Search results for "Chiral"
showing 10 items of 752 documents
Lambda(1405) poles obtained from pi(0)Sigma(0) photoproduction data
2013
We present a strategy to extract the position of the two Lambda(1405) poles from experimental photoproduction data measured recently at different energies in the gamma p -> K+pi(0)Sigma(0) reaction at Jefferson Laboratory. By means of a chiral dynamics motivated potential with free parameters, we solve the Bethe-Salpeter equation in the coupled channels (K) over barN and pi Sigma in isospin I = 0 and parametrize the amplitude for the photonuclear reaction in terms of a linear combination of the pi Sigma -> pi Sigma and (K) over barN -> pi Sigma scattering amplitudes in I = 0, with a different linear combination for each energy. Good fits to the data are obtained with some sets of parameters…
Diquark correlations in hadron physics: Origin, impact and evidence
2020
The last decade has seen a marked shift in how the internal structure of hadrons is understood. Modern experimental facilities, new theoretical techniques for the continuum bound-state problem and progress with lattice-regularised QCD have provided strong indications that soft quark+quark (diquark) correlations play a crucial role in hadron physics. For example, theory indicates that the appearance of such correlations is a necessary consequence of dynamical chiral symmetry breaking, viz. a corollary of emergent hadronic mass that is responsible for almost all visible mass in the universe; experiment has uncovered signals for such correlations in the flavour-separation of the proton's elect…
Chiral Dynamics of the two Lambda(1405) States
2004
Using a chiral unitary approach for the meson--baryon interactions, we show that two octets of J^{\pi}=1/2^- baryon states, which are degenerate in the limit of exact SU(3) symmetry, and a singlet are generated dynamically. The SU(3) breaking produces the splitting of the two octets, resulting in the case of strangeness S=-1 in two poles of the scattering matrix close to the nominal \Lambda(1405) resonance. These poles are combinations of the singlet state and the octets. We show how actual experiments see just one effective resonance shape, but with properties which change from one reaction to another.
Transition form factors of the N(*()1535) as a dynamically generated resonance
2007
We discuss how electromagnetic properties provide useful tests of the nature of resonances, and we study these properties for the N*(1535) which appears dynamically generated from the strong interaction of mesons and baryons. Within this coupled channel chiral unitary approach, we evaluate the A_1/2 and S_1/2 helicity amplitudes as a function of Q^2 for the electromagnetic N*(1535) to gamma* N transition. Within the same formalism we evaluate the cross section for the reactions gamma N to eta N. We find a fair agreement for the absolute values of the transition amplitudes, as well as for the Q^2 dependence of the amplitudes, within theoretical and experimental uncertainties discussed in the…
Evaluation of the polarization observables I-S and I-C in the reaction gamma p -> pi(0)eta p
2010
We evaluate the polarization observables I(S) and I(C) for the reaction gamma p -> pi(0)eta p, using a chiral unitary framework developed earlier. The I(S) and I(C) observables have been recently measured for the first time by the CBELSA/TAPS Collaboration. The theoretical predictions of I(S) and I(C), given for altogether 18 angle-dependent functions, are in good agreement with the measurements. Also, the asymmetry d Sigma/dcos theta evaluated here agrees with the data. We show the importance of the Delta(1700) D(33)-resonance and its S-wave decay into eta Delta(1232). The result can be considered as a further confirmation of the dynamical nature of this resonance. At the highest energies,…
Generalized Polarizabilities and the Chiral Structure of the Nucleon
1997
We are studying the electron scattering process e p to e' p' gamma in order to obtain information on the genuine virtual Compton scattering (VCS) process gamma^* N to gamma N. In addition to the two kinematical variables of real Compton scattering, e.g. the scattering angle theta and the energy omega' of the outgoing photon, the invariant amplitude for VCS depends on a third kinematical variable, which we choose as the absolute value of the three-momentum transfer to the nucleon. The structure-dependent coefficients in the VCS amplitude therefore acquire a momentum dependence and are termed ``generalized polarizabilities'' of the nucleon in analogy to real Compton scattering. Utilizing the …
Properties of the ground-state baryons in chiral perturbation theory
2010
15th High Energy Physics International Conference on Quantum Chromodynamics. Montpellier (FRANCE). JUN 28-JUL 02, 2010
Higher order forward spin polarizability
2010
As a guideline for future experiments to extract the four (leading) spin polarizabilities of the nucleon, we have constructed the forward amplitude for polarized Compton scattering by dispersion integrals. These integrals have been saturated by recently measured helicity-dependent photoabsorption cross sections as well as predictions for pion photoproduction multipoles from several phenomenological descriptions and chiral perturbation theory. The comparison of these results corroborates the strategy to extract the spin polarizabilities by fitting them to polarized Compton data and fixing all higher order spin effects by dispersion relations based on pion photoproduction multipoles.
Measurement of the radiative K-e3 branching ratio
2005
We present a measurement of the relative branching ratio of the decay KL -> pi e nu gamma (Ke3gamma) with respect to KL-> pi e nu (gamma) (Ke3+Ke3gamma) decay. The result is based on observation of 19 000 Ke3gamma and 5.6 x 10^6 Ke3 decays. The value of the branching ratio is Br(Ke3gamma, Egamma^*>30 MeV,theta(e,gamma)^*>20^o)/Br(Ke3)= (0.964+-0.008+0.011-0.009)%. This result agrees with theoretical predictions but is at variance with a recently published result.
Unitarized Chiral Perturbation Theory in a finite volume: scalar meson sector
2011
We develop a scheme for the extraction of the properties of the scalar mesons f0(600), f0(980), and a0(980) from lattice QCD data. This scheme is based on a two-channel chiral unitary approach with fully relativistic propagators in a finite volume. In order to discuss the feasibility of finding the mass and width of the scalar resonances, we analyze synthetic lattice data with a fixed error assigned, and show that the framework can be indeed used for an accurate determination of resonance pole positions in the multi-channel scattering.