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Rare B Decays
Chris Parkes
SUPA Postgraduate Lectures
•Introduction•Radiative decays
bsbd
•Electroweak Penguin b sl+l-
•Rate•Forward backward asymmetry
•Final states with neutrinos
B mesons / Baryons
• Masses known to a few MeV
00 ,, sBBB and various excitations
CB
• Baryonsb
• 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 1998Accurate Mass 2005
What do we mean by a rare B-decay ?
• All decays ‘rare’ as decays out of generation
b
t
s
c
d
u
• Flavour Changing Neutral Currents (FCNC) are even more suppressed as forbidden at tree level in SM– bs– bd
• Rare in this context means not bc
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
OrEffective point-like vertex
e.g.
decay
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
• Form an effective weak Hamiltonian, effective vertices multiplied by effective coupling constants
bs
Discovery of bs, B K*
• FCNC
• CLEO, 1993 (PRL 71,674)
Later extended to inclusive bs rate measurementRate sensitive to new physics
Current Result (BaBar/Belle)
bd
Discovery of bd
And… bd gluon (g )ss
Forward Backward Asymmetry of leptonssensitive to New Physics, determine C7 C9 C10
Determined with low precisionRequires a larger data sampleLHCb or Super-B Factory
Channels with neutrinos
B(s)+-
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•Bs 3.5x10-9, •Bd 1.0x10-10
Current limits from Tevatron
Information Sources
• Varenna CP violation school 2005– http://varenna05.pi.infn.it/– Slides taken from talks of:– Rare B Decays – H. Aihara
• OPE & Wilson Coefficients, A. Buras hep-ph/9806471