pdgLive Home   >   LIGHT UNFLAVORED MESONS ($\mathit S$ = $\mathit C$ = $\mathit B$ = 0)   >   ${{\mathit \eta}}$   >   $\alpha $ PARAMETER FOR ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$

ENERGY DEPENDENCE OF ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}}$ DALITZ PLOTS

$\alpha $ PARAMETER FOR ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$

INSPIRE   JSON  (beta) PDGID:

S014A0

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 $\bf{ -0.0296 \pm0.0016}$ OUR AVERAGE  Error includes scale factor of 1.7.  See the ideogram below. $-0.0406$ $\pm0.0035$ $\pm0.0008$ 272k ABLIKIM 2023 AN BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \eta}}$ $-0.0265$ $\pm0.0010$ $\pm0.0009$ 7M PRAKHOV 2018 CRYB ${{\mathit \gamma}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \eta}}$ $-0.055$ $\pm0.014$ $\pm0.004$ 33k ABLIKIM 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 AMBROSINO 2010 A KLOE ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \phi}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \gamma}}$ $-0.027$ $\pm0.008$ $\pm0.005$ 120k 1 ADOLPH 2009 WASA ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit p}}{{\mathit \eta}}$ $-0.0322$ $\pm0.0012$ $\pm0.0022$ 3M 2 PRAKHOV 2009 CRYB ${{\mathit \gamma}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \eta}}$ $-0.032$ $\pm0.002$ $\pm0.002$ 1.8M 2 UNVERZAGT 2009 CRYB ${{\mathit \gamma}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \eta}}$ $-0.026$ $\pm0.010$ $\pm0.010$ 75k BASHKANOV 2007 WASA ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit p}}{{\mathit p}}{{\mathit \eta}}$ $-0.010$ $\pm0.021$ $\pm0.010$ 12k ACHASOV 2001 C SND ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \phi}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \gamma}}$ $-0.031$ $\pm0.004$ 1M TIPPENS 2001 CRYB ${{\mathit \pi}^{-}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit n}}{{\mathit \eta}}$, 720 MeV $-0.052$ $\pm0.017$ $\pm0.010$ 98k ABELE 1998 C CBAR ${{\overline{\mathit p}}}$ ${{\mathit p}}$ $\rightarrow$ 5 ${{\mathit \pi}^{0}}$ $-0.022$ $\pm0.023$ 50k ALDE 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 AMBROSINO 2008 D KLOE $-0.32$ $\pm0.37$ 192 BAGLIN 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.

$\alpha $ PARAMETER FOR ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$

References

Except where otherwise noted, content of the 2025 Review of Particle Physics is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license. The publication of the Review of Particle Physics is supported by US DOE, MEXT (Japan), INFN (Italy) and CERN. Individual collaborators receive support for their PDG activities from their respective institutes or funding agencies. © 2025. See LBNL disclaimers.