η→π0γγdecay within a chiral unitary approach revisited

Abstract

In view of the recent experimental developments in the ! 0 decay, and the fact that the Particle Data Group in the online edition of 2007 reports sizable changes of the radiative decay widths of vector mesons used as input in the theoretical calculations of E. Oset, J. R. Pelaez, and L. Roca [Phys. Rev. D 67, 073013 (2003)], a reevaluation of the decay width of the in this channel has been done, reducing its uncertainty by almost a factor of 2. The new input of the Particle Data Group is used, and invariant mass distributions and total widths are compared with the most recent results from the AGS and MAMI experiments, and preliminary ones of KLOE. The agreement of the theory with the AGS and MAMI data is very good, both for the total rates and for the invariant mass distributions of the two photons.

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.…”

Theoretical analysis of the γγ→π0η process

“…We saturate them using our vector t-and u-meson exchange terms. This would check the dynamical role of the vector mesons similar to [9,50].…”

“…We find the kaon and pion loop contributions to the η → π 0 γγ decay width as Γ K loop = 0.010(0) eV and Γ π loop = 0.003(0) eV, respectively. The latter was not included in the analysis of [50], which in principle should be enlarged by the rescattering effects which are known to be strong for the η → 3π decay [29,[51][52][53][54]. We leave this study for the future and take this contribution into account at the NLO level.…”

η′ →π0γγandη′ →ηγγ: a primer analysis

“…On the theory side, the η → π 0 γγ process has been studied in many different frameworks, starting from Chiral Perturbation Theory (ChPT) [11] and ending with the most recent chiral unitary approach [12,13], most of them in combination with the Vector Meson Dominance (VMD) prediction. On the contrary, there are no theoretical analyses neither for η → π 0 γγ nor for η → ηγγ.…”