# ${{\boldsymbol \pi}^{+}}{{\boldsymbol \pi}^{-}}{{\boldsymbol \gamma}}$ PARAMETER $\beta$ (${\boldsymbol D}{\mathrm -wave}$) INSPIRE search

Sensitive to a ${\mathit D}{\mathrm -wave}$ contribution: $\mathit dN/\mathit d$cos $\theta$ = sin$^2\theta$ ${}$ (1 + $\beta$ ${}$ cos $^2\theta$).
VALUE EVTS DOCUMENT ID TECN
$\bf{ -0.02 \pm0.07}$ OUR AVERAGE  Error includes scale factor of 1.3.
$0.11$ $\pm0.11$ 35k
 1974 B
OSPK
$-0.060$ $\pm0.065$ 7250
 1970
WIRE
• • • We do not use the following data for averages, fits, limits, etc. • • •
$0.12$ $\pm0.06$ 1
 1972
ASPK
1  The authors don't believe this indicates ${\mathit D}{\mathrm -wave}$ because the dependence of $\beta$ on the ${{\mathit \gamma}}$ energy is inconsistent with the theoretical prediction. A cos $^2\theta$ dependence can also come from $\mathit P$- and ${\mathit F}{\mathrm -wave}$ interference.
Conservation Laws:
 CHARGE CONJUGATION ($\mathit C$) INVARIANCE
References:
 JANE 1974B
PL 48B 265 Measurement of the Charge Asymmetry in the Decay ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$
 THALER 1972
PRL 29 313 Charge Asymmetry in the Decay ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$
 GORMLEY 1970
PR D2 501 Experimental Determination of the Dalitz-Plot Distribution of the Decays ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ and ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$ , and the Branching ratio ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$ $/$ ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$