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${{\mathit \pi}^{0}}$ MEAN LIFE

INSPIRE   PDGID:

S009T

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. 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 $\bf{ 8.43 \pm0.13}$ OUR AVERAGE  Error includes scale factor of 1.2. $8.337$ $\pm0.056$ $\pm0.112$ 1 LARIN 2020 PRMX Primakoff effect $8.5$ $\pm1.1$ 2 BYCHKOV 2009 PIBE ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$ at rest $8.4$ $\pm0.5$ $\pm0.5$ 1182 3 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. • • $8.32$ $\pm0.15$ $\pm0.18$ 5 LARIN 2011 PRMX Primakoff effect $5.6$ $\pm0.6$ BELLETTINI 1970 CNTR Primakoff effect $9$ $\pm0.68$ KRYSHKIN 1970 CNTR Primakoff effect $7.3$ $\pm1.1$ BELLETTINI 1965 B CNTR Primakoff effect 1  LARIN 2020 reported this lifetime value from a measurement of $\Gamma $( ${{\mathit \pi}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$ ) = $7.802$ $\pm0.052$ $\pm0.105$ eV, combining data from PrimEX-II on 12C and 28Si targets with previous PrimEx-I LARIN 2011 measurements. This result supersedes LARIN 2011 . 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 $. 5  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).

References:

LARIN 2020 SCI 368 506 Precision measurement of the neutral pion lifetime 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