Meson Decay Constants Research Articles

A tmQCD mixed-action approach to flavour physics

We discuss a mixed-action approach in which sea quarks are regularised using non-perturbatively O(a) improved Wilson fermions, while a fully-twisted tmQCD action is used for valence quarks. In this setup, automatic O(a) improvement is preserved for valence observables, apart from small residual O(a) effects from the sea. A strategy for matching sea and valence is set up, and carried out for Nf = 2 + 1 CLS ensembles with open boundary conditions at several simulation points. The scaling of basic light-quark observables such as the pseudoscalar meson decay constant is studied, as well as the isospin splitting of pseudoscalar meson masses.

Infrared Confinement: Mass-Scale Dependence of the Strong Effective Coupling, Leptonic Decay Constants and Spectrum of Mesons, the Lowest Glueball Mass

Properties of two-particle bound states composed of spin-zero and spin-half constituents have been investigated within a relativistic field model based on new analytically (infrared) confined propagators. A new mass scale dependence of the strong effective coupling has been obtained. By using this dependence, new estimates on the mass spectrum and leptonic decay constants of mesons have been performed with reasonable accuracy. Independent and new estimates have been obtained for the mass and radius of the lowest (scalar) glueball.

Bottomonium dissociation in a finite density plasma

We present a holographic description of the thermal behavior of bb¯ heavy vector mesons inside a plasma at finite temperature and density. The meson dissociation in the medium is represented by the decrease in the height of the spectral function peaks. In order to find a description for the evolution of the quasi-states with temperature and chemical potential it is crucial to use a model that is consistent with the decay constant behavior. The reason is that the height of a spectral function peak is related to the value of the zero temperature decay constant of the corresponding particle. AdS/QCD holographic models are in general not consistent with the observation that decay constants of heavy vector mesons decrease with radial excitation level. However, it was recently shown that using a soft wall background and calculating the correlation functions at a finite position of anti-de Sitter space, associated with an ultraviolet energy scale, it is possible to describe the observed behavior. Here we extend this proposal to the case of finite temperature T and chemical potential μ. A clear picture of the dissociation of bottomonium states as a function of μ and T emerges from the spectral function. The energy scales where the change in chemical potential leads to changes in the thermal properties of the mesons is consistent with QCD expectations.

First physics results at the physical pion mass from Nf=2 Wilson twisted mass fermions at maximal twist

We present physics results from simulations of QCD using ${N}_{f}=2$ dynamical Wilson twisted mass fermions at the physical value of the pion mass. These simulations are enabled by the addition of the clover term to the twisted mass quark action. We show evidence that compared to previous simulations without this term, the pion mass splitting due to isospin breaking is almost completely eliminated. Using this new action, we compute the masses and decay constants of pseudoscalar mesons involving the dynamical up and down as well as valence strange and charm quarks at one value of the lattice spacing, $a\ensuremath{\approx}0.09\text{ }\text{ }\mathrm{fm}$. Further, we determine renormalized quark masses as well as their scale-independent ratios, in excellent agreement with other lattice determinations in the continuum limit. In the baryon sector, we show that the nucleon mass is compatible with its physical value and that the masses of the $\mathrm{\ensuremath{\Delta}}$ baryons do not show any sign of isospin breaking. Finally, we compute the electron, muon and tau lepton anomalous magnetic moments and show the results to be consistent with extrapolations of older ETMC data to the continuum and physical pion mass limits. We mostly find remarkably good agreement with phenomenology, even though we cannot take the continuum and thermodynamic limits.

Setting the scale for the CLS 2+1 flavor ensembles

We present measurements of a combination of the decay constants of the light pseudoscalar mesons and the gradient flow scale $t_0$, which allow to set the scale of the lattices generated by CLS with $2 + 1$ flavors of non-perturbatively improved Wilson fermions. Mistunings of the quark masses are corrected for by measuring the derivatives of observables with respect to the bare quark masses.

η−γ and η′−γ transition form factors in a nonlocal NJL model

We study the $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}$ distribution amplitudes (DAs) in the context of a nonlocal ${\mathrm{SU}(3)}_{L}\ensuremath{\bigotimes}{\mathrm{SU}(3)}_{R}$ chiral quark model. The corresponding Lagrangian allows us to reproduce the phenomenological values of pseudoscalar meson masses and decay constants, as well as the momentum dependence of the quark propagator arising from lattice calculations. It is found that the obtained DAs have two symmetric maxima, which arise from new contributions generated by the nonlocal character of the interactions. These DAs are then applied to the calculation of the $\ensuremath{\eta}\text{\ensuremath{-}}\ensuremath{\gamma}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}\text{\ensuremath{-}}\ensuremath{\gamma}$ transition form factors. Implications of our results regarding higher twist corrections and/or contributions to the transition form factors originated by gluon-gluon components in the $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}$ mesons are discussed.

Flavour breaking effects in the pseudoscalar meson decay constants

The SU(3) flavour symmetry breaking expansion in up, down and strange quark masses is extended from hadron masses to meson decay constants. This allows a determination of the ratio of kaon to pion decay constants in QCD. Furthermore when using partially quenched valence quarks the expansion is such that SU(2) isospin breaking effects can also be determined. It is found that the lowest order SU(3) flavour symmetry breaking expansion (or Gell-Mann–Okubo expansion) works very well. Simulations are performed for 2+1 flavours of clover fermions at four lattice spacings.

Isospin breaking in the decay constants of heavy mesons from QCD sum rules

We present a study of the strong isospin-breaking (IB) effect, due in QCD to the difference between $u$- and $d$-quark masses, in the leptonic decay constants of charmed and beauty pseudoscalar and vector mesons using the method of QCD sum rules. We apply the sum-rule analysis to the decay constants of mesons containing one heavy quark and one light quark with the light mass in the range from the average $u/d$ quark mass to the strange-quark mass. We then analyse the dependence of the decay constants on the light quark mass and extract with good accuracy the IB ratios of decay constants at leading order in the mass difference $(m_d - m_u)$, obtaining: $(f_{D^+} - f_{D^0}) / f_{D} = 0.0047 (6)$, $(f_{D^{*+}} - f_{D^{*0}}) / f_{D^*} = 0.0068 (9)$, $(f_{B^0} - f_{B^+}) / f_{B} = 0.0047 (6)$, and $(f_{B^{*0}} - f_{B^{*+}}) / f_{B^*} = 0.0045 (5)$, which yield: $f_{D^+} - f_{D^0} = 0.97 \pm 0.13$ MeV, $f_{D^{*+}} - f_{D^{*0}} = 1.73 \pm 0.27$ MeV, $f_{B^0} - f_{B^+} = 0.90 \pm 0.13$ MeV, $f_{B^{*0}} - f_{B^{*+}} = 0.81 \pm 0.11$ MeV. In the case of the $D$-meson our finding is consistent with recent lattice QCD results, whereas it is much lower in the case of the $B$-meson showing a tension of $\approx 3$ standard deviations.

Holographic picture of heavy vector meson melting

The fraction of heavy vector mesons produced in a heavy ion collision, as compared to a proton proton collision, serves as an important indication of the formation of a thermal medium, the quark gluon plasma. This sort of analysis strongly depends on understanding the thermal effects of a medium like the plasma on the states of heavy mesons. In particular, it is crucial to know the temperature ranges where they undergo a thermal dissociation, or melting. AdS/QCD models are know to provide an important tool for the calculation of hadronic masses, but in general are not consistent with the observation that decay constants of heavy vector mesons decrease with excitation level. It has recently been shown that this problem can be overcome using a soft wall background and introducing an extra energy parameter, through the calculation of correlation functions at a finite position of anti-de Sitter space. This approach leads to the evaluation of masses and decay constants of S wave quarkonium states with just one flavor dependent and one flavor independent parameters. Here we extend this more realistic model to finite temperatures and analyse the thermal behavior of the states $1S, 2S$ and $ 3S$ of bottomonium and charmonium. The corresponding spectral function exhibits a consistent picture for the melting of the states where, for each flavor, the higher excitations melt at lower temperatures. We estimate for these six states, the energy ranges in which the heavy vector mesons undergo a transition from a well defined peak in the spectral function to complete melting in the thermal medium. A very clear distinction between the heavy flavors emerges, with bottomonium state $\Upsilon (1S)$ surviving deconfinemet transition at temperatures much larger than the critical deconfinement temperature of the medium.

A Potential Model Approach in the Study of Static and Dynamic Properties of Heavy-Light Quark-Antiquark Systems

We report some approximate analytic form of meson wave function constructed upon solving Schrodinger equation with linear plus Coulomb type Cornell potential. With this wave function, we study Isgur-Wise function and its derivatives for heavy-light mesons in the infinite heavy quark mass limit. We also explore the elastic form factors, charge radii and decay constants of pseudoscalar mesons in this QCD inspired quark model approach.

The ρ(1S, 2S), ψ(1S, 2S), Υ(1S, 2S) and ψ t (1S, 2S) Mesons in a Double Pole QCD Sum Rule

We use the method of double pole QCD sum rule which is basically a fit with two exponentials of the correlation function, where we can extract the masses and decay constants of mesons as a function of the Borel mass. We apply this method to study the mesons: $\rho(1S,2S)$, $\psi(1S,2S)$, $\Upsilon(1S,2S)$ and $\psi_t(1S,2S)$. We also present predictions for the toponiuns masses $\psi_t(1S,2S)$ of m(1S)=357 GeV and m(2S)=374 GeV.

Lattice study of largeNcQCD

We present a lattice simulation study of large $N_c$ regularities of meson and baryon spectroscopy in $SU(N_c)$ gauge theory with two flavors of dynamical fundamental representation fermions. Systems investigated include $N_c=2$, 3, 4, and 5, over a range of fermion masses parametrized by a squared pseudoscalar to vector meson mass ratio between about 0.2 to 0.7. Good agreement with large $N_c$ scaling is observed in the static potential, in meson masses and decay constants, and in baryon spectroscopy. This is an update of the published version of the paper (Phys. Rev. D94 (2016) 034506).

Renormalization of the low-energy constants of chiral perturbation theory from loops with dynamical vector mesons

Starting from a relativistic Lagrangian for pseudoscalar Goldstone bosons and vector mesons in the antisymmetric tensor representation, a one-loop calculation is performed to pin down the divergent structures that appear for the effective low-energy action at chiral orders Q^2 and Q^4. The corresponding renormalisation-scale dependences of all low-energy constants up to chiral order Q^4 are determined. Calculations are carried out for both the pseudoscalar octet and the pseudoscalar nonet, the latter in the framework of chiral perturbation theory in the limit of a large number of colours.

Meson's correlation functions in a nuclear medium

We investigate meson's spectrum, decay constant and form factor in a nuclear medium through holographic two- and three-point correlation functions. To describe a nuclear medium composed of protons and neutrons, we consider a hard wall model on the thermal charged AdS geometry and show that due to the isospin interaction with a nuclear medium, there exist splittings of the meson's spectrum, decay constant and form factor relying on the isospin charge. In addition, we show that the $\rho$-meson's form factor describing an interaction with pseudoscalar fluctuation decreases when the nuclear density increases, while the interaction with a longitudinal part of an axial vector meson increases.

Some heavy vector and tensor meson decay constants in light-front quark model

We study the decay constants ( $$f_M$$ ) of the heavy vector ( $$D^{*}$$ , $$D^{*}_{s}$$ , $$B^{*}$$ , $$B^{*}_{s}$$ , $$B^{*}_{c}$$ ) and tensor ( $$D_{2}^{*}$$ , $$D_{s2}^{*}$$ , $$B^{*}_{2}$$ , $$B^{*}_{s2}$$ ) mesons in the light-front quark model. With the known pseudoscalar meson decay constants of $$f_D$$ , $$f_{D_s}$$ , $$f_B$$ , $$f_{B_s}$$ , and $$f_{B_c}$$ as the input parameters to determine the light-front meson wave functions, we obtain $$f_{D^{*}, D^{*}_{s}, B^{*},B^{*}_s,B^{*}_c} = (252.0^{+13.8}_{-11.6}$$ , $$318.3^{+15.3}_{-12.6}$$ , $$201.9^{+43.2}_{-41.4}$$ , $$244.2\pm 7.0$$ , $$473.4\pm 18.2$$ ) and $$(264.9^{+10.2}_{-9.5}$$ , $$330.9^{+9.9}_{-9.0}$$ , $$220.2^{+49.1}_{-46.2}$$ , $$265.7\pm 8.0$$ , $$487.6\pm 19.2$$ ) MeV with Gaussian and power-law wave functions, respectively, while we have $$f_{D_{2}^{*},D_{s2}^{*},B^{*}_{2},B^{*}_{s2}}$$ = ( $$143.6^{+24.9}_{-21.8}$$ , $$209.5^{+29.1}_{-24.2}$$ , $$80.9^{+33.8}_{-27.7}$$ , $$109.7^{+15.7}_{-15.0}$$ ) MeV with only Gaussian wave functions.

Strong decay constants of heavy tensor mesons in light cone QCD sum rules

Strong decay constants of the heavy tensor to heavy pseudoscalar (vector) and light pseudoscalar mesons are estimated within the light cone QCD sum rules. It is obtained that the values of these coupling constants are very strongly dependent on the choice of the Lorentz structure. Moreover, using these strong coupling constants the corresponding decay widths are calculated.

An exploratory study of heavy domain wall fermions on the lattice

We report on an exploratory study of domain wall fermions (DWF) as a lattice regularisation for heavy quarks. Within the framework of quenched QCD with the tree-level improved Symanzik gauge action we identify the DWF parameters which minimise discretisation effects. We find the corresponding effective 4$d$ overlap operator to be exponentially local, independent of the quark mass. We determine a maximum bare heavy quark mass of $am_h\approx 0.4$, below which the approximate chiral symmetry and O(a)-improvement of DWF are sustained. This threshold appears to be largely independent of the lattice spacing. Based on these findings, we carried out a detailed scaling study for the heavy-strange meson dispersion relation and decay constant on four ensembles with lattice spacings in the range $2.0-5.7\,\mathrm{GeV}$. We observe very mild $a^2$ scaling towards the continuum limit. Our findings establish a sound basis for heavy DWF in dynamical simulations of lattice QCD with relevance to Standard Model phenomenology.

Analysis of the Heavy Pseudoscalar Mesons with Thermal QCD Sum Rules

In this article, we calculate the contributions of the condensates up to dimension-6, including the one-loop corrections to the quark condensates, in the operator product expansion in a consistent way, and study the masses and decay constants of the heavy pseudoscalar mesons with the thermal QCD sum rules. We reproduce the experimental values of the masses of the D, D s , B and B s and obtain the decay constants at zero temperature. Then we study the thermal behaviors of the masses and decay constants, which are useful in explaining the heavy-ion collision experiments.

Study of Heavy-Light Mesons Properties Via the Variational Method for Cornell Interaction

Using the variational method we calculate mesonic wave function. We report masses and decay constants for heavy-light mesons. Leptonic decay widths of charmed and beauty mesons are also calculated. The obtained results are compared with the available experimental and theoretical data.

Decay Constants of Heavy-Light Mesons from QCD

We summarize our recently improved results for the pseudoscalar [S. Narison, Phys.Lett. B718 (2013) 132; S. Narison, Nucl. Phys. Proc. Suppl. 234 (2013) 187; S. Narison, Phys.Lett. B721 (2013) 269], vector and Bc [S. Narison, Int. J. Mod. Phys. A30 (2015) 20, 1550116] meson decay constants from QCD spectral sum rules where N2LO⊕ estimate of the N3LO PT⊕d≤6 condensates have been included in the SVZ expansion. The “optimal results” based on stability criteria with respect to the variations of the Laplace/Moments sum rule variables, QCD continuum threshold and subtraction constant μ are compared with recent sum rules and lattice calculations. To understand the “apparent tension” between some recent results, we present in Section 8 a novel extraction of forfB⁎/fBfrom heavy quark effective theory (HQET) sum rules by including the normalization factor (Mb/MB)2 relating the pseudoscalar to the universal HQET correlators for finite b-quark and B-meson masses. We obtain fB⁎/fB=1.025(16) in good agreement with 1.016(16) from spectral sum rules (SR) in full QCD [3]. We complete the paper by including new improved estimates of the scalar, axial andBc⁎meson decay constants (Sections 11–13). For further phenomenological uses, we attempt to extract a Global Average of the sum rules and lattice determinations which are summarized in Tables 2–6. We do not found any deviation of these SM results from the present data.