11 th July 2003Daniel Bowerman1 2-Body Charmless B-Decays at B A B AR and BELLE Physics at LHC...

11th July 2003 Daniel Bowerman 1

2-Body Charmless B-Decays at BABAR and BELLE

Physics at LHC Prague

Daniel Bowerman Imperial College

11th July 2003


Overview

• Measuring sin2α (sin2φ2) through B ππ

• General analyses overview

• CP results from B π+π- , B K+π-

– How compatible are Belle and BaBar?

• Isospin analyses: Adding in B+ π+π0 and B π0π0

• Results overview and prospects

• What does this mean for LHCb?


Measuring CP Asymmetries• Three observable interference effects:

– CP violation in mixing (|q/p| ≠ 1)

– (direct) CP violation in decay (|A/A| ≠ 1)

– (indirect) CP violation in mixing and decay (Im ≠ 0)CP

CP

CP

ff

f

Aqλ

p A

Observable in time evolution of BB system (assume )

CP

CP

ff 2

f

2Im λ

1 | λ |S

direct CP violation C ≠ 0

indirect CP violation → S ≠ 0

)cos()sin(1),(

)cos()sin(1),(

4

0

40

tmCtmSetfBf

tmCtmSetfBf

dfdft

CPphys

dfdft

CPphys

CPCP

CPCP

0B

0B

CPf

)cos()sin()(

00

00

tmCtmSBNBN

BNBNtA dfdf

tagtag

tagtag

-Af =


Measuring α with B ππ

)2sin(1

)sin(

eff2

/1

/12

CS

C

e ii

ii

eeTP

eeTPi

With Penguins (P):

mixing

*

*

ubud

ubud

VV

VV

*

*

tdtb

tdtb

VV

VV

decay

Tree (T) Level:

)2sin(

0

2

S

C

e i

Need branching fractions for , , and to get from eff : isospin analysis

e-i2β e-i2γ sin(2(π-β-γ))


αeff α :Isospin Analysis• The decays B, , are related by isospin

• Central observation is that states can have I = 2 or 0– (gluonic) penguins only contribute to I = 0 I = 1/2)

– is pure I = 2 I = 3/2) so has only tree amplitude

(|AA)

• Triangle relations allow determination of penguin-induced shift in

22 eff

Gronau and London, Phys. Rev. Lett. 65, 3381 (1991)

Need branching fractions for all three decay modes, and for B0 and B0 separately,

even for π0π0


Analysis Overview for B ππ• Analysis issues: charmless B decays

– Low branching ratios - BR ~ 10-10

– Backgrounds:• Large background from ee qq need background suppression• Modes with suffer backgrounds from other B decays

– Ambiguity between and K - need excellent particle ID

• Time-dependent CP analysis issues:– Need to determine vertex position of both B mesons – Need to know the flavor of “other” B - particle ID

• Use maximum likelihood (ML) fits to extract signal yields and CP-violating asymmetries

– Use as much information as possible

• The data sample corresponds to

– 88 million BB pairs (BaBar) – 85 million BB pairs (Belle)


Analysis Procedure B ππ• Kinematically select B candidates with mES, E

• Suppress/separate qq background with Event-Shape discriminant• Linear Fisher (BaBar), Likelihood selector (Belle)

2*2beamES

*BpEm *

beam* EEE B

•BaBar

–Loose cut on event shape |cos(S)|

–Fit for ππ, Kπ, and KK using mES, E, Fisher, C

–Add tagging and t, fit for S and C

•Belle

–Optimize cut on event-shape

–Select pions

–Cut ~3 in mES and E

–Fit S and C using mES, E, and t


Branching Fraction Results

Projections in E

Mode

Belle BaBar

Yield BR (10-6) ACP(K) Yield BR (10-6) ACP(K)

B→ 133 ± 19 4.4 ± 0.6 ± 0.3 157 ±19 4.7 ± 0.6 ± 0.2

B→ K 596 ± 33 18.5 ± 1.0 ± 0.7 -0.07 ± 0.06 ± 0.01 589 ± 30 17.9 ± 0.9 ± 0.7 -0.10 ± 0.05 ± 0.02

B→ KK-1 ± 7 < 0.7 (90%) CL 1 ± 8 <0.6 (90%) CL

BELLE

•Branching fractions are consistent

•2σ direct CP effect in K

ACP(K)BR (10-6)YieldACP(K)BR (10-6)Yield

<0.6 (90%) CL1 ± 8< 0.7 (90%) CL-1 ± 7B? KK

-0.10 ± 0.05 ± 0.0217.9 ± 0.9 ± 0.7589 ± 30-0.07 ± 0.06 ± 0.0118.5 ± 1.0 ± 0.7596 ± 33B? K

4.7 ± 0.6 ± 0.2157 ±194.4 ± 0.6 ± 0.3133 ± 19B?

BaBarBelle

Mode ACP(K)BR (10-6)YieldACP(K)BR (10-6)Yield

<0.6 (90%) CL1 ± 8< 0.7 (90%) CL-1 ± 7B? KK

-0.10 ± 0.05 ± 0.0217.9 ± 0.9 ± 0.7589 ± 30-0.07 ± 0.06 ± 0.0118.5 ± 1.0 ± 0.7596 ± 33B? K

4.7 ± 0.6 ± 0.2157 ±194.4 ± 0.6 ± 0.3133 ± 19B?

BaBarBelle


<0.6 (90%) CL1 ± 8< 0.7 (90%) CL-1 ± 7B? KK

-0.10 ± 0.05 ± 0.0217.9 ± 0.9 ± 0.7589 ± 30-0.07 ± 0.06 ± 0.0118.5 ± 1.0 ± 0.7596 ± 33B? K

4.7 ± 0.6 ± 0.2157 ±194.4 ± 0.6 ± 0.3133 ± 19B?

BaBarBelle


<0.6 (90%) CL1 ± 8< 0.7 (90%) CL-1 ± 7B? KK

-0.10 ± 0.05 ± 0.0217.9 ± 0.9 ± 0.7589 ± 30-0.07 ± 0.06 ± 0.0118.5 ± 1.0 ± 0.7596 ± 33B? K

4.7 ± 0.6 ± 0.2157 ±194.4 ± 0.6 ± 0.3133 ± 19B?

BaBarBelle

Mode


Reconstructed Vertex and Flavour taggingExclusive Brec reconsctuction

Beam spot

Interaction Point

BREC Vertex

BREC daughters

BTAG direction

TAG tracks, V0s

zBTAG Vertex Example in B →

B →

ee→ qq

• z resolution dominated by tag side

•Same resolution function as charmonium (sin2) sample

•Resolution functions determined in data

c

zt

1

•Same Tagging algorithms as with sin2 analysis

•Primarily use Lepton and Kaon tags, and more complex NN based approach

•Event shape and Δt resolution functions are dependent on tagging category


qq + K

Time Dependent CP Results

(syst) (stat) 41.023.1

(syst) 08.0 stat)( 27.077.008.007.0

S

C

(syst) 0.05 (stat) 34.002.0

(syst) 04.0 stat)( 25.030.0

S

C

)2sin( SWith no penguins expect: 0C

BaBar Belle


Time Dependent CP ResultsVery crudely put both asymmetries on the same scale

BaBar Belle

Highlights how different the measurements are!


Compatibility of the CP results

S C

Belle inconsistent with (C=S=0) at 99.93% C.L.

BaBar is still consistent with C=S=0


Compatibility of the CP results•Belle results and contour plot

•Note the y-axis scale change (-C = A)

•Physical boundary at C2 + S2 = 1

• Inconsistent with (C = S = 0) at the 99.93% CL (3.4)

•BaBar and Belle are compatible at the 2-2.5 level

-Cππ

Belle Result

BaBar Result


Completing the Triangle: B+ π+π0

BaBar

Belle

3-body feedthrough

MESΔE

72.4 ± 17.4

(4.5σ)

125 ± 22

(7.7σ)

No direct CP violation seen here!


Completing the Triangle: B π0π0

N=12 ± 9

(1.9σ)

BaBar

Belle

MES ΔE

N=23 ± 10

(2.5σ)

Most challenging of the modes – lower efficiency, poor resolutions, 3-body background, correlations

•Hints of a signal at :

BR(B π0π0 ) ~ 1.7 * 10-6

•At the very top end of expectations•Have to measure both B0 and B0 rates•Would have big impact on measuring α


Summary of the results

Branching ratio’s show that Penguin contribution is not negligible!


B ππ conclusions

Belle BaBar

Currently an Isospin analysis provides no new information


The need for an Isopsin Analysis

If the Branching fraction for B π0π0 holds up -

Isospin analysis is necessary!

• Can still get information on with only an upper bound on :– For example: Grossman-Quinn bound (assume only isospin)

C.L. %[email protected]

)(

)()(21

)(sin0

000000

eff2

BBR

BBRBBR

C.L. %90@51eff

BaBar


Prospects at the B-factories

•Belle collecting average 450pb-1/day, BaBar collecting 300pb-1/day•Next set of results should fully test B ππ compatibility•Both experiments expect ~500fb-1 by 2006•May go much higher with ‘Super’ B-factories•What does this mean for α through B ππ ?

Belle BaBar


Prospects at the B-factories•Isospin Analysis •Using present BaBar branching fractions extrapolated to 500fb-1

Need much more data!


Prospects for B-factories and LHC

If the branching ratio for B π0π0 holds at (~1.7 *10-6) then:

•

• Will need an Isospin analysis to extract α

• Probably not possible at LHC

• Only possible at Super B-factory (maybe)

We should hope that

• B π0π0 disappears!

• That α through ρπ is feasible at the LHC

20eff

Still much to be learnt from the 2-body modes!• Perhaps measure γ through Kπ• Direct CP violation in Kπ


Conclusions•2-body results have provided many highlights for the B-factory programmes•Belle results are inconsistent with C = S = 0 in B ππ at the 3.4σ level•BaBar and Belle results disagree at the 2σ level•Results indicate large Penguin contributions•B π0π0 results indicate that Isospin analysis will be necessary - but very difficult at B-factories•Probably not possible to measure α through B ππ at LHC (hopefully through ρπ)Thanks to Jim Olsen, Belle and Babar 2-body groups and the

CKM fitters : http://ckmfitter.in2p3.fr


Back up Slides


CP Violation in the SM

)(O

1A)i1(A

A21

1

)i(A21

1

VVV

VVV

VVV

V 4

23

22

32

tbtstd

cbcscd

ubusud

CP violation arises in Standard Model through a single phase in the CKM matrix

0VVVVVV *tbtd

*cbcd

*ubud

CP violating asymmetries A(t) in B0 decays measure

Unitarity of V requires e.g.Can be represented as “unitarity” triangle in the complex plane


CP violation in the SM

World Average sin2 = 0.734 0.055

http://ckmfitter.in2p3.fr


BaBar and Belle crosschecksBoth BaBar and Belle have undertaken many cross-checks:Fitting sideband and B→ KsamplesLifetime and mixing validation with B→ K sampleMore stringent cuts to select signal eventsRepeat analysis on previous published data samplesToy MC validation of errors

Belle

Interesting one event effect in Belle dataset, but overall things seem fine

BaBar


Conclusions: Penguins

• Use data– P from K0+

– Two-body BFs

– S and C

– CKM indirect constraint on

• BaBar prefers:– 0.1 < |P/T| < 0.4

– -170 < arg(P/T) < -40

• Belle prefers:– 0.5 < |P/T| < 1.1

– -70 < arg(P/T) < -30

P/T

Arg

(P/T)

Arg

(P/T)

BELLE

BABAR

P/T

Constraints on P/T

Penguins not negligible!

11 th July 2003Daniel Bowerman1 2-Body Charmless B-Decays at B A B AR and BELLE Physics at LHC...

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