Study of the radiative decay???? + ? ? ?

η, $ \eta{^\prime}$ → πl+l- in a chiral unitary approach

“…= 2.23, the error bands indicate the 1σ confidence level. For the η ′ decay the agreement with the two experimental spectra from [22,23] is very good as already observed in [12]. The experimental situation for the η decay is not as consistent as for η ′ → π + π − γ.…”

“…[11,12,9], it has become clear that resonances and unitarity corrections due to final-state interactions are a necessary ingredient for the realistic description of these processes. One example is the pronounced peak structure caused by the ρ(770) resonance in the 22,23] (see also Fig. 5).…”

“…Afterwards, we can predict the spectra and widths of η (′) → π + π − l + l − within this approach. The data of η (′) → π + π − γ involve the partial decay widths [14] and the di-pion spectra from [28,29,22,23]. In order to perform a global least-squares fit to these different data sets we employ the following definition for the χ 2 -function:…”

“…− γ compared to experimental data from [22] (left) and [23] (right). The solid line corresponds to the fit with minimal χ 2 , the error band indicates the 1σ confidence region.…”

Dilepton spectra from decays of light unflavored mesons

“…[56]. The η ′ → π + π − γ decay is studied experimentally much better (see [57]- [59] and references therein). The last decay is more complicated, since two pions occur in the physical region of the ρ-meson.…”