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We present the status of a lattice calculation for the K-->pipi matrix elements of the (delta S=1) effective weak Hamiltonian, directly with two pion in the final state. We study the energy shift of two pion in a finite volume both in the I=0 and I=2 channels. We explain a method to avoid the Goldstone pole contamination in the computation of renormalization constants for (delta I=3/2) operators. Finally we show some preliminary results for the matrix elements of (delta I=1/2) operators. Our quenched simulation is done at beta=6.0, with Wilson fermions, on a (24^3 X 64) lattice., Comment: 3 pages (5 figs), Lattice2001 (matrixelement)

We investigate the critical dynamics of the Hybrid Monte Carlo algorithm approaching the chiral limit of standard Wilson fermions. Our observations are based on time series of lengths O(5000) for a variety of observables. The lattice sizes are 16^3 x 32 and 24^3 x 40. We work at beta=5.6, and kappa=0.156, 0.157, 0.1575, 0.158, with 0.83 > m_pi/m_rho > 0.55. We find surprisingly small integrated autocorrelation times for local and extended observables. The dynamical critical exponent $z$ of the exponential autocorrelation time is compatible with 2. We estimate the total computational effort to scale between V^2 and V^2.25 towards the chiral limit., 3 pages, Latex with espcrc2.sty and postscript figures, Talk given at Lattice 97

We present results for the Kaon $B$ parameter from a sample of $200$ configurations using the Wilson action and $460$ configurations using the Clover action, on a $18^3 \times 64$ lattice at $\beta=6.0$. A slight improvement of the chiral behaviour of $B_K$ is observed due to the Clover action. We have also compared the results for $B_K$ obtained from two different procedures for the boosting of the coupling constant $g$. We observe a strong dependence of $B_K$ on the prescription adopted for $g$ in the Wilson case, contrary to the results of the Clover case which are almost unaffected by the choice of $g$. Combining some recently obtained non perturbative estimates for the renormalisation constants with our Clover matrix element, we observe a significant improvement in the chiral behaviour of $B_K$., Comment: 3 pages, Latex, Postscript file with figures available at ftp://hpteo.roma1.infn.it/pub/preprints/lat94/donini ; to appear in Lattice '94, Nucl. Phys. (Proc.Suppl.)

We present a study of the heavy-light spectrum and of the D- and B-meson decay constants. The results wer e obtained in the quenched approximation, by using the non-perturbatively improved Clover lattice action at beta=6.2, with a sample of 100 configurations, on a 24^3 x 64 lattice. After a careful analysis of th e systematic errors present in the extraction of the physical results, by assuming quite conservative discretization errors, we find f_Ds=231 +/- 12^{+6}_{-1} MeV, f_D = 211 +/- 14^{+0}_{-12} MeV, f_Ds/f_D=1.10(2), f_Bs = 204 +/- 16^{+28}_{-0} MeV, f_B = 179 +/- 18^{+26}_{-9} MeV, f_Bs/f_B=1.14(3)^{+0}_{-1}. Our results, which have smaller discretization errors than many previous estimates at fixed value of the lattice spacing $a$, support a large value of f_B in the quenched approximation., 26 pages, 9 Postscript figures

We present the results for light hadron spectrum, decay constants and the quark masses obtained with non-perturbatively improved Wilson fermions. We also give our preliminary results for the heavy-light decay constants., 3 pages, 2 figures, corrected some typos and one reference added, LATTICE98(spectrum)

APENEXT is a new generation APE processor, optimized for LGT simulations. The project follows the basic ideas of previous APE machines and develops simple and cheap parallel systems with multi T-Flops processing power. This paper describes the main features of this new development., Comment: Lattice2001(plenary/machinestatus), 4 pages, 1 eps figure

We present the preliminary results obtained on the 6 Gigaflop prototype which is the building block of the APE-100 computer. Results are presented for pseudoscalar and vector mesons for the Wilson and the improved action with a statistics of about 100 configurations. Static heavy-light meson propagator have also been studied for different smeared operators. We find that large smearing (greater-than-or-equal-to 9) are bad projectors on the lightest pseudoscalar states.

We discuss the Ape Collaboration results for the hadronic mass spectrum obtained in the staggered fermion formulation at β =6.0 on a 24 3 × 32 lattice. We underscore the good features that are coming out at higher β values, as for example the value of the σ term, the status of flavor symmetry and the relation with Wilson fermion discretization.

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.

Numerical simulations in theoretical high-energy physics (Lattice QCD) require huge computing resources. Several generations of massively parallel computers optimised for these applications have been developed within the APE (array processor experiment) project. Large prototype systems of the latest generation, apeNEXT, are currently being assembled and tested. This contribution explains how the apeNEXT architecture is optimised for Lattice QCD, provides an overview of the hardware and software of apeNEXT, and describes its new features, like the SPMD programming model and the C compiler.

We propose an approach for calculating $K\to\pi\pi$ decays to the next-to-leading order in chiral expansion. A detailed numerical study of this approach is being performed., Comment: 3 pages, 1 figure, lattice 2001, matrixelement

This paper presents the status of the APEmille project, which is essentially completed, as far as machine development and construction is concerned. Several large installations of APEmille are in use for physics production runs leading to many new results presented at this conference. This paper briefly summarizes the APEmille architecture, reviews the status of the installations and presents some performance figures for physics codes., Lattice2001(algorithms), 3 pages, 1 eps figure

By combining the first unquenched lattice computation of the B-meson binding energy and the two-loop contribution to the lattice HQET residual mass, we determine the (\bar{{MS}}) (b)-quark mass, (\bar{m}_{b}(\bar{m}_{b})). The inclusion of the two-loop corrections is essential to extract (\bar{m}_{b}(\bar{m}_{b})) with a precision of ({\cal O}(\Lambda^{2}_{QCD}/m_{b})), which is the uncertainty due to the renormalon singularities in the perturbative series of the residual mass. Our best estimate is (\bar{m}_{b}(\bar{m}_{b}) = (4.26 \pm 0.09) {\rm GeV}), where we have combined the different errors in quadrature. A detailed discussion of the systematic errors contributing to the final number is presented. Our results have been obtained on a sample of (60) lattices of size (24^{3}\times 40) at (\beta =5.6), using the Wilson action for light quarks and the lattice HQET for the (b) quark, at two values of the sea quark masses. The quark propagators have been computed using the unquenched links generated by the T(\chi)L Collaboration., Comment: 19 pages, 1 figure

The APE project was started in 1984 by a group of theoretical physicist. In this project, the design and construction of a parallel computer optimized for lattice quantum chromo dynamics (LQCD) was submitted to INFN for funding. The result was the APE computer. The development of this machine set a new standard of precision at the end of the 80s.

I report on the recent work done by the Ape Collaboration. © 1990.

We discuss the renormalization of different definitions of quark masses in the Wilson and the tree-level improved SW-Clover fermionic action. For the improved case we give the correct relationship between the quark mass and the hopping parameter. Using perturbative and non-perturbative renormalization constants, we extract quark masses in the $\MSbar$ scheme from Lattice QCD in the quenched approximation at $\beta=6.0$, $\beta=6.2$ and $\beta=6.4$ for both actions. We find: $\bar{m}^{\MSbar}(2 GeV)=5.7 \pm 0.1 \pm 0.8$ MeV, $m_s^{\MSbar}(2GeV)= 130 \pm 2 \pm 18 $ MeV and $m_c^{\MSbar}(2 GeV) = 1662\pm 30\pm 230$ MeV., Comment: 21 pages, 4 figures, typos corrected, no result changed

We determine the chiral condensate from simulations of quenched lattice QCD with Wilson fermions. Our measurements have been obtained with high statistics at three values of the gauge coupling, corresponding to UV cutoffs in the range 2 - 4 GeV. Several improvements have been made with respect to earlier lattice computations. The most important are the non-perturbative renormalization of the condensate, the use of the tree-level improved Clover action and the reduction of the systematic error due to uncertainties in the lattice calibration. Our result for the chiral condensate in the $\msbar$ scheme is (\bar\psi \psi)^{\msbar}(mu = 2 GeV) = - 0.0147(8)(16)(12) GeV^3 = - [245(4)(9)(7) MeV]^3 where the first error is statistical, the second is due to the non-perturbative renormalization and the third due to the lattice calibration., Comment: 34 pages, latex, no figures. Some references and the value of the chiral condensate at 1 GeV added, no conclusions changed

We present results for spectroscopy, quark masses and decay constants obtained from SESAM's and TχL's large statistics simulations of QCD with two dynamical Wilson fermions.

We compute non-perturbatively the renormalization constants of quark bilinears on the lattice in the quenched approximation at three values of the coupling beta=6/g_0^2=6.0,6.2,6.4 using both the Wilson and the tree-level improved SW-Clover fermion action. We perform a Renormalization Group analysis at the next-to-next-to-leading order and compute Renormalization Group invariant values for the constants. The results are applied to obtain a fully non-perturbative estimate of the vector and pseudoscalar decay constants., Comment: 21 pages, latex, five latex figures included

Results from two studies of full QCD with two flavours of dynamical Wilson fermions are presented. At beta=5.6, the region 0.83 > m_pi/m_rho > 0.56 at m_pia > 0.23 L^{-1} is explored. The SESAM collaboration has generated ensembles of about 200 statistically independent configurations on a 16^3 x 32-lattice at three different kappa-values and is entering the final phase of data analysis. The TXL simulation on a 24^3 x 40-lattice at two kappa-values has reached half statistics and data analysis has started recently, hence most results presented here are preliminary. The focus of this report is fourfold: we demonstrate that algorithmic improvements like fast Krylov solvers and parallel preconditioning recently introduced can be put into practise in full QCD simulations, we present encouraging observations as to the critical dynamics of the Hybrid Monte Carlo algorithm in the approach to the chiral limit, we mention signal improvements of noisy estimator techniques for disconnected diagrams to the pi-N sigma term, and we report on SESAM's results for light hadron spectrum, light quark masses, and heavy quarkonia., 24 pages, tex + postscript figures, to appear in Proceedings of Int. Workshop "Lattice QCD on Parallel Computers", University of Tsukuba, Japan

In this talk I give a brief overview of Quantum Chromodynamics on the Lattice and report on some of the most recent results obtained in the field.

The investigation of light sea-quark effects in lattice QCD with dynamical Wilson fermions requires both larger physical volumes and finer lattice resolutions than achieved previously. As high-end supercomputers like the 512-node APE Tower provide the compute power to perform a major step towards the chiral limit (T-chi-L), we have launched a feasibility study on a 24^3 x 40 lattice. We approach the chiral limit--while refining the resolution--, using the standard Wilson fermion action. Following previous work, our Hybrid Monte Carlo simulation runs at beta=5.6 and two kappa-values, 0.1575 and 0.158. From our study, we are confident that, for the APE Tower, a realistic working point has been found corresponding to a volume of 2 fm^3, with chirality characterized by 1/(a m_pi) = 5.6., Comment: Latex, 3 pages, postscript figures

We describe the architecture of the APEmille Parallel Computer, the new generation of the APE family of processors optimized for Lattice Gauge Theory simulations. We emphasize the features of the new machine potentially useful for applications in other areas of computational physics.

We present results on the static potential, and torelon and glueball masses from simulations of QCD with two flavours of dynamical Wilson fermions on $16^3\times 32$ and $24^3\times 40$ lattices at $\beta=5.6$., Comment: Talk presented by Gunnar Bali at International Symposium on Lattice Field Theories (Lattice 97), Edinburgh, July 1997, 3 pages LaTeX (epscrc2.sty) with 4 eps figures

We present the results of a numerical calculation of the B\rightarrow K^* \gamma form factors. The results have been obtained by studying the relevant correlation functions at \beta=6.0, on an 18^3 \times 64 lattice, using the {\rm O(a)}-improved fermion action, in the quenched approximation. From the study of the matrix element \langle K^*\vert \bar s \sigma_{\mu\nu} b \vert B\rangle 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. We present the results of a numerical calculation of the $B\rightarrow K~* \gamma$ form factors. The results have been obtained by studying the relevant correlation functions at $\beta=6.0$, on an $18~3 \times 64$ lattice, using the ${\rm O(a)}$-improved fermion action, in the quenched approximation. From the study of the matrix element $ \langle K~*\vert \bar s \sigma_{\mu\nu} b \vert B\rangle$ 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. 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.

We present results for the kaon $B$-parameter $B_K$ from a sample of $200$ configurations using the Wilson action and $460$ configurations using the SW-Clover action, on a $18^3 \times 64$ lattice at $\beta=6.0$. We compare results obtained by renormalizing the relevant operator with different ``boosted" values of the strong coupling constant $\alpha_s$. In the case of the SW-Clover action, we also use the operator renormalized non-perturbatively. In the Wilson case, we observe a strong dependence of $B_K$ on the prescription adopted for $\alpha_s$, contrary to the results of the Clover case which are almost unaffected by the choice of the coupling. We also find that the matrix element of the operator renormalized non-perturbatively has a better chiral behaviour. This gives us our best estimate of the renormalization group invariant $B$-parameter, $\hat B_K=0.86 \pm 0.15$., Comment: LaTeX, 17 pages, 3 postscript figures uuencoded

We argue that there is strong experimental evidence in the data of b- and c-decays that the pattern of power suppressed corrections predicted by the short distance expansion, the heavy quark effective theory and the assumption of local duality is not correct for the non-leptonic inclusive widths. The data indicate instead the presence of 1/m corrections that should be absent in the above theoretical framework. These corrections can be simply described by replacing the heavy quark mass by the mass of the decaying hadron in the m^5 factor in front of all the non-leptonic widths., 9 pages, 1 figure; Revised: one reference ([11]) has been changed

In this paper we study O(2000) (quenched) lattice configurations from the APE collaboration, for different lattice volumes and for 6.0 \le beta \le 6.4 using both the Wilson and the SW-Clover fermion actions. We determine the light hadronic spectrum and meson decay constants and study the mesonic dispersion relation. We extract the hadronic variable J and the strange quark mass in the continuum at the next-to-leading order obtaining m_s^{MSbar}(mu=2 GeV) = 122 +/- 20 MeV. A study is made of their dependence on lattice spacing. We implement a newly developed technique to extract the inverse lattice spacing using data at the simulated values of the quark mass (i.e. at masses around the strange quark mass)., Comment: 36 pages, LateX with 20 postscript figures. Small numerical errors corrected, no conclusions changed

The decay constant for the B-meson in the static limit is calculated using the Wilson and clover actions at various lattice spacings. We show that both the contamination of our results by excited states and the effects finite lattice spacing are at most the order of the statistical uncertainties. A comparison is made of our results and those obtained in other studies. Values for $f^{stat}_{B_S}/f^{stat}_B$ and $M_{B_S} - M_B$ are also given., Contribution to Lattice'94, 3 pages PostScript, uuencoded compressed

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 $\beta=6.0$, on a $18^3 \times 64$ lattice, using the $O(a)$-improved SW-Clover action.From the study of the matrix element $$, we obtain $f_+ (0)=0.78\pm 0.08$ and from the matrix element $$ we obtain $V(0)=1.08\pm 0.22$, $A_1(0)=0.67\pm 0.11$ and $A_2(0)=0.49\pm 0.34$. We also obtain the ratios $V(0)/A_1(0)=1.6\pm 0.3$ and $A_2(0)/A_1(0)= 0.7\pm 0.4$. 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 $\beta=6.4$, using the standard Wilson action., Comment: LaTeX, 15 pages, postscript figures attached uuencoded

Using the recent relatively precise experimental results on the pion structure function, obtained from Drell--Yan processes, we quantitatively test an old model where the structure function of any hadron is determined by that of its constituent quarks. In this model the pion structure function can be predicted from the known nucleon structure function. We find that the data support the model, at least as a good first approximation., Comment: 9 pages, 3 figures

We present results for the radiative decay B --> K*gamma, obtained by using the Clover action at beta = 6.0 on APE. The compatibility between the scaling laws predicted by the Heavy Quark Effective Theory (HQET) and pole dominance is discussed. The final result depends crucially on the assumed q(2)-dependence of the form factors

We present a calculation of $f_B$ in the static limit, obtained by numerical simulation of quenched QCD, at $\beta=6.2$ on a $18^3 \times 64$ lattice, using the SW-Clover quark action. The decay constant has been extracted by studying heavy(static)-light correlation functions of different smeared operators, on a sample of 220 gauge field configurations. We have obtained $f_B^{static}=(290 \pm 15 \pm 45)$ MeV, where the first error comes from the uncertainty in the determination of the matrix element and the second comes from the uncertainty in the lattice spacing. We also obtain $M_{B_s}-M_{B_d}= (70 \pm 10)$ MeV and $f^{stat}_{B_s}/f^{stat}_{B_d}=1.11(3)$. A comparison of our results with other calculations of the same quantity is made.

The light quark results from three different simulations are summarized. We get consistent results, within our statistics, between smeared and non smeared data. A comparison is performed with similar results from the UKQCD collaboration. All runs have been performed on two 6.4 GF APE computers [1].

Recent results for semi-leptonic decays of $D$ and $B$ mesons at $\beta=6.4$, using the Wilson action, and at $\beta=6.0$, using the Clover action, are reported., Comment: at the Dallas Lattice Conference, October 1993. 3 pages in a single postscript file, uuencoded form. Rome Preprint 93/986

We present a high statistics calculation of f(B) in the static limit. The results have been obtained by numerical simulation of quenched QCD, at beta = 6.0 on a 18(3) x 32 lattice. We compare f(B) 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 L(s) less-than-or-equal-to 3 or L(s) greater-than-or-equal-to 9 are bad projectors on the lightest pseudoscalar state. Combining the information coming from smearing L(s) = 5 and L(s) = 7, we have obtained f(B) = 370 +/- 40 MeV in the Clover case and f(B) = 350 +/- 40 +/- 30 MeV in the Wilson case. Our results support a large value of the pseudoscalar decay constant in the static approximation.

The decay constants of the heavy-light pseudoscalar mesons are studied in a high statistics run using the Wilson action at $\beta=6.0$ and $\beta=6.2$, and the clover action at $\beta=6.0$. The systematics of $O(a)$ discretisation errors are discussed. Our best estimates of the decay constants are: $f_D$ = 218(9) MeV, $f_D/f_{Ds}$ = 1.11(1) and we obtain preliminary values for $f_B$., Comment: at the Dallas Lattice Conference, October 1993. 3 pages in a single postscript file, uuencoded form. Rome Preprint 93/985

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{variant}-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. © 1990.

We study the behavior of the string tension in the SU(3) lattice pure-gauge theory close to the deconfining critical point. We find very large correlation lengths, increasing with the lattice size. This result is strongly suggestive of a second-order phase transition, and excludes the presence of a strong first-order transition. © 1988 The American Physical Society.

A thorough analysis is presented of the hadronic transverse energy produced in association with W± and Z0 weak bosons at p {Mathematical expression} colliders. The complete rapidity and transverse energy distributions are derived, including the perturbative annihilation and Compton terms and the resummation of soft gluons. The first non leading corrections to the corresponding Sudakov exponent are included in full and their effects are discussed. To make contact with the actual data a number of non perturbative inputs is also necessary. We extract this information from minimum bias measurements. A detailed comparison of the resulting theoretical predictions with the available experimental data is finally presented. © 1986 Springer-Verlag.

We investigate the possibility of identifying heavy quarks produced in hadron collision by detecting the multilepton final states. A new algorithm is developed for dilepton and trilepton events, which allows an efficient distinction between different primary heavy flavours. © 1982 Società Italiana di Fisica.

We report the results of a numerical computation of the pion propagator for 40 configurations on an 83 × 16 lattice using the ICL distributed array processor. We use the Wilson form for the fermion action and work in the quenched approximation which neglects dynamical fermion loops. We confirm that, for the chosen gauge coupling g2 = 1, seven or eight lattice spacings are required to see the contribution of the pion pole against the background of excited states. We estimate the critical value of the hopping parameter Kc = 0.157±0.001 and the pion decay constant ⨍ π = 130±45 MeV .

We show that a study of the processes {A figure is presented} can provide information on the pion structure functions. Using a realistic parton distribution for the pion we calculate cross sections and relevant distributions for these processes. The results show that such measurements are experimentally accessible. © 1979.

We report the results of strange and light-quark hadron masses obtained by a simulation of QCD in the zero fermion loops approximation (quenching) on a 10 3 × 20 lattice. The results are sensibly different from those obtained on smaller lattices and show a definite improvement.

A Monte Carlo computation of meson and hadron spectroscopy within lattice QCD is made. We give a detailed discussion of the statistical and systematic errors of the results and analyze the present limitations of our approach. The results are in agreement with the observed spectrum. We also estimate the values of up, down and strange quark masses. © 1982.

We compute the QCD hadronic mass spectrum in quenched lattice QCD at β=5.7 with small statistical and systematic errors by using the APE computer.

We compute the correlation length of an SU(3) gauge system in the neighbourhood of the deconfining phase transition by measuring loop-loop correlation functions. We find values that are linearly divergent with the lattice size at the critical point and fully compatible with our former estimates obtained by using a cold source method. Together with a precise determination of the location of the critical point these results make stronger the evidence for a large ξ at β close to β c .

We study the effect of mass renormalization to the behaviour of iterative methods for the computation of the quark propagator on the lattice.

Predictions on lepton pair production in meson-nucleon collisions, taking into account scale breaking, are compared with the most recent experimental data.

We measure the correlation length of Polyakov loop in the region of the deconfinement transition for a pure gauge SU(3) theory on lattices of different sizes. The correlation length is found to be of the order of lattice size, thus excluding a strong first order transition.