Photon-fusion reactions from the chiral Lagrangian with dynamical light vector mesons

Abstract

We study the reactions γγ → π 0 π 0 , π + π − , K 0K 0 , K + K − , η η and π 0 η based on a chiral Lagrangian with dynamical light vector mesons as formulated within the hadrogenesis conjecture. At present our chiral Lagrangian contains 5 unknown parameters that are relevant for the photon fusion reactions. They parameterize the strength of interaction terms involving two vector meson fields. These parameters are fitted to photon fusion data γγ → π 0 π 0 , π + π − , π 0 η and to the decay η → π 0 γγ. In order to derive gauge invariant reaction amplitudes in the resonance region constraints from maximal analyticity and exac t coupled-channel unitarity are used. Our results are in good agreement with the existing experimental data from threshold up to about 0.9 GeV for the two-pion final states. The a 0 meson in the π 0 η channel is dynamically generated and an accurate reproduction of the γγ → π 0 η data is achieved up to 1.2 GeV. Based on our parameter sets we predict the γγ → K 0K 0 , K + K − , η η cross sections.

Theoretical analysis of the γγ→π0η process

“…All the couplings which enter the dispersion integral are fixed from the radiative decays of the vector mesons into pseudoscalar mesons. In this sense, our analysis is different from an earlier work which has a significant amount of unknown parameters and therefore a limited predictive power [9]. In addition to that, the analyticity constraint, which is hard to implement, is frequently discarded in the literature [10][11][12].…”

ηandη′Physics at MAMI

“…In figure 7 three theoretical calculations are compared with the experimental results: a calculation based on the VMD transition amplitude [44], a revised calculation of this based on a chiral unitary approach [45], and a calculation involving theoretical studies of photon fusion reactions based on a chiral Lagrangian with dynamical light vector mesons [46]. All three theoretical studies agree within the uncertainties with the experimental results.…”

“…[41] (green circles), the Crystal Ball at AGS [42] (blue triangles), and the WASA at COSY collaboration [43] (red open squares) are shown. Also theoretical calculations using VMD transition amplitudes [44] (dashed line), based on a chiral unitary approach [45] (solid line with error band), and based on a chiral Lagrangian with dynamical light vector mesons [46] tal Ball/TAPS determination of the decay width is the most accurate value to date.…”

Spin Observables in Pion Photoproduction and Nucleon Compton Scattering from the Chiral Lagrangian and Dispersion Relations

“…The method has proven successful in describing a variety of hadronic reactions. [3][4][5][6][7][8] In this talk we discuss the predictions for various spin observables made within our approach for neutral pion photoproduction off the proton and proton Compton scattering.…”