R. Sarno

Meson spectroscopy and decay constants with Wilson fermions at β = 6.4

Abstract We present an extensive lattice study of the physical properties of mesons, composed of a heavy, H, and a light, q, quark, at β = 6.4 on a 24 3 × 60 lattice, using the Wilson action in the quenched approximation. We have studied the mass spectrum and the decay constants of vector and pseudoscalar mesons. We find significant violations of the mass scaling law ƒ P √M P = const. . (∼ 50% for D-mesons and ∼ 20% for B-mesons). The results using quenched but propagating quarks are remarkably consistent with the static results when the scale is taken from the pion decay constant. Combining the results obtained by several calculations of the pseudoscalar decay constants as a function of the meson mass, at different values of the lattice spacing, we obtain by extrapolation ƒ B √B B = (220 ± 40) MeV (ƒ B = (205 ± 40) MeV and B B = 1.16 ± 0.07) , where B B is the renormalization group invariant B -parameter relevant for B d − B d mixing. We also find ƒ B s 2 B B s /ƒ B d 2 B B d = 1.19 ± 0.10 . This last result is relevant in experimental studies of B s − B s mixing. The vector-pseudoscalar mass splittings do not follow the predicted behaviour, M V 2 − M P 2 const., which is expected (and found experimentally) in the limit of large heavy quark masses (i.e. when m H ⪢ Λ QCD ).

Lattice calculation of D- and B-meson semileptonic decays, using the clover action at β = 6.0 on APE

Abstract We present the results of a high statistics lattice calculation of hadronic form factors relevant for D - and B -meson semi-leptonic decays into light pseudoscalar and vector mesons. The results have been obtained by averaging over 170 gauge field configurations, generated in the quenched approximation, at β = 6.0, on a 18 3 × 64 lattice, using the O ( α )-improved SW-Clover action. From the study of the matrix element 〈 K − |J μ |D 0 〉, we obtain f + (0) = 0.78 ± 0.08 and from the matrix element 〈 K ∗0 |J μ |D + 〉 we obtain V (0) = 1.08 ± 0.22, A i (0) = 0.67 ± 0.11 and A 2 (0) = 0.49 ± 0.34. We also obtain the ratios V(0) A 1 (0) = 1.6 ± 0.3 and A 2 (0) A 1 (0) = 0.7 ± 0.4 . Our predictions for the different form factors are in good agreement with the experimental data, although, in the case of A 2 (0), the errors are still too large to draw any firm conclusion. With the help of the Heavy Quark Effective Theory (HQET) we have also extrapolated the lattice results to B -meson decays. The form factors follow a behaviour compatible with the HQET predictions. Our results are in agreement with a previous lattice calculation, performed at β = 6.4, using the standard Wilson action.

Lbe Simulations Of Rayleigh-Bénard Convection On The Ape100 Parallel Processor

In this paper we describe an implementation of the Lattice Boltzmann Equation method for fluid-dynamics simulations on the APE100 parallel computer. We have performed a simulation of a two-dimensional Rayleigh-Benard convection cell. We have tested the theory proposed by Shraiman and Siggia for the scaling of the Nusselt number vs. Rayleigh number.

A HARDWARE IMPLEMENTATION OF THE APE100 ARCHITECTURE

APE100 processors are based on a simple Single Instruction Multiple Data architecture optimized for the simulation of Lattice Field Theories or other complex physical systems. This paper describes the hardware implementation of the first APE100 machine.

THE APE-100 COMPUTER: (I) THE ARCHITECTURE

We describe APE-100, a SIMD, modular parallel processor architecture for large scale scientific computation. The largest configuration that will be implemented in the present design will deliver a peak speed of 100 Gflops. This performance is, for instance, required for high precision computations in Quantum Chromo Dynamics, for which APE-100 is very well suited.

The Software Of The Ape100 Processor

We describe the software environment available for the APE100 parallel processor. We discuss the parallel programming language that we have defined for APE100 and its optimizing compiler. We then describe the operating system that allows to control APE100 from a host computer.

β=6.0 quenched Wilson fermions

Abstract We discuss the Ape Collaboration recent results for the Wilson fermions hadronic mass spectrum at β =6.0 on a 24 3 × 32 lattice. Some of the main new points are the results for the nucleon σ term and the estimates for excited states.

Staggered fermions at β = 5.7: Smeared operators on large lattices

Abstract We study staggered quenched QCD at a moderate value of β on large lattices. We introduce smeared Green functions for staggered fermions, and we analyze their effectiveness. We estimate the lattice spacing, and establish that staggered fermions undergo large systematic errors at low β in the estimate of the lattice spacing from the ϱ-mass. The scale ratio of the baryonic and the mesonic sector (mp/mp) is, on the contrary, consistent with the one estimated by using Wilson fermions. Owing to the use of smeared operators on large lattices (up to 243 × 32), we are able to give reliable results for the baryonic states.

A high statistics lattice calculation of ƒB in the static limit on APE

We present a high statistics calculation of ƒB in the static limit. The results have been obtained by numerical simulation of quenched QCD, at β = 6.0 on a 183 × 32 lattice. We compare ƒB calculated by using the Wilson and the Clover quark actions. The decay constant is obtained by studying heavy-light correlation functions of different smeared operators, on a sample of 210 gauge field configurations. We find that cubic smearings of size Ls ⩽ 3 or Ls ⩾ 9 are bad projectors on the lightest pseudoscalar state. Combining the information coming from smearing Ls = 5 and Ls = 7, we have obtained ƒB = 370±40 MeV in the clover case and ƒB = 350±40±30 MeV in the Wilson case. Our results support a large value of the pseudoscalar decay constant in the static approximation.

A lattice study of the exclusive B->K*gamma decay amplitude, using the Clover action at beta=6.0

Abstract We present the results of a numerical calculation of the B → K ∗ γ form factors. The results have been obtained by studying the relevant correlation functions at β = 6.0, on an 18 3 × 64 lattice, using the O ( a )-improved fermion action, in the quenched approximation. From the study of the matrix element 〈K ∗ | s σ μν b|B〉 we have obtained the form factor T 1 (0) which controls the exclusive decay rate. The results are compared with the recent results from CLEO. We also discuss the compatibility between the scaling laws predicted by the Heavy Quark Effective Theory (HQET) and pole dominance, by studying the mass- and q 2 -dependence of the form factors. From our analysis, it appears that the form factors follow a mass behaviour compatible with the predictions of the HQET and that the q 2 -dependence of T 2 is weaker than would be predicted by pole dominance.