Heavy flavor lifetimes and lifetime differences Page: 2 of 8
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Workshop on the CKM Unitarity Triangle, IPPP Durham, April 2003
(N
3 1500
N
1000
500
0-0.05
0 0.05
Residual 6(Az) (cm)Figure 2. Az Resolution at BABAR for B+ -> J/fK+ [11], with
exp(Az/250 pm) superimposed for illustration.
In Fig. 2, the Monte Carlo generated resolution function for
Az at BABAR for the decay B+ -* J/OK+ is shown [11]. An
exponential with a mean decay distance of 250 mum, rep-
resenting approximately the signal distribution before de-
tector effects, is superimposed, illustrating how the signal
is of a similar width as the resolution function, which must
therefore be modeled carefully. This modeling of the res-
olution function, together with the modeling of the back-
ground distribution, is the biggest systematic uncertainty
in both experiments. The so-called "outliers", a relatively
small number of events with very large reconstructed Az,
represent a particular problem. Both experiments are able
to control it well enough to keep the systematic error below
the statistical uncertainty.
Both experiments describe the At = Az/ (c (py)) distri-
bution in terms of three components: signal, background
and outliers. The beam constrained mass (shown in Fig. 3
for BELLE) iS used for an event-by-event signal probabil-
ity. The fraction of outliers is a free fit parameter. The
BO and B+ distributions are fit simultaneously in an un-
binned likelihood fit. Besides these commonalities, there
are some differences in the event selection and modeling
of the resolution function which are described in detail in
the publications by the respective experiments [10] [12].
2.2.2 Results
BELLE
Using the following fully reconstructed hadronic decays:
B0 - D*)-(7r+,p+), J/OK , J/OK*O, B+ - De+, J/OK+,
BELLE find the following Bd and B+ lifetimes [12]:TBO = 1.554 0.030 0.019 ps
. K
S1C00 -c,
.- A
01B4 R
More results from BABAR
As mentioned earlier, the decay kinematics at BABAR and
BELLE allow to find the z position of a decay vertex from as
little as a single track. While in the previously mentioned
measurements, one of the pair of B's is fully reconstructed,
BABAR also published a set of measurements where also
the Brec is reconstructed partially. These are summarised
in Table 1.-
2
100-
L, o I
,, 5, - , 4 5,26 5, - 5.3
At I'GeV,:cj
Figure 3. N2 of events vs Beam Constrained Mass at BELLE [12]
TB+ = 1.695 0.026 0.015 ps
TB+/TB = 1.091 0.023 0.014
The fit result to the data, showing separately the back-
ground and the outlier contribution, is shown in Fig. 4.
BABAR Fully Hadronic
Using the following fully reconstructed hadronic
decays: B0 -* D(*)-(>+,p+, a+), J/OKO,J/OK*o and
B+ -D F D+, J/OK+, 0(2S)K+ BABAR find the following
BO and B+ lifetimes [10]:
TBO = 1.546 0.032 0.022ps
TB+ = 1.673 0.032 0.023 ps
TB+/TBD = 1.082 0.026 0.012
The fit result to the data is shown in Fig. 5.
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Rademacker, Jonas. Heavy flavor lifetimes and lifetime differences, article, September 17, 2003; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc740589/m1/2/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.