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تسجيل مستخدم جديدLight Meson Physics from Maximally Twisted Mass Lattice QCD
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We present a comprehensive investigation of light meson physics using maximally twisted mass fermions for two mass-degenerate quark flavours. By employing four values of the lattice spacing, spatial lattice extents ranging from 2.0 fm to 2.5 fm and pseudo scalar masses in the range 280 MeV to 650 MeV we control the major systematic effects of our calculation. This enables us to confront our data with chiral perturbation theory and extract low energy constants of the effective chiral Lagrangian and derived quantities, such as the light quark mass, with high precision.
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We compute the static-light baryon spectrum by means of Wilson twisted mass lattice QCD using N_f = 2 flavors of sea quarks. As light u/d valence quarks we consider quarks, which have the same mass as the sea quarks with corresponding pion masses in
the range 340 MeV < m_PS < 525 MeV, as well as partially quenched s quarks, which have a mass around the physical value. We consider all possible combinations of two light valence quarks, i.e. Lambda, Sigma, Xi and Omega baryons corresponding to isospin I = 0, 1/2, 1 and strangeness S = 0, -1, -2 as well as angular momentum of the light degrees of freedom j = 0, 1 and parity P = +, -. We extrapolate in the light u/d and in the heavy b quark mass to the physical point and compare with available experimental results. Besides experimentally known positive parity states we are also able to predict a number of negative parity states, which have neither been measured in experiments nor previously been computed by lattice methods.
In this contribution, a first look at simulations using maximally twisted mass Wilson fermions at the physical point is presented. A lattice action including clover and twisted mass terms is presented and the Monte Carlo histories of one run with two
mass-degenerate flavours at a single lattice spacing are shown. Measurements from the light and heavy-light pseudoscalar sectors are compared to previous $N_f = 2$ results and their phenomenological values. Finally, the strategy for extending simulations to $N_f = 2 + 1 + 1$ is outlined.
We present the results of a lattice QCD calculation of the pseudoscalar meson decay constants f_K, f_D and f_Ds, performed with N_f=2 dynamical fermions. The simulation is carried out with the tree-level improved Symanzik gauge action and with the tw
isted mass fermionic action at maximal twist. With respect to our previous study (0709.4574 [hep-lat]), here we have analysed data at three values of the lattice spacing (a=0.10 fm, 0.09 fm, 0.07 fm) and performed the continuum limit, and we have included at a=0.09 fm data with a lighter quark mass (m_pi = 260 MeV) and a larger volume (L = 2.7 fm), thus having at each lattice spacing L >= 2.4 fm and m_pi*L >= 3.6. Our result for the kaon decay constant is f_K=(157.5 +- 0.8|_{stat.} +- 3.3|_{syst.}) MeV and for the ratio f_K/f_pi=1.205 +- 0.006|_{stat.} +- 0.025|_{syst.}, in good agreement with the other N_f=2 and N_f=2+1 lattice calculations. For the D and D_s meson decay constants we obtain f_D=(205 +- 7|_{stat.} +- 7|_{syst.}) MeV, in good agreement with the CLEO-c experimental measurement and with other recent N_f=2 and N_f=2+1 lattice calculations, and f_{Ds}=(248 +- 3|_{stat.} +- 8|_{syst.}) MeV that, instead, is 2.3 sigma below the CLEO-c/BABAR experimental average, confirming the present tension between lattice calculations and experimental measurements.
Results on the electromagnetic form factors of the nucleon using twisted mass fermion configurations are presented. These include a gauge field ensemble simulated with two degenerate light quarks yielding a pion mass of around 130 MeV, as well as two
ensembles that include strange and charm quarks in the sea yielding pion masses of 210 MeV and 373 MeV. Details of the methods used and systematic errors are discussed, such as noise reduction techniques and the effect of excited states contamination.
We present results for the isospin-0 $pipi$ s-wave scattering length calculated in twisted mass lattice QCD. We use three $N_f = 2$ ensembles with unitary pion mass at its physical value, 240~MeV and 330~MeV respectively. We also use a large set of $
N_f = 2 + 1 +1$ ensembles with unitary pion masses varying in the range of 230~MeV - 510~MeV at three different values of the lattice spacing. A mixed action approach with the Osterwalder-Seiler action in the valence sector is adopted to circumvent the complications arising from isospin symmetry breaking of the twisted mass quark action. Due to the relatively large lattice artefacts in the $N_f = 2 + 1 +1$ ensembles, we do not present the scattering lengths for these ensembles. Instead, taking the advantage of the many different pion masses of these ensembles, we qualitatively discuss the pion mass dependence of the scattering properties of this channel based on the results from the $N_f = 2 + 1 +1$ ensembles. The scattering length is computed for the $N_f = 2$ ensembles and the chiral extrapolation is performed. At the physical pion mass, our result $M_pi a^mathrm{I=0}_0 = 0.198(9)(6)$ agrees reasonably well with various experimental measurements and theoretical predictions.
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