arXiv subjects
Publications and source records attributed to J. N. Simone.
We perform a precise calculation of the mass of the B_c meson using unquenched configurations from the MILC collaboration including 2+1 flavours of improved staggered quarks. Lattice NRQCD and the Fermilab formalism are used to describe the b and c quarks respectively. We find the mass of the B_c meson to be 6.304(16) GeV
We extend the Fermilab formalism for heavy quarks to develop an $O(a^2)$ improved relativistic action. We discuss our construction of the action, including the identification of redundant operators and the calculation of the improvement coefficients.
We summarize our lattice QCD study of the form factor at zero recoil in the decay anti-B --> D* lepton anti-neutrino. After careful consideration of all sources of systematic uncertainty, we find, h_A1(1) = 0.913(+0.024-0.017)(+0.017-0.030), where the first uncertainty is from statistics and fitting while the second combined uncertainty is from all other systematic effects.
We describe a model independent lattice QCD method for determining the deviation from unity for h_{A1}(1), the B -> D* l nu form factor at zero recoil. We extend the double ratio method previously used to determine the B -> D l nu form factor. The bulk of statistical and systematic errors cancel in the double ratios we consider, yielding form factors which promise to reduce present theoretical uncertainties in the determination of V_{cb}. We present results from a prototype calculation at a single lattice spacing corresponding to beta=5.7.
The zero recoil limit of the B -> D l nu form factors is calculated on the lattice, which provides a model-independent determination of |Vcb|. Considering a ratio of form factors, in which the bulk of statistical and systematic errors cancel, we obtain a precise result both for h_+(1) and for h_-(1).
The increasing accuracy of experimental results for the exclusive, semileptonic decay B -> pi l nu requires a similarly accurate calculation of the hadronic matrix elements, to determine |Vub|. We present preliminary results for the form factors of the B to light meson decay mode. Using results from three lattices in the range 5.7 <= beta <= 6.1 we study the dependence on the lattice spacing.
We estimate statistical and systematic errors in the extraction of the CKM ratio |Vcd|/|Vcs| from exclusive D-meson semileptonic decays using lattice QCD and anticipated new experimental results.
We present the recent Fermilab calculations of the masses of the light quarks, using tadpole-improved Sheikholeslami-Wohlert (SW) quarks. Various sources of systematic errors are studied. Our final result for the average light quark mass in the quenched approximation evaluated in the $\bar{MS}$ scheme is $\bar{m}_q(μ=2 GeV;n_f=0)= (m_u+m_d)/2=3.6 \pm 0.6 MeV$.
We compute the hyperfine splitting $m_{J/ψ}-m_{η_c}$ on the lattice, using both the Wilson and $O(a)$-improved (clover) actions for quenched quarks. The computations are performed on a $24^3\times48$ lattice at $β= 6.2$, using the same set of 18 gluon configurations for both fermion actions. We find that the splitting is 1.83\err{13}{15} times larger with the clover action than with the Wilson action, demonstrating the sensitivity of the spin-splitting to the magnetic moment term which is present in the clover action. However, even with the clover action the result is less than half of the physical mass-splitting. We also compute the decay constants $f_{η_c}$ and $f^{-1}_{J/ψ}$, both of which are considerably larger when computed using the clover action than with the Wilson action. For example for the ratio $f^{-1}_{J/ψ}/f^{-1}_ρ$ we find 0.32\err{1}{2} with the Wilson action and $0.48\pm 3$ with the clover action (the physical value is 0.44(2)).
We present the first study of the light hadron spectrum and decay constants for quenched QCD using an O(a)-improved nearest-neighbour Wilson fermion action at β=6.2. We compare the results with those obtained using the standard Wilson fermion action, on the same set of 18 gauge field configurations of a 24^3 times 48 lattice. For pseudoscalar meson masses in the range 330-800 MeV, we find no significant difference between the results for the two actions. The scales obtained from the string tension and mesonic sector are consistent, but differ from that derived from baryon masses. The ratio of the pseudoscalar decay constant to the vector meson mass is roughly independent of quark mass as observed experimentally, and in approximate agreement with the measured value.