B Lifetimes and Flavour Tagging at CDF Run II

1. B Lifetimes and Flavour Tagging at CDF Run II Sinéad Farrington University of Glasgow for the CDF Collaboration European Physical Society Aachen, 17th-23rd July 2003

2. Outline • Overview of B Physics at CDF • B lifetimes: • Exclusively reconstructed B’s decaying via J/ • Semileptonically decaying B’s • Flavour Tagging Sinead Farrington EPS Aachen 17th-23rd July 2003

3. B Physics at CDF Run II - pp collisions produce a wide spectrum of B hadrons in a challenging environment Tevatron upgrade to 1.96 TeV CoM energy larger b production cross section Sinead Farrington EPS Aachen 17th-23rd July 2003

4. B Triggers at CDF Run II - - (bb) << (pp)  B events are selected with specialised triggers: Di-Muon (J/) pT()>1.5 GeV/c J/ modes at low (conventional) pT( J/)  0 GeV/c Measure x-section (See talk by Tara Shears) J/ Yield=2x Run I l + displaced track pT(e/)>4 GeV/c Semileptonic modes pT(trk)>2 GeV/c Lifetimes,flavour tagging 120 m<d0(trk)<1mm B Yields 3x Run I NEW! Two displaced tracks pT(trk)>2 GeV/c Hadronic modes 120 m<d0(trk)<1mm Charm Physics, B0s mixing Indivdual data samples of about 140pb-1 accumulated Sinead Farrington EPS Aachen 17th-23rd July 2003

5. B Hadron Lifetimes According to the spectator model all B mesons would have the same lifetime… but that is not the whole story! The HQE predicts by how much the lifetimes differ. Objective 1: Measure lifetimes accurately to form input to theories Objective 2: Prove the detector and triggers are working Objective 3: Measure s/s B0slDs is an admixture of CP even and CP odd states Pair it with fully CP even or CP odd state (or use polarisation analysis) and measure s/s PDG Values Sinead Farrington EPS Aachen 17th-23rd July 2003

6. J/   B+ K+ B Hadron Lifetimes • SEMILEPTONIC • lepton+displaced track trigger • clean • partially reconstructed • - need MC to unfold ct • lifetime biased • good statistics • EXCLUSIVE • J/ trigger • clean • fully reconstructed • lifetime unbiased • low statistics B0 lD(*)- b lc B0s l Ds B0 J/ K0* B+J/ K+ bJ/ B0s J/ • Reconstruct decay length by vertexing • Measure pT of decay products Sinead Farrington EPS Aachen 17th-23rd July 2003

7. Exclusive BJ/X Lifetimes Fit Methodology: Simultaneous fit of M(B)  signal fraction, define sidebands c(B)  lifetime Signal Contribution: Background Parameterisation: Sinead Farrington EPS Aachen 17th-23rd July 2003

8. bJ/  Lifetime andCrosscheck CONTROL SAMPLE Sinead Farrington EPS Aachen 17th-23rd July 2003

9. Exclusive BJ/X Lifetimes: B0s Meson World’s largest sample of fully reconstructed Bs mesons B0s J/ is mostly CP even measures mostly L component Access s/s via angular analysis – coming soon Sinead Farrington EPS Aachen 17th-23rd July 2003

10. Extraction of Semileptonic Lifetimes • Lepton+ displaced track trigger implemented successfully for the first time! •  samples rich in B hadron semileptonic decays • Follow the standard methodology: • reconstruct the D decay near to lepton • B decay not fully reconstructed • extract the  factor from Monte Carlo: • extract lifetime from decay length: • but with one crucial complication: • lifetime bias from the displaced vertex trigger: • 4 GeV lepton + 2 GeV track with 120 m<d0 <1mm • Emulate trigger with Monte Carlo and model the lifetime bias • which is factored into the fit function. Sinead Farrington EPS Aachen 17th-23rd July 2003

11. K Factor and Bias from MC K Factor Distribution P(K) Reconstruction efficiency including trigger bias, as a function of proper lifetime Normalised to unit area Arbitrary vertical scale Sinead Farrington EPS Aachen 17th-23rd July 2003

12. apply PID B Semileptonic Channels CDF Run II Preliminary 70pb-1 b lc l Ds D M(pK) (GeV/c2) Sinead Farrington EPS Aachen 17th-23rd July 2003

13. Semileptonic Decay Fit Model Unbinned maximum likelihood fit to c(B) • Background is parameterised by delta function and positive exp convoluted with Gaussian resolution: Free parameters: D E + f+G • Signal: exp convoluted with Gaussian resolution, K factor distribution, P(K), and bias function,  • Maximum likelihood function: Sinead Farrington EPS Aachen 17th-23rd July 2003

14. CDF Run II Preliminary 70pb-1 B0s  Ds ct(B)(mm) Highest statistical accuracy lifetime fits in B0s and Lb: Semileptonic Lifetime Fits b  c Control Samples • Fit results show discrepancy with world average • Many crosschecks • Currently working to understand all effects of trigger bias etc. Sinead Farrington EPS Aachen 17th-23rd July 2003

15. Flavour Tagging Development SAME OPPOSITE • Determine B flavour at production • and decay to measure • B0 mixing, B0s mixing, CP violation • Figure of merit: D2 • : tag efficiency • D: Right-Wrong/Right+Wrong • CDF has a battery of tags which are • being developed further OPPOSITE SIDE Soft Lepton Tag* Opposite side K Tag Jet charge tag SAME SIDE Same side K/ Tag* Sinead Farrington EPS Aachen 17th-23rd July 2003

16. Same Side Tag Asymmetry • Identify fragmentation pion • Measure raw asymmetry: • Test tagger on B+  should seeNO oscillations! B lD0 B+J/K+ For B0s mixing apply same side K tag: very powerful Sinead Farrington EPS Aachen 17th-23rd July 2003

17. p(e/+D) track  P.V.  Tagger Studies in Semileptonic Sample lepton + displaced track trigger provides high statistics sample of ~150000 B (and D) semileptonic decays Strategy: • trigger lepton  estimate of B flavour at production • count numbers of opposite side tags • can subdivide sample by muon system and pTrel • parameterise relative dilution for use in likelihood fit • cross check consistency with partially reconstructed lepton+D+,0 • consistent results  believe dilution in lepton+Ds • This number is UNBIASED since we’re using an independent (and high statistics) control sample • Detailed sample composition studies: • Mass cut removes D decays: 2<M(l+track)<4GeV/c2 • Background subtraction variable separates B’s from • background: signed IP of displaced track Sinead Farrington EPS Aachen 17th-23rd July 2003

18. Soft Muon Tag D2 Identify  charge on opposite side Sufficient statistics to examine parameterisation of dilution as function of pTrel Background subtraction has been used to obtain measurement of D2 Soft Muon Tagger D2=0.6600.093 % CDF Run I:D2=0.584  0.082 % • Method will be used to evaluate, optimise and compare all taggers • Unbiased way of optimising taggers • Next step: measure D2 for a reconstructed channel Sinead Farrington EPS Aachen 17th-23rd July 2003

19. Summary • Lifetime measurements made in clean BJ/ channels: • Lepton + displaced vertex trigger has been implemented at CDF for the first time • lifetime measurements ongoing: will give best statistical accuracy in B0s and Lb • Flavour Tagging procedure has been established and two taggers have been optimised and evaluated in a non-biased way • Measurements of s/scoming soon and first steps towardsB0s mixing are happening! Sinead Farrington EPS Aachen 17th-23rd July 2003

20. K Factor and Bias from MC ELECTRONS: Sinead Farrington EPS Aachen 17th-23rd July 2003

21. Major upgrades at CDF provide • Increased geometric coverage • Extended muon system • new 3D silicon tracker • faster response drift chamber • Triggers: large bandwidth, background • reduction, displaced vertex triggering Sinead Farrington EPS Aachen 17th-23rd July 2003

22. Determine B flavour at production • and decay to measure • B0 mixing, B0s mixing, CP violation • Figure of merit: D2 • : tag efficiency • D: Right-Wrong/Right+Wrong • CDF has a battery of tags which are • being developed further • Run II’s lepton+displaced vertex trigger  large sample of semileptonic decays • allows us to measure , D and D2 in dataand optimise the taggers • can then apply them in any sample without bias Sinead Farrington EPS Aachen 17th-23rd July 2003

23. Sinead Farrington EPS Aachen 17th-23rd July 2003