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

INSPIRE   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 $\bf{ 1.62 \pm0.17}$ OUR AVERAGE $1.60$ $\pm0.17$ $\pm0.08$ 864 1 ABLIKIM 2015 O BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ $1.7$ $\pm0.4$ 33 1 VIKTOROV 1980 25,33 ${{\mathit \pi}^{-}}$ ${{\mathit p}}$ $\rightarrow$ 2 ${{\mathit \mu}}{{\mathit \gamma}}$ 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.

References:

ABLIKIM 2015O PR D92 012001 Observation of the Dalitz Decay $\rightarrow$ ${{\mathit \gamma}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ VIKTOROV 1980 SJNP 32 520 Further Study of the ${{\mathit \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \gamma}}$ Decay