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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

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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

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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

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Feynman Diagrams for B Processes

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FCNC B decays Forbidden at tree level in SM Occur via Penguin / Box diagrams Sensitive to New Physics heavy particles –SUSY, non-SM Higgs

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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

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bsbs

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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

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Current Result (BaBar/Belle)

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bdbd

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Discovery of b d

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And… b d gluon (g )

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Forward Backward Asymmetry of leptons sensitive to New Physics, determine C 7 C 9 C 10

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Determined with low precision Requires a larger data sample LHCb or Super-B Factory

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Channels with neutrinos

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B (s) + -

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Really really rare! SM box SM Penguin Sensitive to New Physics in SUSY models

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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 1.0x10 -10 Current limits from Tevatron

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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

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