Where has all the antimatter gone? — a quest for new physics at LHCb

1. Where has all the antimatter gone?— a quest for new physics at LHCb Yuehong Xie, University of Edinburgh

2. LHCb core B-physics program • Over-constrain the CKM matrix • Angle g from decays with loop diagrams • Angle g from tree level decays • Measure FCNC transitions where new physics can have large effects • Bs mixing phase (Bs→ J/yf(K+K-) ) • b → sl+l- decays (Bs→ m+m-, Bd→ K* m+m-, B+→ K+ m+m- ) • b → sg decays (Bs→ fg ) • b → sss decays (Bs→ ff andBd→ fKs) In red: where I have made leading contributions. I will use my recent work on Bs→ J/yf to showcase my ability in physics research

3. Physics potential of Bs→ J/yf • Bs mixing phase –2bs sensitive to NP • SM prediction: –2bs= -0.036 • NP: could be very different • Tevatron –2bs = -0.77+0.29-0.37or -2.36+0.37-0.29 about 2s discrepancy • LHCb statistical sensitivity in 2 fb-1: s(2bs) ≈ 0.03 A measurement with discovery potential!

4. Analysis ingredients Signal background • Flavour tagging: separate Bs and Bs-bar • Bs invariant mass: separate signal and background • Angular variables: separate different CP components • Time evolution: extract CP parameter fs = –2bs • An example: // component Bs mass total CP even Flat background CP odd

5. Vital issues • Fully exploit the statistical power • Robust and efficient trigger • Selection optimization • Accurate proper time measurement • Control systematic uncertainties • Flavour tagging calibration • Proper background subtraction • Angular acceptance correction • Control model uncertainties • KK S wave contribution to Bs→ J/yK+K- • CKM suppressed penguin pollution

6. Addressing the issues(more details in backup) • Event selection optimization • I developed a method to optimize for best measurement errors (Y. Xie, arXiv:0901.3305) • KK S wave contribution to Bs→ J/yK+K- • I developed the formalism for unbiased 2bs determination in presence of S wave • I proposed to resolve 2-folded ambiguity in 2bs using S-P interferences (LHCb physics note, P. Clarke, G. Cowan, F. Muheim, Y. Xie)

7. KK S wave • A possible 5-10% K+K- S wave under f(1020) • Impact on –2bs determination (input –2bs=-0.2) Mean –2bs = -0.166 Mean –2bs = -0.200 neglecting 10% S wave including S wave in fit

8. Addressing the issues (2) • Background subtraction • I developed a method for background subtraction w/o using parameterization from sidebands (Y. Xie, arXiv:0905.0724) • Proper time reconstruction • I developed the package for vertex fitting, proper time fitting and primary vertex refitting • Angular acceptance correction • I am developing a method to correct for detector effects on an event-by-event basis

9. Angular acceptance correction(ongoing work) • Single particle efficiency e(P, Pt) from B+→ J/yK+ “real data” • Apply the effects in Bs→ J/yf • Detector geometry • Pt cuts • Particle efficiency e(P, Pt) • Angular distributions well reproduced (diff. < 10%) m+ m- K± P (GeV) reconstructed reproduced (Method can be used for Dalitz acceptance correction) cos(qm)

10. Road to new physics • Repeat the story (of success) in Bs→ J/yf for other key analysis, including gamma measurements • Aim to find indication of new physics in as many measurements as possible • Perform a global analysis of (mostly) FCNC b→s transitions • Aim to identify the new physics scenario

11. Global analysis • Each b→s process probes different form of effective Hamiltonian • Global analysis will find the pattern and discriminate or constrain NP models

12. Future interest: tree level gamma measurement • Develop efficient high level trigger for B→DK • Control systematic uncertainties due to Dalitz acceptance, production asymmetry • Fully exploit the model-independent method for gamma from B±→D(Kspp)K± • Fully exploit other 3- or 4-body D decay modes, including D→KSK+K- and D→Kppp, using knowledge of the D decay structures obtained or to be obtained from CLEO-c

13. Future interest: RICH calibration with L/Ks • Plenty of Land Ks from minimum bias events • 95% purity with only kinematical cuts • Clean and unbiased samples for PID study Λ→pπ ~50k L in 108 MB events 40 minutes @ 1031 cm-2 s-1

14. Enthusiasm for teaching • I will be dedicated to the education of physics students • I am eager to develop my teaching skills • skills to best attract students' attention in classroom • skills to inspire students' interest • My teaching philosophy: interest is the best teacher

15. What can I bring to Oxford? • Curiosity, experiences, and creativity in physics research • The qualities of a good physicist • A plan for discovery of new physics • Immediately strengthen the group’s major role in existing areas of research • Possibly initiate new areas in b→s transitions • Eventually pursue a global analysis for identification of new physics scenario • Enthusiasm for teaching

16. Why the fascination with LHCb? Because antimatter really matters! Thank you!And questions?

17. Event selection optimization • Often one is tempted to maximize • I proposed to directly optimize measurement error (Y. Xie, arXiv:0901.3305) Where fiis “local event purity”. Plan to apply the binned variation of the method in optimization with real data.

18. Background subtraction(Y. Xie, arXiv:0905.0724) • Mass sidebands may have different time distributions • Define event weight function W(m) • Estimate bs by maximizing W(m) Only signal time pdf is needed!

19. Proper time reconstruction • Fast Bs-Bs oscillation requires good proper time resolution • I developed a vertex fitting and proper time fitting package which achieves st ≈ 0.040 ps for Bs→ J/yf Initial Bs Time (ps) • Unbiased proper time measurement is essential • I developed an adaptive tool to refit primary vertex which largely reduces proper time biases

20. Measuring sign of cos(2bs) • Divide the data into bins of KK mass • In each bin find the two solutions physical solution: d// - d0, d┴ - d0, dS - d0, cos(2bs) mirror solution: d0 - d//, p+d0 - d┴, d0 - dS, cos(p-2bs) • Plot dS - d0 as a functio of m(KK) for the two solutions and get two branches dS - d0 as a function of m(Kp) in B0→ J/YKSp0 (PRD 71, 032005)

21. Resolving strong phase ambiguity • The P-wave Breit-Wigne phase d0 is expected to rise rapidly through the f(1020) mass region • The S-wave phase dS should vary relatively slowly • As a result dS - d0 should fall rapidaly as m(KK) increases from below to above the f(1020) resonance • It is straightforward to select the physical solution and get sign of cos(2bs) dS - d0 as a function of m(Kp) in D0→ K+ K-p 0 (PRD 76, 011102)

22. Bs→ ff(A. Amato, J. McCarron, F. Muheim, B. S. de Paula, Y. Xie,LHCb public note 2007-047) • CDF 4.7s Br measurement (PRL 95:031801, 2005) • SM prediction: F(Bs→ ff)=0 • Sensitive to new physics contribution to QCD penguin operators • I performed the first time dependent angular analysis in LHCb CDF Recent LHCb result: 3.4k in 2 fb-1 B/S ≈ 1 s(F) ≈ 0.125

23. Bs→ fg(F. Muheim, Y. Xie, R. Zwicky, Phys. Lett. B664:174-179, 2008) • SM requires left-handed g from b → sg • B factories test • S(Bd→ K*(KSp0)g) ≈ |AR/AL|sin2b ≈ 0 • LHCb lacks sensitivity? • Bd→ K*(KSp0)g inaccessible • S(Bs→ fg) ≈ |AR/AL|sin2f suffers small f • My original idea: exploit the sizable Bs decay width DGs to measure AD(Bs→ fg) ≈ |AR/AL|cos2f Well received!

24. Parameterization of New Physics in mixing • The effects of New Physics in the oscillation can be parameterized as: arXiv:0810.3139

25. Dalitz acceptance examples

26. 108 minimum bias @ 2kHz