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