Measurements of Measurements of Radiative Penguin B Decays at Radiative Penguin B Decays at
BaBarBaBar
Jeffrey BerryhillUniversity of California, Santa Barbara
For the BaBar Collaboration
32nd International Conference on High Energy Physics
August 17, 2004
TM
All results preliminary unless explicitly indicated
ICHEP 17 Aug 04 Jeffrey Berryhill (UCSB) 2
Radiative Penguin Decays and New Radiative Penguin Decays and New PhysicsPhysics
Radiative penguin decays: b → s and b → d FCNC transitions
SM leading order = one EW loopVts, Vtd dependent
FCNCs probe a high virtual energy scale comparable to high-energy collidersRadiative FCNCs have precise SM predictions:
BF(b→s)TH = 3.57 ± 0.30 x 10-4 (SM NLO)BF(b→s)EXP = 3.54 ± 0.30 x 10-4 (HFAG)
Decay rate agreement highly constrains new physics at the electroweak scale!
Further tests presented here:•Exclusive b→s decay rates
•b→s CP asymmetries•b→d penguins
Multiple new BF(b→s)measurements coming soon from BaBar
ICHEP 17 Aug 04 Jeffrey Berryhill (UCSB) 3
Measuring Exclusive Radiative Penguin DecaysMeasuring Exclusive Radiative Penguin Decays
For signal, mES ≈ mB, mES) ≈ 3 MeV E* ≈ 0, (E*) ≈ 50 MeV
Small rates (BF < 10-4) on top of large backgrounds
Common strategy : select photon + hadrons with strict particle ID cut when possible on meson masses reduce continuum background with multivariate methods extract signal with multi-dimensional maximum likelihood fit
583±30 events
Ex: signal fit for B → K*0, K*0 → K+-Best kinematic constraintsfrom B candidate momentum and energy, compared with Ebeam:
* denotes CM frame
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BB KK* * Branching Fractions: Summary Branching Fractions: Summary
•BaBar preliminary measurements on 82 fb-1 •Becoming systematics limited•Exp. vs. theory: data more accurate than form factor predictions!
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Direct CP Asymmetry: b Direct CP Asymmetry: b →→ssandandBB KK* *
Sum of 12 exclusive,self-tagging B→Xs final states
Xs = K/Ks + 1-3 pionsE > 2.14 GeV
b→s b→s
b →s ACP = (N – N)/(N + N) = 0.025 ± 0.050 ± 0.015
B →K* ACP = -0.013 ± 0.036 ± 0.010 submitted to PRL, hep-ex/0407003
0- = (K*0 ) – (K*- ) = 0.050 ± 0.045 ± 0.028 ± 0.024 (K*0 ) + (K*- )
< 1% in the SM, could receive ~10% contributions from new EW physics Either inclusive or exclusive decays could reveal new physics
B or K charge tags the flavor of the b quark with ~1-2% asymmetry systematic
PRL 93 (2004) 021804, hep-ex/0403035
Asymmetries also measured precisely in exclusive K* decays:
preliminary
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bb ss Asymmetries: Summary Asymmetries: Summary
sgn0- = -sgn C7
Can we exclude C7 > 0 ?
•BaBar measurements on 82 fb-1
K*, K2* preliminary; Xs published
•CP asymmetries consistent with SM (0.4%) at the ~5% level•K* isospin asymmetry 0- consistent with C7 < 0•Statistics limited up to ~1 ab-1
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Time-Dependent CP Asymmetry inTime-Dependent CP Asymmetry in B B →→K*K*(113 (113 fbfb-1-1))
As in B0→J/ KS, interference between mixed andnon-mixed decay to same final state required for CPV.
In the SM, mixed decay to K* requires wrong photonhelicity, thus CPV is suppressed:
In SM: C = -ACP ≈ -1% S ≈ 2(ms/mb)sin 2 ≈ 4%
Measuring t of K*(→KS0) events requires novel beam-constrained vertexing techinque:
Vertex signal B with intersection of KS trajectory and beam-line
Usable resolution for KS decaying inside the silicon tracker
Validated with B0→J/ KS events
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First ever measurement of time-dependent CP asymmetries in radiative penguins!
Likelihood fit of three components(qq, BB, K*)to 5D data (mES,E,Fisher,mK*,t)
K* signal = 105 ± 14 events
S = +0.25 ± 0.63 ± 0.14
C = -0.57 ± 0.32 ± 0.09
submitted to PRL, hep-ex/0405082
Consistent with SM
For C fixed to 0, S = 0.25 ± 0.65 ± 0.14
preliminary
Time-Dependent CP Asymmetry inTime-Dependent CP Asymmetry in B B →→K*K*(113 (113 fbfb-1-1))
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Search for B Search for B → → (191 fb(191 fb-1-1))NEW!
Simplest and most “common” b → d exclusive decays are and B+ → → BF ≈ BF K* x |Vtd/Vts|2 ≈ 1.6 x 10-6
B0 → → BF ≈ ½ BF B0 → → BF ≈ ½ BF
Previous BaBar limit: BF < 1.9 x 10-6 90% CL (78 fb-1)Preliminary Belle evidence (3.5): BF = 1.8 ± 0.6 ± 0.1 x 10-6 (140 fb-1)
Comparable to rarest B decays measured!
Ratio of exclusive b → d and b → s decay rates measures |Vtd/Vts| via
Ali et al. hep-ph/0405075
R weak annhilation correction2 SU(3) symmetry breaking of exclusive form factors
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e+e- → qq continuum events arethe dominant background
Combine properties discriminatingB → + X from continuuminto a single-output neural net:
•Event shape variables: spherical B vs. jet-like continuum•B flavor tagging variables: kaons and leptons in the rest of the event•B candidate vertex separation fromrest of the event
Neural net trained on simulated signal and continuum samples
Continuum Background SuppressionContinuum Background Suppression
Neural net distribution for both signal and background described well by simulation
= 76%cut
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B Background SuppressionB Background Suppression
Large (40 x signal) K* backgroundreduced by strict + PID requirements(track dE/dx, DIRC c , DIRC N )
K+ misid 1-2% for most of acceptanceE provides additional separationof K* from
B decays to suppressed by cut on helicity angle
Combine helicity angle, B production angle,Dalitz angle ( only) into B Fisher discriminantfor additional background separation in signal fit
cut
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Validate fit procedure on data with K* sample (0 candidates withno PID requirement)
Unbinned extended MLfit of three background components(qq, Xs , and K* component
to 4D data (mES,E,NN,Fisher)
qq, Xs K* yield are free parameters
Large K* signal yield consistent with BaBar BF measurement
Signal Fit: K*Signal Fit: K* Control Sample Control Sample
background
K* + background
E shifted
preliminary
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Signal Fit: BSignal Fit: B++ → → ++
N(signal) = 26 ± 15 ± 2 significance = 1.9
= 13.2 ± 1.4 %
BF = (0.9 ± 0.6 ± 0.1) x10-6
BF < 1.8 x10-6 90% CL
Fit of four backgrounds(qq, Xs , +), K*)and + signal
qq, Xs , + yield are free parameters
+ + background
background
preliminary
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N(signal) = 0.3
significance = 0.0
= 15.8 ± 1.9 %
BF = (0.0 ± 0.2 ± 0.1) x10-6
BF < 0.4 x10-6 90% CL
Signal Fit: BSignal Fit: B00 → → 00
+7.2 +1.7
- 5.4 - 1.6
Fit of four backgrounds(qq, Xs , 0), K*)and 0 signal
qq, Xs , 0 yield are free parameters
preliminary
small peaking background
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N(signal) = 8.3
significance = 1.5
= 8.6 ± 0.9 %
BF = (0.5 ± 0.3 ± 0.1) x10-6
BF < 1.0 x10-6 90% CL
Signal Fit: BSignal Fit: B00 → →
+5.7 +1.3
- 4.5 – 1.9
Fit of two backgrounds(qq, ))and signal
qq, yield are free parameters
preliminary
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Simultaneous fit to all three samples with the constraint
Combined BF() ≡ BF(+) = 2(+/0) BF(0 ) = 2(+/0) BF( )
BF = (0.6 ± 0.3 ± 0.1) x10-6
significance = 2.1
BF < 1.2 x10-6 90% CL
Combined Fit: B Combined Fit: B → → , ,
preliminary
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bb dd Branching Fractions: Summary Branching Fractions: Summary
central value 90% C.L. upper limit
Comparison of measurements with predictions for individual modes and combined BF
Belle BF vs.BaBar BF2.0difference
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CKM matrix constraintCKM matrix constraint
BaBar BF ratio upper limit < 0.030 → |Vtd/Vts| < 0.19 (90% CL)
Penguins are starting toprovide meaningful CKMconstraint
95% C.L. allowed
(2,R) = (0.85,0.10)
Ali et al. hep-ph/0405075
no theory error
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CKM matrix constraintCKM matrix constraint
BaBar BF ratio upper limit < 0.030 → |Vtd/Vts| < 0.19 (90% CL)
SU(3) breaking of form factors 2= 0.85 ± 0.10
weak annhilation correction R = 0.1 ± 0.1
Penguins are starting toprovide meaningful CKMconstraint
Reduction of theory errorsnecessary to be competitive with Bd,Bs mixing
95% C.L. allowed (2,R) = (0.75,0.00) (2,R) = (0.85,0.10)
Ali et al. hep-ph/0405075
w/ theory errorno theory error
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SummarySummary
•Decay rate measurements of b→ s penguins are well into the precision era.
•CP asymmetries of b→ s penguins are statistics limited and will continue to test the SM
ACP in B → Xs PRL 93 (2004) 021804, hep-ex/0403035 BF, ACP, and Isospin asymmetry in B→ K*submitted to PRL, hep-ex/0407003time-dependent CPV in B0 → K*0 submitted to PRL, hep-ex/0405082
b→ d penguins are only now beginning to reveal themselves in B-factory data.They could also uncover new physics, or measure the poorly known |Vtd|.
BaBar finds no evidence for B → in 211 million BB events submitted to PRL, hep-ex/0408034
BF(B → ) < 1.2 X 10-6 |Vtd/Vts| < 0.19 (90% CL)
First measurement!
Backup SlidesBackup Slides
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B B → K*→ K*(82 fb(82 fb-1-1): Signal fits): Signal fits
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B B → K*→ K*(82 fb(82 fb-1-1): K*): K* lineshape lineshape
K* lineshape forevents with:mES > 5.27 GeV/c2
-0.2 GeV <E < 0.1 GeV
Background subtractedwith shape from mES
sideband
Fit to relativistic Breit-Wigner withPDG K*), mK*
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Time-Dependent CP Asymmetry inTime-Dependent CP Asymmetry in B B →→K*K*
Projection of fit with likelihood cut
Z resolution vs. KS decay radius
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B B → → Neural net performanceNeural net performance
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B B → → Control SampleControl Sample
, no PID , no PID