Investigation on CDF Top Physics Group

1. Investigation on CDF Top Physics Group Ye Li Graduate Student UW - Madison

2. Measurement of Top Mass • Up to 1 fb-1 Luminosity • Combine CDF Run I, Run II and D0 Results • 11 Measurements Used • Mtop = 170.9 ± 1.1 (stat) ± 1.5 (syst) GeV/c2 • Total Uncertainty: 1.8 GeV/c2 • Precision: 1.1%

3. Analysis • Uncertainty of Run II is better than that of Run I due to the availability of tt-bar sample and new analysis technique • Main statistical uncertainty: Jet Energy Scale (JES) uncertainty • New method to constrain JES: in-situ calibration based on invariant mass W->qq’

4. New analysis method (lxy) included: • Use mean decay length of b-tagged jets to determine Mtop • Statistical Sensitivity is not as good as traditional method • Make use of track information only • Independent of JES uncertainty • Offer a nice cross check • Zero (<1%) independent of the assumed top mass found by used MC

5. Correlation: • Stat., Fit and iJES(originated from in-situ calibration) completely uncorrelated among all measurements • Background and other JES uncertainty are considered correlated (see details on hep-ex/0703034v1)

6. Summary of top mass measurements from the CDF and D0 experiments at Fermilab by March 2007

7. Fit for Mtop in all-j, l+j, dilep. The chi2 refers to the consistency btw any 2 channels including all correlations. The determinations of Mtop are consistent with one another

8. Weights of each analysis in the Tevatron combination

9. Search for Single Top using NN • Integrated Luminosity: 955 pb-1 • Two analyses Performed: • Combined t- and s-channel Search • Separate 2 Production Mode Search • Assume Mtop= 175 GeV/c2 • Main obstacle: Large associated background despite the small ratio • Channel: W from t decay leptonically

10. Event Selection: • Two jets with ET>15GeV and |eta|<2.8 (eliminate a large fraction of bkg) • At least one b-tagged jet • Bkg further reduced by the requirement of the angles btw the missingET vector and PT vector • After all requirements, the signal to bkg ratio is about 1/20 • Use Multivariate Technique

11. Common Likelihood Function: • Systematic uncertainties are included as factors modifying the expectation value μk of events in a certain bin k:

12. j runs over all physical processes • β is the cross-section normalized to the SM prediction • Some constraints and assumption are used, which eventually make L only depend on β1: the single-top cross-section (reduced L: Lred) • Hypothesis test based on Q:

13. Hypothesis: • H0: single-top cross-section is zero (β1 = 0) • H1: the cross section is as predicted by SM (β1 = 1) • The probability for H0 to be correct: p-value (often also named 1-CLb) • Define the expected p-value pexp = p(Q1med) • Q1med is the median of the Q-value distribution for the H1 • Under the assumption that H1 is correct one expects to observe pexp with a probability of 50%

14. Combined Search • Distributions of Q-values for two ensemble tests: • one w/ single-top events present at the expected standard model rate • one w/o any single-top events • Observed Q=9.13

15. Separate Search • Distributions of Q-values for two ensemble tests: • one w/ single-top events present at the expected standard model rate • one w/o any single-top events • Observed Q=2.94

16. Find pexp = 0.5%, including all systematic uncertainties, corresponding to a sensitivity of 2.6 σ • Combined Search: p-value 54.6% (Data well compatible with being a bkg fluctuation ) • Separate Search: p-value 21.9%

17. Exclude a combined single-top cross-section above 2.6 pb at 95% CL • Separate Search: • Summary