# ${{\boldsymbol \pi}^{0}}$ MEAN LIFE INSPIRE search

Most experiments measure the ${{\mathit \pi}^{0}}$ width which we convert to a lifetime. ATHERTON 1985 is the only direct measurement of the ${{\mathit \pi}^{0}}$ lifetime. Our average based only on indirect measurement yields ($8.30$ $\pm0.19$) $\times 10^{-17}~$s. The two Primakoff measurements from 1970 have been excluded from our average because they suffered model-related systematics unknown at the time. More information on the ${{\mathit \pi}^{0}}$ lifetime can be found in BERNSTEIN 2013 .
VALUE ($10^{-17}$ s) EVTS DOCUMENT ID TECN  COMMENT
$\bf{ 8.52 \pm0.18}$ OUR AVERAGE  Error includes scale factor of 1.2.
$8.32$ $\pm0.15$ $\pm0.18$ 1
 2011
PRMX Primakoff effect
$8.5$ $\pm1.1$ 2
 2009
PIBE ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$ at rest
$8.4$ $\pm0.5$ $\pm0.5$ 1182 3
 1988
CBAL ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \pi}^{0}}$
$8.97$ $\pm0.22$ $\pm0.17$
 1985
CNTR Direct measurement
$8.2$ $\pm0.4$ 4
 1974
CNTR Primakoff effect
• • • We do not use the following data for averages, fits, limits, etc. • • •
$5.6$ $\pm0.6$
 1970
CNTR Primakoff effect
$9$ $\pm0.68$
 1970
CNTR Primakoff effect
$7.3$ $\pm1.1$
 1965 B
CNTR Primakoff effect
1  LARIN 2011 reported $\Gamma$( ${{\mathit \pi}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$ ) = $7.82$ $\pm0.14$ $\pm0.17$ eV which we converted to mean life $\tau$ = $\hbar{}/\Gamma$(total).
2  BYCHKOV 2009 obtains this using the conserved-vector-current relation between the vector form factor $\mathit F_{V}$ and the ${{\mathit \pi}^{0}}$ lifetime.
3  WILLIAMS 1988 gives $\Gamma\mathrm {( {{\mathit \gamma}} {{\mathit \gamma}} )}$ = $7.7$ $\pm0.5$ $\pm0.5$ eV. We give here $\tau$ = $\hbar{}/\Gamma\mathrm {(total)}$.
4  BROWMAN 1974 gives a ${{\mathit \pi}^{0}}$ width $\Gamma$ = $8.02$ $\pm0.42$ eV. The mean life is $\hbar{}/\Gamma$.
References:
 LARIN 2011
PRL 106 162303 New Measurement of the ${{\mathit \pi}^{0}}$ Radiative Decay Width
 BYCHKOV 2009
PRL 103 051802 New Precise Measurement of the Pion Weak Form Factors in ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$ Decay
 WILLIAMS 1988
PR D38 1365 Formation of Pseudoscalars ${{\mathit \pi}^{0}}$, ${{\mathit \eta}}$ and ${{\mathit \eta}^{\,'}}$ in the Reaction ${{\mathit \gamma}}$ ${{\mathit \gamma}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$
 ATHERTON 1985
PL 158B 81 Direct Measurement of the Lifetime of the Neutral Pion
 BROWMAN 1974
PRL 33 1400 Decay Width of the Neutral ${{\mathit \pi}}$ Meson
 BELLETTINI 1970
NC 66A 243 A New Measurement of the ${{\mathit \pi}^{0}}$ Lifetime Through the Primakoff Effect in Nuclei
 KRYSHKIN 1970
JETP 30 1037 Measurement of Lifetime of the ${{\mathit \pi}^{0}}$ Meson
 BELLETTINI 1965B
NC 40A 1139 Primakoff Effect and ${{\mathit \pi}^{0}}$ Lifetime