# $\alpha$ PARAMETER FOR ${{\boldsymbol \eta}}$ $\rightarrow$ 3 ${{\boldsymbol \pi}^{0}}$ INSPIRE search

See the Note on ${{\mathit \eta}}$ Decay Parameters'' in our 1994 edition, Phys.Rev.$\mathbf {D50}$, 1 August 1994, Part$~$I, p.$~$1454. The value here is of $\alpha$ in $\vert$matrix element$\vert ^2$ = 1 + 2${}\alpha {}\mathit z$.
VALUE EVTS DOCUMENT ID TECN  COMMENT
$\bf{ -0.0288 \pm0.0012}$ OUR AVERAGE  Error includes scale factor of 1.1.
$-0.0265$ $\pm0.0010$ $\pm0.0009$ 7M
 2018
CRYB ${{\mathit \gamma}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \eta}}$
$-0.055$ $\pm0.014$ $\pm0.004$ 33k
 2015 G
BES3 ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \eta}}$
$-0.0301$ $\pm0.0035$ ${}^{+0.0022}_{-0.0035}$ 512k
 2010 A
KLOE ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \phi}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \gamma}}$
$-0.027$ $\pm0.008$ $\pm0.005$ 120k 1
 2009
WASA ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit p}}{{\mathit \eta}}$
$-0.0322$ $\pm0.0012$ $\pm0.0022$ 3M 2
 2009
CRYB ${{\mathit \gamma}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \eta}}$
$-0.032$ $\pm0.002$ $\pm0.002$ 1.8M 2
 2009
CRYB ${{\mathit \gamma}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \eta}}$
$-0.026$ $\pm0.010$ $\pm0.010$ 75k
 2007
WASA ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit p}}{{\mathit \eta}}$
$-0.010$ $\pm0.021$ $\pm0.010$ 12k
 2001 C
SND ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \phi}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \gamma}}$
$-0.031$ $\pm0.004$ 1M
 2001
CRYB ${{\mathit \pi}^{-}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit n}}{{\mathit \eta}}$ , 720 MeV
$-0.052$ $\pm0.017$ $\pm0.010$ 98k
 1998 C
CBAR ${{\overline{\mathit p}}}$ ${{\mathit p}}$ $\rightarrow$ 5 ${{\mathit \pi}^{0}}$
$-0.022$ $\pm0.023$ 50k
 1984
GAM2
• • • We do not use the following data for averages, fits, limits, etc. • • •
$-0.038$ $\pm0.003$ ${}^{+0.012}_{-0.008}$ 1.34M 3
 2008 D
KLOE
$-0.32$ $\pm0.37$ 192
 1970
HLBC
1  This ADOLPH 2009 result is independent of the BASHKANOV 2007 result.
2  The PRAKHOV 2009 and UNVERZAGT 2009 results are independent.
3  This AMBROSINO 2008D value is an indirect result using ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{0}}{{\mathit \pi}^{-}}$ events and a$~$rescattering matrix that mixes isospin decay amplitudes.
References:
 PRAKHOV 2018
PR C97 065203 High-statistics measurement of the $\eta \to 3\pi^0$ decay at the Mainz Microtron
 ABLIKIM 2015G
PR D92 012014 Measurement of the Matrix Elements for the Decays ${{\mathit \eta}}$ $\rightarrow$ ${+}$ ${{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ and ${{\mathit \eta}}$ $/$ ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$
 AMBROSINO 2010A
PL B694 16 Measurement of the ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$ Slope Parameter $\alpha$ with the KLOE Detector
PL B677 24 Measurement of the ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$ Dalitz Plot Distribution with the WASA Detector at COSY
 PRAKHOV 2009
PR C79 035204 Measurement of the Slope Parameter $\alpha$ for the ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$ Decay with the Crystal Ball Detector at the Mainz Microtron (MAMI-C)
 UNVERZAGT 2009
EPJ A39 169 Determination of the Dalitz Plot Parameter $\alpha$ for the Decay ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$ with the Crystal Ball at MAMI-B
 AMBROSINO 2008D
JHEP 0805 006 Determination of ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ Dalitz Plot Slopes and Asymmetries with the KLOE Detector
 BASHKANOV 2007
PR C76 048201 Measurement of the Slope Parameter for the ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$ Decay in the ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit p}}{{\mathit \eta}}$ Reaction
 ACHASOV 2001C
JETPL 73 451 Dynamics of ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$ Decay
 TIPPENS 2001
PRL 87 192001 Determination of the Quadratic Slope Parameter in ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$ Decay
 ABELE 1998C
PL B417 193 Decay Dynamics of the Process ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$
 ALDE 1984
ZPHY C25 225 Neutral Decays of ${{\mathit \eta}}$ Meson
 BAGLIN 1970
NP B22 66 Heavy Liquid Bubble Chamber Analysis of ${{\mathit \eta}}$ Neutral Decay Modes ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$ and ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$