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Philip J. Clark University of Edinburgh

Rare B decays. The Royal Society of Edinburgh 4th February 2004. Philip J. Clark University of Edinburgh. Talk overview. Introduction to rare decays. Ways to measure them experimentally. Theoretical methods for calculating them. Various interesting results. Summary.

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Philip J. Clark University of Edinburgh

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  1. Rare B decays The Royal Society of Edinburgh 4th February 2004 Philip J. ClarkUniversity of Edinburgh

  2. Talk overview Introduction to rare decays Ways to measure them experimentally Theoretical methods for calculating them Various interesting results Summary Rare B Decays

  3. What are rare B decays? (part 1) Small CKM matrix element • exclusive b  u charmless hadronic |Vub/Vcb|~l B0p+p-,K+p-, ... B ppp, Kpp, rr, K*r, … BR~10 -5 ~ -6 • exclusive b  c with Vus (what is rare?) BR~10 -4~-5 B+`D0K+, ... • exclusive b  u, purely leptonic fB|Vub| B+ l+n BR~10 -5~-12 Rare B Decays

  4. What are rare B decays? (part 2) Leading diagram involves a quantum loop (“penguin” loop) • gluonic loop: b  s gluon (`qq) exclusive B fK* … (pure gluonic loop) B Kp, Kh’ (gluonic + small tree) BR~10 –5~ -6 • radiative loop: b  (s,d)g exclusive (b  s,dg) inclusive (b  s g) B K*g,rg,wg B sg BR~10 -5 ~ -7 BR ~10 -4 • electroweak loop B K`nn, K`l l BR~10 -6 Rare B Decays

  5. Charmless hadronic decays How can we organise them? JPC classification of light mesons B  K, , K, ’… PP B  , K*, … VV B  K*, , , K, … PV B  a0, f0 … SP Rare B Decays

  6. Success of the quark model Rare B Decays

  7. Theoretical approaches Effective Hamiltonian Methodology QCD operator product expansion Advantages: Rigorous computation using Wilson coefficients Disadvantages Huge uncertainties in operator matrix elements Solution for B decays: (QCD) factorisation Two main methodologies • Diagrammatic • Methodology • Isospin & SU(3) • Advantages: • Very intuitive • Provides powerful approximate relations between decay channels • Disadvantages: • non exact results Chiang, Gronau, Luo, Rosner & Suprin BPV hep-ph 0307395 BPP hep-ph 0306021 eg. Beneke & Neubert BPV, PP hep-ph 0308039 Rare B Decays

  8. Example: rare 0 modes Colour suppressed trees Gluonic penguins Electroweak penguins Singlet penguins Rare B Decays

  9. Theoretical predictions Experimental dataHeavy Flavor Averaging group (Lepton Photon 2003) Rare B Decays

  10. PEP II/BABAR at SLAC Started construction in1994 Completed in 1999 Reached design luminosity in 2000 PEP II Asymmetric B Factory Luminosity records PEP-II/BABAR at SLAC design peak: best peak: total recorded: 3.0 x 1033 cm-2s-1 ~7.0 x 1033 cm-2s-1 162 fb-1 9 GeV e- on 3.1 GeV e+ Rare B Decays

  11. The BABAR detector 1.5-T Solenoid SVT DCH DIRC EMC IFR SVT Rare B Decays

  12. How do we find the rare decays? qq e+ e- e+ e- Signal B Other B • One method we use is the “event shape” • The continuum is light quark pair production, so there is lots of extra energy. All the decay products bunch into “jets” • B mesons are produced almost at rest in our case  The decay products of the B are distributed roughly spherically. • There any many such event shape variables which are all correlated: • Fisher discriminants (linear weighting) • And in some cases neural networks taking advantage of hidden layers. Rare B Decays

  13. Time dependent meaurements Identify B or anti-B y z x K+  K- D t~ D z/cgbg Full reconstruction of B  Ks0 0 B tag Coherent BB production Rare B Decays

  14. Example of aKsevent Rare B Decays

  15. Maximum Likelihood fits B 0 (  +-0 ) Rare B Decays

  16. Results: some branching fractions Rare decays are not rare anymore! Rare B Decays

  17. Why do we want to study rare decays? CP violation in the kaon system Measurements of |Vub|(b → u transitions) B0 and Bs mixing frequencies Main experimental constraints on the apex of the UT BABAR Phys. Rev. Lett. 89 (2002) 201802 World average(BABAR+Belle+…) Heavy Flavor Averaging Group 2003 Rare B Decays

  18. World-wide status of sin2b Rare B Decays

  19. Direct CP violation • Measurements in many charmless hadronic B decays • These modes are all sensitive to gluonic penguin amplitudes which may interfere to produce an asymmetry • Non-SM effects could cause potentially large asymmetries in some decays Rare B Decays

  20. Latest interesting result: B  +- Latest results from BELLE: S=-1.00  0.21  0.07 C= 0.58  0.15  0.07 hep-ex/0401029 Rare B Decays

  21. Summary What we have covered: • What are rare B decays • Various tree diagrams • Several penguin diagrams • Calculating them • Categorisation of light mesons • The two main theoretical approaches • Where to measure them • Example: The BaBar experiment and PEPII • How to measure them • Mulitivariate discriminants, Particle ID, Maximum Likelihood • Results • Branching fractions • Status of Sin2b • Direct CP violation • Latest News • Lots of new results still to come • Need more data! Rare B Decays

  22. Particle Identification • Need to differentiate kaons from pions. • Crucial to the analysis of many charmless decays • Especially important at high momenta K, p Rare B Decays

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