${{\mathit \pi}^{\pm}}$ FORM FACTORS

$\mathit F_{\mathit V}$, VECTOR FORM FACTOR

INSPIRE   PDGID:
S008FV
VALUE EVTS DOCUMENT ID TECN  COMMENT
$\bf{ 0.0254 \pm0.0017}$ OUR AVERAGE
$0.0258$ $\pm0.0017$ 65k 1
BYCHKOV
2009
PIBE ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$ at rest
$0.014$ $\pm0.009$ 2
BOLOTOV
1990B
 SPEC 17 GeV ${{\mathit \pi}^{-}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{e}}}{{\mathit \gamma}}$
$0.023$ ${}^{+0.015}_{-0.013}$ 98
EGLI
1989
SPEC ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{e}}}{{\mathit e}^{+}}{{\mathit e}^{-}}$
1  The BYCHKOV 2009 $\mathit F_{A}$ and $\mathit F_{V}$ results are highly (anti-)correlated: $\mathit F_{A}$ + 1.0286 $\mathit F_{V}$ = $0.03853$ $\pm0.00014$.
2  BOLOTOV 1990B only determines the absolute value.
References:
BYCHKOV 2009
PRL 103 051802 New Precise Measurement of the Pion Weak Form Factors in ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$ Decay
BOLOTOV 1990B
PL B243 308 The Experimental Study of the ${{\mathit \pi}^{-}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{e}}}{{\mathit \gamma}}$ Decay in Flight
EGLI 1989
PL B222 533 Measurement of the Decay ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{e}}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ and Search for a Light Higgs Boson
Also
PL B175 97 First Observation of the Decay ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{e}}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ and a Determination of the Formfactors F$_{V}$, F$_{A}$, R