ar X iv : h ep - l at / 9 80 91 87 v 2 1 O ct 1 99 8 1 New results from APE with nonperturbatively improved Wilson fermions ∗

We present the results for hadronic spectrum, decay constants and the light quark masses obtained with non-perturbatively improved Wilson fermions. We also give our preliminary results for the heavy-light decay constants. The method for systematic improvement of the Wilson action and bilinear quark operators, recently proposed by Alpha–collaboration [1], provides a full cancellation of the linear discretization errors. In other words, the results of lattice calculations of any on − shell quantity, do converge to the continuum limit (a → 0) much faster , i.e. with the rate O(a 2). To verify and quantify the effect of this improvement (first improved studies of the spec-troscopy were done in [2]), we generated 100 independent gauge field configurations on a 24 3 × 64 lattice, at β = 6.2, in the quenched approximation. We used the non-perturbative(NP) value of the coefficient for the improvement of the action , c SW , which guarantees the full improvement of the hadron mass spectrum. The values of all other counterterms coefficients, as well as of the renormalization constants which we used in this work, are listed in Tab. 1. Note that the NP results for Z S , Z P and Z T (given in Tab. 1 at µa = 1), are new. We calculated several correla-tors for mesons made of f our degenerate quark 'flavors'. In the analysis of all hadronic quantities (spectrum and decay constants), we used the method of 'physical lattice planes', proposed and extensively used in Ref. [3]. Further details on * Talk given by D. Becirevic at " Lattice98 " , Boulder, CO. He acknowledges the partial supports of: IN2P3, CNRS, and the organizers of the conference. Renormalization constants Z J , and the improvement coefficients c J and b J at β = 6.2 (c SW = 1.614). For the constants which are not computed non-perturbatively (×), we take the result of the 1-loop boosted perturbation theory (BPT).