PPT Searches for Rare & Forbidden B and Charm decays with BaBar

Study of B  Kππ γ decays at BaBar

Eugeni Graugés

Universitat de Barcelona

International Conference On High Energy

Physics: ICHEP2014 València

Outline:

– The BaBar Detector & Dataset – Introduction

– Event Selection and reconstruction – Analysis strategy

– Analysis of B + K + π - π + γ – Analysis of B 0  K 0 s π - π + γ – Results

– Conclusions All r esul

ts sh own her e ar e PR ELIM INA RY,

not yet pub lishe d (p ape r in prep arati on)

Dataset:

530/fb recorded in 9 years of operation :

Not only BB pairs:

690M cc pairs 500M τ τ pairs

~470M BB pairs but also:

7 x (Belle + Cleo) ϒ(3s)

0.5 x (Belle + Cleo) ϒ(2s)

– The BKππ γ is an effective FCNC b sγ

– Forbidden in the SM at tree level, they are very suppressed since they can only proceed via loop diagrams 

SM Branching Fractions (BF) of ~ 10

-10

– The presence of physics beyond the SM, could significantly change the BF’s, CP asymetries and the polarization of the decay photon

+ ?

Introduction:

– The photon polarization probes the V-A structure in the loop:

In the SM b (b-bar) decays in left-handed (right-handed) photon up to

~m

/m

≈2%

– The photon polarization can be accessed from the angular

distribution of the kaonic resonance decay into 3 bodies K

Kππ in B K

γ

Ref: Gronau, Grossman, Pirjol & Ryd

PRL88:0511802, 2002 & PRD66:054008, 2002

Introduction:

– NP particle may be present in the loop and enhance right-handed photons

– In the SM b sγ

or b sγ

 CP asymmetry parameters ~ 0

– NP presence  b sγ

or b sγ

 CP asymmetry parameters ≠ 0

– Time dependent CP asymmetry measurement

Introduction:

Objective: Measurement of S in B

 K

ρ(π

π

) γ decays

Event selection & reconstruction

Signal B mesons:

Characterized kinematically by m

and ∆E observables

 Good k/π separation

Background rejection:

Mainly qq continuum: e

e

qq (q=u,d,s,c);

supressed using a Fischer discriminant based on six variables that exploit the different event

topologies

 Background from other B decays: classified by kinematical and topological properties.

Different variables are then combined to be used into a maximum likelihood fit to both signal/bkg separation and to measure the physics

parameters of interest

Analysis strategy

Added challenge:

 Presence of irreducible contribution from from non CP-eigenstates

 Amplitude analysis required to extract the dilution factor

 The limited statistics prevent the amplitude analysis from the B

K

π

π

γ channel.

 Therefore D is extracted from B

K

π

π

γ decays, assuming isospin symmetry

 The 4-body final state makes the boundaries of the (kπ-ππ) phase space to

vary event by event.

Analysis of B +  K + π - π + γ

a) Maximum likelihood fit to mES,

∆E and the Fischer a) Extraction

of the m

and m

spectra (using sPlot technique) a) Fit to m

and m

(projection) to extract

amplitudes  From the amplitudes, the dilution factor D and the BF’s are obtained

Preliminary Preliminary

Preliminary

Preliminary

Dilution factor from B +  K + π - π + γ

Results from B +  K + π - π + γ : BFs

Results from B +  K + π - π + γ : BFs

Several of this

measurements are to be the world best…,

or

measured for the first

time

Results from B 0 K 0 s π - π + γ : S

Conclusions:

– BaBar stopped taking data in 2008, but the available dataset is still a very rich and

fruitful playground for physics analysis.

– All (preliminary) results shown agree with Standard Model predictions

– With the addition of larger samples (LHCb,

Belle-II) it should be possible to disentangle

whether or not there could be indications of

NP processes.

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