157 research outputs found
Chiral Dynamics and the Low Energy Kaon-Nucleon Interaction
We examine the meson-baryon interaction in the strangeness S=-1 sector using
an effective chiral Lagrangian. Potentials are derived from this Lagrangian and
used in a coupled-channel calculation of the low energy observables. The
potentials are constructed such that in the Born approximation the s-wave
scattering amplitude is the same as that given by the effective chiral
Lagrangian, up to order . Comparison is made with the available low energy
hadronic data of the coupled system, which
includes the resonance, elastic and inelastic
scattering, and the threshold branching ratios of the decay. Good fits
to the experimental data and estimates of previously unknown Lagrangian
parameters are obtained.Comment: 20 pages, 10 postscript figures, uses revtex, e-mail addresses:
[email protected], [email protected],
[email protected]
Pentaquark as Kaon-Nucleon Resonance
Several recent experiments have reported evidence for a narrow feature in the
K(+)-neutron system, an apparent resonant state ~ 100 MeV above threshold and
with a width < 25 MeV. This state has been labelled as Theta(+) (previously as
Z(*)), and because of the implied inclusion of a anti-strange quark, is
referred to as a pentaquark, that is, five quarks within a single bag. We
present an alternative explanation for such a structure, as a higher angular
momentum resonance in the isospin zero K(+) -N system. One might call this an
exit channel or a molecular resonance. In a non-relativistic potential model we
find a possible candidate for the kaon-nucleon system with relative angular
momentum L=3, while L=1 and 2 states possess centrifugal barriers too low to
confine the kaon and nucleon in a narrow state at an energy so high above
threshold. A rather strong state-dependence in the potential is essential,
however, for eliminating an observable L=2 resonance at lower energies.Comment: 4 page
Non perturbative chiral approach to s-wave \bar{K}N interactions
The s-wave meson-nucleon interaction in the sector is studied by
means of coupled-channel Lippmann Schwinger equations, using the lowest order
chiral Lagrangian and a cut off to regularize the loop integrals. The method
reproduces succesfully the resonance and the cross
sections at low energies. The inclusion of the
channels in the coupled system is found very important and allows a solution in
terms of only the lowest order Lagrangian.Comment: 34 pages, 11 figures, uses epsf.sty, submitted to Nucl.Phys.
On the K^+D Interaction at Low Energies
The Kd reactions are considered in the impulse approximation with NN
final-state interactions (NN FSI) taken into account. The realistic parameters
for the KN phase shifts are used. The "quasi-elastic" energy region, in which
the elementary KN interaction is predominantly elastic, is considered. The
theoretical predictions are compared with the data on the K^+d->K^+pn,
K^+d->K^0pp, K^+d->K^+d and K^+d total cross sections. The NN FSI effect in the
reaction K^+d->K^+pn has been found to be large. The predictions for the Kd
cross sections are also given for slow kaons, produced from phi(1020) decays,
as the functions of the isoscalar KN scattering length a_0. These predictions
can be used to extract the value of a_0 from the data.Comment: 22 pages, 5 figure
Partial wave contributions to the antikaon potential at finite momentum
The momentum dependence of the antikaon optical potential in nuclear matter
is obtained from a microscopic and self-consistent calculation using the
meson-exchange J\"ulich interaction. Two self-consistent schemes are
discussed, which would lead to substantially different predictions for the
width of nuclear bound states. The effect of higher partial waves of
the interaction, beyond the L=0 component, is studied and found to
have moderate but non-negligible effects on the nuclear potential at
zero momentum. At momenta as large as 500 MeV/c, relevant in the analysis of
heavy-ion collisions, the higher partial partial waves modify the
optical potential by nearly a factor of two.Comment: 20 pages, 7 figure
On kaonic hydrogen. Phenomenological quantum field theoretic model revisited
We argue that due to isospin and U-spin invariance of strong low-energy
interactions the S-wave scattering lengths a^0_0 and a^1_0 of bar-KN scattering
with isospin I=0 and I = 1 satisfy the low-energy theorem a^0_0 + 3 a^1_0 = 0
valid to leading order in chiral expansion. In the model of strong low-energy
bar-KN interactions at threshold (EPJA 21,11 (2004)) we revisit the
contribution of the Sigma(1750) resonance, which does not saturate the
low-energy theorem a^0_0 + 3 a^1_0 = 0, and replace it by the baryon background
with properties of an SU(3) octet. We calculate the S-wave scattering
amplitudes of K^-N and K^-d scattering at threshold. We calculate the energy
level displacements of the ground states of kaonic hydrogen and kaonic
deuterium. The result obtained for kaonic hydrogen agrees well with recent
experimental data by the DEAR Collaboration. We analyse the cross sections for
elastic and inelastic K^-p scattering for laboratory momenta of the incident
K^- meson from the domain 70 MeV/c < p_K < 150 MeV/c. The theoretical results
agree with the available experimental data within two standard deviations.Comment: 20 pages, Latex, We have slightly corrected the contribution of the
double scattering. This changes the S-wave scattering length of K^-d
scattering by 17%, which is commensurable with the theoretical uncertaint
Aspects of Strangeness -1 Meson-Baryon Scattering
We consider meson-baryon interactions in S-wave with strangeness -1. This is
a sector populated by plenty of resonances interacting in several two-body
coupled channels. We consider a large set of experimental data, where the
recent experiments are remarkably accurate. This requires a sound theoretical
description to account for all the data and we employ Unitary Chiral
Perturbation Theory up to and including O(p^2). The spectroscopy of our
solutions is studied within this approach, discussing the rise from the pole
content of two \Lambda(1405) resonances and of the \Lambda(1670),
\Lambda(1800), \Sigma(1480), \Sigma(1620) and \Sigma(1750). We finally argue
about our preferred fit.Comment: 6 figures, 3 figures, talk given in the IVth International Conference
on Quarks and Nuclear Physics (QNP06), Madrid June 5th and 10th, 2006. One
reference is update
New insights into antikaon-nucleon scattering and the structure of the Lambda(1405)
We perform a combined analysis of antikaon-nucleon scattering cross sections
and the recent SIDDHARTA kaonic hydrogen data in the framework of a
coupled-channel Bethe-Salpeter approach at next-to-leading order in the chiral
expansion of the effective potential. We find a precise description of the
antikaon-proton scattering amplitudes and are able to extract accurate values
of the scattering lengths, a0=-1.81^+0.30_-0.28 + i 0.92^+0.29_-0.23 fm,
a1=+0.48^+0.12_-0.11 + i 0.87^+0.26_-0.20 fm. We also discuss the two-pole
structure of the Lambda(1405).Comment: 7 pages, 4 figure
Chiral dynamics in the presence of bound states: kaon-nucleon interactions revisited
We study the S-wave kaon-nucleon interactions for strangeness S=-1 in a novel
relativistic chiral unitary approach based on coupled channels. Dispersion
relations are used to perform the necessary resummation of the lowest order
relativistic chiral Lagrangian. A good description of the data in the K^- p,
\pi \Sigma and \pi \Lambda channels is obtained. We show how this method can be
systematically extended to higher orders, emphasizing its applicability to any
scenario of strong self-interactions where the perturbative series diverges
even at low energies. Discussions about the differences to existing approaches
employing pseudo-potentials in a regulated Lippmann-Schwinger equation are
included. Finally, we describe the resonance content of our meson-baryon
amplitudes and discuss its nature.Comment: 12 pp, LaTeX2e, FZJ-IKP(TH)-2000-2
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