QCD Sum Rule Approach Research Articles

Mass spectra of the heavy baryonsΛQandΣQ(*)from QCD sum rules

We use QCD sum rule approach to calculate the masses of the ground-state {lambda}{sub Q} and {sigma}{sub Q}{sup (*)} baryons. Contributions of the operators up to dimension six are included in operator product expansion. The resulting heavy baryonic masses from the calculations are m{sub {lambda}{sub b}}=5.69{+-}0.13 GeV, and m{sub {lambda}{sub c}}=2.31{+-}0.19 GeV for {lambda}{sub Q}; m{sub {sigma}{sub b}}=5.73{+-}0.21 GeV, m{sub {sigma}{sub b}}{sub *}=5.81{+-}0.19 GeV, m{sub {sigma}{sub c}}=2.40{+-}0.31 GeV and m{sub {sigma}{sub c}}{sub *}=2.56{+-}0.24 GeV for {sigma}{sub Q}{sup (*)}, respectively, which are in good agreement with the experimental values.

Weak productions of new charmonium in semileptonic decays ofBc

We study the weak productions of novel heavy mesons, such as eta'(c), h(c), h'(c), X'(c0), X (3940), Y (3940), X (3872), and Y (4260), in the semileptonic B(c) decays. Since there is still no definite answer for the components of X (3940), Y (3940), X (3872), Y (4260) so far, we will assign them as excited charmonium states with the possible quantum numbers constrained by the current experiments. As for the weak transition form factors, we calculate them in the framework of the light- cone QCD sum rules approach, which has proven to be a powerful tool to deal with the nonperturbative hadronic matrix element. Our results indicate that different interpretations of X ( 3940 ) can result in a remarkable discrepancy of the production rate in the B(c) decays, which would help to clarify the inner structure of the X ( 3940 ) with the forthcoming LHC- b experiments. Besides, the predicted large weak production rates of X ( 3872 ) and Y ( 3940 ) in B(c) decays and the small semileptonic decay rate for B(c) -> Y ( 4260 ) all depend on their quantum number J(PC) assignments. Moreover, the S - D mixing of various vector charmonium states in the weak decay of B(c) is also discussed in this work. The future experimental measurements of these decays will test the inner structures of these particles, according to our predictions here.

Bottom baryons

Recently CDF and D0 collaborations observed several bottom baryons. In this work we perform a systematic study of the masses of bottom baryons up to $1/m_Q$ in the framework of heavy quark effective field theory (HQET) using the QCD sum rule approach. The extracted chromo-magnetic splitting between the bottom baryon heavy doublet agrees well with the experimental data.

Role of four-quark condensates in QCD sum rules

The QCD sum rule approach to the in-medium behavior of hadrons is discussed for the ω meson, nucleon and D meson. Emphasis is placed on the impact of four-quark condensates and on order parameters of spontaneous symmetry breaking.

Mass and width of strange baryon resonances using QCD sum rules

The mass spectra of strange baryons in the octet family are investigated in a finite-energy QCD sum rule approach based on the Gauss-Weierstrass transform. The phenomenological form of the spectral function is saturated by the ground state and two of the lowest excited states, considered as having opposite parities. Treating the ground-state parameters as known quantities, the masses, widths, and couplings to the interpolating fields are determined and compared with experiment.

ON THE Σ0→Λ0 TRANSITION MAGNETIC MOMENT IN THE EFFECTIVE QUARK MODEL WITH CHIRAL SYMMETRY

We calculate the Σ0→Λ0 transition magnetic moment μΣ0Λ0 in the effective quark model with chiral U (3) × U (3) symmetry.5 We find that the dominant contribution is proportional to the quark condensate that indicates the important role of spontaneous breaking of chiral symmetry for its formation. Our result μΣ0Λ0 = -1.62 μN, where μN is a nuclear magneton, agrees well with the experimental data [Formula: see text]. It also agrees well both quantitatively and qualitatively with the result, obtained in the QCD sum rules approach |μΣ0Λ0| = (1.60±0.30)μN,3 where the dominant contribution is proportional to the quark condensate as well.

Nucleon form factors induced by isovector and isoscalar axial-vector currents in QCD

Using the most general form of the baryon current, nucleon form factors, induced by isovector and isoscalar axial-vector currents, are studied in the framework of light cone QCD sum rule approach. Comparison of our results on form factors with the existing results and lattice calculations are presented.

Scalar form-factors fππ(Q2) and fKK(Q2) with light-cone QCD sum rules

In this paper, we calculate the scalar form-factors fππ(Q2) and fKK(Q2) in the framework of the light-cone QCD sum rules approach. The numerical value of fππ(Q2) changes quickly with the variation of Q2 near zero momentum transfer, while fKK(Q2) has a rather good behavior at small momentum transfer. The value fKK(0) = 2.21+0.35−0.19 GeV is compatible with the result from the leading order chiral perturbation theory. At large momentum transfer with Q2 > 6 GeV2, the form-factor fππ(Q2) takes up the asymptotic behavior approximately, while fKK(Q2) decreases more quickly than .

Diquark and light four-quark states

Four-quark states with different internal clusters are discussed within the constituent quark model. It is pointed out that the diquark concept is not meaningful in the construction of a tetraquark interpolating current in the QCD sum-rule approach, and hence existing sum-rule studies of four-quark states are incomplete. An updated QCD sum-rule determination of the properties of diquark clusters is then used as input for the constituent quark model to obtain the masses of light ${0}^{++}$ tetraquark states (i.e. a bound state of two diquark clusters). The results support the identification of $\ensuremath{\sigma}(600)$, ${f}_{0}(980)$, and ${a}_{0}(980)$ as the ${0}^{++}$ light tetraquark states, and seem to be inconsistent with the tetraquark state interpretation of the new BES observations of the near-threshold $p\overline{p}$ enhancements, $X(1835)$ and $X(1812)$, with the possible exception that $X(1576)$ may be an exotic first orbital excitation of ${f}_{0}(980)$ or ${a}_{0}(980)$.

Dynamics of multiquark systems: mass, width and exotics

Exotic multi-quark states are examined in the quark model and in QCD. Current status of theoretical studies of the pentaquark Θ + is reported. We show recent analyses of multiquark components of baryons. A novel method to extract a compact excited state in the lattice QCD is applied. We also discuss how to determine mixings of different Fock components in the hadron in the QCD sum rule approach.

QCD sum rule approach to the new mesons and the gDsJ DK coupling constant

We use diquark-antidiquark currents to investigate the masses and partial decay widths of the recently observed mesons D+sJ(2317), D*0(0)(2308) and X(3872), considered as four-quark states, in a QCD sum rule approach. In particular we investigate the coupling constant gDsJ DK. We found that the gDsJ DK obtained in this four-quark scenario is smaller than the coupling constant obtained when D+sJ(2317) is considered as a conventional cs state.

Analysis of [formula omitted] as a tetraquark state with QCD sum rules

In this article, we take the point of view that Y ( 2175 ) be a tetraquark state which consists of color octet constituents, and calculate its mass and decay constant within the framework of the QCD sum rule approach. We release standard criterion in the QCD sum rules approach and take more phenomenological analysis, the value of the mass of Y ( 2175 ) is consistent with experimental data; there may be some tetraquark components in the state Y ( 2175 ) . If we retain standard criterion, larger mass than experimental data can be obtained, the current J μ ( x ) can interpolate a tetraquark state with larger mass, or Y ( 2175 ) has some components with larger mass. The dominating contribution comes from the perturbative term, which is in contrast to the sum rules with interpolating currents constructed from diquark pairs. The tetraquark states may consist of color octet constituents rather than diquark pairs.

Structure of the axial-vector meson Ds1(2460) and the strong coupling constant with the light-cone QCD sum rules

In this paper, we take the point of view that the charmed axial-vector meson Ds1(2460) is the conventional meson and calculate the strong coupling constant in the framework of the light-cone QCD sum rules approach. The numerical values of strong coupling constants and are very large, and support the hadronic dressing mechanism. Just like the scalar mesons f0(980) and a0(980), the scalar meson Ds0(2317) and axial-vector meson Ds1(2460) may have small kernels of the typical meson size; the strong couplings to the hadronic channels (or the virtual mesons loops) may result in smaller masses than the conventional mesons in the constituent quark models, and enrich the pure states with other components.

Analysis of the verticesρNN,ρΣΣ, andρΞΞwith light-cone QCD sum rules

In this article, we calculate the strong coupling constants of the $\ensuremath{\rho}NN$, $\ensuremath{\rho}\ensuremath{\Sigma}\ensuremath{\Sigma}$, and $\ensuremath{\rho}\ensuremath{\Xi}\ensuremath{\Xi}$ in the framework of the light-cone QCD sum rules approach. The strong coupling constants of the meson-baryon-baryon are the fundamental parameters in the one-boson exchange model which describes the baryon-baryon interactions successfully. The numerical values are in agreement with the existing calculations in part. The electric and magnetic $F/(F+D)$ ratios deviate from the prediction of the vector meson dominance theory; the $SU(3)$ symmetry breaking effects are very large.

Analysis of the vector form factors f+ Kπ(Q2) and f- Kπ(Q2) with light-cone QCD sum rules

In this article, we calculate the vector form factors f+ Kπ(Q2) and f- Kπ(Q2) within the framework of the light-cone QCD sum rule approach. The numerical values of f+ Kπ(Q2) are compatible with existing theoretical calculations, and the central value of f+ Kπ(0) (f+ Kπ(0)=0.97) is in excellent agreement with the values from chiral perturbation theory and lattice QCD. The values of |f- Kπ(0)| are very large compared to the theoretical calculations and experimental data, and they cannot give any reliable prediction. At large momentum transfer with Q2 > 5 GeV2, the form factors f+ Kπ(Q2) and |f- Kπ(Q2)| can either show the asymptotic behavior of \(\frac{1}{Q^2}\) or decrease more quickly than \(\frac{1}{Q^2}\); more experimental data are needed to select the ideal sum rules.

Investigating the tetraquark structure of the new mesons

Using the QCD sum rule approach we investigate the possible four-quark structure of the recently observed mesons $D_{sJ}^{+}(2317)$, firstly observed by BaBaR, X(3872), firstly observed by BELLE and $D_0^{*0}(2308)$ observed by BELLE. We use diquark-antidiquark currents and work in full QCD, without relying on $1/m_c$ expansion. Our results indicate that a four-quark structure is acceptable for these mesons.

Charmed scalar mesons masses within the QCD sum rules framework

In this work, we evaluate the D+sJ(2317), D(0)0(2308), D(0)0(2407) and D+0(2403) masses. These are scalar mesons recently discovered in the BABAR, BELLE and FOCUS Collaborations. The nature of these particles is intensely discussed nowadays. We treat them as a diquark-antidiquark configuration and treat the problem using the QCD sum rules (QCDSR) approach.

X(1835) as a baryonium state with QCD sum rules

In this paper, we take into account that X(1835) be a baryonium state and calculate its mass within the framework of the QCD sum rules approach. The numerical value of the mass of X(1835) is consistent with the experimental data. There may be some baryonium component in the X(1835) state.

Analysis of the Σ–n form-factors with light-cone QCD sum rules

In this work, we study the four form-factors f1(Q2), f2(Q2), g1(Q2) and g2(Q2) of the Σ → n in the framework of the light-cone QCD sum rules approach up to twist-6 three valence quark light-cone distribution amplitudes. The f1(0) is the basic input parameter in extracting the CKM matrix element |Vus| from the hyperon decays. The four form-factors f1(Q2), f2(Q2), g1(Q2) and g2(Q2) at intermediate and large momentum transfers with Q2 > 3 GeV2 have significant contributions from the end-point (soft) terms. The numerical values of the four form-factors f1(0), f2(0), g1(0) and g2(0) are compatible with the experimental data and theoretical calculations (in magnitude), although the uncertainties are large.

Rise and fall of pentaquarks in the QCD Sum Rules approach

We review the existing mass and decay width determinations of pentaquarks with QCD Sum Rules (QCDSR). We give special attention to the intermediate assumptions and choices which we are obliged to do in this approach. As an example, we present the full calculation of the pentaquark mass with Borel sum rules and also with Finite Energy Sum Rules (FESR). We also work out the calculation of the theta decay width. We take the opportunity to comment our publications on this subject and include new and unpublished material.