2. Pakhlov Pavel (ITEP, Moscow) Why B physics is still interesting Belle detector Measurement of sin2  Rare B decays Future plans University of Lausanne 11/12/2001

3. Pakhlov Pavel (ITEP, Moscow)2 B-physics Test of the Standard Model (SM) mechanisms hadronic models, CKM, etc… Measurement of the fundamental parameters of SM exact values can be a hint for new phenomenology Search for physics beyond SM large b-quark mass SM decays suppression (V cb <<1) large contribution from loop and box diagrams

4. Pakhlov Pavel (ITEP, Moscow)3 Why CP is important Test CKM mechanism as a single source of CP violation: During 35 years CP violation measured only in K system. CKM theory  single (free) parameter; Experiment  single measurement . Measurement of CKM matrix elements: sin2  : constrain on CKM matrix elements without QCD uncertainties. sin2  from B  DK, x d /x s, B  : free of model uncertainties, but requires much more statistics. New physics: Need overfull constrain on CKM parameters (better if without QCD uncertainties) to test the SM … or to observe very large discrepancy

5. Pakhlov Pavel (ITEP, Moscow)4 CPV in B mesons at e + e - colliders B 0 B 0 are produced and remain in coherent p-state until one of them decays. If the first B decays to flavor specific mode, the state of the other B is orthogonal at this time. Then the second B propagates (oscillating). If it decays to a CP-final state: two contributions from B and B interfere. If the first B decays to the CP final state and the second to a specific flavor state – the interference results into opposite sign of CP asymmetry. The time integrated asymmetry vanishes!

6. Pakhlov Pavel (ITEP, Moscow)5 Mixing-induced CP asymmetry

7. Pakhlov Pavel (ITEP, Moscow)6 The Belle collaboration ~300 authors from 50 institutions (13 countries) Group from the University of Lausanne joined Belle recently

8. Pakhlov Pavel (ITEP, Moscow)7 KEKB asymmetric e + e - collider Two separate rings e + : 3.5GeV e - : 8.0GeV E cm : 10.58GeV  c   200  m Luminosity: design: 10 34 cm -2 s -1 achieved: 5.46 x 10 33 cm -2 s -1 Crossing angle 22mrad Beam size:  x =100  m  y =3  m

9. Pakhlov Pavel (ITEP, Moscow)8 KEKB/Belle luminosity summary May 1999- December 2001: accumulated: 44.3 /fb analyzed: 32.8 /fb KEKB records on the luminosity peak: 5.466 × 10 33 /cm 2 /sec (World record) per day: 282.5 /pb (> whole ARGUS statistics) per month: 6120. /pb

10. Pakhlov Pavel (ITEP, Moscow)9 The Belle detector

11. Pakhlov Pavel (ITEP, Moscow)10 B-meson reconstruction Reconstruct all low background (cc)K 0 CP-final states:

12. Pakhlov Pavel (ITEP, Moscow)11 B 0  J/  K S K S   +   -  4 MeV/c 2 J/   e + e -  11 MeV/c 2 J/   +  -  10 MeV/c 2

13. Pakhlov Pavel (ITEP, Moscow)12 B 0  J/  K S Energy difference: E=E J/  K S -E cm /2 Beam-constrained mass: M bc =  ( E cm /2) 2 - p J/  K S 2 457 events ~3% bkgd

14. Pakhlov Pavel (ITEP, Moscow)13 All full reconstructed modes Decay mode: signalbkgd J/  K S, K S  +  - 45711.9 J/  K S, K S  0  0 769.4  (2S)K S,  (2S)  + - 391.2  (2S)K S,  (2S)  J/  +  - 462.1  c1 K S,  c1  J/  242.4  c K S,  c  K S K    2311.3  c K S,  c  K + K -  0 4113.6 All CP=-1 modes74758 J/  K *0, K *0  K S  0 416.7

15. Pakhlov Pavel (ITEP, Moscow)14 B 0  J/  K L K L momentum is not measured, only direction is known Reconstruct J/  + - Assume M(J/  K L )=M B to calculate P(K L ) Remove full reconstructed J/  K, J/  K *. Cut on B-candidate likelihood based on kinematics and event shape. Look at P(J/  K L )

16. Pakhlov Pavel (ITEP, Moscow)15 B 0  J/  K L Main background from B  J/  X (quasy two-body) – well understood: use MC. Some backgrounds are CP-finale states: special care when CP-fit. Special case: J/  K *0, K *0  K L  0 - mixture  =-1 and  =+1: from angular analysis B  J/  K * 569 events= 346 signal+ 223 bkgd

17. Pakhlov Pavel (ITEP, Moscow)16 Flavor tagging Use tracks from the accompanying B specific flavor Inclusive leptons High momentum leptons b c - Intermediate momentum leptons s + Inclusive hadrons High momentum pions B 0 D * -  + (X), D -  + (X) Intermediate momentum kaons K + X Low momentum pions D 0  - Take into account correlations

18. Pakhlov Pavel (ITEP, Moscow)17 Multi-dimensional tagging likelihood Each class of tagging / each specific tagging particle have different tagging purity. If sum all events with different purity loose accuracy. Divide all events into several categories depending on tagging purities, then average over independent measurements: Calculate probability for each track to belong to one of the flavor tagging class. Combine information about all tracks into likelihood for event to be B 0 or B 0. Divide the whole likelihood range into 6 bins of different purities. Extract dilution factor for each bin from the data. Use specific flavor channels: B 0 D ( * ) -  +,B 0 D ( * ) - +

19. Pakhlov Pavel (ITEP, Moscow)18 Determination of wrong tag fraction A(  t) measured ~(1-2  )sin(  m d  t);  =N wrong /N. For sin(2  ) we need to know  ! Get  from B 0 B 0 mixing amplitude ~(1-2  )cos(  m d  t); Fit to the data with free  (r). Efficiency >99%  effective =27.0  1.2%

20. Pakhlov Pavel (ITEP, Moscow)19 CP-side vertexing: use prompt tracks from J/ ,  (2S),  c Reject poorly fit vertices  z  75  m Tagging B vertexing: Use well fit tracks Iterative procedure: fit discard worst track  z  140  m Efficiency: 87%,   t  1.5ps not-Gaussian tails 3%, Vertex reconstruction 1137 events are used for CP fit

21. Pakhlov Pavel (ITEP, Moscow)20 Check vertex resolution function B  D ( * )- + B  D ( * )- +  B 0 =1.55  0.02 ps  B + =1.64  0.03 ps

22. Pakhlov Pavel (ITEP, Moscow)21 CP-fit Each event has individual sensitivity to sin2  (depending on signal purity, tagging dilution,  z and vertex fit accuracy, etc…) For each event calculate its likelihood as a function of sin2  : signal fraction wrong tag fraction PDG free parameter Calculate sin2  which maximize the total likelihood  L i Resolution function

23. Pakhlov Pavel (ITEP, Moscow)22 sin2  results sin2  =0.99  0.14  0.06

24. Pakhlov Pavel (ITEP, Moscow)23 Cross-checks Mode dependencies: Check asymmetries in Non- CP sample. “sin2  ”=0.05  0.04

25. Pakhlov Pavel (ITEP, Moscow)24 Compare with other experiments

26. Pakhlov Pavel (ITEP, Moscow)25 Rare B-decays New level of sensitivity to the rare B- decays: Cabibbo-suppressed decays: B D (*) K +,D *+ D (*)- Color-suppressed decays: B 0 D (*)0 X 0 Hadronic penguin decays: B + K + K + K -,K +  +  - Electro-weak penguin decays: B K + - To be used in future for CP violation study

27. Pakhlov Pavel (ITEP, Moscow)26 Cabibbo-suppressed decays B D (*) K + (10.4 /fb): Large background from Cabibbo-allowed is suppressed by PID Remaining background disentangled by  E Branching ratios: Br(DK - )/BR(D  - )~0.068- 0.079 B - D (*)0 K - (D 0 CP) to be used in future for measuring angle 

28. Pakhlov Pavel (ITEP, Moscow)27 Color-suppressed Decays B D (*)0 X 0 have been observed for the first time: ModeBr ( X 10 -4 ) D00D00 3.1  0.4  0.5 D *0  0 2.7  0.8  0.6 D00D00 1.4  0.5  0.3 D *0  0 2.0  0.9  0.4 D00D00 1.8  0.5  0.4 D *0  0 3.1  1.3  0.8 D00D00 D *0  0 D *0  0 D *0  0 D00D00 D00D00

29. Pakhlov Pavel (ITEP, Moscow)28 Electroweak penguin decays FCNC are forbidden at tree level, but loop or box induced. Sensitive to the New Physics.  K  +  - observed for the first timeB  K  +  - observed for the first time

30. Pakhlov Pavel (ITEP, Moscow)29 Future plans Nearest Belle upgrade – summer 2002: reduce beampipe 2cm 1.5cm; new 4 layers silicon detector: Better vertex resolution Higher efficiency for slow track reconstruction e + e - machines competitive with LHCB and BTeV if L ~10 35. SuperKEKB is under investigation

31. Pakhlov Pavel (ITEP, Moscow)30 Summary Belle observed large CP-violation in B decays. sin2  =0.99  0.14  0.06 Many new rare B decays observed for the first time. KEKB/Belle continue successful operation. Many new interesting results are expected in future. KEKB/Belle plan to compete with LHC in B- physics after LHC starts.