${{\mathit \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \ell}^{+}}{{\mathit \ell}^{-}}$ TRANSITION FORM FACTOR SLOPE

INSPIRE   JSON  (beta) PDGID:
M002FFL
Related to the effective virtual meson mass $\Lambda $, via slope $\approx{}$ $\Lambda {}^{-2}$. See e.g. LANDSBERG 1985, eq. (3.8), for a detailed definition.
VALUE (GeV${}^{-2}$) EVTS DOCUMENT ID TECN  COMMENT
$\bf{ 1.53 \pm0.04}$ OUR AVERAGE
$1.524$ $\pm0.041$ 7611 1
ABLIKIM
2024M
 BES3 ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \eta}^{\,'}}$
$1.7$ $\pm0.4$ 33 1
VIKTOROV
1980
25,33 ${{\mathit \pi}^{-}}$ ${{\mathit p}}$ $\rightarrow$ 2 ${{\mathit \mu}}{{\mathit \gamma}}$
• • We do not use the following data for averages, fits, limits, etc. • •
$1.30$ $\pm0.19$ 2
ABLIKIM
2024AK
 BES3 ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ , ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$
$1.60$ $\pm0.17$ $\pm0.08$ 864 1
ABLIKIM
2015O
 BES3 ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit e}^{+}}{{\mathit e}^{-}}$
1  In the single-pole Ansatz where slope = 1/($\Lambda {}^{2}$ + $\gamma {}^{2}$) with $\Lambda $, $\gamma $ being a Breit-Wigner mass, width for the effective contributing vector meson.
2  From a weighted average of the ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ and ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ values. The uncertainty is obtained by combining statistical and systematic uncertainties. TFF slope values go between $1.10$ $\pm0.21$ GeV${}^{-2}$ and $1.61$ $\pm0.71$ GeV${}^{-2}$ for ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$, and between $2.37$ $\pm0.49$ GeV${}^{-2}$ and $2.88$ $\pm0.25$ GeV${}^{-2}$ for ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$, according to the solution of the fitting function model.
References