Measurements of Radiative Penguin B Decays at BaBar

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


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


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!


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


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


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


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))


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


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


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


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


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


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


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


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


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


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)


no theory error


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)


w/ theory errorno theory error


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

TM


B B → K*→ K*(82 fb(82 fb-1-1): Signal fits): Signal fits


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*


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


B B → → Neural net performanceNeural net performance


B B → → Control SampleControl Sample

, no PID , no PID

Documents

Measurements of Radiative Penguin B Decays at BaBar