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.
Highlights
The comprehensive study of the reaction γγ∗ → π0η with one off-shell photon serves as important constraint to the hadronic light-by-light contribution to the anomalous magnetic moment of the muon aμ [1]
Measuring photon-fusion processes with a single tagged technique is a part of two-photon physics program of the BESIII Collaboration [2]
T- and u-channel vector meson exchange terms lead to the logarithmic behavior of the p.w. amplitudes, from which the position of the closest lefthand cut sL can be extracted
Summary
The comprehensive study of the reaction γγ∗ → π0η with one off-shell photon serves as important constraint to the hadronic light-by-light contribution to the anomalous magnetic moment of the muon aμ [1]. Measuring photon-fusion processes with a single tagged technique is a part of two-photon physics program of the BESIII Collaboration [2]. There is only real photon high-statistic data from Belle Collaboration [3], which provides the valuable information on the nature of two resonances: scalar a0(980) and tensor a2(1320). It allows to extract the two-photon strength of the 0++ isovector channel. The proposed dispersive method [7] complies with the fundamental properties of the S -matrix, i.e. analyticity and unitarity, and in principle allows a parameter-free description of both real and single-virtual processes. For studying the low-lying resonances, it is convenient to perform the partial wave (p.w.) expansion of the helicity amplitudes with the fixed isospin (I)
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