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The final oscillation analysis of the complete set of data collected by CHORUS in the years 1994-1997 is presented. Reconstruction algorithms of data extracted by electronic detectors were improved and the data recorded in the emulsion target were analysed by new automated scanning systems, allowing the use of a new method for event reconstruction in emulsion. CHORUS has applied these new techniques to the sample of 1996-1997 events for which no muons were observed in the electronic detectors. Combining the new sample with the data analysed in previous papers, the overall sensitivity of the experiment to the ν τ appearance is thus improved. In a two-neutrino mixing scheme, a 90% C.L. upper limit of sin 2 2θ µτ < 4.4 × 10 −4 is set for large ∆m 2 , improving by a factor 1.5 the previously published CHORUS result.3

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We report on a numerical simulation with 2+1 dynamical flavors of overlap fermions. We calculate pseudo-scalar masses and decay constants on a 16 3 × 48 × (0.11 fm) 4 lattice at five different up and down quark masses and two strange quark masses. The lightest pion mass corresponds to ≈ 310 MeV. We also study the validity of the chiral perturbation theory using the results of the numerical simulation with two dynamical flavors and conclude that the one-loop formulae cannot be directly applied in the strange quark mass region. We therefore extrapolate our 2+1-flavor results to the chiral limit by fitting the data to the two-loop formulae of the chiral perturbation theory.

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