Meson Decay Constants Research Articles

DecaysB(s)→a1(b1)D(s),a1(b1)D(s)*in the perturbative QCD approach

Within the framework of the perturbative QCD approach, we study the branching ratios of the two-body charmed decays ${B}_{(s)}\ensuremath{\rightarrow}{a}_{1}({b}_{1}){D}_{(s)}$, ${a}_{1}({b}_{1}){D}_{(s)}^{*}$, which, including Cabibbo-Kobayashi-Maskawa, allowed and suppressed decays. Our calculations are consistent with the currently available data and the experimental upper limits. Certainly, many of these predicted channels have not been measured by experiments and can be confronted with the future experimental data. We also discuss the polarization factions of the decays ${B}_{(s)}\ensuremath{\rightarrow}{a}_{1}({b}_{1}){D}_{(s)}^{*}$, some of which are sensitive to the distinct Gegenbauer moments of the wave functions and the decay constants of mesons ${a}_{1}$ and ${b}_{1}$.

B-physics from non-perturbatively renormalized HQET in two-flavour lattice QCD

We report on the ALPHA Collaborationʼs lattice B-physics programme based on Nf=2O(a) improved Wilson fermions and HQET, including all NLO effects in the inverse heavy quark mass, as well as non-perturbative renormalization and matching, to fix the parameters of the effective theory. Our simulations in large physical volume cover 3 lattice spacings a≈(0.08−0.05)fm and pion masses down to 190 MeV to control continuum and chiral extrapolations. We present the status of results for the b-quark mass and the B(s)-meson decay constants, fB and fBs.

Bethe-Salpeter equation at leading order in Coulomb gauge

The Bethe-Salpeter equation and leptonic decay constants for pseudoscalar and vector quark-antiquark mesons with arbitrary quark masses are studied in Coulomb gauge, under a leading order truncation. As input, we use a pure linear rising potential, supplemented by a contact term arising from the conservation of total color charge. It is shown how the equations can be written in terms of manifestly finite functions, despite the infrared singular interaction. The resulting equations are solved numerically. Both the pattern of dynamical chiral symmetry breaking and the leading order heavy quark limit are visible.

Study of light-cone distribution amplitudes forp-wave heavy mesons

In this paper, a study of light-cone distribution amplitudes for p-wave heavy mesons is presented in both general and heavy quark frameworks. Within the light-front approach, the leading twist light-cone distribution amplitudes, \phi_M(u) and their relevant decay constants of heavy scalar, axial-vector and tensor mesons, f_M, are formulated. The relations of some decay constants can be simplified when the heavy quark limit is taken into account. After fixing the parameters which appear in a Gaussian wave function, the corresponding decay constants are calculated and compared with those of other theoretical approaches. The curves and the first six \xi moments of \phi_M(u) are plotted and estimated. These results all endorse the requirements of heavy quark symmetry.

Heavy meson masses and decay constants from relativistic heavy quarks in full lattice QCD

We determine masses and decay constants of heavy-heavy and heavy-charm pseudoscalar mesons as a function of heavy quark mass using a fully relativistic formalism known as highly improved staggered quarks for the heavy quark. We are able to cover the region from the charm quark mass to the bottom quark mass using MILC ensembles with lattice spacing values from 0.15 fm down to 0.044 fm. We obtain ${f}_{{B}_{c}}=0.427(6)\text{ }\text{ }\mathrm{GeV}$; ${m}_{{B}_{c}}=6.285(10)\text{ }\text{ }\mathrm{GeV}$ and ${f}_{{\ensuremath{\eta}}_{b}}=0.667(6)\text{ }\text{ }\mathrm{GeV}$. Our value for ${f}_{{\ensuremath{\eta}}_{b}}$ is within a few percent of ${f}_{\ensuremath{\Upsilon}}$, confirming that spin effects are surprisingly small for heavyonium decay constants. Our value for ${f}_{{B}_{c}}$ is significantly lower than potential model values being used to estimate production rates at the LHC. We discuss the changing physical heavy-quark mass dependence of decay constants from heavy-heavy through heavy-charm to heavy-strange mesons. A comparison between the three different systems confirms that the ${B}_{c}$ system behaves in some ways more like a heavy-light system than a heavy-heavy one. Finally we summarize current results on decay constants of gold-plated mesons.

BandBsmeson decay constants from lattice QCD

We present a new determination of the $B$ and ${B}_{s}$ meson decay constants using nonrelativistic quantum chromodynamics (NRQCD) $b$-quarks, highly improved staggered quark (HISQ) light and strange valence quarks and the MILC collaboration ${N}_{f}=2+1$ lattices. The new calculations improve on HPQCD's earlier work with NRQCD $b$-quarks by replacing AsqTad with HISQ valence quarks, by including a more chiral MILC fine ensemble in the analysis, and by employing better tuned quark masses and overall scale. We find ${f}_{B}=0.191(9)\text{ }\text{ }\mathrm{GeV}$, ${f}_{{B}_{s}}=0.228(10)\text{ }\text{ }\mathrm{GeV}$ and ${f}_{{B}_{s}}/{f}_{B}=1.188(18)$. Combining the new value for ${f}_{{B}_{s}}/{f}_{B}$ with a recent very precise determination of the ${B}_{s}$ meson decay constant based on HISQ $b$-quarks, ${f}_{{B}_{s}}=0.225(4)\text{ }\text{ }\mathrm{GeV}$, leads to ${f}_{B}=0.189(4)\text{ }\text{ }\mathrm{GeV}$. With errors of just 2.1% this represents the most precise ${f}_{B}$ available today.

Open flavour charmed mesons in a quantum chromodynamics potential model

We modify the mesonic wave function by using a short distance scale r0 in analogy with hydrogen atom and estimate the values of masses and decay constants of the open flavour charm mesons D, Ds and Bc within the framework of a QCD potential model. We also calculate leptonic decay widths of these mesons to study branching ratios and lifetime. The results are in good agreement with experimental and other theoretical values.

Meson distribution amplitudes in holographic models

We study the wave functions of light and heavy mesons in both hard-wall (HW) and soft-wall (SW) holographic models which use AdS/CFT correspondence. In the case of massless constituents, the asymptotic behaviors of the electromagnetic form factor, the distribution amplitudes, and the decay constants for the two models are the same, if the relation between the dilaton scale parameter and the size of meson is an inverse proportion. On the other hand, by introducing a quark mass dependence in the wave function, the differences of the distribution amplitudes between the two models are obvious. In addition, for the SW model, the dependences of the decay constants of meson on the dilaton scale parameter $\kappa$ differ; especially f_{Qq}\sim \kappa^3/m_Q^2 is consistent with the prediction of the heavy quark effective theory if \kappa\sim m_Q^{1/2}. Thus the parameters of the two models are fit by the decay constants of the distinct mesons; the distribution amplitudes and the \xi-moments are calculated and compared.

Quark matter and meson properties in a Nonlocal SU(3) chiral quark model at finite temperature

We study the finite temperature behavior of light scalar and pseudoscalar meson properties in the context of a three-flavor nonlocal chiral quark model. The model includes mixing with active strangeness degrees of freedom, and takes care of the effect of gauge interactions by coupling the quarks with a background color field. We analyze the chiral restoration and deconfinement transitions, as well as the temperature dependence of meson masses, mixing angles, and decay constants.

Determination of theη-η′mixing angle

We extract $\eta$-$\eta^\prime$ mixing angle and the ratios of decay constants of light pseudoscalar mesons $\pi^0$, $\eta$ and $\eta^\prime$ using recently available BaBar measurements on $\eta$-photon and $\eta^\prime$-photon transition form factors and more accurate experimental data for the masses and two-photon decay widths of the light pseduoscalar mesons.

Bound-state properties from field-theory correlators

We discuss the details of calculating hadron properties from the OPE for correlators of quark currents in QCD, which constitutes the basis of the method of QCD sum rules. The main emphasis is laid on gaining control over the systematic uncertainties of the hadron parameters obtained within this method. We start with examples from quantum mechanics, where bound-state properties may be calculated independently in two ways: exactly, by solving the Schrödinger equation, and approximately, by the method of sum rules. Knowing the exact solution allows us to control each step of the sum-rule extraction procedure. On the basis of this analysis, we formulate several improvements of the method of sum rules. We then apply these modifications to the analysis of the decay constants of heavy mesons.

Decay constants of heavy vector mesons at finite temperature

This study deals with determination of the decay constants of heavy vector mesons in the framework of the thermal QCD sum rules. We calculate both thermal spectral density and non-perturbative contributions taking into account the traditionally existing operators at T = 0 and also additional operators appearing at finite temperature. Analysis of the obtained thermal sum rules shows that the decay constants almost remain unchanged with respect to the variation of temperature up to T ≅ 100 MeV, however after this point, they start to decrease sharply with increasing temperature.

Properties of bound states containing fourth family quarks

The heavy fourth generation of quarks that have sufficiently small mixing with the three known SM families form hadrons. In the present work, we calculate the masses and decay constants of mesons containing either both quarks from the fourth generation or one from fourth family and the other from observed SM quarks, namely charm or bottom quark, in the framework of the QCD sum rules. In the calculations, the two gluon condensate diagrams as nonperturbative contributions are taken into account. The obtained numerical results are reduced to the known masses and decay constants of the b̄b and c̄c quarkonia, when the fourth family quark is replaced by the bottom or charm quark.

Decay constants and form factors of s-wave and p-wave mesons in the covariant light-front quark model

We reanalyze the decay constants of s-wave and p-wave mesons and the D, B → M form factors, where M represents a pseudoscalar meson, a vector meson, a scalar meson or an axial vector meson within a covariant light-front quark model. The parameter β for wavefunctions of most of s-wave mesons and that of a few axial-vector mesons are fixed with the latest experimental information, wherever available or using the lattice calculations. The treatment of masses and mixing angles for strange axial vector mesons is improved for the purpose. We extend our analysis to determine the form factors appearing in the Ds, Bs → M transitions, and to the isoscalar final state mesons. Numerical results of the form factors for transitions between a heavy pseudoscalar meson and an s-wave or a p-wave light meson and their momentum dependence are presented in detail. Further, their sensitivity to uncertainties of the β parameters of the initial as well as the final mesons is investigated. Some experimental measurements of the charmed and bottom meson decays are employed to compare the decay constants and transition form factors obtained in this and other works.

Hadron properties in AdS/QCD

We discuss a holographic soft-wall model developed for the description of mesons and baryons with adjustable quantum numbers n,J,L,S. This approach is based on an action which describes hadrons with broken conformal invariance and which incorporates confinement through the presence of a background dilaton field. Results obtained for heavy-light meson masses and decay constants are consistent with predictions of HQET. In the baryon sector, applications to the baryon masses, nucleon electromagnetic form factors and generalized parton distributions are discussed.

Charm quark system at the physical point of2+1flavor lattice QCD

We investigate the charm quark system using the relativistic heavy quark action on 2+1 flavor PACS-CS configurations previously generated on $32^3 \times 64$ lattice. The dynamical up-down and strange quark masses are set to the physical values by using the technique of reweighting to shift the quark hopping parameters from the values employed in the configuration generation. At the physical point, the lattice spacing equals $a^{-1}=2.194(10)$ GeV and the spatial extent $L=2.88(1)$ fm. The charm quark mass is determined by the spin-averaged mass of the 1S charmonium state, from which we obtain $m_{\rm charm}^{\msbar}(\mu = m_{\rm charm}^{\msbar}) = 1.260(1)(6)(35)$ GeV, where the errors are due to our statistics, scale determination and renormalization factor. An additional systematic error from the heavy quark is of order $\alpha_s^2 f(m_Q a)(a \Lambda_{QCD})$, which is estimated to be a percent level if the factor $f(m_Q a)$ analytic in $m_Q a$ is of order unity. Our results for the charmed and charmed-strange meson decay constants are $f_D=226(6)(1)(5)$ MeV, $f_{D_s}=257(2)(1)(5)$ MeV, again up to the heavy quark errors of order $\alpha_s^2 f(m_Q a)(a \Lambda_{QCD})$. Combined with the CLEO values for the leptonic decay widths, these values yield $|V_{cd}| = 0.205(6)(1)(5)(9)$, $|V_{cs}| = 1.00(1)(1)(3)(3)$, where the last error is on account of the experimental uncertainty of the decay widths.

The Oscillation Frequency of B and B̄ Mesons in a QCD Potential Model with Relativistic Effects

Wavefunction at the origin, with the incorporation of a relativistic effect, leads to singularity in a specific potential model. To regularize the wavefunction, we introduced a short distance scale and used it to estimate the mass and decay constants of Bd and Bs mesons within the QCD potential model. These values were then used to compute the oscillation frequency, ΔmB, of Bd and Bs mesons. The values were found to be in good agreement with experimental and other theoretical values.

Anomaly, mixing and transition form factors of pseudoscalar mesons

We derive the exact non-perturbative QCD sum rule for the transition form factors of η and η ′ using the dispersive representation of axial anomaly. This sum rule allows to express the transition form factors entirely in terms of meson decay constants. Using this sum rule several mixing schemes were analyzed and compared to recent experimental data. A good agreement with experimental data on η , η ′ transition form factors in the range from real to highly virtual photons was obtained.

Axial anomaly and mixing: From real to highly virtual photons

The relation for transition form factors of eta and eta' mesons is obtained by combining the exact nonperturbative QCD sum rule, following from the dispersive representation of axial anomaly, and quark-hadron duality. It is valid at all virtual photon momenta and allows one to express the transition form factors entirely in terms of meson decay constants. This relation is in a good agreement with experimental data.

Decay constants of heavy pseudoscalar mesons from QCD sum rules

We revisit the sum-rule extraction of the decay constants of the D, Ds, B and Bs mesons from the two-point correlator of heavy–light pseudoscalar currents. We use the operator product expansion of this correlator expressed in terms of the heavy-quark mass for which the perturbative expansion exhibits a reasonable convergence. Our main emphasis is laid on the control over the uncertainties in the decay constants, related both to the input quantum chromodynamics (QCD) parameters and to the limited intrinsic accuracy of the method of QCD sum rules. This becomes possible due to the application of our procedure of extracting hadron observables that involves as novel feature dual thresholds depending on the Borel parameter. For charmed mesons, we find the decay constants and . For beauty mesons, the decay constants turn out to be extremely sensitive to the precise value of . By requiring our sum-rule estimate to match the average of the lattice results for fB, a very accurate value is extracted, leading to fB = (193.4 ± 12.3(OPE) ± 4.3(syst)) MeV and .