119380929
s-wave pion nucleon scattering lengths from {pi}N, pionic hydrogen, and deuteron data
The isoscalar and isovector scattering lengths (b{sub 0},b{sub 1}) are determined using a unitarized coupled channel approach based on chiral Lagrangians. Using experimental values of pionic hydrogen and deuterium as well as low energy {pi}N scattering data, the free parameters of the model are calculated. Isospin violation is incorporated to a certain extent by working with physical particle masses. For the deuterium scattering length a{sub {pi}}{sub {sup -}}{sub d} new significant corrections concerning real and imaginary parts are evaluated, putting new constraints from {pi}{sup -}d scattering on the values of (b{sub 0},b{sub 1}). In particular, dispersion corrections, the influence of the {delta}(1232) resonance, crossed terms and multiple scattering in a Faddeev approach are considered.
119447848
Clues to the nature of the Δ∗(1700) resonance from pion- and photon-induced reactions
Abstract We make a study of the π − p → K 0 π 0 Λ , π + p → K + π + Λ , K + K ¯ 0 p , K + π + Σ 0 , K + π 0 Σ + , and η π + p reactions, in which the basic dynamics is given by the excitation of the Δ ∗ ( 1700 ) resonance which subsequently decays into K Σ ∗ ( 1385 ) or Δ ( 1232 ) η . In a similar way we also study the γ p → K 0 π + Λ , K + π − Σ + , K + π + Σ − , K 0 π 0 Σ + , and η π 0 p related reactions. The cross sections are proportional to the square of the coupling of Δ ∗ ( 1700 ) to Σ ∗ K ( Δη ) for which there is no experimental information but which is provided in the context of coupled channels chiral unitary theory where the Δ ∗ ( 1700 ) is dynamically generated. Within present theoretical and experimental uncertainties one can claim a global qualitative agreement between theory and experiment. We provide a list of items which need to be improved in order to make further progress along these lines.
10765600
Photo- and Electron-Production of Mesons on Nucleons and Nuclei
In these lectures I will show some results obtained with the chiral unitary approach applied to the photo and electroproduction of mesons. The results for photoproduction of ηπ 0 p and K 0 π 0 � + , together with related reactions will be shown, having with common denominator the excitation of the �(1700) resonance which is one of those dynamically generated in the chiral unitary approach. Then I will show results obtained for the e + e − → φf0(980) reaction which reproduce the bulk of the data except for a pronounced peak, giving support to a new mesonic resonance, X(2175). Results will also be shown for the electromagnetic form factors of the N ∗ (1535) resonance, also dynamically generated in this approach. Finally, I will show some results on the photoproduction of the ω in nuclei, showing that present experimental results claiming a shift of the ω mass in the medium are tied to a particular choice of background and are not conclusive. On the other hand, the same experimental results show unambiguously a huge increase of the ω width in the nuclear medium.
116702082
Radiative decay of the Delta*(1700)
Electromagnetic properties provide information about the structure of strongly interacting systems and allow for independent tests of hadronic models. The radiative decay of the Delta(1700) is studied, which appears dynamically generated in a coupled channel approach from the rescattering of the (3/2^+) decuplet of baryons with the (0^-) octet of pseudoscalar mesons. The radiative decay is predicted from the well-known couplings of the photon to the mesons and hadrons which constitute this resonance in the dynamical picture.
30722169
Charge fluctuations and electric mass in a hot meson gas
Net charge fluctuations in a hadron gas are studied using an effective hadronic interaction. The emphasis of this work is to investigate the corrections of hadronic interactions to the charge fluctuations of a noninteracting resonance gas. Several methods such as loop, density, and virial expansions are employed. The calculations are also extended to SU(3), and some resummation schemes are considered. Although the various corrections are sizable individually, they cancel to a large extent. As a consequence, we find that charge fluctuations are rather well described by the free resonance gas.
117511031
Chiral dynamics in gamma p ---> pi0 eta p and related reactions
Using a chiral unitary approach for meson-baryon scattering in the strangeness zero sector, where the $N^*(1535)$ and $\Delta^*(1700)$ resonances are dynamically generated, we study the reactions $\gamma p \to \pi^0 \eta p$ and $\gamma p \to \pi^0 K^0 \Sigma^+$ at photon energies at which the final states are produced close to threshold. Among several reaction mechanisms, we find the most important is the excitation of the $\Delta^*(1700)$ state which subsequently decays into a pseudoscalar meson and the $N^*(1535)$. Hence, the reaction provides useful information with which to test current theories of the dynamical generation of the low-lying $1/2^-$ and $3/2^-$ states. Predictions are made for cross sections and invariant mass distributions which can be compared with forthcoming experiments at ELSA.
16407243
Kaon–nucleon scattering lengths from kaonic deuterium experiments revisited
Abstract We analyse the impact of the recent measurement of kaonic hydrogen X rays by the SIDDHARTA collaboration on the allowed ranges for the kaon–deuteron scattering length in the framework of non-relativistic effective field theory. Based on data from K ¯ N scattering only, we predict the kaon–deuteron scattering length A K d = ( − 1.46 + i 1.08 ) fm , with an estimated uncertainty of about 25% in both the real and the imaginary part.
119239270
Meson-baryon interaction in the meson exchange picture
This is the contribution to the proceedings of the MENU 2010 conference. The recent work of Ref. [7] is summarized. Elastic piN scattering and the reaction pi^+ p --> K^+ Sigma^+ are described simultaneously in a unitary coupled-channels approach which respects analyticity. SU(3) flavor symmetry is used to relate the t- and u- channel exchanges that drive the meson-baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. The pole structure of the amplitudes is extracted from the analytic continuation.
119185139
Pion photoproduction in a dynamical coupled‐channel model
Pion photoproduction reactions are investigated in a dynamical coupled‐channel approach based on the Julich πN model, which presently includes the hadronic πN and ηN stable channels as well as the πΔ, σN and ρN effective channels. This model has been quite successful in the description of πN→πN scattering for center‐of‐mass energies up to 1.9 GeV. The full pion photoproduction amplitude is constructed to satisfy the generalized Ward‐Takahashi identity and hence, it is fully gauge invariant. The calculated differential cross sections and photon spin asymmetries up to 1.65 GeV center‐of‐mass energy for the reactions γp→π+n, γp→π0p and γn→π−p are in good agreement with the experimental data.
209866482
On eta and pi0 eta photoproduction
118726376
On eta photoproduction on the neutron and pi^0 eta photoproduction
The recently discovered enhancement of eta photoproduction on the quasi-free neutron at energies around s^1/2 ~ 1.67 GeV is addressed within an SU(3) coupled channels model. The K Sigma threshold plays a significant role and the quasi-free cross sections on proton and neutron, sigma_n and sigma_p, can be quantitatively explained. For the reaction gamma p --> pi^0 eta p, we evaluate the polarization observables I^S and I^C from a chiral unitary amplitude developed earlier. The I^S and I^C observables have been recently measured for the first time by the CBELSA/TAPS collaboration. We show the significance of the Delta(1700)D33 resonance and its S-wave decay into eta Delta(1232) which further confirms the dynamical nature of this resonance.