B Flavor Tagging Using Opposite Side Jet Charge
Text for the blessed web page - CDF note 7131
The CDF Collaboration
August 13, 2004
Abstract:
We describe a Jet Charge algorithm for flavor tagging
of B mesons. The algorithm determines the flavor of the signal B candidate
by calculating the effective charge of the opposite side b jet. This version
is our current best incorporating Silicon Stand Alone Tracking and 3 groups
of different quality tags, including jets with high displaced track content.
We measure the tagging power of the algorithm to be
%
on the inclusive
e-SVT data sample of 290 pb
.
Description
This study measures performance of the Jet Charge Tagger (JQT) on a sample
of semileptonic B decays. We use 290
of data collected with
e-SVT and -SVT
triggers. By applying subtraction in signed impact parameter of the displaced
track to suppress light quark background and cutting on the invariant mass
of the lepton and the displaced track to remove
contamination we achieve an equivalent of a 100% pure sample of semileptonic
B decays.
The current version of the algorithm uses cone clustering algorithm
to find track based jets. The cone size in
is 1.5 tuned for the best performance on data. As the first step of the
algorithm all jets in each event are found on the opposite side from the
trigger B meson. Next, the tagging jet is selected out of all available
jets. There are three mutually exclusive groups of events.
-
first, we look for a jet that contains a secondary vertex. These are the
best, highest dilution jets, further referred as ``SecVtx jets''
-
in the events with no SecVtx jet found we look for a jet that with the
highest probability to contain displaced tracks. The probability for a
jet to have high displaced track content is required to satisfy a certain
cut. The events with such jets found fall into the second group called
``
jtes''
-
finally, if an event has neither SecVtx nor
jets while does have *some* jets, the highest
jet is selected for tagging. These is the ``high
group.
After the tagging jet is selected, the jet charge
is calculated adding all tracks with weights proportional to the
of the tracks and the probability to be displaced. The sign of the jet
charge determines the tagger decision.
The JQT is applied to the semileptonic B candidates. We measure the
tagging power using the sign of the trigger lepton as an indicator for
the trigger side B production flavor. The effects of mixing and sequential
decays on the trigger side on the dilution are corrected for by a scale
factor known from MC.
Blessed Numbers
This section summarizes the numbers which have been blessed for this analysis.
Tuned JQT performance on the
e-SVT sample
The value for
is corrected for the trigger side mixing and sequential decays. It is obtained
by adding subsamples of events with different quality tags. We have separated
events into subsamples depending on whether the tagging jet contains a
SevVtx,
or high
jet and into 11 bins of the jet charge
value.
Note: the error blessed is statistical only, however systematics have
been estimated as well. Although we do not want to quote the values for
systematics we have verified that the total systematic uncertainty is fairly
close to the statistical one.
The full table below contains a more full picture for efficiencies and
dilutions. The dilutions in the table correspond to the ``effective'' true
dilution calculated as
where
is the combined value with all subsamples added.
The e-SVT sample used in this analysis contains 484000
signal candidates after all cuts and background subtraction.
Blessed Figures
The following figures have been blessed for the mass difference measurement.
More text can be found in CDF note 7131.
Figure 1: Jet charge distribution for the SecVtx,
and high
groups of jets for the e-SVT sample. Notice a better separation
for jets with a secondary vertex.
Figure 2: Dilution dependence on the jet charge for the SecVtx,
and high
groups of jets for the e-SVT sample. Notice a generally higher dilution
for jets with a secondary vertex.
About this document ...
B Flavor Tagging Using Opposite Side Jet Charge
Text for the blessed web page - CDF note 7131
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