1,173 research outputs found
Proton Decay: Improving the sensitivity through nuclear dynamics?
The kinematics of the decay of a bound proton is governed by the proton
spectral function. We evaluate this quantity in 16O using the information from
nuclear physics experiments. It also includes a correlated part. The
reliability of this evaluation is sufficient to open the possibility of
correlated cuts in the missing mass and momentum variables in order to identify
the decay events from the bound protons with a possible increase of the signal
to noise ratio.Comment: 6 pages, 6 figures. CERN preprint: CERN-PH-TH/2010-036. To appear in
Phys Rev
Chiral Dynamics of Deeply Bound Pionic Atoms
We present and discuss a systematic calculation, based on two-loop chiral
perturbation theory, of the pion-nuclear s-wave optical potential. A proper
treatment of the explicit energy dependence of the off-shell pion self-energy
together with (electromagnetic) gauge invariance of the Klein-Gordon equation
turns out to be crucial. Accurate data for the binding energies and widths of
the 1s and 2p levels in pionic ^{205}Pb and ^{207}Pb are well reproduced, and
the notorious "missing repulsion" in the pion-nuclear s-wave optical potential
is accounted for. The connection with the in-medium change of the pion decay
constant is clarified.Comment: preprint ECT*-02-16, 4 pages, 3 figure
Hyperon production in near threshold nucleon-nucleon collisions
We study the mechanism of the associated Lambda-kaon and Sigma-kaon
production in nucleon-nucleon collisions over an extended range of near
threshold beam energies within an effective Lagrangian model, to understand of
the new data on pp --> p Lambda K+ and pp --> p Sigma0 K+ reactions published
recently by the COSY-11 collaboration. In this theory, the hyperon production
proceeds via the excitation of N*(1650), N*(1710), and N*(1720) baryonic
resonances. Interplay of the relative contributions of various resonances to
the cross sections, is discussed as a function of the beam energy over a larger
near threshold energy domain. Predictions of our model are given for the total
cross sections of pp --> p Sigma+K0, pp --> n Sigma+K+, and pn --> n Lambda K+
reactions.Comment: 16 pages, 4 figures, one new table added and dicussions are updated,
version accepted for publication by Physical Review
Renormalization of the Deuteron with One Pion Exchange
We analyze the deuteron bound state through the One Pion Exchange Potential.
We pay attention to the short distance peculiar singularity structure of the
bound state wave functions in coordinate space and the elimination of short
distance ambiguities by selecting the regular solution at the origin. We
determine the so far elusive amplitude of the converging exponential solutions
at the origin. All bound state deuteron properties can then be uniquely deduced
from the deuteron binding energy, the pion-nucleon coupling constant and pion
mass. This generates correlations among deuteron properties. Scattering phase
shifts and low energy parameters in the 3S1-3D1 channel are constructed by
requiring orthogonality of the positive energy states to the deuteron bound
state, yielding an energy independent combination of boundary conditions. We
also analyze from the viewpoint of short distance boundary conditions the weak
binding regime on the light of long distance perturbation theory and discuss
the approach to the chiral limit.Comment: 22 pages, 11 figure
Two pion mediated scalar isoscalar NN interaction in the nuclear medium
We study the modification of the nucleon nucleon interaction in a nuclear
medium in the scalar isoscalar channel, mediated by the exchange of two
correlated ( channel) or uncorrelated pions. For this purpose we use a
standard approach for the renormalization of pions in nuclei. The corrections
obtained for the interaction in the medium in this channel are of the
order of 20% of the free one in average, and the consideration of short range
correlations plays an important role in providing these moderate changes. Yet,
the corrections are sizable enough to suggest further studies of the stability
and properties of nuclear matter.Comment: 27 page
Charged Current Neutrino Nucleus Interactions at Intermediate Energies
We have developed a model to describe the interactions of neutrinos with
nucleons and nuclei, focusing on the region of the quasielastic and Delta(1232)
peaks. We describe neutrino nucleon collisions with a fully relativistic
formalism which incorporates state-of-the-art parametrizations of the form
factors for both the nucleon and the N-Delta transition. The model has then
been extended to finite nuclei, taking into account nuclear effects such as
Fermi motion, Pauli blocking (both within the local density approximation),
nuclear binding and final state interactions. The in-medium modification of the
Delta resonance due to Pauli blocking and collisional broadening have also been
included. Final state interactions are implemented by means of the
Boltzmann-Uehling-Uhlenbeck (BUU) coupled-channel transport model. Results for
charged current inclusive cross sections and exclusive channels as pion
production and nucleon knockout are presented and discussed.Comment: 26 pages, 24 figures; v2: 2 figures and discussion added, version
accepted for publication in Phys. Rev.
N-Delta(1232) axial form factors from weak pion production
The N-Delta axial form factors are determined from neutrino induced pion
production ANL & BNL data by using a state of the art theoretical model, which
accounts both for background mechanisms and deuteron effects. We find
violations of the off diagonal Goldberger-Treiman relation at the level of 2
sigma which might have an impact in background calculations for T2K and
MiniBooNE low energy neutrino oscillation precision experiments.Comment: 4 pages, 1 figur
Feynman diagrams with the effective action
A derivation is given of the Feynman rules to be used in the perturbative
computation of the Green's functions of a generic quantum many-body theory when
the action which is being perturbed is not necessarily quadratic. Some
applications are discussed.Comment: Extended revised version. RevTex, 19 pages, 10 figure
Neutrino induced threshold production of two pions and N^*(1440) electroweak form factors
We study the threshold production of two pions induced by neutrinos in
nucleon targets. The contribution of nucleon, pion and contact terms are
calculated using a chiral Lagrangian. The contribution of the Roper resonance,
neglected in earlier studies, has also been taken into account. The numerical
results for the cross sections are presented and compared with the available
experimental data. It has been found that in the two pion channels with
and in the final state, the contribution of the
is quite important and could be used to determine the
electroweak transition form factors if experimental data with better statistics
become available in the future.Comment: This version corrects a mistake on the helicity amplitudes sign.
Additional comments on resonance-background relative sign are added. Other
minor corrections. Matches published version. 17 pages, 7 figure
Chiral symmetry and the axial nucleon to Delta(1232) transition form factors
We study the momentum and the quark mass dependence of the axial nucleon to
Delta(1232) transition form factors in the framework of non-relativistic chiral
effective field theory to leading-one-loop order. The outcome of our analysis
provides a theoretical guidance for chiral extrapolations of lattice QCD
results with dynamical fermions.Comment: 18 pages, 3 figure
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