143 research outputs found
Density distributions in the meson
We report on a two-flavor lattice QCD study of the axial, charge and matter
distributions of the meson and its first radial excitation. As our
framework is the static limit of Heavy Quark Effective Theory (HQET), taking
their Fourier transform gives access to several form factors at the kinematical
point . Moreover they provide some useful information on the nature of
an excited state, i.e. a radial excitation of a quark-antiquark bound state or
a multihadron state.Comment: 26 pages, 25 figures, 12 tables; published versio
On the nature of an excited state
In many lattice simulations with dynamical quarks, radial or orbital
excitations of hadrons lie near multihadron thresholds: it makes the extraction
of excited states properties more challenging and can introduce some
systematics difficult to estimate without an explicit computation of
correlators using interpolating fields strongly coupled to multihadronic
states. In a recent study of the strong decay of the first radial excitation of
the meson, this issue has been investigated and we have clues that a
diquark interpolating field is very weakly coupled to a -wave state while the situation is quite different if we consider an
interpolating field of the kind , where is a
covariant derivative: those statements are based on examining the charge
density distribution.Comment: Proceedings of the 34th International Symposium on Lattice Field
Theory (Lattice 2016), 25 - 30 July 2016, Southampton, Great Britai
Lattice calculation of the pion transition form factor with Wilson quarks
We present a lattice QCD calculation of the double-virtual neutral pion
transition form factor, with the goal to cover the kinematic range relevant to
hadronic light-by-light scattering in the muon . Several improvements have
been made compared to our previous work. First, we take into account the
effects of the strange quark by using the CLS gauge ensembles.
Secondly, we have implemented the on-shell -improvement of the
vector current to reduce the discretization effects associated with Wilson
quarks. Finally, in order to have access to a wider range of photon
virtualities, we have computed the transition form factor in a moving frame as
well as in the pion rest-frame. After extrapolating the form factor to the
continuum and to physical quark masses, we compare our results with
phenomenology. We extract the normalization of the form factor with a precision
of 3.5\% and confirm within our uncertainty previous somewhat conflicting
estimates for a low-energy constant that appears in chiral perturbation theory
for the decay at NLO. With additional input from
experiment and theory, we reproduce recent estimates for the decay width
. We also study the asymptotic large-
behavior of the transition form factor in the double-virtual case. Finally, we
provide as our main result a more precise model-independent lattice estimate of
the pion-pole contribution to hadronic light-by-light scattering in the muon
: . Using
in addition the normalization of the form factor obtained by the PrimEx
experiment, we get the lattice and data-driven estimate
.Comment: 29 pages, 14 figures. v2: minor corrections to match the published
version. A file with the transition form factor data at the physical pion
mass and in the continuum is included in the submissio
Investigation of the hadronic light-by-light contribution to the muon using staggered fermions
Hadronic contributions dominate the uncertainty of the standard model
prediction for the anomalous magnetic moment of the muon. In this work, we
describe an ongoing lattice calculation of the hadronic light-by-light
contribution, performed with staggered fermions. The presence of quarks with
different tastes complicates the analysis of the position-space correlation
function. We present a suitable adaption of the "Mainz method". As a first
numerical test, we reproduce the well-known lepton-loop contribution. Results
at a single lattice spacing for the light quark contribution, using two
volumes, are then discussed. Our study of the long distance behavior and
finite-volume effects is supplemented by considering the contribution of the
light pseudoscalar-pole. The corresponding transition form factors have been
evaluated in previous simulations on the same ensembles.Comment: 7 pages, 6 figures, LATTICE2023 conference proceedings, submitted to
Po
Exploratory studies for the position-space approach to hadronic light-by-light scattering in the muon
The well-known discrepancy in the muon between experiment and theory
demands further theory investigations in view of the upcoming new experiments.
One of the leading uncertainties lies in the hadronic light-by-light scattering
contribution (HLbL), that we address with our position-space approach. We focus
on exploratory studies of the pion-pole contribution in a simple model and the
fermion loop without gluon exchanges in the continuum and in infinite volume.
These studies provide us with useful information for our planned computation of
HLbL in the muon using full QCD.Comment: 8 pages, 11 figures, 1 table, Lattice 2017 proceedings, Granada,
Spai
Pion couplings to the scalar B meson
We present two-flavor lattice QCD estimates of the hadronic couplings
and that parametrise the non leptonic
decays and . We use CLS two-flavour
gauge ensembles. Our framework is the Heavy Quark Effective Theory (HQET) in
the static limit and solving a Generalized Eigenvalue Problem (GEVP) reveals
crucial to disentangle the () state from the ()
state. This work brings us some experience on how to treat the possible
contribution from multihadronic states to correlation functions calculated on
the lattice, especially when -wave states are involved.Comment: 12 pages, 10 figures, published versio
On the transition
We present a first lattice estimate of the hadronic coupling
which parametrizes the strong decay of a radially excited meson
into the ground state meson at zero recoil. We work in the static limit of
Heavy Quark Effective Theory (HQET) and solve a Generalised Eigenvalue Problem
(GEVP), which is necessary for the extraction of excited state properties.
After an extrapolation to the continuum limit and a check of the pion mass
dependence, we obtain .Comment: Proceedings of the 31st International Symposium on Lattice Field
Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German
The leading hadronic contribution to the running of the Weinberg angle using covariant coordinate-space methods
We present a preliminary study of the leading hadronic contribution to the
running of the Weinberg angle . The running is extracted
from the correlation function of the electromagnetic current with the vector
part of the weak neutral current using both the standard time-momentum
representation method and the Lorentz-covariant coordinate-space method
recently introduced by Meyer. Both connected and disconnected contributions
have been computed on non-perturbatively -improved
Wilson fermions configurations from the CLS initiative. Similar covariant
coordinate-space methods can be used to compute the leading hadronic
contribution to the anomalous magnetic moment of the muon and to
the running of the QED coupling .Comment: 7 pages, 2 figures, talk presented at The 36th Annual International
Symposium on Lattice Field Theory, July 22-28, 2018, East Lansing, MI, US
Hadronic light-by-light scattering in the anomalous magnetic moment of the muon
Hadronic light-by-light scattering in the anomalous magnetic moment of the
muon is one of two hadronic effects limiting the precision of the
Standard Model prediction for this precision observable, and hence the
new-physics discovery potential of direct experimental determinations of
. In this contribution, we report on recent progress in the calculation
of this effect achieved both via dispersive and lattice QCD methods.Comment: 14 pages, 7 figures; submitted as proceedings contribution for the
15th International Workshop on Tau Lepton Physic
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