Each measurement of the ${{\mathit B}}$ mean life is an average over an admixture of various bottom mesons and baryons which decay weakly. Different techniques emphasize different admixtures of produced particles, which could result in a different ${{\mathit B}}~$mean life.

“OUR EVALUATION” is an average using rescaled values of the data listed below. This is a weighted average of the lifetimes of the five main ${{\mathit b}}$-hadron species (${{\mathit B}^{+}}$, ${{\mathit B}^{0}}$, ${{\mathit B}_{{{sH}}}^{0}}$, ${{\mathit B}_{{{sL}}}^{0}}$, and ${{\mathit \Lambda}_{{{b}}}}$) that assumes the production fractions in ${{\mathit Z}}$ decays (given at the end of this section) and equal production fractions of ${{\mathit B}_{{{sH}}}^{0}}$ and ${{\mathit B}_{{{sL}}}^{0}}$ mesons.

VALUE ($ 10^{-12} $ s) EVTS DOCUMENT ID TECN  COMMENT $\bf{ 1.5673 \pm0.0029}$ OUR EVALUATION  $~~$(Produced by HFLAV) • • We do not use the following data for averages, fits, limits, etc. • • $1.570$ $\pm0.005$ $\pm0.008$ 1 ABDALLAH 2004 E DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.533$ $\pm0.015$ ${}^{+0.035}_{-0.031}$ 2 ABE 1998 B CDF ${{\mathit p}}{{\overline{\mathit p}}}$ at $1.8$ TeV $1.549$ $\pm0.009$ $\pm0.015$ 3 ACCIARRI 1998 L3 ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.611$ $\pm0.010$ $\pm0.027$ 4 ACKERSTAFF 1997 F OPAL ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.582$ $\pm0.011$ $\pm0.027$ 4 ABREU 1996 E DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.575$ $\pm0.010$ $\pm0.026$ 5 ABREU 1996 E DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.533$ $\pm0.013$ $\pm0.022$ 19.8k 6 BUSKULIC 1996 F ALEP ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.564$ $\pm0.030$ $\pm0.036$ 7 ABE,K 1995 B SLD ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.542$ $\pm0.021$ $\pm0.045$ 8 ABREU 1994 L DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.50$ ${}^{+0.24}_{-0.21}$ $\pm0.03$ 9 ABREU 1994 P DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.46$ $\pm0.06$ $\pm0.06$ 5344 10 ABE 1993 J CDF Repl. by ABE 1998B $1.23$ ${}^{+0.14}_{-0.13}$ $\pm0.15$ 188 11 ABREU 1993 D DLPH Sup. by ABREU 1994L $1.49$ $\pm0.11$ $\pm0.12$ 253 12 ABREU 1993 G DLPH Sup. by ABREU 1994L $1.51$ ${}^{+0.16}_{-0.14}$ $\pm0.11$ 130 13 ACTON 1993 C OPAL ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.523$ $\pm0.034$ $\pm0.038$ 5372 14 ACTON 1993 L OPAL ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.535$ $\pm0.035$ $\pm0.028$ 7357 14 ADRIANI 1993 K L3 Repl. by ACCIARRI 1998 $1.511$ $\pm0.022$ $\pm0.078$ 15 BUSKULIC 1993 O ALEP ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.28$ $\pm0.10$ 16 ABREU 1992 DLPH Sup. by ABREU 1994L $1.37$ $\pm0.07$ $\pm0.06$ 1354 17 ACTON 1992 OPAL Sup. by ACTON 1993L $1.49$ $\pm0.03$ $\pm0.06$ 18 BUSKULIC 1992 F ALEP Sup. by BUSKULIC 1996F $1.35$ ${}^{+0.19}_{-0.17}$ $\pm0.05$ 19 BUSKULIC 1992 G ALEP ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.32$ $\pm0.08$ $\pm0.09$ 1386 20 ADEVA 1991 H L3 Sup. by ADRIANI 1993K $1.32$ ${}^{+0.31}_{-0.25}$ $\pm0.15$ 37 21 ALEXANDER 1991 G OPAL ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $1.29$ $\pm0.06$ $\pm0.10$ 2973 22 DECAMP 1991 C ALEP Sup. by BUSKULIC 1992F $1.36$ ${}^{+0.25}_{-0.23}$ 23 HAGEMANN 1990 JADE ${\it{}E}^{\it{}ee}_{\rm{}cm}$= 35 GeV $1.13$ $\pm0.15$ 24 LYONS 1990 RVUE $1.35$ $\pm0.10$ $\pm0.24$ BRAUNSCHWEIG 1989 B TASS ${\it{}E}^{\it{}ee}_{\rm{}cm}$= 35 GeV $0.98$ $\pm0.12$ $\pm0.13$ ONG 1989 MRK2 ${\it{}E}^{\it{}ee}_{\rm{}cm}$= 29 GeV $1.17$ ${}^{+0.27}_{-0.22}$ ${}^{+0.17}_{-0.16}$ KLEM 1988 DLCO ${\it{}E}^{\it{}ee}_{\rm{}cm}$= 29 GeV $1.29$ $\pm0.20$ $\pm0.21$ 25 ASH 1987 MAC ${\it{}E}^{\it{}ee}_{\rm{}cm}$= 29 GeV $1.02$ ${}^{+0.42}_{-0.39}$ 301 26 BROM 1987 HRS ${\it{}E}^{\it{}ee}_{\rm{}cm}$= 29 GeV 1  Measurement performed using an inclusive reconstruction and ${{\mathit B}}$ flavor identification technique. 2  Measured using inclusive ${{\mathit J / \psi}{(1S)}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ vertex. 3  ACCIARRI 1998 uses inclusively reconstructed secondary vertex and lepton impact parameter. 4  ACKERSTAFF 1997F uses inclusively reconstructed secondary vertices. 5  Combines ABREU 1996E secondary vertex result with ABREU 1994L impact parameter result. 6  BUSKULIC 1996F analyzed using 3D impact parameter. 7  ABE,K 1995B uses an inclusive topological technique. 8  ABREU 1994L uses charged particle impact parameters. Their result from inclusively reconstructed secondary vertices is superseded by ABREU 1996E. 9  From proper time distribution of ${{\mathit b}}$ $\rightarrow$ ${{\mathit J / \psi}{(1S)}}$ anything. 10  ABE 1993J analyzed using ${{\mathit J / \psi}{(1S)}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit \mu}}$ vertices. 11  ABREU 1993D data analyzed using ${{\mathit D}}$ / ${{\mathit D}^{*}}{{\mathit \ell}}$ anything event vertices. 12  ABREU 1993G data analyzed using charged and neutral vertices. 13  ACTON 1993C analysed using ${{\mathit D}}$ / ${{\mathit D}^{*}}{{\mathit \ell}}$ anything event vertices. 14  ACTON 1993L and ADRIANI 1993K analyzed using lepton (${{\mathit e}}$ and ${{\mathit \mu}}$) impact parameter at ${{\mathit Z}}$. 15  BUSKULIC 1993O analyzed using dipole method. 16  ABREU 1992 is combined result of muon and hadron impact parameter analyses. Hadron tracks gave ($12.7$ $\pm0.4$ $\pm1.2){\times }10^{-13}~$s for an admixture of ${{\mathit B}}$ species weighted by production fraction and mean charge multiplicity, while muon tracks gave ($13.0$ $\pm1.0$ $\pm0.8){\times }10^{-13}~$s for an admixture weighted by production fraction and semileptonic branching fraction. 17  ACTON 1992 is combined result of muon and electron impact parameter analyses. 18  BUSKULIC 1992F uses the lepton impact parameter distribution for data from the 1991 run. 19  BUSKULIC 1992G use ${{\mathit J / \psi}{(1S)}}$ tags to measure the average ${{\mathit b}}$ lifetime. This is comparable to other methods only if the ${{\mathit J / \psi}{(1S)}}$ branching fractions of the different ${{\mathit b}}$-flavored hadrons are in the same ratio. 20  Using ${{\mathit Z}}$ $\rightarrow$ ${{\mathit e}^{+}}$ X or ${{\mathit \mu}^{+}}$ X, ADEVA 1991H determined the average lifetime for an admixture of ${{\mathit B}}$ hadrons from the impact parameter distribution of the lepton. 21  Using ${{\mathit Z}}$ $\rightarrow$ ${{\mathit J / \psi}{(1S)}}$ X, ${{\mathit J / \psi}{(1S)}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}$, ALEXANDER 1991G determined the average lifetime for an admixture of ${{\mathit B}}$ hadrons from the decay point of the ${{\mathit J / \psi}{(1S)}}$. 22  Using ${{\mathit Z}}$ $\rightarrow$ ${{\mathit e}}$ X or ${{\mathit \mu}}$ X, DECAMP 1991C determines the average lifetime for an admixture of ${{\mathit B}}$ hadrons from the signed impact parameter distribution of the lepton. 23  HAGEMANN 1990 uses electrons and muons in an impact parameter analysis. 24  LYONS 1990 combine the results of the ${{\mathit B}}$ lifetime measurements of ONG 1989, BRAUNSCHWEIG 1989B, KLEM 1988, and ASH 1987, and JADE data by private communication. They use statistical techniques which include variation of the error with the mean life, and possible correlations between the systematic errors. This result is not independent of the measured results used in our average. 25  We have combined an overall scale error of 15$\%$ in quadrature with the systematic error of $\pm0.7$ to obtain $\pm2.1$ systematic error. 26  Statistical and systematic errors were combined by BROM 1987.

References