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

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

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

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

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

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 ds

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

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

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 ==

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

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

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

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

B B tagging 3 essential measurements

Production of B B in experiment

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

Typical decay modes for B B Leptonic decay mode for tagging

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

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.

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

Results of  m B measurement Measured  m B is in agreement with other measurements Mixing asymmetry = eV

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

Literature Selected Theoretical Issues in B Meson Physics: CKM matrix and Semileptonic Decays I.M.Narodetskii hep-ph/ The BaBar Physics Book A study of time dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the  (4S) hep-ex/

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