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Search for the FCNC Decay tex2html_wrap_inline1294
Text for the blessed web page - CDF note 6273

The CDF Collaboration

March 14, 2003

Abstract:

We present a search for the flavor changing neutral current (FCNC) decay tex2html_wrap_inline1294. With tex2html_wrap_inline1298 of two-track trigger (TTT) data we set an upper limit on the branching ratio of
displaymath1300

displaymath1302
This is nearly a factor of 2 improvement over the previous best limit of tex2html_wrap_inline1304.

Description

For the FCNC decay tex2html_wrap_inline1294, the Standard Model predicts tex2html_wrap_inline1368. The present experimental limit is tex2html_wrap_inline1304 from BEATRICE (tex2html_wrap_inline1372 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. tex2html_wrap_inline1294 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:
displaymath1376
where:

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 tex2html_wrap_inline1390. We select events that satisfy a tex2html_wrap_inline1354 requirements, with both tex2html_wrap_inline1342 tracks fiducial to the CMU, and satisfying

1371 tex2html_wrap_inline1390 events satisfy these requirements.

We divide our background estimate into two parts:

Using an overall tex2html_wrap_inline1404 misID probability of 1.3% yields tex2html_wrap_inline1406 expected misID background. Five events in a tex2html_wrap_inline1408 high mass sideband yields tex2html_wrap_inline1410 expected combinatoric background. Total expected background is tex2html_wrap_inline1412 events.

With these values, our sensitivity (expected limit for 1.7 observed events) is tex2html_wrap_inline1414.

We now ``unblind'' the search window and find zero events. This gives tex2html_wrap_inline1416 at 90% confidence level, and tex2html_wrap_inline1418 at 95% confidence level.

Blessed Numbers

This section summarizes the numbers which have been blessed for this analysis.

Fit results

  table302
Table 1: Probability (in percent) to misidentify a tex2html_wrap_inline1560 or tex2html_wrap_inline1424 as a muon for the tex2html_wrap_inline1562 bins listed.

Systematic errors

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.

Final result


eqnarray325

This result improves on the existing best limits by almost a factor of 2 (tex2html_wrap_inline1304 from BEATRICE, and tex2html_wrap_inline1372 from E771 at 90% confidence level).

Our 95% CL limit is tex2html_wrap_inline1608

Blessed Figures

The following figures have been blessed for the tex2html_wrap_inline1294 search. More text can be found in CDF note 6273.

  figure345
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 tex2html_wrap_inline1640.

  figure352
Figure 2: The misidentification background is determined from the number of tex2html_wrap_inline1390 events that fall into the search window when reconstructed as tex2html_wrap_inline1294, times the square of the average pion misID probability.

  figure359
Figure 3: The combinatoric background is determined from the number of dimuon events in a tex2html_wrap_inline1408 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.

  figure366
Figure 4: Using tex2html_wrap_inline1354 tagged tex2html_wrap_inline1648 decays we determine the probability that a pion is misidentified as a muon. The tex2html_wrap_inline1562 dependence is shown, and the average probability is 1.3%.

  figure373
Figure 5: We performed the same misidentification analysis with the kaons. Note that the tex2html_wrap_inline1630 misidentification probability is significantly higher than the tex2html_wrap_inline1632 owing to the smaller tex2html_wrap_inline1630 interaction cross section.

  figure380
Figure 6: The unblinding of the search window (red hatched region) reveals zero events.

About this document ...

Search for the FCNC Decay tex2html_wrap_inline1294
Text for the blessed web page - CDF note 6273

This document was generated using the LaTeX2HTML translator Version 96.1-h (September 30, 1996) Copyright © 1993, 1994, 1995, 1996, Nikos Drakos, Computer Based Learning Unit, University of Leeds.

The command line arguments were:
latex2html blessed-d0mumu.tex.

The translation was initiated by Robert Harr on Fri Mar 14 17:03:07 CST 2003


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Robert Harr
Fri Mar 14 17:03:07 CST 2003