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تسجيل مستخدم جديدPrecision $B_c$ and $B_s$ mass calculations
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We give improved results for B meson masses using NRQCD $b$ quarks and HISQ light valence quarks for a range of lattice spacings and sea quark masses enabling controlled extrapolation to the physical point.
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We present a new determination of the $B_s$ leptonic decay constant from lattice QCD simulations that use gluon configurations from MILC and a highly improved discretization of the relativistic quark action for both valence quarks. Our result, $f_{B_
s} = 0.225(4)$,GeV, is almost three times more accurate than previous determinations. We analyze the dependence of the decay constant on the heavy quarks mass and obtain the first empirical evidence for the leading $1/sqrt{m_h}$ dependence predicted by Heavy Quark Effective Theory (HQET). As a check, we use our analysis technique to calculate the $m_{B_s}-m_{eta_b}/2$ mass difference. Our result agrees with experiment to within errors of $11,mathrm{MeV}$ (better than 2%). We discuss how to extend our analysis to other quantities in $B_s$ and $B$ physics, making 2%-precision possible for the first time.
Recently, many new excited states of heavy mesons, especially the radially excited states, are discovered. The study of the production processes of these states from the ground b-flavored mesons is of interest. In this paper, we use the improved Beth
e-Salpeter method to study the semi-leptonic and non-leptonic decays of $B$, $B_s$, and $B_c$ mesons, where the final states are focused on the radial excited $2S$ and $3S$ states. We find that many channels have branching ratios up to $10^{-4}$, which are within the detection accuracy of current experiments.
Finite energy QCD sum rules with Legendre polynomial integration kernels are used to determine the heavy meson decay constant $f_{B_c}$, and revisit $f_B$ and $f_{B_s}$. Results exhibit excellent stability in a wide range of values of the integration
radius in the complex squared energy plane, and of the order of the Legendre polynomial. Results are $f_{B_c} = 528 pm 19$ MeV, $f_B = 186 pm 14$ MeV, and $f_{B_s} = 222 pm 12$ MeV.
Measurements of $B_c^+$ production and mass are performed with the decay mode $B_c^+ to J/psi pi^+$ using 0.37 fb$^{-1}$ of data collected in $pp$ collisions at $sqrt{s}=7$ TeV by the LHCb experiment. The ratio of the production cross-section times b
ranching fraction between the $B_c^+ to J/psi pi^+$ and the $B^+ to J/psi K^+$ decays is measured to be $(0.68 pm 0.10,({rm stat.}) pm 0.03,({rm syst.}) pm 0.05,({rm lifetime}))$% for $B_c^+$ and $B^+$ mesons with transverse momenta $p_{rm T}>4 $GeV/$c$ and pseudorapidities $2.5<eta<4.5$. The $B_c^+$ mass is directly measured to be $6273.7 pm 1.3,({rm stat.}) pm 1.6 ,({rm syst.})$ MeV/$c^2$, and the measured mass difference with respect to the $B^+$ meson is $M(B_c^+)-M(B^+) = 994.6 pm 1.3,({rm stat.}) pm 0.6,({rm syst.})$ MeV/$c^2$.
Semi-leptonic $B_s to K ell u$ and $B_s to D_s ell u$ decays provide an alternative $b$-decay channel to determine the CKM matrix elements $|V_{ub}|$ and $|V_{cb}|$ or to obtain $R$-ratios to investigate lepton flavor universality violations. In ad
dition, these decays may shed further light on the discrepancies seen in the analysis of inclusive vs. exclusive decays. Using the nonperturbative methods of lattice QCD, theoretical results are obtained with good precision and full control over systematic uncertainties. This talk will highlight ongoing efforts of the $B$-physics program by the RBC-UKQCD collaboration.
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