Rare B Decays Chris Parkes SUPA Postgraduate Lectures Introduction Radiative decays b s b d Electroweak Penguin b sl + l - Rate Forward backward asymmetry Final states with neutrinos
B mesons / Baryons Masses known to a few MeV and various excitations Baryons In spectator model b lifetimes would all be the same –Non-spectator effects give rise to a hierarchy Theory and experimental pattern in agreement Evidence 1998 Accurate Mass 2005
What do we mean by a rare B-decay ? All decays ‘rare’ as decays out of generation Flavour Changing Neutral Currents (FCNC) are even more suppressed as forbidden at tree level in SM –b s –b d Rare in this context means not b c
Feynman Diagrams for B Processes
FCNC B decays Forbidden at tree level in SM Occur via Penguin / Box diagrams Sensitive to New Physics heavy particles –SUSY, non-SM Higgs
Operator Product Expansion (OPE) A method of formulating an effective theory of the interaction Feynman diagram full process description Or Effective point-like vertex e.g. decay Contains : 1)CKM elements V CKM 2)Matrix Element Operators non-perturbative - Lattice Calculations, HQET 3)Wilson Coupling Coefficients C i (there are 10) Aim to measure these – sensitive to new physics Form an effective weak Hamiltonian, effective vertices multiplied by effective coupling constants
bsbs
Discovery of b s , B K* FCNC CLEO, 1993 (PRL 71,674) Later extended to inclusive b s rate measurement Rate sensitive to new physics
Current Result (BaBar/Belle)
bdbd
Discovery of b d
And… b d gluon (g )
Forward Backward Asymmetry of leptons sensitive to New Physics, determine C 7 C 9 C 10
Determined with low precision Requires a larger data sample LHCb or Super-B Factory
Channels with neutrinos
B (s) + -
Really really rare! SM box SM Penguin Sensitive to New Physics in SUSY models
B (s) + - Unique Experimental signature Easy to identify / trigger – good for ATLAS/CMS Really really rare! Needs LHC data sample for SM B s 3.5x10 -9, B d 1.0x Current limits from Tevatron
Information Sources Varenna CP violation school 2005 – –Slides taken from talks of: –Rare B Decays – H. Aihara OPE & Wilson Coefficients, A. Buras hep-ph/