Radiative B meson Decays at BaBar

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Radiative B meson Decays at BaBar

• Colin Jessop
• University of Notre Dame

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Motivations

• Window to new Physics
• Help measure the unitarity triangle
• Test QCD technology

Radiative Penguin Decays
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The Penguin Zoo
Several different types of penguins (not
including gluonic penguins)
Electro-Magnetic
Electroweak
Vertical Electromagnetic
Vertical electroweak
I will focus today mostly on electromagnetic
penguins. BaBar has results on all these
processes
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Sensitivity to New Physics
Example If SUSY exact B(b-sg) 0
SUSY
g
g
H
W

..
b
S/d
b
S/d
t
t
New Physics enters at same order (1-loop) as
Standard Model
Sensitive to many models very extensive
literature
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Penguin Theory A brief Overview
B mesons are low energy decays at scale m mb
5 GeV
Formulate a low energy effective theory
g
b
S/d
Generalization of Fermi Theory of b-decay.
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Operator Product Expansion
Ci Wilson Coefficients contains short
distance (high energy)
perturbative component
Qi Local Operators contains long distance
(low energy)
non-perturbative component
m(renormalization) scale dependence cancels in C
and Q
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Wilson Coefficients
Ci i1,2 current-current, i3-6 gluonic
penguins i7-10 Electroweak Penguins Ci
calculated at mMw and evolved down to mmb.
Effects of new high mass physics appear in C
DC8
e.g constraints on C7 and C8 from B(B-Xsg)
DC7
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Matrix Elements
are long distance (low-energy )
non-perturbative component

• If X is exclusive state e.g Kg two
  possibilities
• Lattice QCD Lattice spacing compton
  wavelength of b - Large errors
• QCD sum rules Relates resonances to vacuum
  structure of QCD

Neither approach gives precise estimates limits
exclusive physics. Uncertainties cancel in ratios
of modes or asymmetries.
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Inclusive Matrix Elements
If X is an inclusive state

0
Leading term is short distance quark contribution
and non- perturbative effects appears at 1/mb2
i.e (O(1)) corrections
Inclusive measurements are much more sensitive
to new physics
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General Considerations
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B factories ee- ? Y(4S) ? BB

• B factories operate at the Y(4S) resonance (10.58
  GeV)
• hadronic cross-sections
• udscbb 3.41.1 nb
• in the Y(4S) frame the B mesons are practically
  at rest
• ? PEP-II is an asymmetric collider
• 9.0 GeV electrons vs
• 3.1 GeV positrons

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PEP-II and BaBar at SLAC
linac
PEP-II storage ring
SLD
BaBar
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Integrated luminosity
Currently 10 BB event per second. since 2000
BaBar has recorded 430M BB events about 8 of
data is taken below the Y(4S) resonance results
presented here are based on 90 fb-1 - 340
fb-1 on-resonance data
Shutdown due to accident
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Other B meson experiments
CLEO did much of the pioneering work. Stopped in
2001
BaBar forced to shut down for a year in
2004-2005 by DOE safety after accident
Though BELLE has larger datasets BaBar remains
competitive
BaBar will stop running in 2008. Hope for 1000
fb-1 at that time.
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The BaBar detector
Electromagnetic Calorimeter 6580 CsI crystals e
ID, p0 and ? reco
Instrumented Flux Return 19 layers of RPCs µ and
KL ID
Cherenkov Detector (DIRC) 144 quartz bars K, p, p
separation
3 GeV positrons
Drift Chamber 40 layers, tracking dE/dx
9 GeV electrons
Silicon Vertex Tracker 5 layers of
double-sided silicon strips
1.5 T magnet
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Radiative penguin decays of B mesons
CLEO Observation of B?K g 1993
BaBar B?K g 2006
First observation of penguins by CLEO. Now its
a background !
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Radiative penguin portrait
B? K? (K-Ksp) candidate
Muon from other B decay
Detached vertex from Ks ? pp
High energy photon in EMC
Note Event tends To be isotropic In center of
mass frame
p from K
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Continuum Backgrounds
Production of u,d,s,c quark and t pairs
underneath U(4s)
Lorentz boost makes a jet-like topology
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Event Shape Variables
Construct Shape variables to distinguish
between isotropy and jets
Neural net combination of suite of topology
variables effective with multicomponent background
cos ?T
Angle between thrust and photon
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Additional Continuum separation Variables
g
B
K
B
Net Flavor 0
DZvertex
Bs have lifetime and decay weakly. uds decays
promptly and strongly
Net Flavor (N(e) N(e-)) (N(m)-N(m-))
(N(k)-N(k-))
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Signal Variables for Exclusive Reconstruction
analyses
Beam Constrained Mass
Reconstructed Energy - beam Energy
Sensitivity can be enhanced by performing two
dimensional likelihood fits to signal and
background.
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A Colony of Penguins
r,w
dd (Vtd)
(Vts)
sd
K(892) K1(1270) K2(1430)
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The CKM matrix
leptons
quarks
Standard model explanation of CP violation is a
single phase in the CKM matrix V.
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The unitarity triangle
Photon spectrum in B-Xsg helps reduce error on
Vub
Photon spectrum in B-Xsg helps reduce error on
Vbc
Overconstraining the triangle may reveal new
sources of CP violation.
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Matter-Antimatter Asymmetry in Universe
CP violation is an essential component of the
presumed mechanism for generating this asymmetry
But The Standard model has insufficient CP
violation to account for the observed asym.
Presumably extra CP violation comes from new
physics that couples to quarks or leptons
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Measurement of b?d g Decays
B?rg
B0?r0g
signal bkgnd
bkgnd
signal
Mass projections from 4d fit 6.3 sigma
observation
BABAR, hep-ex/0607099, 347 M BB
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Comparison of b?d g Branching Fractions
CKM fitter includes CDF Bs mixing result. Error
on CKM Fitter prediction includes uncert. on B?Vg
form-factor ratio.
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Observation of b?d g and Measurement of Vtd/Vts
W annihilation diagram (small)
Ali, Lunghi, Parkhomenko, PLB 595, 323 (2004)
Ball and Zwicky, JHEP 0604, 046 (2006)
I-spin (r), quark model (w). Expect small I-spin
violation(1.1/-3.9).
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Extracting Vtd /Vts from b?d g Decays
Belle, PRL 96, 221601 (2006).
courtesy M. Bona (UTfit collab.)
BABAR, hep-ex/0607099 (preliminary)
CDF, hep-ex/0606027 (preliminary)
Consistent within errors.
Theoretical uncertainties limiting both
approaches.
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Inclusive Penguins G(B-Xsg)
Quark-hadron duality
The non-perturbative corrections are a few
percent.
Recently a new NNLO calculation for B(B-Xsg )
has been completed
(Misiak,Asatrian,Bieri,Czakon,Czarnecki,Ewerth,Fer
roglia,Gambino Gorbahn,Greub,Haisch,Hovhannisyan,H
urth,Mitov,Poghosyan,Slusarczyh)
Major undertaking involving thousands of
diagrams. New precise Calculation has renewed
interest in the field
Compare to NLO
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Theory Errors on B(B-Xsg)
Scale dependence on mb
Theory errors from choice of Renormalization
scales
LO
As go to higher orders this is reduced as
expected.
NLO
NLO
NNLO
Scale dependence on mc
mb (GeV)
NLO
At NLO the choice of charm quark renormalization
scale had been a Problem. New calculation
resolves this issue and errors are now understood
LO
NNLO
mc (GeV)
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Quark-Hadron duality
Hadrons
Quarks
B(b - sg) B(B - Xsg)
A fully inclusive measurement can be related
directly to quark calculation
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Inclusive Photon Spectrum
Confinement
To be fully inclusive must measure all the photon
spectrum
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Inclusive Photon Spectrum
FirstMoment
Second Moment
(Kinetic energy of b)2
Information about motion of b-quark should be
universal i.e like a structure function and so
can be applied to other inclusive processes
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Experimental Challenge
g Model Dependence
Monte Carlo Just require g

qq
BB
B - Xsg
Note additional BB background
To reduce large backgrounds without cutting on g
or Xs i.e a fully inclusive measurement
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Two Methods for inclusive B? Xs g
Differ in treatment of Xs
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Technique 1 Semi-Inclusive
g
Exclusively Reconstruct as many of the final
states of Xs as possible
Fundamental problem is that composition of final
states must be guessed - large systematic
Xs
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Missing Final States
Reconstructed Final States
K K, Ks
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Technique II Fully Inclusive B - Xsg
Suppress continuum background by requiring a
lepton tag from recoiling B
(5 Efficiency for x1200 reduction in
background)
BB
B-Xsg
Remaining continuum subtracted with off-resonance
data - statistical uncertainty
Multi-component BB background
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Fully Inclusive BB background
BB
B-Xsg
Each BB component measured independently in data.
Precision of these measurements is dominant
systematic.
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BABAR Fully Inclusive B? Xs g, w/lepton tag
(PRL Oct 23 2006)
Spectrum from best fit to kinetic scheme.
Spectrum from best fit to shape function scheme.
(measured)
(extrapolated, kinetic scheme)
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Summary of B? Xs g Branching Fraction
Measurements
Theory is NNLO prediction (2006)
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B(B-Xsg) constraints many models
Error x 10-4
World Av3.55-0.26 x 10-4
B(B-Xsg) x 10-4
Example Two Higgs doublet model MH300 GeV cf.
direct search 79.3 GeV
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Future Precision of B(B-Xsg)
Expect 5 precision from full dataset
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Direct CP asymmetry is sensitive to non MFV SUSY
Fully-Inclusive Lepton charge tags flavor.
Dilution from mixing.
Asymmetry consistent with Standard Model and
previous measurements
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Extracting Vbc and Vbu
Use inclusive measurements of lepton spectra Moti
on of b quark is dominant theoretical Uncertainty
Use B-Xsg to significantly increase precision
decay rate
El lepton energy
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Moments

• Fit predicted moments of inclusive processes
  b?clv and b?sg for various cuts on kinematic
  variables in HQE
• Calculations available in kinetic and 1S
  renormalization schemes
• 47 measured moments used from DELPHI, CLEO,
  BABAR, BELLE, CDF (and, of course, the B lifetime)

Matrix elements appearing at order 1/mb2 and 1/mb3
e or l energy cut
c-quark mass
b-quark mass
Benson, Bigi, Gambino, Mannel, Uraltsev(several
papers)
Bauer, Ligeti, Luke, Manohar, TrottPRD 70094017
(2004)
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Results Spectrum Moments vs Eg
most precise moments from BaBar fully inclusive
Curves are theory prediction using measured
b-Xclv moments
Demonstrates assertion that b quark motion is
universal
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Extraction of Vbc,mb,mp
b-sg
B-clv

• Vcb determined to

Buchmüller and Flächer,PRD 73 073008 (2006)
mb to 1 crucial for Vub
kin/1S values agree after scheme translation
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Extracting Vub
Inclusive B-Xuln
n
mb enters as mb5 so 1 error in mb gives 2.5
error in Vub
Other HQE parameters estimated from B-Xsg enter
into non-perturbative terms
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Vub from B-Xln
Error dominated by theory (mb and HQE parameter
estimation)
?2/dof 6.1/6
7.2 error down from 15 in 2003. 5 ultimately
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Current status of Unitarity Triangle
sin(2b) measured to 4.7 Vtd/Vts measured to
3.7 Vub/Vcb measured to 7.6
2-s bands
All constraints consistent with Standard model
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Summary
Large datasets have allowed us to catalog the
rare penguin decays Penguins contributing to
precision measurement of the triangle precision
measurements of b-sg strongly constrains new
physics
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Backup Slides
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Technique 1 Semi-Inclusive
Reconstruct in bins of MXs and convert to
Eg Multicomponent fit to extract
signal Dominant systematic is modelling missing
final states
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BABAR B? Xs g with Sum of Exclusive Final States
BABAR, PRD 72, 052004 (2005)
K(890)

• averages over two shape-function schemes
• errors stat, sys, variation of shape fcn params

K(890)

• Eg (min) 1.897 GeV

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Other Results on Fully inclusive B? Xs g
Belle, PRL 87, 061803 (2004), 140 fb-1 Belle,
hep-ex/0508005
CLEO, PRL 87, 215807 (2001), 9.1 fb-1
Measure for Eg2.0 extrap. to Eg0.25 GeV
Measure for Eg1.8 GeV extrap. to full
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Constraining SUSY
MH
tan(b)
Excludes MH coupling (4x range of direct searches)
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mb and mp from b-sg
Kinetic Scheme (Benson,Bigi and Uraltsev)
Fit to moments in kinetic scheme scheme to obtain
mp and mb Ellipse because of correlations
between first and second moments
Fermi -momentum
Fit includes theory errors
Mass of b quark (GeV)
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Results Moments
(kinetic energy of b)2
Theory is Bigi,Benson and Uraltsev (Nucl Phys B
710 371 2005) using BaBar measured B-Xcln
moments PRL 93 011803 2004
Curves are theory prediction using measured
b-Xclv moments
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b-sg and Vub
Vub is extracted from inclusive B-Xulv decays.
Photon spectrum from b-sg helps reduce the
uncertainty in determination.

• e.g. BaBar result PRL 96221801 (2006)

Fully reconstruct recoiling B and Study
semileptonic decay Mx in B-Xulv
Vub(4.43 0.38(stat.) 0.25(sys.)
0.29(theory) x 10-3