(home , top , next, previous )
bhadron species  average lifetime  lifetime ratio 
B^{0}  1.519 ± 0.004 ps  
B^{+}  1.638 ± 0.004 ps  B^{+}/B^{0} = 1.076 ± 0.004 
B_{s}^{0}  1.516 ± 0.006 ps  B_{s}^{0}/B^{0} = 0.998 ± 0.005 
B_{s}_{L}  1.427 ± 0.007 ps  
B_{s}_{H}  1.616 ± 0.010 ps  
B_{c}^{+}  0.510 ± 0.009 ps  
Λ_{b}  1.471 ± 0.009 ps  Λ_{b}/B^{0} = 0.969 ± 0.006 
Ξ_{b}^{−}  1.572 ± 0.040 ps  
Ξ_{b}^{0}  1.480 ± 0.030 ps  Ξ_{b}^{0}/Ξ_{b}^{−} = 0.929 ± 0.028 
Ω_{b}^{−}  1.64 +0.18 −0.17 ps  
bhadron average (weighted by fractions in Z decays) 
1.5667 ± 0.0029 ps 
The tables below give a number of effective B_{s} lifetime averages, measured from single exponential fits of the proper time distributions of B_{s} decays to a number of interesting final states. In general each final state may be a different mixture of the two B_{s} mass eigenstates, and hence the effective lifetime falls somewhere between 1/Γ_{L} and 1/Γ_{H}. The "B_{s} → flavour specific" lifetime is measured mainly with B_{s} → D_{s} lepton X decays; it is used as input to extract the long and short lifetimes of the B_{s} system (see next section). The "B_{s} → J/ψ φ" lifetime is an average of the results from single exponential fits. Nowadays, the time dependence and the angular dependence of the B_{s} → J/ψ φ decays is analysed in a more sophisticated way in order to extract separately the long and short lifetimes (see further below). The B_{s} → μ^{+}μ^{} effective lifetime is expected to be equal to the long lifetime in the Standard Model, but could be a mixture.
mixture of the two B_{s} mass eigenstates 
effective lifetime from single exponential fits 
B_{s} → flavour specific  1.527 ± 0.011 ps 
B_{s} → J/ψφ  1.480 ± 0.007 ps 
B_{s} → μ^{+}μ^{}  1.91 +0.37 −0.35 ps 
The two tables below report effective B_{s} lifetime averages for final states that are either pure CPeven or pure CPodd eigenstates. If the corresponding B_{s} decays are dominated by a single weak phase and if CP violation can be neglected, then the effective lifetime for decays to CPeven (CPodd) eigenstates corresponds to 1/Γ_{L} (1/Γ_{H}). These averages are used as constraints in the fit to determine Γ_{s} and ΔΓ_{s} (see further below).
CPeven final states  effective lifetime from single exponential fits 
B_{s} → J/ψη, D_{s}^{+}D_{s}^{−}  1.422 ± 0.023 ps 
CPodd final states  effective lifetime from single exponential fits 
B_{s} → J/ψf_{0}(980), J/ψπ^{+}π^{−}  1.666 ± 0.024 ps 
Combined result on the relative decay width difference in the B^{0} system:
s×ΔΓ_{d}/Γ_{d} = 0.001 ± 0.010  from DELPHI, BABAR, Belle, ATLAS, CMS and LHCb 
The quantity s = sign(Re(λ_{CP})), where λ_{CP} = (q/p)×A_{CP}/A_{CP} refers to a CPeven final state (e.g. J/ψK_{L}), is predicted to be equal to s= +1 to a high degree of confidence from the Standard Model fits to all available constraints on the unitarity triangle.
The timedependent and tagged angular analyses of the B_{s} → J/ψ φ decay by ATLAS, CMS, CDF and D0, as well as those of the B_{s} → J/ψKK and B_{s} → ψ(2S)φ decays by LHCb, provide information on Γ_{s}, ΔΓ_{s} and the weak phase φ_{s}^{ccs}, defined as the phase difference between the mixing amplitude and the b→ccs decay amplitude of the B_{s} meson. Combined values of the average decay width Γ_{s} and the decay width difference ΔΓ_{s} are obtained from of a multidimensional fit of the experimental results, extracting several other physics parameters in addition to Γ_{s}, ΔΓ_{s} and φ_{s}^{ccs}. The φ_{s}^{ccs}average is given further below. The correlation matrix between all physics parameters in each analysis is taken into account. Due to tensions between analyses for some of the measured parameters, scale factors are applied on their errors. The scale factors are calculated per parameter, in one dimension, using the PDG prescription. For example the scale factors of the errors of Γ_{s}, ΔΓ_{s} and φ_{s}^{ccs} are 2.5, 1.77 and 1, respectively. The scale factors are applied in a way that preserves the total correlation matrix of each analysis. The following additional constraints are then applied, using effective lifetime measurements:
Fit results from ATLAS, CDF, CMS, D0 and LHCb data 
without constraint from effective lifetime measurements 
with constraints I and II 
with constraints I, II and III 
Γ_{s}  0.6628 ± 0.0035 ps^{−1}  0.6596 ± 0.0031 ps^{−1}  0.6597 ± 0.0026 ps^{−1} 
1/Γ_{s}  1.509 ± 0.008 ps  1.516 ± 0.007 ps  1.516 ± 0.006 ps 
τ_{Short} = 1/Γ_{L}  1.426 ± 0.008 ps  1.427 ± 0.008 ps  1.427 ± 0.007 ps 
τ_{Long} = 1/Γ_{H}  1.601 ± 0.013 ps  1.616 ± 0.012 ps  1.616 ± 0.010 ps 
ΔΓ_{s}  +0.077 ± 0.006 ps^{−1}  +0.082 ± 0.005 ps^{−1}  +0.082 ± 0.005 ps^{−1} 
ΔΓ_{s}/Γ_{s}  +0.115 ± 0.009  +0.124 ± 0.008  +0.124 ± 0.008 
correlation ρ(Γ_{s}, ΔΓ_{s})  −0.240  −0.170  −0.070 
Δm_{d} = 0.5065 ± 0.0019 ps^{−1}  from timedependent measurements at ALEPH, DELPHI, L3, OPAL, CDF, D0, BABAR, BELLE, LHCb 
χ_{d} = 0.182 ± 0.015  from timeintegrated measurements at ARGUS and CLEO 
Assuming no CP violation in the mixing and no width difference in the B^{0} system, and using the B^{0} lifetime average of 1.519 ± 0.004 ps (the experimental average listed above), all above measurements can be combined to yield the following world averages:
Δm_{d} =
0.5065
±
0.0019
ps^{−1}
x_{d} = 0.769 ± 0.004 χ_{d} = 0.1858 ± 0.0011 
from all ALEPH, DELPHI, L3, OPAL, CDF, D0, BABAR, BELLE, LHCb, ARGUS and CLEO measurements 
In the plot below, all individual measurements are listed as quoted by the experiments; they might assume different physics inputs. The averages (which take into account all known correlations) are quoted after adjusting the individual measurements to the common set of physics inputs. The χ_{d} average from ARGUS and CLEO is converted to a Δm_{d} measurement assuming no CP violation, no width difference in the B^{0} system and a B^{0} lifetime of 1.519 ± 0.004 ps.
colour gif /
colour eps /
blackandwhite eps /
Same without average including timeintegrated (χ_{d}) measurements:
colour eps /
blackandwhite eps /
Only measurements and average at LEP:
colour eps /
blackandwhite eps /
Only measurements and average at Tevatron:
colour eps /
blackandwhite eps /
Only measurements and average at asymmetric B factories:
colour eps /
blackandwhite eps /
In the plot below,
the individual experiment averages are listed as quoted by the experiments
(or computed by the working group without performing any adjustments);
they might assume different physics inputs. The global averages are quoted
after adjusting the individual measurements to the common set of physics
inputs. The χ_{d} average from ARGUS and CLEO is converted to a Δm_{d} measurement
assuming no CP violation, no width difference in the B^{0} system and a
B^{0} lifetime of
1.519
±
0.004
ps.
colour gif /
colour eps /
blackandwhite eps /
Δm_{s} = 17.741 ± 0.020 ps^{−1}  CDF, LHCb, CMS 
With a mean B^{0}_{s} lifetime of 1/Γ_{s} = 1.516 ± 0.006 ps, a decay width difference of ΔΓ_{s} = +0.082 ± 0.005 ps^{−1} and the assumption of no CP violation in B^{0}_{s} mixing, this leads to
x_{s} = 26.89 ± 0.11 
χ_{s} = 0.499312 ± 0.000006 
The parameters q/p, A_{SL} and Re(ε_{B})/(1+ε_{B}^{2}) are thus equivalent. There is CP violation in the mixing if q/p is different from 1, i.e. A_{SL} is different from 0.
Averages are given below separately for the B^{0} and the B_{s} systems. Two sets of averages are given for the B^{0} system in the first table: a first set using only measurements performed at Υ(4S) machines, and a second set using all measurements (excluding those that assume no CP violation in B_{s} mixing). The second table presents an average for the B_{s} system. Measurements performed at high energy that do not separate the B^{0} and B_{s} contributions are no longer used to obtain the final averages (at this time, the only measurements at high energy used in the averages are from D0 and LHCb).
CP violation parameter in B^{0} mixing  
q/p =
1.0009
±
0.0013
A_{SL} = −0.0019 ± 0.0027 Re(ε_{B})/(1+ε_{B}^{2}) = −0.0005 ± 0.0007 
from measurements at the Υ(4S) 
q/p =
1.0010
±
0.0008
A_{SL} = −0.0021 ± 0.0017 Re(ε_{B})/(1+ε_{B}^{2}) = −0.0005 ± 0.0004 
world average 
CP violation parameter in B_{s} mixing  
q/p =
1.0003
±
0.0014
A_{SL} = −0.0006 ± 0.0028 
world average 
The above world averages A_{SL}(B^{0}) = −0.0021 ± 0.0017 and A_{SL}(B_{s}) = −0.0006 ± 0.0028 are obtained from a twodimensional fit of the CLEO, BABAR, Belle, D0 and LHCb results: the correlation coefficient between them is found to be −0.054 . This is illustrated in the plot below, where the vertical band shows the Bfactory average of A_{SL}(B^{0}) (measurements performed by CLEO, BABAR and Belle at the Υ(4S)), the green ellipses the D0 measurements, the blue ellipse the LHCb measurements, and the red ellipse the result of the twodimensional averaging of all measurements. The red point close to (0,0) is the Standard Model prediction [M. Artuso, G. Borissov and A. Lenz, arXiv:1511.09466 [hepph]] with errors bars multiplied by 10. The prediction and experimental average deviate from each other by 0.5 σ.
colour gif /
colour eps /
colour pdf /
CP violation in B_{s} mixing is caused by the weak phase difference
φ_{12}=arg[−M_{12}/Γ_{12}],
where M_{12} and Γ_{12}
are the offdiagonal elements of the mass and decay matrices. The tangent of this phase difference
can be estimated (approximately) as A_{SL}(B_{s}) Δm_{s}/ΔΓ_{s}=
−0.1
±
0.6
using the above averages of A_{SL}(B_{s}), Δm_{s} and
ΔΓ_{s}.
Combined result from CDF, D0, ATLAS, CMS and LHCb data (complete list of inputs and references) 

φ_{s}^{ccs}  −0.050 ± 0.019 
The two plots below show some of the results of the multidimentional fit. The plot on the left shows, in the (φ_{s}^{ccs}, ΔΓ_{s}) plane, the individual 68% confidencelevel contours of ATLAS, CMS, CDF, D0 and LHCb, their combined contour (black solid line and shaded area), as well as the Standard Model predictions (very thin white rectangle). The prediction for φ_{s}^{ccs} is taken as the indirect determination of −2β_{s} via a global fit to experimental data within the Standard Model, −2β_{s} = −0.0370 ^{ +0.0007 }_{ −0.0008 } [CKMfitter, Phys. Rev. D84, 033005 (2011), updated with Summer 2019 results], while the Standard Model prediction for ΔΓ_{s} is 0.091 ±0.013 ps^{−1} [A. Lenz and G. TetlalmatziXolocotzi, JHEP 07 (2020) 177]. The combined result is consistent with these predictions. The plot on the right shows, in the (Γ_{s}, ΔΓ_{s}) plane, the individual 68% confidencelevel contours of ATLAS, CMS, CDF, D0 and LHCb, their combined contour (black solid line and shaded area), as well as the Standard Model prediction for ΔΓ_{s} (horizontal gray band). Because of tensions between the measurements, the errors on Γ_{s} and ΔΓ_{s} have been scaled by 2.5 and 1.77, respectively (the ellipses representing the results of each experiment are shown before scaling, while the combined ellipses include the scale factors).
Left plot in several formats:
jpg /
png /
eps /
pdf /
Right plot in several formats:
jpg /
png /
eps /
pdf /
[This section is no longer updated. The averages computed for PDG 2020 are reported.]
The B^{+} and B^{0} fractions below are for an unbiased sample of B mesons produced in Υ(4S) decays. Most analyses measure the ratio f^{+−}/f^{00} assuming isospin invariance in charged and neutral B decays, and relying on our knowledge of the B^{+}/B^{0} lifetime ratio. Combining all these analyses from BABAR, BELLE and CLEO leads to the average f^{+−}/f^{00} = 1.059 ± 0.027 after adjusting to a common B^{+}/B^{0} lifetime ratio of 1.076 ± 0.004 (the current average given above). On the other hand, BABAR measured directly f^{00} = 0.487 ± 0.013 without assuming isospin invariance nor relying on the B^{+}/B^{0} lifetime ratio.
f^{+−}/f^{00} = 1.059 ± 0.027  from ratios of reconstructed B^{+} and B^{0} mesons
at BABAR, BELLE and CLEO
(assumptions made, see text above) 
f^{00} = 0.487 ± 0.013  from absolute measurement of
B^{0} mesons at BABAR
(no assumptions) 
Assuming f^{+−} + f^{00} = 1, the above two independent results
(which are consistent with each other)
can be combined to yield:
bhadron species  fraction in Υ(4S) decay  ratio 
B^{+} B^{−}  f^{+−} = 0.514 ± 0.006  f^{+−}/f^{00} = 1.058 ± 0.024 
B^{0} B^{0}  f^{00} = 0.486 ± 0.006 
[This section is no longer updated. The averages computed for PDG 2020 are reported.]
The table below show the fraction of events containing nonstrange B mesons (f_{u,d}), strange B mesons (f_{s}), or no B mesons at all (f_{noB}) in a sample of Υ(5S) decays, or more precisely in a sample of bb events produced in e^{+}e^{−} collisions at a centreofmass energy equal to the Υ(5S) mass. The sum of the three fractions is constrained to unity: f_{u,d}+f_{s}+f_{noB}=1. Their combined values have been obtained by combining modeldependent estimates of CLEO3 and Belle based on the measurements of several inclusive Υ(5S) branching fractions, after performing adjustments to common external inputs. A onesided constraint on f_{noB} from the direct measurements of Υ(5S) decays to final states without bottom mesons has been used, causing the strongly asymmetric uncertainty on the final value of f_{noB}.final states  fraction in Υ(5S) decays  ratio of fractions 
B_{u,d}^{(*)} B_{u,d}^{(*)}(π(π))  f_{u,d} = 0.757 +0.027 −0.039  
B_{s}^{(*)} B_{s}^{(*)}  f_{s} = 0.199 +0.030 −0.029  f_{s} / f_{u,d} = 0.262 +0.052 −0.043 
no open bottomness  f_{noB} = 0.045 +0.045 −0.005 
The plot below shows the published measurements of f_{s}.
All values have been obtained assuming f_{noB}=0.
They are quoted as in the original publication,
except for the most recent measurement of Belle which
is quoted as f_{s} = 1−f_{ud}. The average value of
all these measurements is quoted with or without the assumption that
f_{noB}=0,
after performing adjustments
to common external inputs.
colour gif /
colour eps /
blackandwhite eps /
[This section is no longer updated. The averages computed for PDG 2020 are reported.]
The table below shows the bhadron fractions in an unbiased sample of weakly decaying bhadrons produced in Z decays. These fractions have been calculated by combining direct rate measurements performed at LEP with the LEP combined measurement of the timeintegrated mixing probability averaged over an unbiased sample of semileptonic bhadron decays, χ = f'(B_{d})χ_{d}+f'(B_{s})χ_{s} = 0.1259 ± 0.0042 . This combination relies on the world average of χ_{d}, on the assumption χ_{s} = 1/2, as well as on the world averages of the lifetimes of the individual bhadrons species. The B^{+} and B^{0} mesons are assumed to be produced in equal amount, the B_{c} production is neglected and the sum of the fractions is constrained to unity.bhadron species  fraction in Z decays  correlation with f(B_{s})  correlation with f(bbaryon) 
B_{s}  f(B_{s}) = 0.100 ± 0.008  
b baryons  f(bbaryon) = 0.084 ± 0.011  +0.064  
B^{0} or B^{+}  f(B_{d}) = f(B_{u}) = 0.408 ± 0.007  −0.633  −0.813 
B_{s} / (B^{0} or B^{+}) ratio  f(B_{s})/f(B_{d}) = 0.246 ± 0.023 
χ(LEP) = 0.1259 ± 0.0042  LEP average from LEP EW WG 
[This section is no longer updated. The averages computed for PDG 2020 are reported.]
The table below shows the bhadron fractions in an unbiased sample of weakly decaying bhadrons produced in pp collisions at √s = 1.8−2 TeV. These fractions have been calculated by combining direct rate measurements performed at Tevatron with the Tevatron combined measurement of the timeintegrated mixing probability averaged over an unbiased sample of semileptonic bhadron decays, χ = 0.147 ± 0.011 . This combination relies on the world average of χ_{d}, on the assumption χ_{s} = 1/2, as well as on the world averages of the lifetimes of the individual bhadrons species. The B^{+} and B^{0} mesons are assumed to be produced in equal amount, the B_{c} production is neglected and the sum of the fractions is constrained to unity.bhadron species  fraction in pp collisions at 1.8−2 TeV 
correlation with f(B_{s})  correlation with f(bbaryon) 
B_{s}  f(B_{s}) = 0.115 ± 0.013  
b baryons  f(bbaryon) = 0.198 ± 0.046  −0.429  
B^{0} or B^{+}  f(B_{d}) = f(B_{u}) = 0.344 ± 0.021  +0.159  −0.960 
B_{s} / (B^{0} or B^{+}) ratio  f(B_{s})/f(B_{d}) = 0.333 ± 0.040 
χ(Tevatron) = 0.147 ± 0.011  Average of CDF and D0 measurements 