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

$\mathit F_{\mathit A}$, AXIAL-VECTOR FORM FACTOR

INSPIRE   PDGID:
S008FA
VALUE EVTS DOCUMENT ID TECN  COMMENT
$0.0119$ $\pm0.0001$ 65k 1, 2
BYCHKOV
2009
PIBE ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$ at rest
• • We do not use the following data for averages, fits, limits, etc. • •
$0.0115$ $\pm0.0004$ 41k 1, 3
FRLEZ
2004
PIBE ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$ at rest
$0.0106$ $\pm0.0060$ 4, 1
BOLOTOV
1990B
 SPEC 17 GeV ${{\mathit \pi}^{-}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}{{\mathit \gamma}}$
$0.021$ ${}^{+0.011}_{-0.013}$ 98
EGLI
1989
SPEC ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{e}}}}{{\mathit e}^{+}}{{\mathit e}^{-}}$
$0.0135$ $\pm0.0016$ 4, 1
BAY
1986
SPEC ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$
$0.006$ $\pm0.003$ 4, 1
PIILONEN
1986
SPEC ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$
$0.011$ $\pm0.003$ 5, 4, 1
STETZ
1978
SPEC ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$
1  These values come from fixing the vector form factor at the CVC prediction, ${{\mathit F}_{{{V}}}}$ = $0.0259$ $\pm0.0005$.
2  When $\mathit F_{V}$ is released, the BYCHKOV 2009 $\mathit F_{A}$ is $0.0117$ $\pm0.0017$, and $\mathit F_{A}$ and $\mathit F_{V}$ results are highly (anti-)correlated: $\mathit F_{A}$ + 1.0286 $\mathit F_{V}$ = $0.03853$ $\pm0.00014$.
3  The sign of ${{\mathit \gamma}}$ = ${{\mathit F}_{{{A}}}}$ /${{\mathit F}_{{{V}}}}$ is determined to be positive.
4  Only the absolute value of $\mathit F_{\mathit A}$ is determined.
5  The result of STETZ 1978 has a two-fold ambiguity. We take the solution compatible with later determinations.
References