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Register a new userCharm sea effects on charmonium decay constants and heavy meson masses
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We estimate the effects on the decay constants of charmonium and on heavy meson masses due to the charm quark in the sea. Our goal is to understand whether for these quantities $N_f=2+1$ lattice QCD simulations provide results that can be compared with experiments or whether $N_f=2+1+1$ QCD including the charm quark in the sea needs to be simulated. We consider two theories, $N_f=0$ QCD and QCD with $N_f=2$ charm quarks in the sea. The charm sea effects (due to two charm quarks) are estimated comparing the results obtained in these two theories, after matching them and taking the continuum limit. The absence of light quarks allows us to simulate the $N_f=2$ theory at lattice spacings down to $0.023$ fm that are crucial for reliable continuum extrapolations. We find that sea charm quark effects are below $1%$ for the decay constants of charmonium. Our results show that decoupling of charm works well up to energies of about $500$ MeV. We also compute the derivatives of the decay constants and meson masses with respect to the charm mass. For these quantities we again do not see a significant dynamical charm quark effect, albeit with a lower precision. For mesons made of a charm quark and a heavy antiquark, whose mass is twice that of the charm quark, sea effects are only about $0.1%$ in the ratio of vector to pseudoscalar masses.
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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) GeV; m_{B_c} = 6.285(10) GeV and f_{eta_b} = 0.667(6) GeV. Our value for f_{eta_b} is within a few percent of f_{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 summarise current results on decay constants of gold-plated mesons.
Meson masses and decay constants in the large $N$ limit of SU($N$) gauge theory are determined using the twisted Eguchi-Kawai reduced model. To this end, we make use of a recently defined smearing method valid on the one-point lattice. This procedure, in combination with a variational analysis, allows to obtain reliable values for these quantities.
We present improved results for the B and D meson spectrum from lattice QCD including the effect of u/d,s and c quarks in the sea. For the B mesons the Highly Improved Staggered Quark action is used for the sea and light valence quarks and NonRelativistic QCD for the b quark including O(alpha_s) radiative corrections to many of the Wilson coefficients for the first time. The D mesons use the Highly Improved Staggered Quark action for both valence quarks on the same sea. We find M_{B_s}-M_B=84(2) MeV, M_{B_s}=5.366(8) GeV, M_{B_c}=6.278(9) GeV, M_{D_s}=1.9697(33) GeV, and M_{D_s}-M_{D}=101(3) MeV. Our results for the B meson hyperfine splittings are M_{B^*}-M_{B}=50(3) MeV, M_{B_s^*}-M_{B_s}=52(3) MeV, in good agreement with existing experimental results. This demonstrates that our perturbative improvement of the NRQCD chromo-magnetic coupling works for both heavyonium and heavy-light mesons. We predict M_{B_c^*}-M_{B_c}=54(3) MeV. We also present first results for the radially excited B_c states as well as the orbitally excited scalar B_c0^* and axial vector B_c1 mesons.
We compute decay constants of heavy-light mesons in quenched lattice QCD with a lattice spacing of a ~ 0.04 fm using non-perturbatively O(a) improved Wilson fermions and O(a) improved currents. We obtain f_{D_s} = 220(6)(5)(11) MeV, f_D = 206(6)(3)(22) MeV, f_{B_s} = 205(7)(26)(17) MeV and f_B = 190(8)(23)(25) MeV, using the Sommer parameter r_0 = 0.5 fm to set the scale. The first error is statistical, the second systematic and the third from assuming a +-10% uncertainty in the experimental value of r_0. A detailed discussion is given in the text. We also present results for the meson decay constants f_K and f_pi and the rho meson mass.
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.
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