${{\boldsymbol \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\boldsymbol \eta}}{{\boldsymbol \pi}}{{\boldsymbol \pi}}$ DECAY PARAMETERS
$\vert $MATRIX ELEMENT$\vert ^2$ = $\vert $1 + $\alpha {}\boldsymbol Y\vert ^2$ + $\boldsymbol C{}\boldsymbol X$ + $\boldsymbol D{}\boldsymbol X{}^{2}$

$\mathit X$ and $\mathit Y$ are Dalitz variables; $\alpha $ is complex and $\mathit C$, and $\mathit D$ are real-valued. Parameters $\mathit C$ and $\mathit D$ are not necessarily equal to $\mathit c$ and $\mathit d$, respectively, in the generalized parameterization following this one. May be different for ${{\mathit \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ and ${{\mathit \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ decays. Because of different initial assumptions and strong correlations of the parameters we do not average the parameters in the section below.

$\boldsymbol C$ decay parameter INSPIRE search

VALUE EVTS DOCUMENT ID TECN  COMMENT
• • • We do not use the following data for averages, fits, limits, etc. • • •
$0.0027$ $\pm0.0024$ $\pm0.0015$ 351k
ABLIKIM
2018
BES3 ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$
$0.018$ $\pm0.009$ $\pm0.003$ 44k 1
ABLIKIM
2011
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$
$0.020$ $\pm0.018$ $\pm0.004$ 7k 2
AMELIN
2005A
VES 28 ${{\mathit \pi}^{-}}$ ${{\mathit A}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{-}}{{\mathit A}^{*}}$
1  See ABLIKIM 2011 for the full correlation matrix.
2  Superseded by DOROFEEV 2007 , which found this parameterization unacceptable. See below.
  References:
ABLIKIM 2018
PR D97 012003 Measurement of the Matrix Elements for the Decays ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ and ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$
ABLIKIM 2011
PR D83 012003 Measurement of the Matrix Element for the Decay ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$
AMELIN 2005A
PAN 68 372 Measurement of Form Factors for the Decay ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{-}}{{\mathit \pi}^{+}}$