Chris Parkes Rare B Decays Introduction Radiative decays
Chris Parkes Rare B Decays • Introduction • Radiative decays b d • Electroweak Penguin b sl+l • Rate • Forward backward asymmetry • Final states with neutrinos SUPA Postgraduate Lectures
B mesons / Baryons and various excitations • Masses known to a few Me. V Evidence 1998 Accurate Mass 2005 • 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
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 e. g. decay Feynman diagram full process description Or Effective point-like vertex • Form an effective weak Hamiltonian, effective vertices multiplied by effective coupling constants Contains : 1)CKM elements VCKM 2)Matrix Element Operators non-perturbative - Lattice Calculations, HQET 3)Wilson Coupling Coefficients Ci (there are 10) Aim to measure these – sensitive to new physics
b s
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 (Ba. Bar/Belle)
b d
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
• Really rare! B(s) 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 rare! • Needs LHC data sample for SM • Bs 3. 5 x 10 -9, • Bd 1. 0 x 10 -10 Current limits from Tevatron
Information Sources • Varenna CP violation school 2005 – http: //varenna 05. pi. infn. it/ – Slides taken from talks of: – Rare B Decays – H. Aihara • OPE & Wilson Coefficients, A. Buras hep-ph/9806471
- Slides: 29