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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

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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

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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

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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 11 V bc V ub

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

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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

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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

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

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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 ==

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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

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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

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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

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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

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B B tagging 3 essential measurements

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Production of B B in experiment

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

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Typical decay modes for B B Leptonic decay mode for tagging

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

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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

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

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

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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

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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

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

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