PARAMETER $\beta$ IN ${{\boldsymbol \phi}}$ $\rightarrow$ ${{\boldsymbol P}}{{\boldsymbol e}^{+}}{{\boldsymbol e}^{-}}$ DECAYS

In the one-pole approximation the electromagnetic transition form factor for ${{\mathit \phi}}$ $\rightarrow$ ${{\mathit P}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ (${{\mathit P}}$ = ${{\mathit \pi}},{{\mathit \eta}}$) is given as a function of the ${{\mathit e}^{+}}{{\mathit e}^{-}}$ invariant mass squared, ${{\mathit q}^{2}}$, by the expression: $\vert \mathit F({{\mathit q}^{2}})\vert ^2$ = (1 $−$ ${{\mathit q}^{2}}/{{\mathit \Lambda}^{2}}){}^{-2}$, where vector meson dominance predicts parameter $\Lambda \approx{}$0.770 GeV ($\Lambda {}^{-2}\approx{}$1.687 GeV${}^{-2}$). The slope of this form factor, $\beta$ = d$\mathit F$/d${{\mathit q}^{2}}({{\mathit q}^{2}}$=0), equals $\Lambda {}^{-2}$ in this approximation.
The measurements below obtain $\beta$ in the one-pole approximation.

PARAMETER $\beta$ IN ${{\boldsymbol \phi}}$ $\rightarrow$ ${{\boldsymbol \pi}^{0}}{{\boldsymbol e}^{+}}{{\boldsymbol e}^{-}}$ DECAY INSPIRE search

VALUE (GeV${}^{-2}$) EVTS DOCUMENT ID TECN  COMMENT
$2.02$ $\pm0.11$ 9.5k 1
 2016 B
KLOE 1.02 ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit e}^{+}}{{\mathit e}^{-}}$
1  The error combines statistical and systematic uncertainties.
References:
 ANASTASI 2016B
PL B757 362 Measurement of the ${{\mathit \phi}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ Transition Form Factor with the KLOE Detector