Light Cone QCD Sum Rules Research Articles

Theory determination of varvec{bar{B}rightarrow D^{(*)}ell ^-bar{nu }} form factors at varvec{mathcal {O}(1/m_c^2)}

We carry out an analysis of the full set of ten bar{B}rightarrow D^{(*)} form factors within the framework of the Heavy-Quark Expansion (HQE) to order mathcal {O}left( alpha _s,,1/m_b,,1/m_c^2right) , both with and without the use of experimental data. This becomes possible due to a recent calculation of these form factors at and beyond the maximal physical recoil using QCD light-cone sum rules, in combination with constraints from lattice QCD, QCD three-point sum rules and unitarity. We find good agreement amongst the various theoretical results, as well as between the theoretical results and the kinematical distributions in bar{B}rightarrow D^{(*)}lbrace e^-,mu ^-rbrace bar{nu } measurements. The coefficients entering at the 1/m_c^2 level are found to be of mathcal {O}(1), indicating convergence of the HQE. The phenomenological implications of our study include an updated exclusive determination of |V_{cb}| in the HQE, which is compatible with both the exclusive determination using the BGL parametrization and with the inclusive determination. We also revisit predictions for the lepton-flavour universality ratios R_{D^{(*)}}, the tau polarization observables P_tau ^{D^{(*)}}, and the longitudinal polarization fraction F_L. Posterior samples for the HQE parameters are provided as ancillary files, allowing for their use in subsequent studies.

Decay modes of the scalar exotic meson Tbs;u¯d¯−

We investigate the semileptonic decay of the scalar tetraquark $T_{bs; \overline{u}\overline{d}}^{-}$ to final state $T_{cs;\overline{u}\overline{d} }^{0} l \overline{\nu}_l$, which proceeds due to the weak transition $b \to c l \overline{\nu}_l$. For these purposes, we calculate the spectroscopic parameters of the final-state scalar tetraquark $T_{cs;\overline{u}\overline{ d}}^{0}$. In calculations we use the QCD sum rule method by taking into account the quark, gluon, and mixed condensates up to dimension 10. The mass of the $T_{cs;\overline{u}\overline{d}}^{0}$ obtained in the present work $( 2878 \pm 128 )~\mathrm{MeV}$ indicates that it is unstable against the strong interactions, and can decay to the mesons $D^{0}\overline{K}^{0}$ and $D^{+}K^{-}$. Partial widths of these $S$-wave modes as well as the full width of the tetraquark $T_{cs;\overline{u}\overline{d}}^{0}$ are found by means of the QCD light-cone sum rule method and technical tools of the soft-meson approximation. The partial widths of the main semileptonic processes $T_{bs;\overline{u}\overline{d}}^{-} \to T_{cs;\overline{u} \overline{d}}^{0}l\overline{\nu}_l$, $l=e, \mu$, and $\tau$ are computed by employing the weak form factors $G_{1}(q^2)$ and $G_{2}(q^2)$, which are extracted from the QCD three-point sum rules. We also trace back the weak transformations of the stable tetraquark $T_{bb;\overline{u}\overline{d} }^{-} $ to conventional mesons. The obtained results for the full width $ \Gamma_{\mathrm{full}}=(3.28\pm 0.60) \times 10^{-10}~\mathrm{MeV} $ and mean lifetime $\tau=2.01_{-0.31}^{+0.44}~\mathrm{ps}$ of $T_{bs;\overline{u} \overline{d}}^{-}$, as well as predictions for decay channels of the tetraquark $T_{bb;\overline{u}\overline{d}}^{-}$ can be used in experimental studies of these exotic states. \end{abstract}

B→T transition form factors in light-cone sum rules

We present a new calculation of the semileptonic tree-level and flavor-changing neutral current form factors describing $B$-meson transitions to tensor mesons $T=D_2^*,K_2^*,a_2,f_2$ ($J^{P}=2^{+}$). We employ the QCD Light-Cone Sum Rules approach with $B$-meson distribution amplitudes. We go beyond the leading-twist accuracy and provide analytically, for the first time, higher-twist corrections for the two-particle contributions up to twist four terms. We observe that the impact of higher twist terms to the sum rules is noticeable. We study the phenomenological implications of our results on the radiative ${B} \to K_2^{*}\gamma$ and semileptonic ${B} \to D_2^* \ell {\bar \nu}_\ell$, ${B} \to K_2^{*}\ell^+\ell^-$ decays.

Light axial-vector and vector resonances X(2100) and X(2239)

We study features of the resonances X(2100) and X(2239) by treating them as the axial-vector and vector tetraquarks with the quark content sss‾s‾, respectively. The spectroscopic parameters of these exotic mesons are calculated in the framework of the QCD two-point sum rule method. Obtained prediction for the mass m=(2067±84)MeV of the axial-vector state is in excellent agreement with the mass of the structure X(2100) recently observed by the BESIII Collaboration in the decay J/ψ→ϕηη′ as the resonance in the ϕη′ mass spectrum. We also explore the decays X(2100)→ϕη′ and X(2100)→ϕη using QCD light-cone sum rule approach and technical methods of the soft-meson approximation. The width of the axial-vector tetraquark, Γ=(130.2±30.1)MeV, saturated by these two processes is comparable with the measured full width of the resonance X(2100). Our prediction for the vector sss‾s‾ tetraquark's mass m˜=(2283±114)MeV is consistent with the experimental result (2239.2±7.1±11.3)MeV of the BESIII Collaboration for the mass of the resonance X(2239).

N*(1535)→N transition form-factors due to the axial current

The form-factors for the transition $ N^*(1535)\to N $ induced by isovector and isoscalar axial currents within the framework of light-cone QCD sum rules by using the most general form of the interpolating current are calculated. In numerical calculations, we use two sets of values of input parameters. It is observed that the $ Q^2 $ dependence of the form-factor $ G_A $ can be described by the dipole form. Moreover, the form-factors $ G_P^{(S)} $ are found to be highly sensitive to the variations in the auxiliary parameter $ \beta $.

Semileptonic D(s) → Aℓ+ν and nonleptonic D → K1(1270, 1400)π decays in LCSR

In this work, the transition form factors are calculated for the semileptonic D(s) → Aℓ+ν where A = a1, b1, K1(1270, 1400), i.e. , , and in the frame work of the light-cone QCD sum rules (LCSR) approach up to the twist-3 distribution amplitudes (DAs). Since the masses of these axial vector mesons are comparable to the charm quark mass, we keep out in our calculations all terms including mA/mc (all orders) in expansion of two-parton DAs. Branching ratio values are estimated for the semileptonic D(s) → Aℓν and nonleptonic D→K1 (1270, 1400) π decays. A comparison is also made between our results and predictions of other methods and the existing experimental values.

Determination of the quantum numbers of Σb(6097)± via their strong decays

The progresses in the experimental sector have been the harbinger of the observations of many new hadrons. Very recently, LHCb Collaboration announced the observation of two new $\Sigma_b(6097)^{\pm}$ states in the $\Lambda^0_b\pi^{\pm}$ invariant mass distribution, which are considered as the excited states of the ground state $\Sigma^{(*)}_b$ baryon. Though, almost all of the ground state baryons have been observed, having a limited number of excited states observed so far makes them intriguing. Understanding the properties of the excited baryons improve our knowledge on the strong interaction as well as the nature and internal structures of these baryons. To specify the quantum numbers of the $\Sigma_b(6097)^{\pm}$ an analysis on their strong decays to $\Lambda_b^0$ and $\pi^{\pm}$ is performed within the light cone QCD sum rule formalism. To this end, they are considered as possible $1P$ or $2S$ excitation of either the ground state $\Sigma_b$ baryon with $J=\frac{1}{2}$ or $\Sigma_b^{*}$ baryon with $J=\frac{3}{2}$. The corresponding masses are also calculated considering the same scenarios for their quantum numbers. The results of the analyses indicate that the $\Sigma_b(6097)^{\pm}$ baryons are excited $1P$ baryons having quantum numbers $J^P=\frac{3}{2}^-$.

Study of the Lambda _{b} rightarrow N^*ell ^+ ell ^- decay in light cone sum rules

The form factors of the Lambda _{b} rightarrow N^*ell ^+ ell ^- decay are calculated in the framework of the light cone QCD sum rules. In the calculations the contribution of the negative parity Lambda _b^* baryon is eliminated by constructing the sum rules for different Lorentz structures. Furthermore the branching ratio of the semileptonic Lambda _b rightarrow N^*ell ^+ ell ^- decay is calculated. The numerical study for the branching ratio of the Lambda _{b} rightarrow N^*ell ^+ ell ^- decay indicates that it is quite large and could be measurable at future planned experiments to be conducted at LHCb.

Radiative decays of the p-wave charmed heavy baryons

The radiative decays of the p-wave charmed heavy baryons to the ground state baryon states are studied in the framework of the light cone QCD sum rules method. Firstly, the transition form factors that describe these transitions are estimated and then, using these form factors, the corresponding decay widths are calculated. A comparison of our results for the decay widths with those predicted by the other approaches existing in the literature is performed.

New charged resonance Z_{c}^{-}(4100): the spectroscopic parameters and width

The mass, coupling and width of the newly observed charged resonance Z_{c}^{-}(4100) are calculated by treating it as a scalar four-quark system with a diquark–antidiquark structure. The mass and coupling of the state Z_{c}^{-}(4100) are calculated using the QCD two-point sum rules. In these calculations we take into account contributions of the quark, gluon and mixed condensates up to dimension ten. The spectroscopic parameters of Z_{c}^{-}(4100) obtained by this way are employed to study its S-wave decays to eta _c(1S)pi ^{-}, eta _c(2S)pi ^{-}, D^{0}D^{-}, and J/psi rho ^{-} final states. To this end, we evaluate the strong coupling constants corresponding to the vertices Z_{c}eta _c(1S)pi ^{-}, Z_{c}eta _c(2S)pi ^{-}, Z_{c}D^{0}D^{-}, and Z_{c}J/psi rho ^{-} respectively. The couplings g_{Z_ceta _{c1} pi }, g_{Z_{c}eta _{c2} pi }, and g_{Z_{c}DD} are computed by means of the QCD three-point sum rule method, whereas g_{Z_{c}J/psi rho } is obtained from the QCD light-cone sum rule approach and soft-meson approximation. Our results for the mass m=(4080 pm 150)~text {MeV} and total width Gamma =(147 pm 19)~mathrm { MeV} of the resonance Z_{c}^{-}(4100) are in excellent agreement with the existing LHCb data.

Magnetic moments of doubly heavy baryons in light-cone QCD

The magnetic dipole moments of the spin- doubly heavy baryons are extracted in the framework of the light-cone QCD sum rule using the photon distribution amplitudes. The electromagnetic properties of the doubly heavy baryons encodes important information of their internal structure and geometric shape. The results for the magnetic dipole moments of doubly heavy baryons acquired in this work are compared with the predictions of the other theoretical approaches. The agreement of the estimations with some (but not all) theoretical estimations is good.

Radiative decays of the heavy tensor mesons in light cone QCD sum rules

The transition form factors of the radiative decays of the heavy tensor mesons to heavy pseudoscalar and heavy vector mesons are calculated in the framework of the light cone QCD sum rules method at the point $Q^2=0$. Using the obtained values of the transition form factors at the point $Q^2=0$ the corresponding decay widths are estimated. The results show that the radiative decays of the heavy--light tensor mesons can be measurable in the future planned experiments at LHCb.

QCD calculations of B \u2192 \u03c0, K form factors with higher-twist corrections

We update QCD calculations of B → π, K form factors at large hadronic recoil by including the subleading-power corrections from the higher-twist B-meson light-cone distribution amplitudes (LCDAs) up to the twist-six accuracy and the strange-quark mass effects at leading-power in Λ/mb from the twist-two B-meson LCDA ϕB+(ω, μ). The higher-twist corrections from both the two-particle and three-particle B-meson LCDAs are computed from the light-cone QCD sum rules (LCSR) at tree level. In particular, we construct the local duality model for the twist-five and -six B-meson LCDAs, in agreement with the corresponding asymptotic behaviours at small quark and gluon momenta, employing the method of QCD sum rules in heavy quark effective theory at leading order in αs. The strange quark mass effects in semileptonic B → K form factors yield the leading-power contribution in the heavy quark expansion, consistent with the power-counting analysis in soft-collinear effective theory, and they are also computed from the LCSR approach due to the appearance of the rapidity singularities. We demonstrate explicitly that the SU(3)-flavour symmetry breaking effects between B → π and B → K form factors, free of the power suppression in Λ/mb, are suppressed by a factor of {alpha}_sleft(sqrt{m_bLambda}right) in perturbative expansion, and they also respect the large-recoil symmetry relations of the heavy-to-light form factors at least at one-loop accuracy. An exploratory analysis of the obtained sum rules for B → π, K form factors with two distinct models for the B-meson LCDAs indicates that the dominant higher-twist corrections are from the Wandzura-Wilczek part of the two-particle LCDA of twist five gB−(ω, μ) instead of the three-particle B-meson LCDAs. The resulting SU(3)-flavour symmetry violation effects of B → π, K form factors turn out to be insensitive to the non-perturbative models of B-meson LCDAs. We further explore the phenomenological aspects of the semileptonic B → πℓν decays and the rare exclusive processes B → Kνν, including the determination of the CKM matrix element |Vub|, the normalized differential q2 distributions and precision observables defined by the ratios of branching fractions for the above-mentioned two channels in the same intervals of q2.

B \u2192P and B \u2192V form factors from B-meson light-cone sum rules beyond leading twist

We provide results for the full set of form factors describing semileptonic B-meson transitions to pseudoscalar mesons π, K, overline{D} and vector mesons ρ, K∗, {overline{D}}^{ast } . Our results are obtained within the framework of QCD Light-Cone Sum Rules with B-meson distribution amplitudes. We recalculate and confirm the results for the leading-twist two-particle contributions in the literature. Furthermore, we calculate and provide new expressions for the two-particle contributions up to twist four. Following new developments for the three-particle distribution amplitudes, we calculate and provide new results for the complete set of three-particle contributions up to twist four. The form factors are computed numerically at several phase space points using up-to-date input parameters, including correlations across phase space points and form factors. We use a model ansatz for all contributing B-meson distribution amplitudes that is self-consistent up to twist-four accuracy. We find that the higher-twist two-particle contributions have a substantial impact on the results, and dominate over the three-particle contributions. Our numerical results, including correlations, are provided as machine-readable files in the supplementary material. We discuss the qualitative phenomenological impact of our results on the present b anomalies.

Structure of the Ξb(6227)− resonance

We explore the recently observed $\Xi_b(6227)^{-}$ resonance to fix its quantum numbers. To this end, we consider various possible scenarios: It can be considered as either 1P/2S excitations of the $\Xi_b^-$ and $\Xi_b'(5935)^{-}$ ground state baryons with spin-$\frac{1}{2}$ or 1P/2S excitations of the ground state $\Xi_b(5955)^{-}$ with spin-$\frac{3}{2}$. We calculate the masses of the possible angular-orbital $1P$ and $2S$ excited states corresponding to each channel employing the QCD sum rule technique. It is seen that all the obtained masses are in agreement with the experimentally observed value, implying that the mass calculations are not enough to distinguish the quantum numbers of the state under question. Therefore, we extend the analysis to investigate the possible decays of the same excited states into $\Lambda_b^0 K^-$ and $\Xi_b^-\pi$. Using the light cone QCD sum rule method, we calculate the corresponding strong coupling constants, which are used to extract the decay widths of the modes under consideration. Our results on decay widths indicate that the $\Xi_b(6227)^{-}$ is $1P$ angular-orbital excited state of the $\Xi_b(5955)^{-}$ baryon with quantum numbers $J^P=\frac{3}{2}^{-}$.

Nature of the Omega (2012) through its strong decays

We extend our previous analysis on the mass of the recently discovered Omega (2012) state by investigation of its strong decays and calculation of its width employing the method of light cone QCD sum rule. Considering two possibilities for the quantum numbers of Omega (2012) state, namely 1P orbital excitation with J^P=frac{3}{2}^- and 2S radial excitation with J^P=frac{3}{2}^+, we obtain the strong coupling constants defining the Omega (1P/2S)rightarrow Xi K decays. The results of the coupling constants are then used to calculate the decay width corresponding to each possibility. Comparison of the obtained results on the total widths in this work with the experimental value and taking into account the results of our previous mass prediction on the Omega (2012) state, we conclude that this state is 1P orbital excitation of the ground state Omega baryon, whose quantum numbers are J^P=frac{3}{2}^-.

The electromagnetic multipole moments of the possible charm-strange pentaquarks in light-cone QCD

We investigate the electromagnetic properties of possible charm-strange pentaquarks in the framework of the light-cone QCD sum rule using the photon distribution amplitudes. In particular, by calculating the corresponding electromagnetic form factors defining the radiative transitions under consideration we estimate the magnetic dipole and electric quadrupole moments of the pentaquark systems of a charm, an anti-strange and three light quarks. We observe that the values of magnetic dipole moments are considerably large, however, the quadrupole moments are very small. Any future measurements of the electromagnetic parameters under consideration and comparison of the obtained data with the theoretical predictions can shed light on the quark–gluon organization as well as the nature of the pentaquarks.

Form factors for the rare Λb(Λb*)→Nℓ+ℓ− decays in light cone QCD sum rules

Form factors of the rare $\Lambda_{b}(\Lambda_{b}^*)\to N\ell^{+}\ell^{-}$ decays are calculated in the framework of the light cone QCD sum rules by taking into account of the contributions from the negative parity baryons. Using the obtained results on the form factors, the branching ratios of the considered decays are estimated. The numerical survey for the branching ratios of the $\Lambda_b \rar N\ell^+\ell^- $ and $\Lambda_b^\ast \rar N\ell^+\ell^- $ decays indicate that these transitions could be measurable in LHCb in near future. Comparison of our predictions on the form factors and branching ratios with those existing in the literature is also performed.

The strong decays of the light scalar mesons f0(500) and f0(980)

The partial width of the decay channels f0(500)→ππ, f0(980)→ππ and f0(980)→KK¯ are calculated using QCD light-cone sum rules method and a technique of the soft meson approximation. The scalar particles are treated as mixtures of the heavy |H〉=([su][s¯u¯]+[sd][s¯d¯])/2 and light |L〉=[ud][u¯d¯] scalar diquark–antidiquark components. Obtained results for the full width of the f0(500) meson Γth.=434.7±72.3MeV and for the f0(980) meson Γth.=42.12±6.70MeV are compared with the world averages for these parameters, and a reasonable agreement between them is found.

Radiative leptonic decay B \u2192 \u03b3\u2113\u03bd\u2113 with subleading power corrections

We reconsider the QCD predictions for the radiative decay B → γℓνℓ with an energetic photon in the final state by taking into account the 1/Eγ, 1/mb power-suppressed hard-collinear and soft corrections from higher-twist B-meson light-cone distribution amplitudes (LCDAs). The soft contribution is estimated through a dispersion relation and light-cone QCD sum rules. The analysis of theoretical uncertainties and the dependence of the decay form factors on the leading-twist LCDA ϕ+(ω) shows that the latter dominates. The radiative leptonic decay is therefore well suited to constrain the parameters of ϕ+(ω), including the first inverse moment, 1/λB, from the expected high-statistics data of the BELLE II experiment.