Thesis Defense of Luminda Kulasiri Dept. of Physics, University of Cincinnati 05.09.2005

1. Search for exclusive two body decays of B→D h at Belle * S Thesis Defense of Luminda Kulasiri Dept. of Physics, University of Cincinnati 05.09.2005

2. c c s s *- *- W- W- DS DS * * Vcs Vcs b b u u Vub Vub B0 B- p+ p0 d d u u Motivation- Decay via b → u spectator Diagram Clean measurement for Vub No penguin terms Model independent No yet seen Importantinput for measuring Sin(2β+γ)

3. b *+ DS * Vcb Vud s W s K- d u Motivation- • Evidence for W-exchange • First seen in B0→ Ds-K+decay • PRL 89, 231804(2002) • Not seen • Role of the final state interactions • Br can be as large as 10-4 • D+-, D00 can turn out to beDs*-K+ • (B. Block et al. PRL 78, 3999, 1997) c B0

4. @ 90% C.L. @ 90% C.L. @ 90% C.L. -PDG 2004 Past Measurements & Theoretical Predictions Theoretical predictions A. Deandrea et al. Phy. Lett. B 318, 549(1993)

5. → → Theoretical predictions a1~1.0, Vub~.003, Vcs~0.97 D. Choudhry et al. Phy. Rev. D, 45, 217(1992)

6. KEKB Accelerator • Asymmetric Collider with, • 8.0 GeV e- x 3.5 GeV e+ • 22 mrad crossing angle • Lpeak = 13.92nb-1s-1 • ∫Ldt ~400 fb-1 • Ecm = 10.58 GeV operates at (4S) resonance e+e-→ (4S) →BB (4S)  center of mass frame

7. Belle Detector Aerogel Cherenkov cnt. KL/µ Detector CsI Calorimeter 3.5 GeV e+ TOF counter SC solenoid 8GeV e- Silicon Vertex Detector(SVD) Central Drift Chamber(CDC)

8. Belle Detector • Silicon Vertex Detector (SVD) • Tracks low momentum particles with CDC • Vertex reconstruction,  18 µm • Central Drift Chamber (CDC)Mom. of charged particles is measured from the curvature of the track traversing in the magnetic field • PID using dE/dx - energy loss by ionizationin the matter • Aerogel Cerenkov Counter (ACC) • Index of refraction ranges from 1.01 to 1.03 • K/ ID between 1.2 – 4.0 GeV/c TOF counter K/ seperation using timing of plastic scintillation counters CsI Calorimeter Measure energy of e’ns and  via detection of scintillation light from e.m. showers. KL/µ Detector Detect high mom.(>600 MeV) K/µ SC Solenoid Generates 1.5 T mag. field

9. Particle ID at Belle • Uses information from CDC, TOF, and ACC • Combine the information using Likelihood method Pi – likelihood for signal species Pj – likelihood for background species Where i, j {e, , K, , p}

10. Used 250 fb-1 data at (4S) center of Mass resonance • 274.8 million BB events Decay Chain B0→ Ds*+-, B0→ Ds*-K+, B+→ Ds*+0 Ds*+→ Ds+ Ds+ → {+, KSK+, K*K+} →K+K-, KS→+-, K*→K+- Conjugate modes are also assumed

11. Data Data Reconstruction of , K0s, and K*0 →K+K- Kaon ID>0.6 1.0116<M(KK)<1.0272 GeV (±3 of the nominal mass) K*0→K+- K/ ID>0.6 |M(KK) – 0.8961| < 0.060 GeV (±3 of the nominal mass)

12. Helicity Angle Helicity angle(θh) – Angle between momentum of DS and momentum of K in (K*) frame. • Flat dist. for background evts. • Cos2(θ) dist. for signal evts. • Selection requirement, • |cos(θh)| > 0.3 Bg. evts. Signal evts.

13. Data Reconstruction of , K0s, and K*0 - Cont. K0s→+- Pion ID>0.6 0.4902<M(+-)<0.5051 GeV (±3 of the nominal mass) 2<30 (vertex reconstruction fit) Other cuts: dr>0.009 cm; d<0.2 rad dr – smaller of dr1 and dr2, where dr1 and dr2 are the smallest approach from the IP to the two tracks in x-y plane d- angle betn. the momentum vector and decay vertex displacement vector in r- plane Signal Events Background Events dr(cm) dr(cm) d(rad) d(rad)

14. Photon Energy (Eg) Bg. Signal Reconstruction of DS+and DS*+ momentum selection 1.7<P(cms)<2.5 GeV M=M(DS*)-M(DS) M has better resolution than mass. 0.124<M<0.164 GeV A large portion of the background is accounted by photons that are not really coming from DS*. E(cms)>110 MeV 0 veto ±3 of the nominal mass (1968.5±0.6 MeV) 1.9539<M()<1.9833 GeV 1.9471<M(KSK)<1.9901GeV 1.9495<M(K*K)<1.9877GeV GeV

15. GeV GeV/c2 B→Ds*+- (Ds+→+) Selection of the B Candidate Two quantities M(B) and E are defined as, E vs. M(B) Signal MC where Ebeam =5.29 GeV, Pi – mom. of B, Ei –energy of B Signal Region, –0.05<E<0.05 GeV for h {, K} –0.10<E<0.05 GeV for h {0} 5.27<M(B)<5.29 GeV/c2

16. Largest background source is e+e-→ qq events Fisher Discriminant is a powerful tool to discriminate signal and background • A linear combination of 9 variables • Optimized to discriminate signal from background Background Suppression – Fisher Discriminant

17. Where is a unit vector s. t. it maximizes T is the mom. of the ith particle in CM frame Combine all 9 variables into F Background Suppression – Fisher Discriminant (cont.) • Cos(θth) – Angle between thrust axis of the B cand., • and the thrust axis of the remaining particles. • Cos(B) – Angle between the B momentum & beam axis • qr x (QDS) – qr contains flavor information of the • other B; q = ±1; 0<r<1;

18. Used Figure of Merit (FOM) plots to decide the best selection Background Suppression – Fisher Discriminant (cont.) All the parameters are optimized to get the maximum discrimination between signal and background continuum Signal Arbitrary units S - Signal B - background FD

19. N – inclusive M yield ;  - efficiency ; Reconstruction Efficiencies • First used Sig. MC – fitting M(B) • Observed inconsistency among the yields of DS sub modes • Minimized MC dependence by using inclusive M • Efficiency for  mode obtained using sig. MC • Total eff. obtained by multiplying by eff. of the other cuts Following relationships can be obtained

20. Sideband Study • Sidebands of Ds and M used • 3 from lower and upper side of the signal region • Can be used to compare data and MC • Background shapes and rates can be obtained Observations: • Bg. shapes of data and MC agree each other • Observed a disagreement in bg. levels ~12% – 22% • Bg. of Ds not random – real Ds but not from Ds*→Ds

21. Simultaneous Fitting • Simultaneous fitting of 3 DS sub decay modes • Common branching fraction for all 3 DS sub-decay modes M-1D • Signal-Gaussian shape with mean &  fixed to sig. MC shape • Bg. – linear shape, by fitting data excluding the signal region E-1D • Signal-Gaussian shape with mean &  fixed to sig. MC shape • Bg. – sideband shapes of M Significance

22. Simultaneous fitting - cont. Ds*+- Ds*-K+ E fit Solid line (red) – total fit dotted line (blue) - background Ds*+0

23. Simultaneous fitting - cont. DS*+- DS*+K- • M fit • Solid line (red) – total fit • dotted line (blue) - background DS*+0

24. Systematic Uncertainties Since 3 Ds modes, Total Syst. error = common syst. errors + indept. syst. errors Common Errors (%)

25. Systematic Uncertainties-cont. Independent Errors

26. RD* for Sin(21+3) D* - strong phase,c – Cabibbo angle D. Becirevic, Nucl. Phys. Proc. Suppl. 94, 337 (2001 - good agreement with the expected result which is ~0.02

27. Estimation of Vub -Good agreement with the world average for |Vub| which is (3.67±0.47)x10-3

28. Used 278.4 million events • M fits give more consistent results • Both M and E results agree within errors • Obtained estimates for Vub and RD* Summary

29. Combined yields from M fit (274.8 m evts.) DS*+- 19.0±5.7 evts DS*-K+ 11.0±4.8 evts DS*+0 9.4±5.5 evts

30. Combined yields from M(B) fit (274.8 m evts.) DS*+- 21.4±5.9 evts. DS*-K+ 10.6±4.9 evts. DS*+0 8.1±5.7 evts.

31. Combined yields from E fit (274.8 m evts.) 4.48.4 evts. 15.15.6 evts. 8.24.7 evts.