6,820 research outputs found
New Results From Lattice QCD: Non-Perturbative Renormalization and Quark Masses
For the first time, we compute non-perturbatively, i.e. without lattice
perturbation theory, the renormalization constants of two-fermion operators in
the quenched approximation at , 6.2 and 6.4 using the Wilson and the
tree-level improved SW-Clover actions. We apply these renormalization constants
to fully non-perturbatively estimate quark masses in the scheme from
lattice simulations of both the hadron spectrum and the Axial Ward Identity in
the quenched approximation. Some very preliminary unquenched Wilson results
obtained from the gluon configurations generated by the TL Collaboration
at and are also discussed.Comment: 4 pages, 2 figures. Invited talk given at the QCD 98 Euroconference,
Montpellier, France, 2-8 July 199
NNLO Unquenched Calculation of the b Quark Mass
By combining the first unquenched lattice computation of the B-meson binding
energy and the two-loop contribution to the lattice HQET residual mass, we
determine the (\bar{{MS}}) (b)-quark mass, (\bar{m}_{b}(\bar{m}_{b})). The
inclusion of the two-loop corrections is essential to extract
(\bar{m}_{b}(\bar{m}_{b})) with a precision of ({\cal
O}(\Lambda^{2}_{QCD}/m_{b})), which is the uncertainty due to the renormalon
singularities in the perturbative series of the residual mass. Our best
estimate is (\bar{m}_{b}(\bar{m}_{b}) = (4.26 \pm 0.09) {\rm GeV}), where we
have combined the different errors in quadrature. A detailed discussion of the
systematic errors contributing to the final number is presented. Our results
have been obtained on a sample of (60) lattices of size (24^{3}\times 40) at
(\beta =5.6), using the Wilson action for light quarks and the lattice HQET for
the (b) quark, at two values of the sea quark masses. The quark propagators
have been computed using the unquenched links generated by the T(\chi)L
Collaboration.Comment: 19 pages, 1 figur
Lattice quark masses: a non-perturbative measurement
We discuss the renormalization of different definitions of quark masses in
the Wilson and the tree-level improved SW-Clover fermionic action. For the
improved case we give the correct relationship between the quark mass and the
hopping parameter. Using perturbative and non-perturbative renormalization
constants, we extract quark masses in the \MSbar scheme from Lattice QCD in
the quenched approximation at , and for both
actions. We find: \bar{m}^{\MSbar}(2 GeV)=5.7 \pm 0.1 \pm 0.8 MeV,
m_s^{\MSbar}(2GeV)= 130 \pm 2 \pm 18 MeV and m_c^{\MSbar}(2 GeV) = 1662\pm
30\pm 230 MeV.Comment: 21 pages, 4 figures, typos corrected, no result change
A Theoretical Prediction of the Bs-Meson Lifetime Difference
We present the results of a quenched lattice calculation of the operator
matrix elements relevant for predicting the Bs width difference. Our main
result is (\Delta\Gamma_Bs/\Gamma_Bs)= (4.7 +/- 1.5 +/- 1.6) 10^(-2), obtained
from the ratio of matrix elements, R(m_b)=/<\bar
B_s^0|Q_L|B_s^0>=-0.93(3)^(+0.00)_(-0.01). R(m_b) was evaluated from the two
relevant B-parameters, B_S^{MSbar}(m_b)=0.86(2)^(+0.02)_(-0.03) and
B_Bs^{MSbar}(m_b) = 0.91(3)^(+0.00)_(-0.06), which we computed in our
simulation.Comment: 21 pages, 7 PostScript figure
Quark masses and the chiral condensate with a non-perturbative renormalization procedure
We determine the quark masses and the chiral condensate in the MSbar scheme
at NNLO from Lattice QCD in the quenched approximation at beta=6.0, beta=6.2
and beta=6.4 using both the Wilson and the tree-level improved SW-Clover
fermion action. We extract these quantities using the Vector and the Axial Ward
Identities and non-perturbative values of the renormalization constants. We
compare the results obtained with the two methods and we study the O(a)
dependence of the quark masses for both actions.Comment: LATTICE98(spectrum), 3 pages, 1 figure, Edinburgh 98/1
Combined Relativistic and static analysis for all Delta B=2 operators
We analyse matrix elements of Delta B=2 operators by combining QCD results
with the ones obtained in the static limit of HQET. The matching of all the QCD
operators to HQET is made at NLO order. To do that we have to include the
anomalous dimension matrix up to two loops, both in QCD and HQET, and the one
loop matching for all the Delta B=2 operators. The matrix elements of these
operators are relevant for the prediction of the B-\bar B mixing, B_s meson
width difference and supersymmetric effects in Delta B=2 transitions.Comment: 3 pages, 1 figure. Lattice2001(heavyquark
Teaching Nanoscience and thinking nano at the macroscale: Nanocapsules of wisdom
One of the challenges for Nanotechnology is education, which is considered as a bottleneck for Nanotechnology development and implementation. This work contributes to nanoscale education by designing a wide variety of cutting-edge documentaries which assist high-educational level students in learning the underlying concepts of Nanoscience, the last advances and furure prospects. In addition, documentaries seek to bring and disseminate the scientific activity of Nanotechnology to society. In this sense, the secondary goals of the proposed approach nanotech activity are: 1) Transfer of knowledge generated in the nanotechnology field and 2) The promotion of scientific culture and innovation between the public objectives. Based on the results observed in students's assessment and You Tube metrics, it was concluded that the developed of nanoscale based documentaries enabled a fast and efficent comprehension of complex concepts related to Nanoscience and Nanotechnology. In addition, the opinion of You Tube audience is highly promising and shows that You Tube and documentaries are an excellent channel to disseminate Nanoscience to society
Calculation of the continuum--lattice HQET matching for the complete basis of four--fermion operators: reanalysis of the - mixing
In this work, we find the expressions of continuum HQET four-fermion
operators in terms of lattice operators in perturbation theory. To do so, we
calculate the one--loop continuum--lattice HQET matching for the complete basis
of and operators (excluding penguin diagrams),
extending and completing previous studies. We have also corrected some errors
in previous evaluations of the matching for the operator . Our results
are relevant to the lattice computation of the values of unknown hadronic
matrix elements which enter in many very important theoretical predictions in
--meson phenomenology: - mixing, and
lifetimes, SUSY effects in transitions and the
width difference . We have reanalyzed our
lattice data for the parameter of the - mixing on
600 lattices of size at computed with the
SW-Clover and HQET lattice actions. We have used the correct lattice--continuum
matching factors and boosted perturbation theory with tadpole improved
heavy--light operators to reduce the systematic error in the evaluation of the
renormalization constants. Our best estimate of the renormalization scale
independent --parameter is , where the
first error is statistical and the second is systematic coming from the
uncertainty in the determination of the renormalization constants. Our result
is in good agreement with previous results obtained by extrapolating Wilson
data. As a byproduct, we also obtain the complete one--loop anomalous dimension
matrix for four--fermion operators in the HQET.Comment: 34 pages, 1 figure. Revised version including the referee's comments.
Some references have been also added. Accepted to be published in
Nucl.Phys.B. No result change
Kaon oscillations in the Standard Model and Beyond using Nf=2 dynamical quarks
We compute non-perturbatively the B-parameters of the complete basis of
four-fermion operators needed to study the Kaon oscillations in the SM and in
its supersymmetric extension. We perform numerical simulations with two
dynamical maximally twisted sea quarks at three values of the lattice spacing
on configurations generated by the ETMC. Unwanted operator mixings and O(a)
discretization effects are removed by discretizing the valence quarks with a
suitable Osterwalder-Seiler variant of the Twisted Mass action. Operators are
renormalized non-perturbatively in the RI/MOM scheme. Our preliminary result
for BK(RGI) is 0.73(3)(3).Comment: 7 pages, 3 figures, 1 table, proceedings of the XXVII Int'l Symposyum
on Lattice Field Theory (LAT2009), July 26-31 2009, Peking University,
Beijing (China
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