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

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

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’

–New analysis method (lxy) included: Use mean decay length of b-tagged jets to determine M top 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

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/ v1)

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

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

Weights of each analysis in the Tevatron combination

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 M top = 175 GeV/c 2 Main obstacle: Large associated background despite the small ratio Channel: W from t decay leptonically

Event Selection: –Two jets with E T >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 missingE T vector and P T vector After all requirements, the signal to bkg ratio is about 1/20 Use Multivariate Technique

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

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 β 1 : the single-top cross-section (reduced L: L red ) Hypothesis test based on Q:

Hypothesis: –H 0 : single-top cross-section is zero (β 1 = 0) –H 1 : the cross section is as predicted by SM (β 1 = 1) The probability for H 0 to be correct: p- value (often also named 1-CL b ) Define the expected p-value p exp = p(Q 1 med ) Q 1 med is the median of the Q-value distribution for the H 1 Under the assumption that H 1 is correct one expects to observe p exp with a probability of 50%

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

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

Find p exp = 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%

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