First CDF II Results on B s Mixing Joseph Kroll (Penn) Franco Bedeschi (INFN-Pisa) for the CDF B s Mixing Group La Jolla, CA – site of CKM2005

17 March 2005Kroll/Bedeschi2 The CDF II B s Mixing Group ~ 70 contributors 25 institutions Everyone contributed to some aspect of this analysis or future analyses

17 March 2005Kroll/Bedeschi3 CDF II B s Mixing Analysis Status of analysis documented in Still updating web pages with latest blessed results – preparing public documentation Road map to blessing and overview of analysis provided in Today’s presentation not a complete discussion of the analysis: just show you the results

17 March 2005Kroll/Bedeschi4 Two Limits on  m s Fully reconstructed hadronic decays, e.g., B s ! D s  –Fully reconstructed so excellent proper time resolution –lower statistics Partially reconstructed semileptonic modes, e.g., B s ! D s l –incomplete reconstruction so poorer proper time resolution: important limitation at large  m s –larger statistics Both analyses use opposite side flavor tags only Many significant improvements planned for Summer 05

17 March 2005Kroll/Bedeschi5 Experimental Steps for Measuring B s Mixing 1. Extract B 0 s signal – decay mode must identify b-flavor at decay (SVT) Examples: 2. Measure decay time (t) in B rest frame (L = distance travelled) (L00) 3. Determine b-flavor at production “flavor tagging” (TOF) “unmixed” means production and decay flavor are the same “mixed” means flavor at production opposite flavor at decay Flavor tag quantified by dilution D = 1 – 2w, w = mistag probability

17 March 2005Kroll/Bedeschi6 Measuring B s Mixing (cont.) 4. Measure asymmetry these formulas assume perfect resolution for t Asymmetry is conceptual: actually perform likelihood fit to expected “unmixed” and “mixed” distributions Measure  m d to validate procedure All 70 authors contributed significantly to ≥1 of these steps correct for D, then A = 1

17 March 2005Kroll/Bedeschi7 Examples of Signals Measurement along the way:  (B 0 s ) = 479 § 29 (stat.) § 5 (syst.)  m (PDG = 438 § 17  m) Separate group did this analysis

17 March 2005Kroll/Bedeschi8 Result from Hadronic Modes Impact here is not limit but error at larger values of  m s Signal: 900 § 43  D 2 = (1.1 § 0.2)% = 100 fs

17 March 2005Kroll/Bedeschi9 Results from Semileptonic Modes Larger statistics allow significant exclusion Signal: 7700 § 150  D 2 = (1.4 § 0.1)% Two parallel efforts cross-checked each other

17 March 2005Kroll/Bedeschi10 Combined Hadronic and Semileptonic Best single experiment limit is 10.9 ps -1 (sensitivity 15.2 ps -1 )

17 March 2005Kroll/Bedeschi11 Impact on World Average Sensitivity We increase sensitivity by 0.4 ps -1, limit is unchanged

17 March 2005Kroll/Bedeschi12 Increase effective statistics (we are not systematics limited) –Same side kaon tagging (potential gain: factor 2 to 4) –improve OST (only modest gain expected: maybe 30%) –add more decay modes (including partially reconstructed) –add more data Exploit different trigger strategy –include flavor tag in trigger: e.g.,  in TTT path we have this data and have not used it in current measurement Improve proper time resolution –add event by event primary vertex to hadronic analysis –important at larger values of  m s How Can We Improve? These improvements planned for Summer 2005 results