No abstract

We present a theoretical study of the γγ → πη process from the threshold up to 1.4 GeV in the πη invariant mass. For the s-wave a0(980) resonance state we adopt a dispersive formalism using a coupled-channel Omnès representation, while the d-wave a2(1320) state is described as a Breit-Wigner resonance. An analytic continuation to the a0(980) pole position allows us to extract its two-photon decay width as Γa 0 →γγ = 0.27(4) keV.

In this paper, we present a dispersive analysis of the double-virtual photon-photon scattering to two pions up to 1.5 GeV. Through unitarity, this process is very sensitive to hadronic final state interaction. For the s-wave, we use a coupled-channel ππ, KK analysis which allows a simultaneous description of both f 0 (500) and f 0 (980) resonances. For higher energies, f 2 (1270) shows up as a dominant structure which we approximate by a single channel ππ rescattering in the d-wave. In the dispersive approach, the latter requires taking into account t-and u-channel vector-meson exchange left-hand cuts which exhibit an anomalous-like behavior for large space-like virtualities. In our paper, we show how to readily incorporate such behavior using a contour deformation. Besides, we devote special attention to kinematic constraints of helicity amplitudes and show their correlations explicitly.

No abstract

The theoretical analysis of the γγ → π0η process is presented within the energy range up to 1.4 GeV. The S -wave resonance a0(980) is described involving the coupled channel dispersive framework and the D-wave a2(1320) is approximated as a Breit-Wigner resonance. For the a0(980) the pole is found on the IV Riemann sheet resulting in a two-photon decay width of Γa0 → γγ = 0.27(4) keV. The first dispersive prediction is provided for the single-virtual γγ*(Q2) → π0η process in the spacelike region up to Q2 = 1 GeV2.