A Limit on the Branching Ratio of the Flavor-Changing Top quark decay t→Zc Alexander Paramonov, Henry Frisch, Carla Pilcher, Collin Wolfe, Dan Krop Exotics Meeting. April 03, 2008 Internal reviewers: Beate Heinemann, Kevin Lannon, and Jason Nielsen CDF

Outline Figures to bless Additional statistical test of the expected result for Br(t  Zc) = 20% Understanding of the expected limits for the null-hypothesis “Evolution” of the limits (requests) MC-driven mistags (normalization) Conclusions and Results

Figures to bless. Tier 1

Figures to bless. Tier 2

Statistical test for Br(t  Zc) = 20% 50 pseudo experiments 100% longitudinally polarized Z’s MC-driven mistags

The expected limits for the null-hypothesis We did 50 pseudo-experiments with Data-driven mistags two times and we got slightly different results each time: a. 8.3±2.5% (Gaussian Prior) & 9.2±2.8% b. 8.7±2.8% (Gaussian Prior) & 9.6±3.1% The code looks fine. We did add statistical uncertainties in backgrounds to pseudo-experiments. There’s a slight dependence on the number of ensembles in numerical integration. We run 50 more pseudo-experiments twice to calculate the expected limits for MC-Driven mistags: a. 8.9±2.8% (Gaussian Prior) & 9.9±3.2% b. 8.X±2.X% (Gaussian Prior) & 9.X±2.X%

Evolution of the limits 1.Request from the internal reviewers to change the limit estimation procedure to a more conventional Bayesian approach. The limit moved from ~12.8% (this in not a Bayesian limit) to ~9.9-11% (depending on the prior). 2.The internal reviewers asked to improve the uncertainty of the mistagged events by using MC samples. This changed the limits to % (depending on the prior).

MC-driven Mistags We normalize MC using pre- tagged sample of Z+jets. Z+HF events are taken into account. Them we run the mistagg matrix We get the following numbers of expected mistaggs: –A. Data: 2.96±0.50 (electrons), 2.2±0.5 (muons) –B. MC: 3.3±0.03 (electrons), 2.30±0.02 (muons)

Conclusions and Results Upper limits on Br(t  Zc) for five longitudinal polarizations of the Z- bosons. The results are model-independent. The expected limits are consistent with observations