Unless otherwise specified,
all results available publicly (published and preliminary)
have been included in the averages computed by the
lifetime and oscillations sub-group
of the Heavy Flavour Average Group (HFAG).
The following material is available publicly:
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b hadron species | average lifetime | average lifetime relative to B0 average lifetime |
B0 | 1.536 +- 0.014 ps | |
B+ | 1.671 +- 0.018 ps | 1.086 +- 0.017 |
Bs | 1.461 +- 0.057 ps | 0.951 +- 0.038 |
Bc | 0.46 +0.18 -0.16 ps | |
Lambda_b | 1.229 +0.080 -0.080 ps | |
Xi_b-, Xi_b0 mixture | 1.39 +0.34 -0.28 ps | |
b-baryon mixture | 1.208 +- 0.051 ps | 0.786 +- 0.034 |
b-hadron mixture | 1.564 +- 0.014 ps |
no combined value of DGd/Gd available yet | published results from DELPHI and CLEO (BABAR preprint submitted, not accepted yet) |
DGs/Gs =
0.16
+0.15
-0.16
DGs/Gs < 0.54 at 95% CL |
from ALEPH, CDF, DELPHI, L3 and OPAL measurements |
DGs/Gs =
0.07
+0.09
-0.07
DGs/Gs < 0.29 at 95% CL |
same as above but constraining the mean Bs decay width to be equal to 1/tau(B0) where tau(B0) = 1.536 +- 0.014 ps |
The plot below shows the 68%, 95% and 99% CL 2D-contours of the negative log-likelihood in the plane DGs/Gs - 1/Gs, where DGs is the decay width difference and Gs is the mean decay width in the Bs system. Here DGs is defined as DGs = Gamma_short - Gamma_long > 0, and the CP-even eigenstate is assumed to have the largest decay width (Gamma_short), i.e. the smallest lifetime.
2D eps /
Probability density distribution for DGs/Gs:
1D colour eps /
1D black-and-white eps /
Same as above but constraining
the mean Bs decay width to be equal to 1/tau(B0) where tau(B0) =
1.536
+-
0.014
ps:
2D eps /
1D colour eps /
1D black-and-white eps /
dmd = 0.502 +- 0.007 ps-1 | from time-dependent measurements at ALEPH, BABAR, BELLE, CDF, DELPHI, L3, OPAL |
chid = 0.182 +- 0.015 | from time-integrated measurements at ARGUS and CLEO |
Assuming no CP violation in the mixing and no width difference in the B0 system, and assuming a B0 lifetime of 1.536 +- 0.014 ps (the experimental average listed above), all above measurements can be combined to yield the following world averages:
dmd =
0.502
+-
0.007
ps-1
xd = 0.771 +- 0.012 chid = 0.186 +- 0.004 |
from all ALEPH, BABAR, BELLE, CDF, DELPHI, L3, OPAL, 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 all the individual measurements to the common set of physics inputs. The chid average from ARGUS and CLEO is converted to a dmd measurement assuming no CP violation, no width difference in the B0 system and a B0 lifetime of 1.536 +- 0.014 ps.
colour ps /
colour eps /
black-and-white ps /
black-and-white eps /
Same without average including time-integrated (chid) measurements:
colour ps /
colour eps /
black-and-white ps /
black-and-white eps /
Only measurements and average at high energy colliders:
colour ps /
colour eps /
black-and-white ps /
black-and-white eps /
Only measurements and average at LEP:
colour ps /
colour eps /
black-and-white ps /
black-and-white eps /
Only measurements and average at asymmetric B factories:
colour ps /
colour eps /
black-and-white ps /
black-and-white eps /
In the plot below,
all 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 all the individual measurements to the common set of physics
inputs. The chid average from ARGUS and CLEO is converted to a dmd measurement
assuming no CP violation, no width difference in the B0 system and a
B0 lifetime of
1.536
+-
0.014
ps.
colour ps /
colour eps /
black-and-white ps /
black-and-white eps /
dms >
14.5
ps-1 at 95% CL
xs > 20.8 at 95% CL chis > 0.49885 at 95% CL |
from all ALEPH, CDF, DELPHI, OPAL and SLD studies of dms with a combined 95% CL sensitivity on dms of 18.3 ps-1 |
In the plot below, the combined Bs amplitude is displayed as function of dms. All measurements have been adjusted to the common set of inputs before averaging. Systematic correlations are taken into account. An amplitude consistent with 1 is expected at the true value of dms. An amplitude consistent with 0 is expected far below the true value of dms. All values of dms for which the combined amplitude plus 1.645 times its total uncertainty is smaller than 1 (in this case all values of dms below 14.5 ps-1) are excluded at 95% CL. The combined sensitivity for 95% CL exclusion (equal to 18.3 ps-1 in this case) is defined as the value of dms at which the total uncertainty on the measured amplitude is equal to 1/1.645.
colour ps /
colour eps /
colour ps (up to 20 ps-1 only) /
colour eps (up to 20 ps-1 only) /
ASCII file with numerical data /
Same, but using an additional unpublished result from SLD:
colour ps /
colour eps /
colour ps (up to 20 ps-1 only) /
colour eps (up to 20 ps-1 only) /
ASCII file with numerical data /
Same, but using only LEP data:
colour ps /
colour eps /
colour ps (up to 20 ps-1 only) /
colour eps (up to 20 ps-1 only) /
ASCII file with numerical data /
In the plot below,
all individual measurements of the Bs oscillation amplitude at a fixed
value of dms are listed as quoted by the experiments
(or obtained by a linear interpolation between other dms values at which
the experiment did the measurements);
they might assume different physics inputs. The sensitivity quoted
for each experiment is obtained from the positive amplitude uncertainty,
without performing adjustments.
The average and combined sensitivity are obtained
after adjusting all the individual measurements to the common set of physics
inputs. The sensitivites are defined as the value of dms at which
the positive uncertainty on the measured amplitude is equal to 1/1.645;
they correspond to sensitivites for 95% CL exclusion limits.
colour ps /
colour eps /
black-and-white ps /
black-and-white eps /
Same, but at dms=10 ps-1:
colour ps /
colour eps /
black-and-white ps /
black-and-white eps /
Same, but at dms=19 ps-1:
colour ps /
colour eps /
black-and-white ps /
black-and-white eps /
chid = 0.182 +- 0.015 | from time-integrated measurements at ARGUS and CLEO |
chid = 0.186 +- 0.004 | average including time-dependent measurements of dmd and based on different assumptions, as explained above |
Time-integrated mixing probability for a mixtures of b-hadrons at high-energy decaying semi-leptonically:
chibar = 0.1257 +- 0.0042 | LEP average from LEP EW WG |
chibar = 0.152 +- 0.013 | CDF measurement |
chibar = 0.1282 +- 0.0077 | weighted average of above two, with rescaled error according to PDG prescription |
b hadron species | fraction at high energy | correlation with f(Bs) | correlation with f(b-baryon) |
Bs | f(Bs) = 0.105 +- 0.015 | ||
b baryons | f(b-baryon) = 0.099 +- 0.017 | -0.179 | |
B0 or B+ | f(Bd) = f(Bu) = 0.398 +- 0.010 | -0.565 | -0.711 |
Note: more precise fractions could be obtained by ignoring the Tevatron
data and using only LEP measurements (because one would use a more
precise chibar value, from LEP only). In the future, we will try to
provide two additional sets of fraction averages: one obtained from LEP
data only, and one obtained from Tevatron data only.
The B+ and B0 fractions below are for an unbiased sample of B-mesons produced in Upsilon(4S) decays.
They have been obtained by combining measurements from BABAR, BELLE and CLEO, assuming that
the a B+/B0 lifetime ratio of
1.086
+-
0.017
(the current average given above). The sum of these two fractions is constrained to unity.
b hadron species | fraction in Upsilon(4S) decay | ratio |
B+ B- | f+- = 0.511 +- 0.012 | f+-/f00 = 1.044 +- 0.050 |
B0 anti-B0 | f00 = 0.489 +- 0.012 |