Philip J. Clark University of Edinburgh Rare B decays The Royal Society of Edinburgh 4th February 2004

Philip J. ClarkRare B DecaysPage 2 Talk overview Introduction to rare decays Ways to measure them experimentally Theoretical methods for calculating them Various interesting results Summary

Philip J. ClarkRare B DecaysPage 3 Small CKM matrix element |V ub /V cb |~ exclusive b  u charmless hadronic B 0       K +   ... B   K  K *  … BR ~10 -5 ~ -6 B +   D 0 K +,... exclusive b  c with V us (what is rare?) BR ~10 -4~-5 exclusive b  u, purely leptonic B +  l + BR ~10 -5~-12 f B |V ub | What are rare B decays? (part 1)

Philip J. ClarkRare B DecaysPage 4 Leading diagram involves a quantum loop (“penguin” loop) What are rare B decays? (part 2) gluonic loop: b  s gluon (  qq ) radiative loop: b  (s,d)  electroweak loop exclusive B   K* … (pure gluonic loop) B  K , K  ’ (gluonic + small tree) BR ~10 –5 ~ -6 exclusive ( b  s,d  ) inclusive ( b  s  ) B  K* , ,  B  s  B  K , K  l l BR ~10 -6 BR ~10 -5 ~ -7 BR ~10 -4

Philip J. ClarkRare B DecaysPage 5 Charmless hadronic decays J PC classification of light mesons How can we organise them? B  K, , K, ’… B  K *, , , K, … B  , K *, … PP PV VV SP B  a 0 , f 0  …

Philip J. ClarkRare B DecaysPage 6 Success of the quark model

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

Philip J. ClarkRare B DecaysPage 8 Example: rare  0 modes Colour suppressed trees Gluonic penguins Singlet penguins Electroweak penguins

Philip J. ClarkRare B DecaysPage 9 Theoretical predictions Experimental data Heavy Flavor Averaging group (Lepton Photon 2003)

Philip J. ClarkRare B DecaysPage 10 PEP II/B A B AR at SLAC PEP II Asymmetric B Factory design peak: best peak: total recorded: x    cm  s  x    cm  s   fb  PEP-II/ BABAR at SLAC Luminosity records Started construction in1994 Completed in 1999 Reached design luminosity in GeV e  on 3.1 GeV e +

Philip J. ClarkRare B DecaysPage 11 SVT  -T Solenoid The BABAR detector SVT EMC IFR DCH DIRC

Philip J. ClarkRare B DecaysPage 12  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. e+e+ e-e- e+e+ e-e- qq Signal B Other B How do we find the rare decays?  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.

Philip J. ClarkRare B DecaysPage 13 Time dependent meaurements 0 tag B Coherent BB production Identify B or anti-B Identify B or anti-B z x y  t  z/c     Full reconstruction of B   K s 0 Full reconstruction of B   K s 0  K+K+ K-K-

Philip J. ClarkRare B DecaysPage 14 Example of a K s event

Philip J. ClarkRare B DecaysPage 15 Maximum Likelihood fits          

Philip J. ClarkRare B DecaysPage 16 Results: some branching fractions Rare decays are not rare anymore!

Philip J. ClarkRare B DecaysPage 17 Why do we want to study rare decays? Phys. Rev. Lett. 89 (2002) B A B AR World average ( B A B AR +Belle+…) Heavy Flavor Averaging Group 2003 Main experimental constraints on the apex of the UT CP violation in the kaon system Measurements of | V ub | ( b → u transitions) B  and B s mixing frequencies

Philip J. ClarkRare B DecaysPage 18 World-wide status of sin2 

Philip J. ClarkRare B DecaysPage 19 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 Direct CP violation

Philip J. ClarkRare B DecaysPage 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/

Philip J. ClarkRare B DecaysPage 21 Summary  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 Sin2 Direct CP violation Latest News  Lots of new results still to come  Need more data! What we have covered:

Philip J. ClarkRare B DecaysPage 22 Need to differentiate kaons from pions. Crucial to the analysis of many charmless decays –Especially important at high momenta K,  Particle Identification