O. Pène

Light hadrons from lattice QCD with light (u, d), strange and charm dynamical quarks

We present results of lattice QCD simulations with mass-degenerate up and down and mass-split strange and charm (Nf = 2 + 1 + 1) dynamical quarks using Wilson twisted mass fermions at maximal twist. The tuning of the strange and charm quark masses is performed at two values of the lattice spacing a ≈ 0:078 fm and a ≈ 0:086 fm with lattice sizes ranging from L ≈ 1:9 fm to L ≈ 2:8 fm. We measure with high statistical precision the light pseudoscalar mass mPS and decay constant fPS in a range 270 ≲ mPS ≲ 510 MeV and determine the low energy parameters f0 and

Standard model CP-violation and baryon asymmetry (II). Finite temperature

{\bar{l}_{3,4}}

The Infrared Behaviour of the Pure Yang–Mills Green Functions

of SU(2) chiral perturbation theory. We use the two values of the lattice spacing, several lattice sizes as well as different values of the light, strange and charm quark masses to explore the systematic effects. A first study of discretisation effects in light-quark observables and a comparison to Nf = 2 results are performed.

The Kaon B-parameter and K-π and K-ππ transition amplitudes on the lattice

Abstract We consider quantum effects in a world with two coexisting symmetry phases, unbroken and spontaneously broken, as a result of a first order phase transition. The discrete symmetries of the problem are discussed in general. We compute the exact two-point Green function for a free fermion, when a thin wall separates the two phases. The Dirac propagator displays both massive and massless poles, and new CP -even phases resulting from the fermion reflection on the wall. We discuss the possible quark-antiquark CP -asymmetries produced in the Standard Model (SM) for the academic T = 0 case. General arguments indicate that an effect first appears at order α W in the reflection amplitude, as the wall acts as a source of momentum and the on-shell one-loop self-energy cannot be renormalized away. The asymmetries stem from the interference of the SM CP -odd couplings and the CP -even phases in the propagator. We perform a toy computation that indicates the type of GIM cancellations of the problem. The behaviour can be expressed in terms of two unitarity triangles.

Strong decays of ψdblac; (4.028) as a radial excitation of charmonium

We review the infrared properties of the pure Yang–Mills correlators and discuss recent results concerning the two classes of low-momentum solutions for them reported in literature, i.e. decoupling and scaling solutions. We will mainly focus on the Landau gauge and pay special attention to the results inferred from the analysis of the Dyson–Schwinger equations of the theory and from “quenched” lattice QCD. The results obtained from properly interplaying both approaches are strongly emphasized.

Computing K and D meson masses with N_f = 2+1+1 twisted mass lattice QCD

We present the results of a computation of the K0−K0 and ΔI = 32 K−π and K−ππ amplitudes in lattice QCD. The numerical simulation has been done using the standard one-plaquette action and Wilson fermions, in the quenched approximation. Combining the tesults obtained at β = 6 on a 102 × 20 × 40 lattice with 30 configurations with those at β = 6.2 on a 163 × 48 lattice with 15 configurations, we have obtained for the kaon B-parameterBK0 − K0 = 0.65 ± 0.15 at μ = 3 GeV. We have also evaluated the ΔI = 32K−π and K−π weak hamiltonian matrix elements. The relevant renormalized operator O4 has been found to satisfy soft-pion theorems and chiral lagrangian relations at the 30% level, and this makes us confident about our results. We find (〈K+|HW|π+π0〉/mK) = (7 ± 2) × 10−8 to be compared with the experimental value of 3.7 × 10−8.

Heavy flavour weak transitions on the lattice

Abstract The decay rates of ψdblac; (4.028)→ D D, D D ∗ + D D ∗ , D ∗ , D ∗ D ∗ can be fairly well understood with the assignment this state as a second radial excitation of charmonium. The nodes of the wave function and the different Q -value in each of these decays allow to understand the failure of the simple quark spin counting prediction.

Why is ψ(4.414) so narrow

We discuss the computation of the mass of the K and D mesons within the framework of N-f = 2 + 1 + 1 twisted mass lattice QCD from a technical point of view. These quantities are essential, already at the level of generating gauge configurations, being obvious candidates to tune the strange and charm quark masses to their physical values. In particular, we address the problems related to the twisted mass flavor and parity symmetry breaking, which arise when considering a non-degenerate (c, s) doublet. We propose and verify the consistency of three methods to extract the K and D meson masses in this framework. (c) 2010 Elsevier By. All rights reserved.

Semi-leptonic decays of heavy flavours on a fine grained lattice

Abstract The pseudoscalar meson decay constant and the B parameter of charmed mesons are calculated by Monte Carlo simulation of lattice QCD, with Wilson fermions and in the quenched approximation. The combined results on two lattices, 10 2 × 20 × 40 and 16 3 × 48, at β = 6 and β = 6.2 respectively, yield ƒ D = 194±15 and ƒ F = 215±17 , and B D D = 0.82±0.10 at μ = 3 GeV. Within the non-relativistic quark model, predictions for the b system can be obtained by extrapolation of the previous results: ƒ B d ⋍120 MeV , ƒ B s ⋍150 MeV . We have also computed the hyperfine splitting and photon coupling of the charmonium system: M (1 − )− M (0 − ) = 50±10 MeV (experiment 117 MeV), (ƒ J/ψ ) − ⋍0.100 (experiment 0.125).

Non-leptonic hyperon decays and the baryon spectrum

Abstract The width of ψ(4.414) is surprisingly small for a c c state far above the charm threshold, Γexp ≈ 33 MeV. This fact can be qualitatively understood if one makes the conservative assignment 4 3S1. The nodes of the wave function reflect as zeros of the decay amplitude in the momentum of the decay products, and are responsible for the suppression of the couplings to the ground state charmed mesons, Γ(ψ(4.414)→D D + D D ∗ + D D∗ + D∗ D ∗ + F F + F F ∗ + F F∗ + F∗ F ∗) ≈ 15 MeV. All the modes are suppressed by factors of the order of 103 with respect to the k3 spin counting prediction. The dominant modes are predicted to be D∗ D ∗, F F ∗ + F F∗ and D D . Moreover, we show that the contributions from P-wave charmed mesons are reasonably expected to be suppressed either by phase space or by the nodes if their masses lie within certain range. We emphasize however that the smallness of the photon coupling remains to be understood.