Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userB meson B-parameters and the decay constant in two-flavor dynamical QCD
74
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present a two-flavor dynamical QCD calculation of the B meson B parameters and decay constant. We use NRQCD for heavy quark and the nonperturbatively O(a)-improved Wilson action for light quark at $beta$=5.2 on a $20^3times 48$ lattice. We confirm that the sea quark effect increases the heavy-light decay constant, while estimate of its magnitude depends significantly on the fitting form in the chiral extrapolation. For the B parameters, on the other hand, we do not find a significant sea quark effect. The chiral extrapolation with logarithmic term is examined for both quantities and compared with the prediction of ChPT.
rate research
Read More
We present a study of leptonic $B$ meson decay constants in lattice QCD with two flavors ($N_f=2$) of light dynamical quarks using NRQCD for the heavy quark. Gauge configurations are generated with a renormalization-group improved gauge action and a meanfield-improved clover light quark action. Measurements are carried out at two values of $beta=6/g^2$, each for four sea quark masses, corresponding to the inverse lattice spacing $a^{-1}approx 1.3$ and 1.8 GeV in the chiral limit of sea quark. The continuum values of the decay constants are derived by evaluating the discretization errors at each finite lattice spacing. We find $f_B^{N_f=2}=204(8)(29)(+44) $ MeV, $f_{B_s}^{N_f=2} = 242(9)(34)(+38)$ MeV, and $f_{B_s}^{N_f=2}/f_B^{N_f=2} = 1.179(18)(23)$, where the errors listed are statistical, systematic and uncertainty due to choice of the physical quantity used to fix the scale. Comparison is made to quenched results ($N_f=0$) obtained with the same action combination and matching lattice spacings. We find $f_B^{N_f=2}/f_B^{N_f=0}=1.07(5)$, $f_{B_s}^{N_f=2}/f_{B_s}^{N_f=0}=1.10(5)$ and $(f_{B_s}/f_B)^{N_f=2}/(f_{B_s}/f_B)^{N_f=0}=1.03(2)$, which indicates a 5--10% increase in the values of the decay constants, but no appreciable change in the ratio $f_{B_s}/f_B$, due to sea quarks.
We calculate the leptonic decay constants of B_{(s)} and D_{(s)} mesons in lattice QCD using staggered light quarks and Fermilab bottom and charm quarks. We compute the heavy-light meson correlation functions on the MILC asqtad-improved staggered gauge configurations which include the effects of three light dynamical sea quarks. We simulate with several values of the light valence- and sea-quark masses (down to ~m_s/10) and at three lattice spacings (a ~ 0.15, 0.12, and 0.09 fm) and extrapolate to the physical up and down quark masses and the continuum using expressions derived in heavy-light meson staggered chiral perturbation theory. We renormalize the heavy-light axial current using a mostly nonperturbative method such that only a small correction to unity must be computed in lattice perturbation theory and higher-order terms are expected to be small. We obtain f_{B^+} = 196.9(8.9) MeV, f_{B_s} = 242.0(9.5) MeV, f_{D^+} = 218.9(11.3) MeV, f_{D_s} = 260.1(10.8) MeV, and the SU(3) flavor-breaking ratios f_{B_s}/f_{B} = 1.229(26) and f_{D_s}/f_{D} = 1.188(25), where the numbers in parentheses are the total statistical and systematic uncertainties added in quadrature.
We calculate the leptonic decay constants of heavy-light pseudoscalar mesons with charm and bottom quarks in lattice quantum chromodynamics on four-flavor QCD gauge-field configurations with dynamical $u$, $d$, $s$, and $c$ quarks. We analyze over twenty isospin-symmetric ensembles with six lattice spacings down to $aapprox 0.03$~fm and several values of the light-quark mass down to the physical value $frac{1}{2}(m_u+m_d)$. We employ the highly-improved staggered-quark (HISQ) action for the sea and valence quarks; on the finest lattice spacings, discretization errors are sufficiently small that we can calculate the $B$-meson decay constants with the HISQ action for the first time directly at the physical $b$-quark mass. We obtain the most precise determinations to-date of the $D$- and $B$-meson decay constants and their ratios, $f_{D^+} = 212.7(0.6)$~MeV, $f_{D_s} = 249.9(0.4)$~MeV, $f_{D_s}/f_{D^+} = 1.1749(16)$, $f_{B^+} = 189.4 (1.4)$~MeV, $f_{B_s} = 230.7(1.3)$~MeV, $f_{B_s}/f_{B^+} = 1.2180(47)$, where the errors include statistical and all systematic uncertainties. Our results for the $B$-meson decay constants are three times more precise than the previous best lattice-QCD calculations, and bring the QCD errors in the Standard-Model predictions for the rare leptonic decays $overline{mathcal{B}}(B_s to mu^+mu^-) = 3.64(11) times 10^{-9}$, $overline{mathcal{B}}(B^0 to mu^+mu^-) = 1.00(3) times 10^{-10}$, and $overline{mathcal{B}}(B^0 to mu^+mu^-)/overline{mathcal{B}}(B_s to mu^+mu^-) = 0.0273(9)$ to well below other sources of uncertainty. As a byproduct of our analysis, we also update our previously published results for the light-quark-mass ratios and the scale-setting quantities $f_{p4s}$, $M_{p4s}$, and $R_{p4s}$. We obtain the most precise lattice-QCD determination to date of the ratio $f_{K^+}/f_{pi^+} = 1.1950(^{+16}_{-23})$~MeV.
We report on the status of our calculation of the hadronic matrix elements for neutral $B$-meson mixing with asqtad sea and valence light quarks and using the Wilson clover action with the Fermilab interpretation for the $b$ quark. We calculate the matrix elements of all five local operators that contribute to neutral $B$-meson mixing both in and beyond the Standard Model. We use MILC ensembles with $N_f=2+1$ dynamical flavors at four different lattice spacings in the range $a approx 0.045$--$0.12$~fm, and with light sea-quark masses as low as 0.05 times the physical strange quark mass. We perform a combined chiral-continuum extrapolation including the so-called wrong-spin contributions in simultaneous fits to the matrix elements of the five operators. We present a complete systematic error budget and conclude with an outlook for obtaining final results from this analysis.
We describe a recent lattice-QCD calculation of the leptonic decay constants of heavy-light pseudoscalar mesons containing charm and bottom quarks and of the masses of the up, down, strange, charm, and bottom quarks. Results for these quantities are of the highest precision to date. Calculations use 24 isospin-symmetric ensembles of gauge-field configurations with six different lattice spacings as small as approximately 0.03 fm and several values of the light quark masses down to physical values of the average up- and down-sea-quark masses. We use the highly-improved staggered quark (HISQ) formulation for valence and sea quarks, including the bottom quark. The analysis employs heavy-quark effective theory (HQET). A novel HQET method is used in the determination of the quark masses.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
