${{\boldsymbol \pi}^{0}}$ 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.

$8.32$ $\pm0.15$ $\pm0.18$

LARIN

2011

PRMX

Primakoff effect

$8.5$ $\pm1.1$

BYCHKOV

2009

PIBE

${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$ at rest

$8.4$ $\pm0.5$ $\pm0.5$

1182

WILLIAMS

1988

CBAL

${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \pi}^{0}}$

$8.97$ $\pm0.22$ $\pm0.17$

ATHERTON

1985

CNTR

Direct measurement

$8.2$ $\pm0.4$

⁴

BROWMAN

1974

CNTR

Primakoff effect

• • • We do not use the following data for averages, fits, limits, etc. • • •

$5.6$ $\pm0.6$

BELLETTINI

1970

CNTR

Primakoff effect

$9$ $\pm0.68$

KRYSHKIN

1970

CNTR

Primakoff effect

$7.3$ $\pm1.1$

BELLETTINI

1965

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