1. The BaBarians are coming Neil Geddes Standard Model CP violation BaBar Sin2  The future

2. The Aims Complex phase in CKM matrix produces different phases for B 0  anti-B 0 and anti-B 0  B 0 J/  K 0 s B0B0 B0B0 B0B0 B0B0   CP Standard Model CP Asymmetry: CP violation in B mesons: w w uct b d b d b c d d c s  = CP of final state = -1 for J/  K 0 s, +1 for J/  K 0 L  = arg[-V cd V cb * /V td V tb * ]

3. Unitarity Triangle Quark mixing described by complex Cabibbo-Kobayashi-Maskawa matrix V CKM unitary  V † V = 1 V * i1 V 1j +V * i2 V 2j +V * i3 V 3j = 0/1 V * ub V ud V * tb V td V * cb V cd    (  (  (  (rescale sides by 1/|V * cb V cd | and choose V * cb V cd real ) B d      ±    B d  J/  K s,D* ± D ,.. B  D ± K 

4. Constraining The Triangle sin2  = (0.5, 0.8)

5. Asymmetric B-factories e + e -   (4s)  B 0 B 0 (50%) B + B - (50%) PEP-II design luminosity 3x10 33 cm -2 sec -1 + Continuous high precision running 9GeV e - + 3.1GeV e +   boosted in lab Y(4s) e,  K tag ++ -- e-e- e+e+ B0B0 K0K0 _B0_B0 J/   z~  t measure Small branching ratio for f CP

6. PEP-II and BaBar Canada China France Germany Italy Norway Russia UK USA ~ 600 Collaborators 9 Countries ~ 70 Institutions

7. The BaBar Detector (4) Electromagnetic Calorimeter (6) Instrumented Iron Yoke (3) Cerenkov- Detector (5) 1.5 T Solenoid (2) Drift Chamber (1) Silicon Vertex Detector e-e- e+e+

8. Chronology 1995 - Approval 1998 - Construction completed 1999 - Started taking data - events !! 2000 - Taking data 2,000,000 events per day, 20,000 Bs per day 2001 - Taking data 20,000,000 events per day 100,000 Bs per day 2002 - “Results” 120,000,000 Bs 2002-2005 - Detailed results 1,000,000 Bs per day first measurements first results

9. The Method 1)Reconstruct CP eigenstates, J/  K 0 2)“tag” other B flavour 3)Measure  z   t 4)Fit A(t) for sin(2  ) Complicated by: Mistags Finite time (vertex) resolution Also need B mass difference  M(B 0 ) B 0 lifetime B 0  f CP (f + ) B 0  f CP (f - )

10. K 0,  0 and J/  Reconstruction K0s+-K0s+- K0s0-K0s0-

11. B Reconstruction Completely reconstruct many (anti-)B 0 ’s B 0  J/  K *0 (K +   ),D ( * )-  ,D ( * )-  ,D ( * )- a 1   c.c. Flavour Sample Total sample ~6000 From this sample determine. A) Tagging efficiency B) Mistag fraction

12. B Mixing MBMB Mistags di-lepton events A = (N u -N m )/(N u +N m ) Semi-leptonic decays Dilution D = 1-2w A measured = Da true

13. CP B Reconstruction B 0  J/  K 0 L EMC IFR all B 0  J/  K 0 s All K 0 s modes B 0   (2s) K 0 s For K L : We do not know K L momentum. We know direction Impose M B constraint Imply momentum Measure  E

14. Tagging Non CP vertex “tagged” as B or anti-B by: Presence of charged lepton Electron P cm >1.0 GeV/c; Muon P cm >1.1 GeV/c Presence of charged Kaons   Kaon Charge  0 Overall event properties (l,K,slow-  ) Neural Network b c e,  s

15. Time Resolution Dominated by vertex resolution for Tagging B Common parameterisation for CP and flavour samples Sum of three Gaussians: Core (88%), Tail (11%), and Outliers (1%) Parameters determined from likelihood fit and other consistency checks B flavor eigenstates B charmonium  z = 180  m for tagging vertex,  z = 70  m for fully reconstructed vertex

16. Mistags and  (t) preliminary Quality factor Q =  (1-2 w ) 2.  (sin2  )  1 /  QN rec if no background Flavour Sample Determines Mistag and  t Resolution parameters  m(B 0 ) = (0.519 ± 0.020 ± 0.016)  ps -1

17. Fit for sin2  sin2 b is measured with a 35 parameter simultaneous fit to data flavour and CP samples:  m B and  B are fixed at the PDG world average values:  m B = 0.472  ps -1  B = 1.548 ps

18. Fit Parameters Sin2 b 4 signal dilutions (D=1-2w) 4 values of D D for the 4 signal categories 9 parameters for the signal D t resolution function 8 background dilutions 3 parameters describing the background resolution function 1 parameter for the fraction of CP background 5 parameters for the fractions and lifetime of the B flav background

19. Measured Asymmetries sin2  = 0.34  0.20  0.05 2  = CP +1 CP -1

20. Cross Checks

21. Systematic Errors

22. BaBar, Belle and the Rest Allowed region (blue) is determined using theoretical inputs and fitting many experimental measurements Feb 2001 Belle (~10 fb -1 ) sin(2  ) = 0.58 ±0.33±0.1 BaBar (~22fb-1) sin(2  ) = 0.34 ±0.20±0.05

23. What if sin(2  ) is < 0.5 ? Standard model bound ~ 0.59  sin2   0.82 SM constraints are wrong because : SM valid but: |V ub | smaller than theoretically favoured range SU(3) breaking in B d 0 /B s 0 mixing larger than favoured range B K larger than theoretically favoured range SM incomplete; new flavour violating and/or CP violating physics: New contributions to B d 0 mixing and B s 0 mixing New CP violating contribution to B 0 mixing New CP violating contribution to K 0 mixing (and K  ) Eyal, Nir and Perez hep-ph/008009

24. Covering the Angles B A B AR can measure the phase angles    Very clean, Eff B.R. ~ 10 - 4 B.R. ~ few 10 - 6 Theoretically uncertain Eff B.R ~10 - 7 ; tough!! B 0 d  J/  K 0 S B 0 d  B 0 d  DK

25. ‘80 ‘90 ‘00 Prospects 6 12 1818 (fb -1 ) ‘80‘90‘00 CESR/CLEO (from CESR Web page) PEPII/B A B AR ‘05 30 fb -1

26. Conclusions PEP-II and BaBar collected/analysed ~25 fb -1 in 2000 More than double our data by the end of the run in August By 2005, we should accumulate ~ 500 fb -1 Measure sin 2 , compare sin 2  in individual modes Measurements of direct CP violation and rare decays. sin 2  = 0.34  0.20  0.05 The BaBarians have already arrived !