Light Cone QCD Sum Rules Research Articles

Analysis of the structure of Xi (1690) through its decays

The mass and pole residue of the first orbitally and radially excited Xi state as well as the ground state residue are calculated by means of the two-point QCD sum rules. Using the obtained results for the spectroscopic parameters, the strong coupling constants relevant to the decays Xi (1690)rightarrow Sigma K and Xi (1690) rightarrow Lambda K are calculated within the light-cone QCD sum rules and width of these decay channels are estimated. The obtained results for the mass of {widetilde{Xi }} and ratio of the Br(widetilde{Xi }rightarrow Sigma K)/Br(widetilde{Xi }rightarrow Lambda K), with widetilde{Xi } representing the orbitally excited state in Xi channel, are in nice agreement with the experimental data of the Belle Collaboration. This allows us to conclude that the Xi (1690) state, most probably, has negative parity.

Electromagnetic multipole moments of the $$P_c^+(4380)$$ P c + ( 4380 ) pentaquark in light-cone QCD

We calculate the electromagnetic multipole moments of the P_c^+(4380) pentaquark by modeling it as the diquark–diquark–antiquark and {bar{D}}^*Sigma _c molecular state with quantum numbers J^P = frac{3}{2}^-. In particular, the magnetic dipole, electric quadrupole and magnetic octupole moments of this particle are extracted in the framework of light-cone QCD sum rule. The values of the electromagnetic multipole moments obtained via two pictures differ substantially from each other, which can be used to pin down the underlying structure of P_c^+(4380). The comparison of any future experimental data on the electromagnetic multipole moments of the P_c^+(4380) pentaquark with the results of the present work can shed light on the nature and inner quark organization of this state.

Longitudinal leading-twist distribution amplitude of the J/ψ meson within the background field theory

We make a detailed study on the $J/\psi$ meson longitudinal leading-twist distribution amplitude $\phi_{2;J/\psi}^\|$ by using the QCD sum rules within the background field theory. By keeping all the non-perturbative condensates up to dimension-six, we obtain accurate QCD sum rules for the moments $\langle\xi_{n;J/\psi}^\|\rangle$. The first three ones are $\langle\xi_{2;J/\psi}^\|\rangle=0.083(12)$, $\langle\xi_{4;J/\psi}^\|\rangle=0.015(5)$ and $\langle\xi_{6;J/\psi}^\|\rangle=0.003(2)$, leading to a single peaked behavior for $\phi_{2;J/\psi}^\|$ which is sharper than the previous ones around the region of $x\sim0.5$. As an application, we adopt the QCD light-cone sum rules to calculate the $B_c$ meson semileptonic decay $B_c^+ \to J/\psi \ell^+ \nu_\ell$. We obtain $\Gamma(B_c^+ \to J/\psi \ell^+ \nu_\ell) = (89.67^{+24.76}_{-19.06}) \times 10^{-15}~{\rm GeV}$ and $\Re(J/\psi \ell^+ \nu_\ell) = 0.217^{+0.069}_{-0.057}$, which agree with the next-to-leading order pQCD prediction and the new CDF measurement within errors.

The electromagnetic multipole moments of the charged open-flavor states

The electromagnetic multipole moments of the open-flavor states are investigated by assuming a diquark–antidiquark picture for their internal structure and quantum numbers for their spin-parity. In particular, their magnetic and quadrupole moments are extracted in the framework of light-cone QCD sum rule by the help of the photon distribution amplitudes. The electromagnetic multipole moments of the open-flavor states are important dynamical observables, which encode valuable information on their underlying structure. The results obtained for the magnetic moments of different structures are considerably large and can be measured in future experiments. We obtain very small values for the quadrupole moments of states indicating a nonspherical charge distribution.

Magnetic dipole moments of the negative parity J^{PC}=2^{--} mesons in QCD

Magnetic dipole moments of the negative parity light and heavy tensor mesons are calculated within the light cone QCD sum rules method. The results are compared with the positive parity counterparts of the corresponding tensor mesons. The results of the analysis show that the magnetic dipole moments of the negative parity light mesons are smaller compared to those of the positive parity mesons. Contrary to the light meson case, magnetic dipole moments of the negative parity heavy mesons are larger than the ones for the positive parity mesons.

Asymmetries of the B→K*μ+μ− decay and the search of new physics beyond the standard model

In this paper, we compute the forward-backward asymmetry and the isospin asymmetry of the $B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ decay. The $B\ensuremath{\rightarrow}{K}^{*}$ transition form factors (TFFs) are key components of the decay. To achieve a more accurate QCD prediction, we adopt a chiral correlator for calculating the QCD light cone sum rules for those TFFs with the purpose of suppressing the uncertain high-twist distribution amplitudes. Our predictions show that the asymmetries under the standard model and the minimal supersymmetric standard model with minimal flavor violation are close in shape for ${q}^{2}\ensuremath{\ge}6\text{ }\text{ }{\mathrm{GeV}}^{2}$ and are consistent with the Belle, LHCb, and CDF data within errors. When ${q}^{2}<2\text{ }\text{ }{\mathrm{GeV}}^{2}$, their predictions behave quite differently. Thus, a careful study on the $B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ decay within the small ${q}^{2}$ region could be helpful for searching new physics beyond the standard model. As a further application, we also apply the $B\ensuremath{\rightarrow}{K}^{*}$ TFFs to the branching ratio and longitudinal polarization fraction of the $B\ensuremath{\rightarrow}{K}^{*}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ decay within different models.

Magnetic dipole moment of Zb(10610) in light-cone QCD

The magnetic dipole moment of the exotic $Z_b(10610)$ state is calculated within the light cone QCD sum rule method using the diquark-antidiquark and molecule interpolating currents. The magnetic dipole moment is obtained as $\mu_{Z_b}=1.73\pm 0.63~\mu_N$ in diquark-antidiquark picture and $\mu_{Z_b}=1.59\pm 0.58~\mu_N$ in the molecular case. The obtained results in both pictures together with the results of other theoretical studies on the spectroscopic parameters of the $Z_b(10610)$ state may be useful in determination of the nature and quark organization of this state.

Reanalysis of Ωc→Ξc+K- Decay in QCD

The strong coupling constants of newly observed Ωc0 baryons with spins J=1/2 and J=3/2 decaying into Ξc+K- are estimated within light cone QCD sum rules. The calculations are performed within two different scenarios on quantum numbers of Ωc baryons: (a) all newly observed Ωc baryons are negative parity baryons; that is, the Ωc(3000), Ωc(3050), Ωc(3066), and Ωc(3090) have quantum numbers JP=1/2- and JP=3/2- states, respectively; (b) the states Ωc(3000) and Ωc(3050) have quantum numbers JP=1/2- and JP=1/2+, while the states Ωc(3066) and Ωc(3090) have the quantum numbers JP=3/2- and JP=3/2+, respectively. By using the obtained results on the coupling constants, we calculate the decay widths of the corresponding decay. The results on decay widths are compared with the experimental data of LHC Collaboration. We found out that the predictions on decay widths within these scenarios are considerably different from the experimental data; that is, both considered scenarios are ruled out.

The Mass and Decay Properties of the 1−+ Light Hybrid Meson

We calculate the complete form of the dimension-8 condensate contributions in the two-point correlator of the (1−+,0++) light hybrid current considering the operator mixing under renormalization. We find the inclusion these higher power corrections as well as the update of 〈g3G3〉 increase the QCD sum rule mass prediction for the 1−+ light hybrid. The obtained conservative mass range 1.72–2.60 GeV does not favor the π1(1400) and the π1(1600) to be pure hybrid states and suggests the π1(2015) observed by E852 is more likely to have much of a hybrid constituent. We also study the b1π and ρπ decay patterns of the 1−+ light hybrid with light-cone QCD sum rules. We obtain a relatively large partial decay width of the b1π mode, which is consistent with the predictions from the flux tube models and lattice QCD. More interestingly, using the tensor interpolating current we find the partial decay width of the ρπ mode is very small due to the lack of the leading twist contribution in the light-cone expansion of the correlation function.

Uncertainties of the Brightarrow D transition form factor from the D-meson leading-twist distribution amplitude

The Brightarrow D transition form factor (TFF) f^{Brightarrow D}_+(q^2) is determined mainly by the D-meson leading-twist distribution amplitude (DA) , phi _{2;D}, if the proper chiral current correlation function is adopted within the light-cone QCD sum rules. It is therefore significant to make a comprehensive study of DA phi _{2;D} and its impact on f^{Brightarrow D}_+(q^2). In this paper, we calculate the moments of phi _{2;D} with the QCD sum rules under the framework of the background field theory. New sum rules for the leading-twist DA moments leftlangle xi ^nrightrangle _D up to fourth order and up to dimension-six condensates are presented. At the scale mu = 2 ,mathrm{GeV}, the values of the first four moments are: leftlangle xi ^1rightrangle _D = -0.418^{+0.021}_{-0.022}, leftlangle xi ^2rightrangle _D = 0.289^{+0.023}_{-0.022}, leftlangle xi ^3rightrangle _D = -0.178 pm 0.010 and leftlangle xi ^4rightrangle _D = 0.142^{+0.013}_{-0.012}. Basing on the values of leftlangle xi ^nrightrangle _D(n=1,2,3,4), a better model of phi _{2;D} is constructed. Applying this model for the TFF f^{Brightarrow D}_+(q^2) under the light cone sum rules, we obtain f^{Brightarrow D}_+(0) = 0.673^{+0.038}_{-0.041} and f^{Brightarrow D}_+(q^2_{mathrm{max}}) = 1.117^{+0.051}_{-0.054}. The uncertainty of f^{Brightarrow D}_+(q^2) from phi _{2;D} is estimated and we find its impact should be taken into account, especially in low and central energy region. The branching ratio mathcal {B}(Brightarrow Dlbar{nu }_l) is calculated, which is consistent with experimental data.

Subleading power corrections to the pion-photon transition form factor in QCD

We reconsider QCD factorization for the leading power contribution to the γ*γ → π0 form factor Fγ*γ→π0(Q2) at one loop using the evanescent operator approach, and demonstrate the equivalence of the resulting factorization formulae derived with distinct prescriptions of γ5 in dimensional regularization. Applying the light-cone QCD sum rules (LCSRs) with photon distribution amplitudes (DAs) we further compute the subleading power contribution to the pion-photon form factor induced by the “hadronic” component of the real photon at the next-to-leading-order in mathcal{O}left({alpha}_sright) , with both naive dimensional regularization and ’t Hooft-Veltman schemes of γ5. Confronting our theoretical predictions of Fγ*γ→π0 (Q2) with the experimental measurements from the BaBar and the Belle Collaborations implies that a reasonable agreement can be achieved without introducing an “exotic” end-point behaviour for the twist-2 pion DA.

Spectroscopic parameters and decays of the resonance $$Z_b(10610)$$ Z b ( 10610 )

The resonance Z_b(10610) is investigated as the diquark–antidiquark Z_b=[bu][overline{bd}] state with spin–parity J^{P}=1^{+}. The mass and current coupling of the resonance Z_b(10610) are evaluated using QCD two-point sum rule and taking into account the vacuum condensates up to ten dimensions. We study the vertices Z_bUpsilon (nS)pi (n=1,2,3) by applying the QCD light-cone sum rule to compute the corresponding strong couplings g_{Z_bUpsilon (nS)pi } and widths of the decays Z_b rightarrow Upsilon (nS)pi . We explore also the vertices Z_b h_{b}(mP)pi (m=1,2) and calculate the couplings g_{Z_b h_{b}(mP)pi } and the widths of the decay channels Z_b rightarrow h_{b}(mP)pi . To this end, we calculate the mass and decay constants of the h_b(1P) and h_b(2P) mesons. The results obtained are compared with experimental data of the Belle Collaboration.

Magnetic and quadrupole moments of the Zc(3900)

The electromagnetic properties of the tetraquark state $Z_c(3900)$ are investigated in the diquark-antidiquark picture and its magnetic and quadrupole moments are extracted. To this end, the light-cone QCD sum rule in electromagnetic background field is used. The magnetic and quadrupole moments encode the spatial distributions of the charge and magnetization in the particle. The result obtained for the magnetic moment is quite large and can be measured in future experiments. We obtain a nonzero but small value for the quadrupole moment of $Zc(3900)$ indicating a nonspherical charge distribution.

Direct CP asymmetry in D → π−π+ and D → K−K+ in QCD-based approach

We present the first QCD-based calculation of hadronic matrix elements with penguin topology determining direct CP-violating asymmetries in D0→π−π+ and D0→K−K+ nonleptonic decays. The method is based on the QCD light-cone sum rules and does not rely on any model-inspired amplitude decomposition, instead leaning heavily on quark–hadron duality. We provide a Standard Model estimate of the direct CP-violating asymmetries in both pion and kaon modes and their difference and comment on further improvements of the presented computation.

Timelike-helicity B→ππ form factor from light-cone sum rules with dipion distribution amplitudes

We complete the set of QCD light-cone sum rules for $B\to \pi\pi$ transition form factors, deriving a new sum rule for the timelike-helicity form factor $F_t$ in terms of dipion distribution amplitudes. This sum rule, in the leading twist-2 approximation, is directly related to the pion vector form factor. Employing a relation between $F_t$ and other $B\to \pi\pi$ form factors we obtain also the longitudinal-helicity form factor $F_0$. In this way, all four (axial-)vector $B\to \pi\pi$ form factors are predicted from light-cone sum rules with dipion distribution amplitudes. These results are valid for small dipion masses with large momentum.

Study of D→a0(980)e+νe decay in the light-cone sum rules approach

Within the QCD light-cone sum rule (LCSR) approach, we investigate the transition form factors of $D\rightarrow a_0(980)$ up to the twist-3 light-cone distribution amplitudes (LCDAs) of the scalar meson $a_0(980)$ in the two-quark picture. Using these form factors, we calculate the differential decay widths and branching ratios of the $D\rightarrow a_0(980) e^+ \nu_e$ semileptonic decays. We obtain ${\mathcal B}(D^0\rightarrow a_0^- (980) e^+ \nu_e)=(4.08^{+1.37}_{-1.22})\times 10^{-4}$ and ${\mathcal B}(D^+\rightarrow a_0^0 (980) e^+ \nu_e)=(5.40^{+1.78}_{-1.59})\times 10^{-4}$. The results are sensitive to the $a_0(980)$ inner structure. These decays can be searched for at BESIII experiment, and any experimental observations will be useful to identify internal quark contents of the $a_0(980)$ meson, which will shed light on understanding theoretical models.

Bs \u2192 K\u2113\u03bd\u2113 and B(s) \u2192 \u03c0(K)\u2113+\u2113\u2212 decays at large recoil and CKM matrix elements

We provide hadronic input for the B-meson semileptonic transitions to a light pseudoscalar meson at large recoil. The Bs → K form factor calculated from QCD light-cone sum rule is updated, to be used for a |Vub| determination from the Bs → Kℓν width. Furthermore, we calculate the hadronic input for the binned observables of B → πℓ+ℓ− and B → Kℓ+ℓ−. In addition to the form factors, the nonlocal hadronic matrix elements are obtained, combining QCD factorization and light-cone sum rules with hadronic dispersion relations. We emphasize that, due to nonlocal effects, the ratio of branching fractions of these decays is not sufficient for an accurate extraction of the |Vtd/Vts| ratio. Instead, we suggest to determine the Wolfenstein parameters A, ρ, η of the CKM matrix, combining the branching fractions of B → Kℓ+ℓ− and B → πℓ+ℓ− with the direct CP -asymmetry in the latter decay. We also obtain the hadronic matrix elements for a yet unexplored channel Bs → Kℓ+ℓ−.

Light cone distribution amplitudes of excited p -wave heavy quarkonia at leading twist

Leading twist light cone distribution amplitudes (LCDAs) are key ingredients in calculating various hadronic amplitudes using light cone QCD sum rules. This work concentrates on calculating the leading twist LCDAs of P-wave heavy quarkonia. Quark model wavefunctions for the ground, first and second excited states of P-wave charmonia and bottomonia have been calculated, and are used for calculating the relevant LCDAs and leptonic decay constants.

Higher-twist effects in light-cone sum rule for the Brightarrow pi form factor

We calculate the higher-twist corrections to the QCD light-cone sum rule for the B rightarrow pi transition form factor. The light-cone expansion of the massive quark propagator in the external gluonic field is extended to include new terms containing the derivatives of the gluon-field strength. The resulting analytical expressions for the twist-5 and twist-6 contributions to the correlation function are obtained in a factorized approximation, expressed via the product of the lower-twist pion distribution amplitudes and the quark-condensate density. The numerical analysis reveals that new higher-twist effects for the B rightarrow pi form factor are strongly suppressed. This result justifies the conventional truncation of the operator product expansion in the light-cone sum rules up to twist-4 terms.

Exploring the resonances X(4140) and X(4274) through their decay channels

Investigation of the resonances $X(4140)$ and $X(4274)$, which were recently confirmed by the LHCb Collaboration [1], is carried out by treating them as the color triplet and sextet $[cs][\bar{c}\bar {s}]$ diquark-antidiquark states with the spin-parity $J^{P}=1^{+}$, respectively. We calculate the masses and meson-current couplings of these tetraquarks in the context of QCD two-point sum rule method by taking into account the quark, gluon and mixed vacuum condensates up to eight dimensions. We also study the vertices $X(4140)J/\psi\phi$ and $X(4274)J/\psi\phi$, and evaluate corresponding strong couplings $g_{X(4140)J/\psi\phi}$ and $ g_{X(4274)J/\psi\phi}$ by means of QCD light-cone sum rule method, and a technique of the soft-meson approximation. In turn, these couplings contain a required information to determine the width of the $X(4140)\to J/\psi\phi$ and $X(4274) \to J/\psi\phi$ decay channels. We compare our results for the masses and decay widths of the $X(4140)$ and $X(4274)$ resonances with the LHCb data, and alternative theoretical predictions.