1,305 research outputs found
semileptonic form factors with Twisted Mass fermions
We present a lattice QCD determination of the vector and scalar form factors
of the semileptonic decay which are relevant for the
extraction of the CKM matrix element from experimental data. Our
results are based on the gauge configurations produced by the European Twisted
Mass Collaboration with dynamical fermions, which include in the
sea, besides two light mass degenerate quarks, also the strange and the charm
quarks. We use data simulated at three different values of the lattice spacing
and with pion masses as small as MeV. Our final result for the vector
form factor at zero momentum transfer is , where the
uncertainty is both statistical and systematic combined in quadrature. Using
the latest experimental value of from decays, we
obtain , which allows to test the unitarity constraint
of the Standard Model below the permille level once the determination of
from superallowed nuclear decays is adopted. A slight
tension with unitarity at the level of standard deviations is
observed. Moreover we present our results for the semileptonic scalar
and vector form factors in the whole range of values of
the squared four-momentum transfer measured in decays,
obtaining a very good agreement with the momentum dependence of the
experimental data. We provide a set of synthetic data points representing our
results for the vector and scalar form factors at the physical point for
several selected values of .Comment: 37 pages, 5 tables, 9 figures; version to appear in PR
\Delta S=2 and \Delta C=2 bag parameters in the SM and beyond from Nf=2+1+1 twisted-mass LQCD
We present unquenched lattice QCD results for the matrix elements of
four-fermion operators relevant to the description of the neutral K and D
mixing in the Standard Model and its extensions. We have employed simulations
with Nf = 2 + 1 + 1 dynamical sea quarks at three values of the lattice
spacings in the interval 0.06 - 0.09 fm and pseudoscalar meson masses in the
range 210 - 450 MeV. Our results are extrapolated to the continuum limit and to
the physical pion mass. Renormalization constants have been determined
non-perturbatively in the RI-MOM scheme. In particular, for the Kaon
bag-parameter, which is relevant for the \overline{K}^0-K^0 mixing in the
Standard Model, we obtain B_K^{RGI} = 0.717(24).Comment: Added comments to error budget discussion; fig.19 corrected. Version
to appear in PR
Average up/down, strange and charm quark masses with Nf=2 twisted mass lattice QCD
We present a high precision lattice calculation of the average up/down,
strange and charm quark masses performed with Nf=2 twisted mass Wilson
fermions. The analysis includes data at four values of the lattice spacing and
pion masses as low as ~270 MeV, allowing for accurate continuum limit and
chiral extrapolation. The strange and charm masses are extracted by using
several methods, based on different observables: the kaon and the eta_s meson
for the strange quark and the D, D_s and eta_c mesons for the charm. The quark
mass renormalization is carried out non-perturbatively using the RI-MOM method.
The results for the quark masses in the MSbar scheme read: m_ud(2 GeV)= 3.6(2)
MeV, m_s(2 GeV)=95(6) MeV and m_c(m_c)=1.28(4) GeV. We also obtain the ratios
m_s/m_ud=27.3(9) and m_c/m_s=12.0(3).Comment: 20 pages, 5 figures. Typos corrected in eqs. (15)-(17). Version
published in Phys. Rev.
Quark masses with Nf=2 twisted mass lattice QCD
We present the results of the recent high precision lattice calculation of
the average up/down, strange and charm quark masses performed by ETMC with Nf=2
twisted mass Wilson fermions. The analysis includes data at four values of the
lattice spacing and pion masses as low as ~270 MeV, allowing for accurate
continuum limit and chiral extrapolation. The strange and charm masses are
extracted by using several methods, based on different observables: the kaon
and the eta_s meson for the strange quark and the D, D_s and eta_c mesons for
the charm. The quark mass renormalization is carried out non-perturbatively
using the RI-MOM method. The results for the quark masses in the MSbar scheme
read: m_ud(2 GeV)= 3.6(2) MeV, m_s(2 GeV)=95(6) MeV and m_c(m_c)=1.28(4) GeV.
We have also obtained the ratios m_s/m_ud=27.3(9) and m_c/m_s=12.0(3).
Moreover, we provide the updated result for the bottom quark mass,
m_b(m_b)=4.3(2) GeV, obtained using the method presented in 0909.3187
[hep-lat].Comment: 7 pages, 7 figures, talk given at the XXVIII International Symposium
on Lattice Field Theory (Lattice 2010), June 14-19 2010, Villasimius, Ital
TMS-evoked long-lasting artefacts: A new adaptive algorithm for EEG signal correction
OBJECTIVE:
During EEG the discharge of TMS generates a long-lasting decay artefact (DA) that makes the analysis of TMS-evoked potentials (TEPs) difficult. Our aim was twofold: (1) to describe how the DA affects the recorded EEG and (2) to develop a new adaptive detrend algorithm (ADA) able to correct the DA.
METHODS:
We performed two experiments testing 50 healthy volunteers. In experiment 1, we tested the efficacy of ADA by comparing it with two commonly-used independent component analysis (ICA) algorithms. In experiment 2, we further investigated the efficiency of ADA and the impact of the DA evoked from TMS over frontal, motor and parietal areas.
RESULTS:
Our results demonstrated that (1) the DA affected the EEG signal in the spatiotemporal domain; (2) ADA was able to completely remove the DA without affecting the TEP waveforms; (3). ICA corrections produced significant changes in peak-to-peak TEP amplitude.
CONCLUSIONS:
ADA is a reliable solution for the DA correction, especially considering that (1) it does not affect physiological responses; (2) it is completely data-driven and (3) its effectiveness does not depend on the characteristics of the artefact and on the number of recording electrodes.
SIGNIFICANCE:
We proposed a new reliable algorithm of correction for long-lasting TMS-EEG artifacts
Mass of the b-quark and B-decay constants from Nf=2+1+1 twisted-mass Lattice QCD
We present precise lattice computations for the b-quark mass, the quark mass
ratios mb/mc and mb/ms as well as the leptonic B-decay constants. We employ
gauge configurations with four dynamical quark flavors, up/down, strange and
charm, at three values of the lattice spacing (a ~ 0.06 - 0.09 fm) and for pion
masses as low as 210 MeV. Interpolation in the heavy quark mass to the bottom
quark point is performed using ratios of physical quantities computed at nearby
quark masses exploiting the fact that these ratios are exactly known in the
static quark mass limit. Our results are also extrapolated to the physical pion
mass and to the continuum limit and read: mb(MSbar, mb) = 4.26(10) GeV, mb/mc =
4.42(8), mb/ms = 51.4(1.4), fBs = 229(5) MeV, fB = 193(6) MeV, fBs/fB =
1.184(25) and (fBs/fB)/(fK/fpi) = 0.997(17).Comment: Version to appear in PRD. Added comments to simulation setup and
error budget discussion. 1+20 pages, 9 figure
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