${{\boldsymbol K}_S^0}$ MEAN LIFE

For earlier measurements, beginning with BOLDT 1958B, see our 1986 edition, Physics Letters 170B 130 (1986).
OUR FIT is described in the note on $\mathit CP$ violation in ${{\mathit K}_{{L}}}$ decays'' in the ${{\mathit K}_L^0}$ Particle Listings. The result labeled OUR FIT Assuming $\mathit CPT$'' [OUR FIT Not assuming $\mathit CPT$''] includes all measurements except those with the comment Not assuming $\mathit CPT$'' [Assuming $\mathit CPT$'']. Measurements with neither comment do not assume $\mathit CPT$ and enter both fits.

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VALUE ($10^{-10}$ s) EVTS DOCUMENT ID TECN  COMMENT
$\bf{ 0.89564 \pm0.00033}$ OUR FIT  Not assuming $\mathit CPT$
$\bf{ 0.8954 \pm0.0004}$ OUR FIT  Error includes scale factor of 1.1.  Assuming $\mathit CPT$
$0.89589$ $\pm0.00070$ 1, 2
 2011
KTEV Not assuming $\mathit CPT$
$0.89623$ $\pm0.00047$ 1, 3
 2011
KTEV Assuming $\mathit CPT$
$0.89562$ $\pm0.00029$ $\pm0.00043$ 20M 4
 2011
KLOE Not assuming $\mathit CPT$
$0.89598$ $\pm0.00048$ $\pm0.00051$ 16M
 2002 C
NA48
$0.8971$ $\pm0.0021$
 1997
NA31
$0.8941$ $\pm0.0014$ $\pm0.0009$
 1995
E773 Assuming $\mathit CPT$
$0.8929$ $\pm0.0016$
 1993
E731 Assuming $\mathit CPT$
• • • We do not use the following data for averages, fits, limits, etc. • • •
$0.8965$ $\pm0.0007$ 5
 2003
KTEV Assuming $\mathit CPT$
$0.8958$ $\pm0.0013$ 6
 2003
KTEV Not assuming $\mathit CPT$
$0.8920$ $\pm0.0044$ 214k
 1987
SPEC
$0.905$ $\pm0.007$ 7
 1982 B
SPEC
$0.881$ $\pm0.009$ 26k
 1976
SPEC
$892.6 \pm3.2 \pm0.2 \times 10^{-3}$ 8
 1975
SPEC
$0.8937$ $\pm0.0048$ 6M
 1974 B
ASPK
$0.8958$ $\pm0.0045$ 50k 9
 1972
HBC
$0.856$ $\pm0.008$ 19994 10
 1968 B
HBC
$0.872$ $\pm0.009$ 20000 9, 10
 1968
DBC
1  The two ABOUZAID 2011 values use the same full KTeV dataset from 1996, 1997, and 1999. The first enters the ''assuming $\mathit CPT$'' fit and the second enters the ''not assuming $\mathit CPT$'' fit.
2  ABOUZAID 2011 fit has $\Delta \mathit m$, ${{\mathit \tau}_{{s}}}$, ${{\mathit \phi}_{{\epsilon}}}$, Re(${{\mathit \epsilon}^{\,'}}/{{\mathit \epsilon}}$), and Im(${{\mathit \epsilon}^{\,'}}/{{\mathit \epsilon}}$) as free parameters. See Im(${{\mathit \epsilon}^{\,'}}/{{\mathit \epsilon}}$) in the ''${{\mathit K}_L^0}$ $\mathit CP$ violation'' section for correlation information.
3  ABOUZAID 2011 fit has $\Delta \mathit m$ and ${{\mathit \tau}_{{s}}}$ free but constrains ${{\mathit \phi}_{{\epsilon}}}$ to the Superweak value, i.e. assumes $\mathit CPT$. This ${{\mathit \tau}_{{s}}}$ value is correlated with their $\Delta \mathit m$ = ${\mathit m}_{{{\mathit K}_L^0} }–{\mathit m}_{{{\mathit K}_S^0} }$ measurement in the ${{\mathit K}_L^0}$ listings. The correlation coefficient ${{\mathit \rho}}({{\mathit \tau}_{{s}}}$, $\Delta \mathit m$) = $-0.670$.
4  Fit to the proper time distribution.
5  This ALAVI-HARATI 2003 fit has $\Delta \mathit m$ and $\tau _{{{\mathit s}}}$ free but constrains $\phi _{+−}$ to the Superweak value, i.e. assumes $\mathit CPT$. This $\tau _{{{\mathit s}}}$ value is correlated with their $\Delta \mathit m$ = ${\mathit m}_{{{\mathit K}_L^0} }–{\mathit m}_{{{\mathit K}_S^0} }$ measurement in the ${{\mathit K}_L^0}$ listings. The correlation coefficient $\rho\mathrm {(\tau _{{{\mathit s}}},\Delta \mathit m)}$ = $-0.396$. Superseded by ABOUZAID 2011 .
6  This ALAVI-HARATI 2003 fit has $\Delta \mathit m$, $\phi _{+−}$, and $\tau _{{{\mathit K}_{{S}}}}$ free. See $\phi _{+−}$ in the ${{\mathit K}_{{L}}}$ $\mathit CP$ violation'' section for correlation information. Superseded by ABOUZAID 2011 .
7  ARONSON 1982 find that ${{\mathit K}_S^0}$ mean life may depend on the kaon energy.
8  CARITHERS 1975 measures the $\Delta \mathit m$ dependence of the total decay rate (inverse mean life) to be $\Gamma\mathrm {({{\mathit K}_S^0} )}$ = $\lbrack{}(1.122$ $\pm0.004)+0.16{}(\Delta \mathit m-0.5348)/\Delta \mathit m\rbrack{}10^{10}$/s, or, in terms of mean life, CARITHERS 1975 measures ${{\mathit \tau}_{{s}}}$ = ( $0.8913$ $\pm0.0032$ ) $–$ $0.238$ [ $\Delta \mathit m$$–$ $0.5348$ ] . We have adjusted the measurement to use our best values of ( $\Delta \mathit m$ = $0.5293$ $\pm0.0009$ ) . Our first error is their experiment's error and our second error is the systematic error from using our best values.
9  HILL 1968 has been changed by the authors from the published value ($0.865$ $\pm0.009$) because of a correction in the shift due to $\eta _{+−}$. SKJEGGESTAD 1972 and HILL 1968 give detailed discussions of systematics encountered in this type of experiment.
10  Pre-1971 experiments are excluded from the average because of disagreement with later more precise experiments.
References:
 ABOUZAID 2011
PR D83 092001 Precise Measurements of Direct $\mathit CP$ Violation, $\mathit CPT$ Symmetry, and other Parameters in the Neutral Kaon System
 AMBROSINO 2011
EPJ C71 1604 Precision Measurement of ${{\mathit K}_S^0}$ Meson Lifetime with the KLOE Detector
 ALAVI-HARATI 2003
PR D67 012005 Measurements of Direct $\mathit CP$ Violation, $\mathit CPT$ Symmetry, and other Parameters in the Neutral Kaon System
 LAI 2002C
PL B537 28 A Measurement of the ${{\mathit K}_S^0}$ Lifetime
 BERTANZA 1997
ZPHY C73 629 Measurement of the ${{\mathit K}_S^0}$ Mean Lifetime from ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ and ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ Decays using ${{\mathit K}_L^0}$ Decays to Determine the Acceptance
 SCHWINGENHEUER 1995
PRL 74 4376 $\mathit CPT$ Tests in the Neutral Kaon System
 GIBBONS 1993
PRL 70 1199 New Measurements of the Neutral Kaon Parameters $\Delta _{m}$, $\tau _{S}$, $\Phi _{00}$ $−$ $\Phi _{+-}$, and $\Phi _{+-}$
 GROSSMAN 1987
PRL 59 18 Measurement of the Lifetime of ${{\mathit K}_S^0}$ Mesons in the Momentum Range 100 to 350 ${\mathrm {GeV/}}\mathit c$
 ARONSON 1982B
PRL 48 1306 Determination of the Fundamental Parameters of the ${{\mathit K}^{0}}{{\overline{\mathit K}}^{0}}$ System in the Energy Range 30-110 GeV
 ARONSON 1976
NC 32A 236 New Measurement of the ${{\mathit K}_S^0}$ Lifetime
 CARITHERS 1975
PRL 34 1244 Measurement of the Phase of the $\mathit CP$ Nonconservation Parameter $\eta _{+−}$ and ${{\mathit K}_S^0}$ Total Decay Rate
 GEWENIGER 1974B
PL 48B 487 A New Determination of the ${{\mathit K}^{0}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ Decay Parameters
NP B48 343 Measurement of the ${{\mathit K}_S^0}$ Mean Life
PR 171 1418 Measurement of the Lifetime of the Short-Lived Neutral ${{\mathit K}}$ Meson