution amplitudes to determine the full set of local overline{B} → π form factors. To this end, we determine all duality threshold parameters from a Bayesian fit for the first time. Our results, obtained at small momentum transfer q2, are extrapolated to large q2 where they agree with precise lattice QCD results. We find that a modification to the commonly used BCL parametrization is crucial to interpolate the scalar form factor between the two q2 regions. We provide numerical results for the form factor parameters — including their covariance — based on simultaneous fit of all three form factors to both the sum rule and lattice QCD results. Our predictions for the form factors agree well with measurements of the q2 spectrum of the semileptonic decay {overline{B}}^0to {pi}^{+}{mathrm{ell}}^{-}{overline{nu}}_{mathrm{ell}} . From the world average of the latter we obtain |Vub| = (3.77 ± 0.15) · 10−3, which is in agreement with the most recent inclusive determination at the 1 σ level.

Ds -meson leading-twist distribution amplitude within the QCD sum rules and its application to the Bs→Ds transition form factor

We make a detailed study of the ${D}_{s}$-meson leading-twist light-cone distribution amplitude ${\ensuremath{\phi}}_{2;{D}_{s}}$ by using the QCD sum rules within the framework of the background field theory. To improve the precision, its moments $⟨{\ensuremath{\xi}}^{n}{⟩}_{2;{D}_{s}}$ are calculated up to dimension-six condensates. At the scale $\ensuremath{\mu}=2\text{ }\text{ }\mathrm{GeV}$, we obtain $⟨{\ensuremath{\xi}}^{1}{⟩}_{2;{D}_{s}}=\ensuremath{-}{0.261}_{\ensuremath{-}0.020}^{+0.020}$, $⟨{\ensuremath{\xi}}^{2}{⟩}_{2;{D}_{s}}={0.184}_{\ensuremath{-}0.012}^{+0.012}$, $⟨{\ensuremath{\xi}}^{3}{⟩}_{2;{D}_{s}}={\ensuremath{-}0.111}_{\ensuremath{-}0.012}^{+0.007}$, and $⟨{\ensuremath{\xi}}^{4}{⟩}_{2;{D}_{s}}={0.075}_{\ensuremath{-}0.005}^{+0.005}$. Using those moments, the ${\ensuremath{\phi}}_{2;{D}_{s}}$ is then constructed by using the light-cone harmonic oscillator model. As an application, we calculate the transition form factor ${f}_{+}^{{B}_{s}\ensuremath{\rightarrow}{D}_{s}}({q}^{2})$ within the light-cone sum rules (LCSR) approach by using a right-handed chiral current, in which the terms involving ${\ensuremath{\phi}}_{2;{D}_{s}}$ dominate the LCSR. It is noted that the extrapolated ${f}_{+}^{{B}_{s}\ensuremath{\rightarrow}{D}_{s}}({q}^{2})$ agrees with the lattice QCD prediction. After extrapolating the transition form factor to the physically allowable ${q}^{2}$ region, we calculate the branching ratio and the CKM matrix element, which give $\mathcal{B}({\overline{B}}_{s}^{0}\ensuremath{\rightarrow}{D}_{s}^{+}\ensuremath{\ell}{\ensuremath{\nu}}_{\ensuremath{\ell}})=({2.03}_{\ensuremath{-}0.49}^{+0.35})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ and $|{V}_{cb}|=({40.00}_{\ensuremath{-}4.08}^{+4.93})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$.

Newly discovered $$\Xi _c^{0}$$ resonances and their parameters

The aim of the present article is investigation of the newly observed resonances $\Xi_c(2923)^{0}$, $\Xi_c(2939)^{0}$, and $\Xi_c(2965)^{0}$ which are real candidates to charm-strange baryons. To this end, we calculate the mass and pole residue of the ground-state and excited $1P$ and $2S$ spin-$% 1/2 $ flavor-sextet baryons $\Xi_{c}^{\prime 0}$, $\Xi_{c}^{\prime 0}(1/2^{-})$ and $\Xi_{c}^{\prime 0}(1/2^{+})$ with quark content $csd$, respectively. The masses and pole residues of the ground-state and excited spin-$3/2$ baryons $\Xi_{c}^{\star 0}$ are found as well. Spectroscopic parameters of these particles are computed in the context of the QCD two-point sum rule method. Widths of the excited baryons are evaluated through their decays to final states $\Lambda_{c}^{+}K^{-}$ and $% \Xi_{c}^{\prime 0}\pi$. These processes are explored by means of the full QCD light-cone sum rule method necessary to determine strong couplings at relevant vertices. Obtained predictions for the masses and widths of the four excited baryons, as well as previous results for $1P$ and $2S$ flavor-antitriplet spin-1/2 particles $\Xi_c^{0}$ are confronted with available experimental data on $\Xi_{c}^{0}$ resonances to fix their quantum numbers. Our comparison demonstrates that the resonances $\Xi_c(2923)^{0}$ and $\Xi_c(2939)^{0}$ can be considered as $1P$ excitations of the spin-$1/2$ flavor-sextet and spin-$3/2$ baryons, respectively. The resonance $\Xi _{c}(2965)^{0}$ may be interpreted as the excited $2S$ state of either spin-$% 1/2$ flavor-sextet or antitriplet baryon.

Extending the application of the light-cone sum rules method to low momenta using QCD renormalization-group summation: Theory and phenomenology

We show that using renormalization-group summation to generate the QCD radiative corrections to the $\pi-\gamma$ transition form factor, calculated with lightcone sum rules (LCSR), renders the strong coupling free of Landau singularities while preserving the QCD form-factor asymptotics. This enables a reliable applicability of the LCSR method to momenta well below 1 GeV$^2$. This way, one can use the new preliminary BESIII data with unprecedented accuracy below 1.5 GeV$^2$ to fine tune the prefactor of the twist-six contribution. Using a combined fit to all available data below 3.1 GeV$^2$, we are able to determine all nonperturbative scale parameters and a few Gegenbauer coefficients entering the calculation of the form factor. Employing these ingredients, we determine a pion distribution amplitude with conformal coefficients $(b_2,b_4)$ that agree at the $1\sigma$ level with the data for $Q^2 \leqslant 3.1$ GeV$^2$ and fulfill at the same time the lattice constraints on $b_2$ at N$^3$LO together with the constraints from QCD sum rules with nonlocal condensates.The form-factor prediction calculated herewith reproduces the data below 1 GeV$^2$ significantly better than analogous predictions based on a fixed-order power-series expansion in the strong coupling constant.

Tensor form factors of [formula omitted] state via light-cone QCD

We have achieved the isovector and isoscalar tensor form factors of the N(1535) state in the framework of the light-cone QCD sum rule approach. In numerical computations, we have considered the most general forms of the interpolating current for the nucleon and the tensor current together with the distribution amplitudes of the N(1535) resonance. We have shown that the squared momentum transfer, Q2, dependence of N(1535) tensor form factors is characterized by a multipole fit function. Our results provide a perspective of the momentum dependence of the tensor form factors and can help to improve our understanding of the internal structure of nucleon states.

Light-cone sum rules for proton decay

We estimate the form factors that parametrise the hadronic matrix elements of proton-to-pion transitions with the help of light-cone sum rules. These form factors are relevant for semi-leptonic proton decay channels induced by baryon-number violating dimension-six operators, as typically studied in the context of grand unified theories. We calculate the form factors in a kinematical regime where the momentum transfer from the proton to the pion is space-like and extrapolate our final results to the regime that is relevant for proton decay. In this way, we obtain estimates for the form factors that show agreement with the state-of-the-art calculations in lattice QCD, if systematic uncertainties are taken into account. Our work is a first step towards calculating more involved proton decay channels where lattice QCD results are not available at present.

Chiral dynamics and S-wave contributions in {bar{B}}^0/D^0 rightarrow pi ^{pm }eta l^{mp } nu decays

In this work, we analyze the semi-leptonic decays bar{B}^0/D^0 rightarrow (a_0(980)^{pm }rightarrow pi ^{pm }eta ) l^{mp } nu within light-cone sum rules. The two and three-body light-cone distribution amplitudes (LCDAs) of the B meson and the only available two-body LCDA of the D meson are used. To include the finite-width effect of the a_0(980), we use a scalar form factor to describe the final-state interaction between the pi eta mesons, which was previously calculated within unitarized Chiral Perturbation Theory. The result for the decay branching fraction of the D^0 decay is in good agreement with that measured by the BESIII Collaboration, while the branching fraction of the {bar{B}}^0 decay can be tested in future experiments.

Strong $$ B _{QQ'}^* B_{QQ'} V $$ vertices and the radiative decays of $$ B _{QQ}^* \rightarrow B_{QQ} \gamma $$ in the light-cone sum rules

The strong coupling constants of spin-3/2 to spin-1/2 doubly heavy baryon transitions with light vector mesons are estimated within the light-cone QCD sum rules method. Moreover, using the vector-meson dominance ans\"atz, the widths of radiative decays $B_{QQ}^* \to B_{QQ} \gamma$ are calculated. The results for the said decay widths are compared to the predictions of other approaches.

Vector resonance X1(2900) and its structure

The new vector resonance X1(2900) observed recently by LHCb in the D−K+ invariant mass distribution in the decay B+→D+D−K+ is studied to uncover internal structure of this state, and calculate its physical parameters. In the present paper, the resonance X1(2900) is modeled as an exotic vector state, JP=1−, built of the light diquark uTCγ5d and heavy antidiquark c‾γμγ5Cs‾T. The mass and current coupling of X1(2900) are computed using the QCD two-point sum rule approach by taking into account various vacuum condensates up to dimension 10. The width of the resonance X1(2900) is saturated by two decay channels X1→D−K+ and X1→D‾0K0. The strong couplings g1 and g2 corresponding to the vertices X1D−K+ and X1D‾0K0 are evaluated in the context of the QCD light-cone sum rule method and technical tools of the soft-meson approximation. Results for the mass of the resonance X1(2900)m=(2890±122)MeV, and for its full width Γfull=(93±13)MeV are smaller than their experimental values reported by the LHCb collaboration. Nevertheless, by taking into account theoretical and experimental errors of investigations, interpretation of the state X1(2900) as the vector tetraquark does not contradict to the LHCb data. We also point out that analysis of the invariant mass distribution D+K+ in the same decay B+→D+D−K+ may reveal doubly charged four-quark structures [uc][s‾d‾].

Magnetic dipole moments of the hidden-charm pentaquark states: P_c(4440), P_c(4457) and P_{cs}(4459)

In this work, we employ the light-cone QCD sum rule to calculate the magnetic dipole moments of the P_c(4440), P_c(4457) and P_{cs}(4459) pentaquark states by considering them as the diquark–diquark–antiquark and molecular pictures with quantum numbers J^P = frac{3}{2}^-, J^P = frac{1}{2}^- and J^P = frac{1}{2}^-, respectively. In the analyses, we use the diquark–diquark–antiquark and molecular form of interpolating currents, and photon distribution amplitudes to obtain the magnetic dipole moment of pentaquark states. Theoretical examinations on magnetic dipole moments of the hidden-charm pentaquark states, are essential as their results can help us better figure out their substructure and the dynamics of the QCD as the theory of the strong interaction. As a by product, we extract the electric quadrupole and magnetic octupole moments of the P_c(4440) pentaquark. These values show a non-spherical charge distribution.

Strong vertices of doubly heavy spin- 3/2 –spin- 1/2 baryons with light mesons in light-cone QCD sum rules

In this paper, we analyze the doubly heavy spin-3/2--spin-1/2 baryons and light meson vertices within the method of light-cone QCD sum rules. These vertices are parametrized in terms of one (three) coupling constant(s) for the pseudoscalar (vector) mesons. The said coupling constants are calculated for all possible transitions. The results presented here can serve to be useful information in experimental as well as theoretical studies of the properties of doubly heavy baryons.

Phenomenology of τ−→π−ντγ using light cone sum rules

We present the study of radiative tau decay (${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\nu}}_{\ensuremath{\tau}}\ensuremath{\gamma}$), computing the structure dependent contribution using light cone sum rules. This decay includes the same form factors as the radiative pion decay with the crucial difference that the momentum transfer squared, $t$, between the pion-photon system is positive, which makes these form factors timelike and also as $t$ can now take values up to ${m}_{\ensuremath{\tau}}^{2}$, it can produce real hadronic resonances. The analytical form for these form factors has been calculated using the light cone sum rules method and the invariant mass spectrum in the $\ensuremath{\pi}\ensuremath{-}\ensuremath{\gamma}$ system and the decay width are presented. The structure dependent parameter, $\ensuremath{\gamma}$, the ratio of the axial vector to vector form factor is found to be in good agreement with the experimental determination.

Revisiting the production of J/ψ+ηc via the e+e− annihilation within the QCD light-cone sum rules

We make a detailed study on the typical production channel of double charmoniums, $e^+e^-\to J/\psi+\eta_c$, at the center-of-mass collision energy $\sqrt{s}=10.58$ GeV. The key component of the process is the form factor $F_{\rm VP}(q^2)$, which has been calculated within the QCD light-cone sum rules (LCSR). To improve the accuracy of the derived LCSR, we keep the $J/\psi$ light-cone distribution amplitude up to twist-4 accuracy. Total cross sections for $e^+e^-\to J/\psi+\eta_c$ at three typical factorization scales are $\sigma|_{\mu_s} = 22.53^{+3.46}_{-3.49}~{\rm fb}$, $\sigma|_{\mu_k} = 21.98^{+3.35}_{-3.38}~{\rm fb}$ and $\sigma|_{\mu_0} = 21.74^{+3.29}_{-3.33}~{\rm fb}$, respectively. The factorization scale dependence is small, and those predictions are consistent with the BABAR and Belle measurements within errors.

Revisit to the b → cτν transition: In and beyond the SM

We perform an analysis of the b→cτν data, including R(D(⁎)), R(J/ψ), Pτ(D⁎) and FLD⁎, within and beyond the Standard Model (SM). We fit the B→D(⁎) hadronic form factors in the HQET parametrization to the lattice and the light-cone sum rule (LCSR) results, applying the general strong unitarity bounds corresponding to JP=1−, 1+, 0− and 0+. Using the obtained HQET relations between helicity amplitudes, we give the strong unitarity bounds on individual helicity amplitudes, which can be used in the BGL fits. Using the fitted form factors and taking into account the most recent Belle measurement of R(D(⁎)) we investigate the model-independent and the leptoquark model explanations of the b→cτν anomalies. Specifically, we consider the one-operator, the two-operator new physics (NP) scenarios and the NP models with a single R2, S1 or U1 leptoquark which is supposed to be able to address the b→cτν anomalies, and our results show that the R2 leptoquark model is in tension with the limit B(Bc→τν)<10%. Furthermore, we give predictions for the various observables in the SM and the NP scenarios/leptoquark models based on the present form factor study and the analysis of NP.

Determination of the possible quantum numbers for the newly observed \u039eb(6227)0 state

The LHCb Collaboration recently reported the observation of a new excited bottom baryon Ξb(6227)0 and announced an improvement in the measurements related to the previously observed Ξb(6227)− state. We conduct an analysis for Ξb(6227)0 state considering it as isospin partner of the Ξb(6227)− resonance and possibly 1P or 2S excited state with spin J = frac{3}{2} . The corresponding masses for both possibilities have consistent results with the experimental data, indicating that only with the mass sum rules, one can not make exact decision on the nature and quantum numbers of this state. To go further, the decays of these possible excited states to {Xi}_b^{-}{pi}^{+} final state are also considered and the relevant strong coupling constants are extracted from the light cone sum rules. The obtained decay width values support the possibility of Ξb(6227)0 to be the 1P excited state of Ξb(5945)0 baryon.

Gravitational formfactors of the ρ , π , and K mesons in the light-cone QCD sum rules

Taking into account only the quark part of the energy-momentum tensor, the gravitational form-factors of the $ \pi $ and $ K $ mesons are calculated within the light-cone sum rules method using the distribution amplitudes of these pseudoscalar mesons. The $ Q^2 $-dependence of the relevant form-factors are obtained. Moreover, the mean square mass radii of $ \pi $ and $ K $ mesons are calculated and we find that $ \sqrt{\langle r_{\pi}^2 \rangle} = 0.31 {\rm\ fm} $ and $ \sqrt{\langle r_{K}^2 \rangle} = 0.24 {\rm\ fm} $, respectively. We compare our results for gravitational form-factors with the existing literature results. We obtain that our results on $ \sqrt{\langle r_\pi^2 \rangle} $ are in good agreement with the predictions of NJL model, AdS/QCD model, and other models as well as with the existing experimental data.

The D\u2217D\u03c0 and B\u2217B\u03c0 couplings from light-cone sum rules

We revisit the calculation of the strong couplings D∗Dπ and B∗Bπ from the QCD light-cone sum rules using the pion light-cone distribution amplitudes. The accuracy of the correlation function, calculated from the operator product expansion near the light-cone, is upgraded by taking into account the gluon radiative corrections to the twist-3 terms. The double spectral density of the correlation function, including the twist-2, 3 terms at mathcal{O}left({alpha}_sright) and the twist-4 LO terms, is presented in an analytical form for the first time. This form allows us to use various versions of the quark-hadron duality regions in the double dispersion relation underlying the sum rules. We predict {g}_{D^{ast } Dpi}={14.1}_{-1.2}^{+1.3} and {g}_{B^{ast } Bpi}={30.0}_{-2.4}^{+2.6} when the decay constants of heavy mesons entering the light-cone sum rule are taken from lattice QCD results. We compare our results with the experimental value for the charmed meson coupling and with the lattice QCD calculations.