4,573 research outputs found
QCD+QED lattice calculation of hadronic decay rates
Isospin is an almost exact symmetry of strong interactions and the
corrections to the isosymmetric limit are, in general, at the percent level.
For several hadronic quantities relevant for flavour physics phenomenology,
such as pseudoscalar meson masses or the kaon leptonic and semileptonic decay
rates, these effects are of the same order of magnitude of the uncertainties
quoted in current large-scale QCD simulations on the lattice and cannot be
neglected anymore. In this contribution I discuss some recent results for the
leptonic decay rates of light pseudoscalar mesons obtained by the Soton--RM123
Collaboration including the leading-order electromagnetic and strong
isospin-breaking corrections in first principles lattice simulations. The
adopted strategy is within the reach of present lattice technologies and it
allows to determine electromagnetic corrections to physical observables for
which delicate cancellations of infrared divergences occur in the intermediate
steps of the calculation. The application of the developed method to the study
of heavy-light meson and semileptonic decay rates is currently underway.Comment: Plenary talk at IFAE 2018, Milano (Italy), 04-06 April 2018. v2:
updated references and minor changes, matches version published in NC
Leading isospin-breaking effects on the lattice
Isospin is an almost exact symmetry of strong interactions and the
corrections to the isosymmetric limit are, in general, at the percent level.
For several hadronic quantities, such as pseudoscalar meson masses or the kaon
leptonic and semileptonic decay rates, these effects are of the same order of
magnitude of the errors quoted in nowadays lattice calculations and cannot be
neglected any longer. In this talk I discuss some recent results for the
pseudoscalar meson spectrum obtained by the RM123 Collaboration including
isospin breaking corrections in first principles lattice simulations.Comment: Plenary talk at IFAE 2017, Trieste (Italy), 19-21 April 201
Electromagnetic proton-neutron knockout off 16O: new achievements in theory
Results for the cross sections of the exclusive 16O(e,e'pn)14N and
16O(gamma,pn)14N knockout reactions are presented and discussed in different
kinematics. In comparison with earlier work, a complete treatment of the
center-of-mass (CM) effects in the nuclear one-body current is considered in
connection with the problem of the lack of orthogonality between initial bound
and final scattering states. The effects due to CM and orthogonalization are
investigated in combination with different treatments of correlations in the
two-nucleon overlap function and for different parametrizations of the two-body
currents. The CM effects lead in super-parallel kinematics to a dramatic
increase of the 16O(e,e'pn) cross section to the 1_2^+ excited state (3.95 MeV)
of 14N. In all the situations considered the results are very sensitive to the
treatment of correlations. A crucial role is played by tensor correlations, but
also the contribution of long-range correlations is important.Comment: 13 pages, 10 figure
Photon-induced two-nucleon knockout reactions to discrete final states
Cross sections and photon asymmetries of the exclusive 16O(\gamma,pn)14N and
16O(\gamma,pp)14C knockout reactions are calculated for transitions to the
low-lying discrete final states of the residual nucleus in the photon-energy
range between 100 and 400 MeV. Exclusive reactions may represent a test of
reaction mechanisms and a promising tool for investigating the dynamics of
nucleon pairs in different states. Cross sections and asymmetries for both
(\gamma,pn) and (\gamma,pp) turn out to be only slightly affected by
short-range correlations and dominated by two-body currents. Therefore,
two-nucleon knockout reactions induced by real photons appear well suited to
investigate the nuclear current and the selectivity of individual transitions
to its different components.Comment: 21 pages, 16 postscript figure
NN final-state interaction in two-nucleon knockout from
The influence of the mutual interaction between the two outgoing nucleons
(NN-FSI) in electro- and photoinduced two-nucleon knockout from has
been investigated perturbatively. It turns out that the effect of NN-FSI
depends on the kinematics and on the type of reaction considered. The effect is
generally larger in pp- than in pn-knockout and in electron induced than in
photoinduced reactions.
In superparallel kinematics NN-FSI leads in the channel to a
strong increase of the cross section, that is mainly due to a strong
enhancement of the -current contribution. In pn-emission, however, this
effect is partially cancelled by a destructive interference with the seagull
current. For photoreactions NN-FSI is considerably reduced in superparallel
kinematics and can be practically negligible in specific kinematics.Comment: 16 pages, 9 figure
The light-quark contribution to the leading HVP term of the muon from twisted-mass fermions
We present a lattice calculation of the leading Hadronic Vacuum Polarization
(HVP) contribution of the light u- and d-quarks to the anomalous magnetic
moment of the muon, , adopting the gauge configurations
generated by the European Twisted Mass Collaboration with
dynamical quarks at three values of the lattice spacing with pion masses in the
range 210 - 450 MeV. Thanks to several lattices at fixed values of the
light-quark mass and scale but with different sizes we perform a careful
investigation of finite-volume effects (FVEs). In order to remove FVEs we
develop an analytic representation of the vector correlator, which describes
the lattice data for time distances larger than fm. The
representation is based on quark-hadron duality at small and intermediate time
distances and on the two-pion contributions in a finite box at larger time
distances. After extrapolation to the physical pion point and to the continuum
limit we obtain . Adding the
contribution of strange and charm quarks, obtained by ETMC, and an estimate of
the isospin-breaking corrections and quark-disconnected diagrams from the
literature we get , which is
consistent with recent results based on dispersive analyses of the experimental
cross section data for annihilation into hadrons. Using our analytic
representation of the vector correlator, taken at the physical pion mass in the
continuum and infinite volume limits, we provide the first eleven moments of
the polarization function and we compare them with recent results of the
dispersive analysis of the channels. We estimate also the
light-quark contribution to the missing part of not covered
in the MUonE experiment.Comment: 34 pages, 20 figures, 7 tables. Version to appear in PR
Neutrino-Nucleus Quasi-Elastic Scattering in a Relativistic Model
A relativistic distorted-wave impulse-approximation model is applied to
neutral-current and charged-current quasi-elastic neutrino-nucleus scattering.
The effects of final state interactions are investigated and the sensitivity of
the results to the strange nucleon form factors is discussed in view of their
possible experimental determinationComment: 7 pages, 3 figures Proc. of the XXV International Workshop on Nuclear
Theory, 26 June- 1 July, 2006 Rila, Bulgari
Proton recoil polarization in exclusive (e,e'pp) reactions
The general formalism of nucleon recoil polarization in the () reaction is given. Numerical predictions are presented for the
components of the outgoing proton polarization and of the polarization transfer
coefficient in the specific case of the exclusive O()C knockout reaction leading to discrete states in the residual
nucleus. Reaction calculations are performed in a direct knockout framework
where final-state interactions and one-body and two-body currents are included.
The two-nucleon overlap integrals are obtained from a calculation of the
two-proton spectral function of O where long-range and short-range
correlations are consistently included. The comparison of results obtained in
different kinematics confirms that resolution of different final states in the
O()C reaction may act as a filter to
disentangle and separately investigate the reaction processes due to
short-range correlations and two-body currents and indicates that measurements
of the components of the outgoing proton polarization may offer good
opportunities to study short-range correlations.Comment: 12 pages, 6 figure
On the NN-final-state-interaction in the reaction
The influence of the mutual interaction between the two outgoing nucleons
(NN-FSI) in the reaction has been investigated.
Results for various kinematics are discussed. In general, the effect of
NN-FSI depends on kinematics and the chosen final state in the excitation
spectrum of .Comment: 12 pages Revtex including 4 postscript figure
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