Text for the blessed web page - CDF note 6273
The CDF Collaboration
March 14, 2003
We present a search for the flavor changing neutral current (FCNC)
decay .
With 
of two-track trigger (TTT) data we set an upper limit on the
branching ratio of
This is nearly a factor of 2 improvement over the previous best
limit of 
.
For the FCNC decay , the Standard Model predicts 
.
The present experimental limit is from BEATRICE
(
from E771), 7 orders of magnitude from the
prediction.
New physics can substantially enhance this mode.
In charm meson decays we are constraining couplings to up-type quarks
not necessarily constrained by B decays.
presents and immaculate and unexplored region to search
for new physics.
We use the TTT data for a clean analysis (all information can be
determined from the data).
The limit on the branching ratio is computed as:
where:
is the 90% limit on the number of observed decays,
is the number of 
reconstructed in the
normalization mode,
is the ratio of efficiencies
between the signal and normalization modes, 
, and
is the branching ratio of the normalization
mode, 
We performed a ``blind'' analysis.
The selction cuts were optimized on a kinematically similar but
statistically independent set of events.
We normalize to the kinimatically similar decay 
.
We select events that satisfy a 
requirements, with both tracks
fiducial to the CMU, and satisfying
,
, and
.
events satisfy these requirements.
We divide our background estimate into two parts:
misidentification, and
misID probability of 1.3% yields 
expected misID background.
Five events in a 
high mass sideband yields 
expected combinatoric background.
Total expected background is 
events.
With these values, our sensitivity (expected limit for 1.7 observed
events) is 
.
We now ``unblind'' the search window and find zero events.
This gives 
at 90% confidence level, and 
at 95% confidence level.
This section summarizes the numbers which have been blessed for this analysis.
Table 1: Probability (in percent) to misidentify a 
or 
as a muon for the 
bins listed.
The uncertainties on the number of events in the normalization mode, the ratio of efficiencies, and the branching ratio to the normalization mode are included in the limit following the procedure outlined by Cousins&Highland. All of the mentioned uncertainties are of order 5%, and have a negligible effect on the limit.
This result improves on the existing best limits by almost a factor of
2 ( from BEATRICE, and from E771
at 90% confidence level).
Our 95% CL limit is 
The following figures have been blessed for the search.
More text can be found in CDF note 6273.
Figure 1: The calculation of the normalization.
Both tracks are assigned the pion mass and required to project into a
CMU chamber (CMU fiducial).
The fit is to a Gaussian plus linear function, and we count the events
in the range 1.840 to 
.
Figure 2: The misidentification background is determined from the
number of events that fall into the search window when
reconstructed as , times the square of the average pion misID
probability.
Figure 3: The combinatoric background is determined from the number of
dimuon events in a wide high mass sideband.
We assume the background is linear in mass, and scale by the ratio of
the search window width to the sideband width.
Figure 4: Using tagged 
decays we determine the
probability that a pion is misidentified as a muon.
The dependence is shown, and the average probability is 1.3%.
Figure 5: We performed the same misidentification analysis with the
kaons.
Note that the 
misidentification probability is significantly
higher than the 
owing to the smaller interaction cross
section.
Figure 6: The unblinding of the search window (red hatched region)
reveals zero events.
Search for the FCNC Decay
Text for the blessed web page - CDF note 6273
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