1. Flavor mixing in the BB system Motivation of studying B B system Measuring the B B flavor oscillation BaBar experiment Production of B B B B tagging Particle detection B B mixing Results of  m B measurement

2. Motivation of studying B B system What is the CKM matrix Magnitude of the CKM matrix elements Advantage of studying BB V ij magnitude for KK and BB

3. What is the CKM matrix “weak eigenstates”“flavor eigenstates” V ud can be studied in  decay V us can be studied in K decay d u d u u d n p W e - e V ij can be studied by selecting appropriate decay s qq K W u  V ud V us

4. Magnitude of the CKM matrix elements “weak eigenstates”“flavor eigenstates” Close to Cabibo angle sin  =0.22 b qq B W u // b qq B W c D*D* ~7% ~0.04% Diagrams with V ub and V td are difficult to measure but they contain the imaginary part of the CKM sin 2  11 V bc V ub

5. Motivation of BB studying Unitarily of CKM matrix implies: Areas of triangles are equal but lengths of the sides are not +

6. Motivation of BB studying K  K (ds  ds) B  B (db  db) For KK and BB the interaction differs strongly ds WW sd K0K0 K0K0 WW sd K0K0 K0K0 WW s d K0K0 K0K0 u u c c t t u u c c t t WW d db b B0B0 B0B0 WW d db b B0B0 B0B0 WW d db b B0B0 B0B0 ds 2 2 6 6 4 6 ds

7. Consequence of the small V ij for KK and BB systems 5 GeV ~0.5 GeV +’+’    ’ <<  =3  eV  =320  eV flavor eigenstate CP eigenstate (CPT) mass eigenstate flavor eigenstate KK third family contribution is very small  small CP violation (CPT) mass eigenstate BB all 3 contribution are similar  large CP violation In BB CP violation is more pronounced than in KK K1K1 KLKL K2K2 KSKS BLBL BHBH K0K0 _K0_K0 B0B0 _B0_B0

8. Measuring the B B flavor oscillation Time evolution of BB Schrödinger-like equation Probability for flavor oscillation

9. Time evolution of BB In case of CP violation mass eigenstates of BB are: Time evolution of the mass eigenstates mass eigenstates propagate not the flavor eigenstates ==

10. Schrödinger-like equation The time evolution of flavored B (B) obey Schrödinger-like equation M is the mass matrix  is the decay matrix Solving eigenvalue equation:  m B =Re( + - - ) and  B = -2Im( + - - ) + = H and - = L

11. Flavor oscillation  can be used for flavor propagation in time The time-dependent probabilities proportional to: ~1 B Flavor oscillation depends on  m B : Measure by B  B as function of time

12. BaBar experiment Production of B B B B tagging in BaBar Typical decay modes for B B Particle detection B B mixing Results of  m B measurement

13. Production of B B in experiment 3.1 Gev e + + on 9 GeV e - cms boost =0.55 e - + e +  Y(4S) (bb resonance)  96% of B B

14. B B tagging 3 essential measurements

15. Production of B B in experiment

16. Typical decay modes for B B B0B0 D *- Tagging channel Flavor eigenstate

17. Typical decay modes for B B Leptonic decay mode for tagging

18. Particle detection in BaBar the particle collision rate 50 times more than the original facility

19. Particle detection in BaBar BaBar detector for photons, leptons & hadrons The maximum possible acceptance in c.m.s. Excellent vertex resolution Tracking over range ~0.6 GeV<pc<~4 GeV.

20. Experimental observation of B B mixing Take into account the finite resolution of the measurement Probability

21. Results of  m B measurement Measured  m B is in agreement with other measurements Mixing asymmetry =3.388 10 -4 eV

22. Conclusions The importance of B B measurement Flavor mixing Principles of BaBar Results on  m B CP violation will be discussed in coming talk by Moslem

23. Literature Selected Theoretical Issues in B Meson Physics: CKM matrix and Semileptonic Decays I.M.Narodetskii hep-ph/0309229 The BaBar Physics Book http://www.slac.stanford.edu/BFROOT/www/doc/PhysBook/physBook.html A study of time dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the  (4S) hep-ex/0201020

24. -1/3 b t2/3 -1/3 s c2/3 -1/3 d u2/3