For a discussion of ${{\mathit B}}-{{\overline{\mathit B}}}$ mixing, see the note on “${{\mathit B}^{0}}-{{\overline{\mathit B}}^{0}}$ Mixing” in the ${{\mathit B}^{0}}$ Particle Listings.

${{\mathit \chi}_{{b}}}$ is the average ${{\mathit B}}-{{\overline{\mathit B}}}$ mixing parameter at high-energy ${{\mathit \chi}_{{b}}}$= ${{\mathit f}_{{d}}^{\,'}}{{\mathit \chi}_{{d}}}{+}$ ${{\mathit f}_{{s}}^{\,'}}{{\mathit \chi}_{{s}}}$ where ${{\mathit f}_{{d}}^{\,'}}$ and ${{\mathit f}_{{s}}^{\,'}}$ are the fractions of ${{\mathit B}^{0}}$ and ${{\mathit B}_{{s}}^{0}}$ hadrons in an unbiased sample of semileptonic ${{\mathit b}}$-hadron decays.

“OUR EVALUATION” is an average using rescaled values of the data listed below. The average and rescaling were performed by the Heavy Flavor Averaging Group (HFLAV) and are described at https://hflav.web.cern.ch/. The averaging/rescaling procedure takes into account correlations between the measurements.

VALUE EVTS DOCUMENT ID TECN  COMMENT $\bf{ 0.1284 \pm0.0069}$ OUR EVALUATION $\bf{ 0.129 \pm0.004}$ OUR AVERAGE $0.132$ $\pm0.001$ $\pm0.024$ 1 ABAZOV 2006 S D0 ${{\mathit p}}{{\overline{\mathit p}}}$ at 1.96 TeV $0.152$ $\pm0.007$ $\pm0.011$ 2 ACOSTA 2004 A CDF ${{\mathit p}}{{\overline{\mathit p}}}$ at $1.8$ TeV $0.1312$ $\pm0.0049$ $\pm0.0042$ 3 ABBIENDI 2003 P OPAL ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $0.127$ $\pm0.013$ $\pm0.006$ 4 ABREU 2001 L DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $0.1192$ $\pm0.0068$ $\pm0.0051$ 5 ACCIARRI 1999 D L3 ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $0.121$ $\pm0.016$ $\pm0.006$ 6 ABREU 1994 J DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $0.114$ $\pm0.014$ $\pm0.008$ 7 BUSKULIC 1994 G ALEP ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $0.129$ $\pm0.022$ 8 BUSKULIC 1992 B ALEP ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $0.176$ $\pm0.031$ $\pm0.032$ 1112 9 ABE 1991 G CDF ${{\mathit p}}{{\overline{\mathit p}}}$ $1.8$ TeV $0.148$ $\pm0.029$ $\pm0.017$ 10 ALBAJAR 1991 D UA1 ${{\mathit p}}{{\overline{\mathit p}}}$ 630 GeV • • We do not use the following data for averages, fits, limits, etc. • • $0.131$ $\pm0.020$ $\pm0.016$ 11 ABE 1997 I CDF Repl. by ACOSTA 2004A $0.1107$ $\pm0.0062$ $\pm0.0055$ 12 ALEXANDER 1996 OPAL Rep. by ABBIENDI 2003P $0.136$ $\pm0.037$ $\pm0.040$ 13 UENO 1996 AMY ${{\mathit e}^{+}}{{\mathit e}^{-}}$ at $57.9$ GeV $0.144$ $\pm0.014$ ${}^{+0.017}_{-0.011}$ 14 ABREU 1994 F DLPH Sup. by ABREU 1994J $0.131$ $\pm0.014$ 15 ABREU 1994 J DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $0.123$ $\pm0.012$ $\pm0.008$ ACCIARRI 1994 D L3 Repl. by ACCIARRI 1999D $0.157$ $\pm0.020$ $\pm0.032$ 16 ALBAJAR 1994 UA1 $\sqrt {\mathit s }$ = 630 GeV $0.121$ ${}^{+0.044}_{-0.040}$ $\pm0.017$ 1665 17 ABREU 1993 C DLPH Sup. by ABREU 1994J $0.143$ ${}^{+0.022}_{-0.021}$ $\pm0.007$ 18 AKERS 1993 B OPAL Sup. by ALEXANDER 1996 $0.145$ ${}^{+0.041}_{-0.035}$ $\pm0.018$ 19 ACTON 1992 C OPAL ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $0.121$ $\pm0.017$ $\pm0.006$ 20 ADEVA 1992 C L3 Sup. by ACCIARRI 1994D $0.132$ $\pm0.22$ ${}^{+0.015}_{-0.012}$ 823 21 DECAMP 1991 ALEP ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $0.178$ ${}^{+0.049}_{-0.040}$ $\pm0.020$ 22 ADEVA 1990 P L3 ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $0.17$ ${}^{+0.15}_{-0.08}$ 23, 24 WEIR 1990 MRK2 ${{\mathit e}^{+}}{{\mathit e}^{-}}$ 29 GeV $0.21$ ${}^{+0.29}_{-0.15}$ 23 BAND 1988 MAC ${\it{}E}^{\it{}ee}_{\rm{}cm}$= 29 GeV $>0.02 at 90\%\mathit CL$ 23 BAND 1988 MAC ${\it{}E}^{\it{}ee}_{\rm{}cm}$= 29 GeV $0.121$ $\pm0.047$ 25, 23 ALBAJAR 1987 C UA1 Repl. by ALBAJAR 1991D $<0.12 at 90\%\mathit CL$ 26, 23 SCHAAD 1985 MRK2 ${\it{}E}^{\it{}ee}_{\rm{}cm}$= 29 GeV 1  Uses the dimuon charge asymmetry. Averaged over the mix of ${{\mathit b}}$-flavored hadrons. 2  Measurement performed using events containing a dimuon or an ${{\mathit e}}/{{\mathit \mu}}$ pair. 3  The average ${{\mathit B}}$ mixing parameter is determined simultaneously with ${{\mathit b}}$ and ${{\mathit c}}$ forward-backward asymmetries in the fit. 4  The experimental systematic and model uncertainties are combined in quadrature. 5  ACCIARRI 1999D uses maximum-likelihood fits to extract ${{\mathit \chi}_{{b}}}$ as well as the $\mathit A{}^{{{\mathit b}}}_{\mathit FB}$ in ${{\mathit Z}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$ events containing prompt leptons. 6  This ABREU 1994J result is from 5182 ${{\mathit \ell}}{{\mathit \ell}}$ and 279 ${{\mathit \Lambda}}{{\mathit \ell}}$ events. The systematic error includes $0.004$ for model dependence. 7  BUSKULIC 1994G data analyzed using ${{\mathit e}}{{\mathit e}}$ , ${{\mathit e}}{{\mathit \mu}}$ , and ${{\mathit \mu}}{{\mathit \mu}}$ events. 8  BUSKULIC 1992B uses a jet charge technique combined with electrons and muons. 9  ABE 1991G measurement of $\chi $ is done with ${{\mathit e}}{{\mathit \mu}}$ and ${{\mathit e}}{{\mathit e}}$ events. 10  ALBAJAR 1991D measurement of $\chi $ is done with dimuons. 11  Uses di-muon events. 12  ALEXANDER 1996 uses a maximum likelihood fit to simultaneously extract ${{\mathit \chi}}$ as well as the forward-backward asymmetries in ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$ and ${{\mathit c}}{{\overline{\mathit c}}}$ . 13  UENO 1996 extracted $\chi $ from the energy dependence of the forward-backward asymmetry. 14  ABREU 1994F uses the average electric charge sum of the jets recoiling against a ${{\mathit b}}$-quark jet tagged by a high $\mathit p_{\mathit T}$ muon. The result is for ${{\overline{\mathit \chi}}}$ = ${{\mathit f}_{{d}}}{{\mathit \chi}_{{d}}}$ $+0.9$ ${{\mathit f}_{{s}}}{{\mathit \chi}_{{s}}}$ . 15  This ABREU 1994J result combines ${{\mathit \ell}}{{\mathit \ell}}$ , ${{\mathit \Lambda}}{{\mathit \ell}}$ , and jet-charge ${{\mathit \ell}}$ (ABREU 1994F) analyses. It is for ${{\overline{\mathit \chi}}}$ = $\mathit f_{\mathit d}{{\mathit \chi}_{{d}}}+0.96\mathit f_{\mathit s}{{\mathit \chi}_{{s}}}$. 16  ALBAJAR 1994 uses dimuon events. Not independent of ALBAJAR 1991D. 17  ABREU 1993C data analyzed using ${{\mathit e}}{{\mathit e}}$ , ${{\mathit e}}{{\mathit \mu}}$ , and ${{\mathit \mu}}{{\mathit \mu}}$ events. 18  AKERS 1993B analysis performed using dilepton events. 19  ACTON 1992C uses electrons and muons. Superseded by AKERS 1993B. 20  ADEVA 1992C uses electrons and muons. 21  DECAMP 1991 done with opposite and like-sign dileptons. Superseded by BUSKULIC 1992B. 22  ADEVA 1990P measurement uses ${{\mathit e}}{{\mathit e}}$ , ${{\mathit \mu}}{{\mathit \mu}}$ , and ${{\mathit e}}{{\mathit \mu}}$ events from 118k events at the ${{\mathit Z}}$. Superseded by ADEVA 1992C. 23  These experiments are not in the average because the combination of ${{\mathit B}_{{s}}}$ and ${{\mathit B}_{{d}}}$ mesons which they see could differ from those at higher energy. 24  The WEIR 1990 measurement supersedes the limit obtained in SCHAAD 1985 . The 90$\%$ CL are $0.06$ and $0.38$. 25  ALBAJAR 1987C measured $\chi $ = ( ${{\overline{\mathit B}}^{0}}$ $\rightarrow$ ${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}$ X) divided by the average production weighted semileptonic branching fraction for ${{\mathit B}}$ hadrons at 546 and 630 GeV. 26  Limit is average probability for hadron containing ${{\mathit B}}$ quark to produce a positive lepton.

References:

ABAZOV 2006S PR D74 092001 Measurement of the $\mathit CP$-violation Parameter of ${{\mathit B}^{0}}$ Mixing and Decay with ${{\mathit p}}$ ${{\overline{\mathit p}}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit \mu}}{{\mathit X}}$ Data ACOSTA 2004A PR D69 012002 Measurement of the Average Time-Integrated Mixing Probability of ${\mathit {\mathit b}}$-Flavored Hadrons Produced at the Tevatron ABBIENDI 2003P PL B577 18 Measurement of Heavy Quark Forward Backward Asymmetries and Average ${{\mathit B}}$ Mixing using Leptons in Hadronic ${{\mathit Z}}$ Decays ABREU 2001L EPJ C20 455 Measurement of the Semileptonic ${\mathit {\mathit b}}$ Branching Fractions and Average ${\mathit {\mathit b}}$ Mixing Parameter in ${{\mathit Z}}$ Decays ACCIARRI 1999D PL B448 152 Measurement of the ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit Z}}$ $\rightarrow$ ${\mathit {\mathit b}}$ ${\mathit {\overline{\mathit b}}}$ Forward Backward Asymmetry and the ${{\mathit B}^{0}}{{\overline{\mathit B}}^{0}}$ Mixing Parameter using Prompt Leptons ABE 1997I PR D55 2546 Measurement of ${\mathit {\mathit b}}{\mathit {\overline{\mathit b}}}$ Production Correlations, ${{\mathit B}^{0}}{{\overline{\mathit B}}^{0}}$ Mixing, and a Limit on ${{\mathit \epsilon}_{{b}}}$ in ${{\mathit p}}{{\overline{\mathit p}}}$ Collisions at $\sqrt {s }$ = 1.8 TeV ALEXANDER 1996 ZPHY C70 357 Measurement of the Heavy Quark Forward Backward Asymmetries and Average ${{\mathit B}}$ Mixing using Leptons in MultiHadronic Events UENO 1996 PL B381 365 Measurement of the Forward Backward Asymmetry in ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${\mathit {\mathit b}}$ ${\mathit {\overline{\mathit b}}}$ and the ${\mathit {\mathit b}}$ Quark Branching Ratio to Muons at TRISTAN using Neural Networks ABREU 1994F PL B322 459 Measurement of the ${{\mathit B}^{0}}−{{\overline{\mathit B}}^{0}}$ Mixing using the Average Electric Charge of Hadron-Jets in ${{\mathit Z}^{0}}$ Decays ABREU 1994J PL B332 488 Measurement of the ${{\mathit B}^{0}}{{\overline{\mathit B}}^{0}}$ Mixing Parameter in DELPHI ACCIARRI 1994D PL B335 542 Measurement of the ${{\mathit B}^{0}}$ $\leftrightarrow$ ${{\overline{\mathit B}}^{0}}$ Mixing Parameter and the ${{\mathit Z}}$ $\rightarrow$ ${\mathit {\mathit b}}$ ${\mathit {\overline{\mathit b}}}$ Forward-Backward Asymmetry ALBAJAR 1994 ZPHY C61 41 Measurement of ${\mathit {\mathit b}}{\mathit {\overline{\mathit b}}}$ Correlations at the CERN ${{\mathit p}}{{\overline{\mathit p}}}$ Collider BUSKULIC 1994G ZPHY C62 179 Heavy Flavor Production and Decay with Prompt Leptons in the ALEPH Detector ABREU 1993C PL B301 145 A Study of ${{\mathit B}^{0}}{{\overline{\mathit B}}^{0}}$ Mixing Using Semileptonic Decays of ${{\mathit B}}$ Hadrons Produced from ${{\mathit Z}^{0}}$ AKERS 1993B ZPHY C60 199 Measurements of ${{\mathit B}^{0}}−{{\overline{\mathit B}}^{0}}$ Mixing, $\Gamma\mathrm {( {{\mathit Z}^{0}} \rightarrow {\mathit {\mathit b}} {\mathit {\overline{\mathit b}}})}/\Gamma\mathrm {( {{\mathit Z}^{0}} \rightarrow hadrons)}$ and Semileptonic Branching Ratios for ${{\mathit b}}$-Flavored Hadrons in Hadronic ${{\mathit Z}^{0}}$ Decays ACTON 1992C PL B276 379 Measurement of ${{\mathit B}^{0}}{{\overline{\mathit B}}^{0}}$ Mixing in Hadronic ${{\mathit Z}^{0}}$ Decays ADEVA 1992C PL B288 395 An Improved Measurement of ${{\mathit B}^{0}}−{{\overline{\mathit B}}^{0}}$ Mixing in ${{\mathit Z}^{0}}$ Decays BUSKULIC 1992B PL B284 177 Measurement of ${{\mathit B}^{0}}$ $\leftrightarrow$ ${{\overline{\mathit B}}^{0}}$ Mixing at the ${{\mathit Z}}$ Using a Jet Charge Method ABE 1991G PRL 67 3351 Measurement of ${{\mathit B}^{0}}{{\overline{\mathit B}}^{0}}$ Mixing at the Fermilab Tevatron Collider ALBAJAR 1991D PL B262 171 Measurement of ${{\mathit B}^{0}}$ $\leftrightarrow$ ${{\overline{\mathit B}}^{0}}$ Mixing at the CERN S${{\mathit p}}{{\overline{\mathit p}}}$S Collider DECAMP 1991 PL B258 236 Measurement of ${{\mathit B}}$ $−$ ${{\overline{\mathit B}}}$ Mixing at the ${{\mathit Z}^{0}}$ ADEVA 1990P PL B252 703 A Measurement of ${{\mathit B}^{0}}{{\overline{\mathit B}}^{0}}$ Mixing in ${{\mathit Z}^{0}}$ Decays WEIR 1990 PL B240 289 A Reanalysis of ${{\mathit B}^{0}}$ $−$ ${{\overline{\mathit B}}^{0}}$ Mixing in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilation at 29 GeV BAND 1988 PL B200 221 Additional Evidence for ${{\mathit B}^{0}}$ $−$ ${{\overline{\mathit B}}^{0}}$ Mixing ALBAJAR 1987C PL B186 247 Search for ${{\mathit B}^{0}}-{{\overline{\mathit B}}^{0}}$ Oscillations at the CERN Proton Antiproton Collider. Paper 2 SCHAAD 1985 PL 160B 188 Upper Limit on ${{\mathit B}^{0}}{{\overline{\mathit B}}^{0}}$ Mixing in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilation at 29 GeV