7,054 research outputs found
First calculation of D+ -> K*0bar e+ nu-e in Lattice QCD
No full textWe present the results of a calculation of the matrix elements of the quark weak current which are relevant for semileptonic decays of D-mesons into light pseudoscalar and vector mesons. The computations are performed by averaging the results over 15 gauge field configurations, generated in the quenched approximation by the Metropolis algorithm, at beta = 6.0, on a 20 X 10(2) X 40 lattice, with Wilson fermions. From the study of the matrix elements and we find that the partial rate for the semi-leptonic decay of the D+ into KBAR*0e + nu-e is given by GAMMA(D+ --> KBAR*0e + nu-e) = (5.2 +/- 1.9) X 10(10) s-1, in good agreement with the experimental result (4.1 +/- 0.7 +/- 0.5) X 10(10) s-1, and that the ratio of the partial rates GAMMA(D+ --> KBAR*0e + nu-e)/GAMMA(D0 --> K-e + nu-e) is given by 1.1 +/- 0.3, which is larger than the experimental value 0.45 +/- 0.09 +/- 0.07. We also compute the ratio of the longitudinal to transverse polarization rates in KBAR*0 decays and find 1.7 +/- 0.6, to be compared to the experimental value 2.4(-0.9)(+1.7) +/- 0.2. We finally discuss future improvements in the accuracy of our theoretical predictions
Semileptonic decays of D-mesons in Lattice QCD
No full textThe results of a lattice calculation of D-meson semi-leptonic decays into pseudoscalar and vector particles are presented. With respect to our previous studies of D --> K, K*, pi and rho-decays we have doubled the statistics and have studied the SU(3) breaking effects on the relevant form factors. In this letter we also predict the Zweig allowed contributions to the form factors and the corresponding partial rates for the semi-leptonic decays of D and D(s) into phi, omega, eta and eta' mesons
Finite volume effects in weak hadronic decays
No full textIn this talk we discuss finite-volume computations of two-body hadronic decays below the inelastic threshold (e.g. K -> decays). In particular we show how the relation between finite-volume matrix elements and physical amplitudes, recently derived by Lellouch and Luscher, can be extended to all elastic states under the inelastic threshold. We also provide a derivation of the Luscher quantization condition directly in quantum field theory
A lattice computation of the decay constant of the B-meson
No full textWe compute the decay constant of the B-meson, f(B), on a 10(2) x 20 x 40 lattice at beta = 6.0, with Wilson fermions, using 30 gauge field configurations, generated in the quenched approximation. For the propagator of the b-quark we keep only the leading term in the 1/m(b) expansion. To improve our results we use, as the interpolating fields for the B-meson, lattice operators which are "smeared" over several lattice sites. We observe a clear signal for the lightest B-meson state, and obtain the value f(B) = 310 +/- 25 +/- 50 MeV, where the first error is statistical and the second represents our uncertainity in the value of the lattice spacing. This result, combined with earlier lattice measurements of f(D) (f(D) congruent-to 180 MeV), denomstrates that the asymptotic scaling law for the decay constants of heavy pseudoscalar mesons P, (i.e. f(P) square-root-M-(P) approximately constant), has large corrections for charmed mesons. We estimate that the non-scaling corrections will reduce the above value of f(B) by about 25%
Finite-volume two-pion amplitudes in the I = 0 channel
No full textWe perform a calculation in one-loop chiral perturbation theory of the two-pion matrix elements and correlation functions of an I = 0 scalar operator, in finite and infinite volumes for both full and quenched QCD. We show that major difficulties arise in the quenched theory due to the lack of unitarity. Similar problems are expected for quenched lattice calculations of K →ππ amplitudes with ΔI = 1/2. Our results raise the important question of whether it is consistent to study K →ππ amplitudes beyond leading order in chiral perturbation theory in quenched or partially quenched QCD.
Results from a non-perturbative renormalization of lattice operators
No full textWe propose a general renormalization method, which avoids completely the use of lattice perturbation theory. We present the results from its numerical applications to two-fermion operators on a 16^3 \times 32 lattice, at \beta=6.0.We propose a general renormalization method, which avoids completely the use of lattice perturbation theory. We present the results from its numerical applications to two-fermion operators on a lattice, at
An exploratory lattice study of Delta I=3/2 K ->pi pi decays at next-to-leading order in the chiral expansion
No full textWe present the first direct evaluation of Delta I = 3/2K -> pi pi matrix elements with the aim of determining all the low-energy constants at NLO in the chiral expansion. Our numerical investigation demonstrates that it is indeed possible to determine the K -> pi pi matrix elements directly for the masses and momenta used in the simulation with good precision. In this range however, we find that the matrix elements do not satisfy the predictions of NLO chiral perturbation theory. For the chiral extrapolation we therefore use a hybrid procedure which combines the observed polynomial behavior in masses and momenta of our lattice results, with NLO chiral perturbation theory at lower masses. In this way we find stable results for the quenched matrix elements of the electroweak penguin operators ((1=2) = (0.68 +/- 0.09) GeV3 and (1=2) = (0.12 +/- 0.02) GeV3 in the NDR-(MS) over bar scheme at the scale 2 GeV), but not for the matrix elements Of 04 (for which there are too many low-energy constants at NLO for a reliable extrapolation). For all three operators we find that the effect of including the NLO corrections is significant (typically about 30%). We present a detailed discussion of the status of the prospects for the reduction of the systematic uncertainties
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