measurements of the cp angle with the babar...

Princeton University, Department of PhysicsJadwin Hall, Washington Rd.

Princeton, NJ 08542-0708, U.S.A.

E-mail: [email protected]

XXXIII International Conference on High Energy PhysicsMoscow, Russia

Session 8: CP violation, Rare decays, CKMFriday, July 28, 2006, 10:06

Alexandre V. TelnovPrinceton University

for the BaBar Collaboration

Measurements of the CP angle Measurements of the CP angle αα

with the BaBar experimentwith the BaBar experiment

Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 2

Current BaBar dataset: 347 million BB pairs (±1.1%)_

Theoretical and experimental introduction to the CKM angle α

New BaBar results; their interpretation and implications for α :

B → π+π−, π±π0 , π0π0

B → ρ0ρ0, ρ±ρ0, ρ+ρ−

B0 → (ρπ)0

Summary and outlook

OutlineOutline


g

u

u

−− ρπ ,d

++ ρπ ,d

−W

0B d

b

Penguin

Measuring Measuring αα

ACP(t) in decay to a CP eigenstate at the tree level :duub →

Measure SM)(in arg 180 *

*

⎥⎦

⎤⎢⎣

⎡−≡=−−°

ubud

tbtd

VVVVαγβ

Penguins: ACP (t ) ⇒ sin(2αeff); αeff = α−∆α; direct ACP ≠ 0

0B ++ ρπ ,

−− ρπ ,

uud

d

−Wb

d

Tree


IsospinIsospin analysis in analysis in B B →→ ππππ , , ρρρρ

−+A2

1−+A~

21

00 ~ −+ = AA

00~A00A

α∆2

)(~)()(~)()(~)(

00

00

00000

00000

0

0

ππ

ππ

ππ

ππ

ππ

ππ

−−−

+++

−+−+

−+−+

→=

→=

→=

→=

→=

→=

BAA

BAABAA

BAABAA

BAA

In B → ρρ, there are 3 such relations (one for each polarization)

M. Gronau, D. London, Phys. Rev. Lett. 65, 3381 (1990)

PeTeA

PeTeAii

hh

iihh

βγ

βγ

+−

−+

+=

+=~

21)22sin( CS −∆+= αα

000

000

~~2

1~2

1

AAA

AAA

+=

+=

−+−

−++

)(~)( 00 hhBAhhBA −−++ →=→

Neglecting EW penguins, ±0 is a pure tree mode, and so the two triangles share a common side:

4-fold ambiguity in 2∆α : either triangle can flip up or down

6 unknowns, 6 observables in ππ (there is no vertex to measure Sπ0π0)5 observables in ρρ (or 7, when both Cρ0ρ0 and Sρ0ρ0 are measured)


TheThe BB00 →→ ππ++ππ−− analysisanalysisSimultaneous ML fit to B0 → π+π−, K+π−, π+K−, K+K−

Using DIRC Cherenkov angle to separate pions and kaonsAdditional ππ /Kπ /KK separation from ∆E

1.8 2.2 2.6 3.0 3.4 3.8 4.2

pLAB

0

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4

6

8

10

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DIR

C π

/K s

epar

atio

n, s

tand

ard

devi

atio

ns

Also measure AK+π− : see talk by Emanuele Di Marco at 12:12 today

DIRC: 144 quartz bars 0.84 x 4π coverage; 97% eff. @ 3 GeV/c

12σ π /K separation at 1.5 GeV/c, 2σ at 4.5 GeV/cCalibration sample: B− → π−D0, D0 → π+K−


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BABARPreliminary

New New BaBarBaBar results: results: BB00 →→ ππ++ππ−− (1)

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signalbackground

mES

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∆t ∆t

M. Pivk and F. R. Le Diberder, “sPlot: a statistical tool to unfold data distributions,”

Nucl. Instrum. Meth. A 555, 356 (2005) [arXiv:physics/0402083].

B0 tags

B0 tags_

asymmetry

BaBar-CONF-06/039

Nπ+π− = 675 ± 42

sPlot:Builds a histogram of x excluding it from the Maximum-Likelihood fit, assigning a weight to each event, keeping all signal events, getting rid of all background events, and keeping track of the statistical errors in each x bin


ππS-1 -0.5 0 0.5 1

ππC

-1

-0.5

0

0.5

1

CL=0.6827

CL=0.9545

CL=0.9973

CL=0.999937

BABARpreliminary

CL=0.9997

New New BaBarBaBar results: results: BB00 →→ ππ++ππ−− (2)

BaBar has observed a 3.63.6σσ evidence for CP violation in B0 → π+π−

SSππππ = = −−0.53 0.53 ±± 0.14 0.14 ±± 0.020.02

CCππππ = = −−0.16 0.16 ±± 0.11 0.11 ±± 0.030.03

(S,C) = (0.0, 0.0) is excluded at a confidence level of 0.99970 (3.6σ)

BaBar-CONF-06/039


TheThe B B →→ ππ±±ππ00, , ππ00 ππ00 analysisanalysis

Simultaneous fit to B0 → π+π0, K+π0 (using DIRC Cherenkov angle to separate pions and kaons)B0 → π0π0: branching fraction and time-integrated direct CP asymmetry

new: in addition to π0 → γγ, we use merged π0 and γ → e+e− conversions⇒ 10% efficiency increase per π0 (4% from merged π0 , 6% from γ conversions)

merged π0 :

the two photons are too close to one another in the EMC to be reconstructed individually; can be recovered using

,

where S is the second EMC moment of the merged π0 → γγ

The control sample: τ → ρν

)( 00022

γπππSSEM −≈

γ → e+e− conversions: result from interactions with detector elements

beam pipebeam pipebeam pipe

inner SVT layersinner SVT layersinner SVT layers DCH inner wallDCH inner wall

SVT outer layersSVT outer layers


New New BaBarBaBar results: results: B B →→ ππ±±ππ00, , ππ00 ππ00

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mES π0π0

Nπ0π0 = 140 ± 25Nπ±π0 = 572 ± 53

CCππ00ππ00 = = −−0.33 0.33 ±± 0.36 0.36 ±± 0.080.08

BrBrππ00ππ00 = = (1.48 (1.48 ±± 0.26 0.26 ±± 0.12) 0.12) ×× 1010−−66

BrBrππ±±ππ00 = = (5.12 (5.12 ±± 0.47 0.47 ±± 0.29) 0.29) ×× 1010−−66

B± → ρ±π0 background

BaBar-CONF-06/039

sPlot


Here is one of the possible solutions to the Gronau-London isospin triangle in B →ππ according to the

central values of the latest BaBar results:

An interpretation An interpretation of the new of the new B B →→ ππππ resultsresults

∆∆αα αα

This is a frequentist interpretation: we use only the B →ππ isospin-triangle relations in arriving at these constraints on ∆α = α − αeff

and on α itself

|∆α | < 41º at 90% C.L.

BaBar-CONF-06/039

α = 0 excluded at 1−C.L. = 4.4 × 10−5

α near 0 can be disfavored by additional experimental information


B B →→ ρρρρ angular analysisangular analysis

DSA32

31 :alLongitudin 0 +−=

PDSA

PDSA

21

61

31 :Transverse

21

61

31 :Transverse

1

1

−+=

++=

−

+

pure CP = +1

transverse is not a CP eigenstate

π 0

π +

ρ+

0π

θ 2

ρ_

_

π

θ 1

φ

“helicity frame”

B → ρρ is a vector-vector state; angular analysis is required to determine CP content:

Fortunately, the fraction fL of the helicity-zero state in B → ρρ decays is very close to 1:

Heavy Flavor Averaging Group, April 2006 update: http://www.slac.stanford.edu/xorg/hfag/rare/winter06/polar/index.html

fL(B0 → ρ+ρ−)WA= 0.967+0.023−0.028

fL(B± → ρ±ρ0)WA= 0.96 ± 0.06


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∆ΕmES ρ0f0

ρ0ρ0

New New BaBarBaBar results: results:

Incremental improvements in the event selection and the analysis techniqueResults are statistically consistent with the previous BaBar analyses

Nρ0ρ0 = 98+32 ± 22−31

Brρ0ρ0 = (1.16+0.37 ± 0.27) × 10−6−0.36 fL(B0 → ρ0ρ0)= 0.86+0.11 ± 0.05−0.13

3.03.0 σσ evidence forevidence for BB00 →→ ρρ00ρρ00

The systematic error is dominated by interference with B0 → a± (1260)πm and by PDF parameter uncertainties1

BaBar-CONF-06/027

hep-ex/0603050,accepted by PRLBr (B0 → a± (1260)πm ) × Br (a± (1260) → πm π± π± ) = (16.6 ± 1.9 ± 1.5) × 10−6

1 1

Br (B0 → ρ0f0 ) × Br ( f0 → π+ π−) < 0.68 × 10−6 (at 90% C.L.)

Br (B0 → f0 f0) × Br 2( f0 → π+ π−) < 0.33 × 10−6 (at 90% C.L.)Also measure:


New New BaBarBaBar results: results: BB±± →→ ρρ±±ρρ00

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Brρ±ρ0 = (16.8 ± 2.2 ± 2.3) × 10−6

The systematic error is dominated by modeling of backgrounds, signal misreconstruction, and by statistical PDF uncertainties

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Nρ±ρ0 = 390 ± 49 BABARpreliminary BABAR

preliminary

Based on 232 million BB pairs; BaBar-PUB-06/052 _

Phys. Rev. Lett. 91, 221801 (2003)Phys. Rev. Lett. 91, 171802 (2003)

PDG 2004: (26 ± 6) × 10−6

Belle: (31.7 ± 7.1+3.8) × 10−6

Previous BaBar : (22.5+5.7 ± 5.8 ) × 10−6−6.7

−5.4}

+0

00+−/√2“before”:

old ρ±ρ0 WA

isospin prediction

fL(B± → ρ±ρ0) = 0.905 ± 0.042+0.023−0.027

The new BaBar measurement in B± → ρ±ρ0 allows the ρρ isospin triangle to close


Br (B0 → a±ρm ) × Br (a± → π+ π−π± ) < 30 × 10−6 (90% C.L.)1 1

B0 tags

B0 tags_

asymmetry

∆t (ps)

New New BaBarBaBar results:results: BB00 →→ ρρ++ρρ−−

Nρ+ρ− = 615 ± 57

fL(B0 → ρ+ρ−) = 0.977 ± 0.024+0.015−0.013

Slong = −0.19 ± 0.21+0.05−0.07Br ρ+ρ− = (23.5 ± 2.2 ± 4.1) × 10−6

Clong = −0.07 ± 0.15 ± 0.06

dominated by self-crossfeed

distributions for the highest-purity tagged events

mES sum of backgrounds

∆Ε

mπ±π0ρ helicity

BaBar-CONF-06/016

BABARpreliminary

reduced systematics thanks to hep-ex/0605024,accepted by PRD


As datasets increase, determination of both C and S will become possible in B0 →ρ0ρ0, leading to an improvement in the precision of the the ρρ isospin analysis

BaBar-CONF-06/27, BaBar-CONF-06/016

An interpretation An interpretation of the new of the new B B →→ ρρρρ resultsresults

This is a frequentist interpretation: we use only the B →ρρ branching fractions, polarization fractions and isospin-triangle relations in

arriving at these constraints on ∆α = α − αeff and α

(deg)ρρα∆ -30 -20 -10 0 10 20 30

2χ

∆

0

5

10

15

20

25

∆∆αα

|∆α | < 21º at 90% C.L.

|∆α | < 18º at 68% C.L.

BABARpreliminary

(deg)α 0 20 40 60 80 100 120 140 160 180

1-C

.L.

0

0.2

0.4

0.6

0.8

1

αα

[74, 117]ºat 68.3% C.L.

BABARpreliminary

Due to the new B0 →ρ0ρ0 BF result, the constraint on α from B →ρρ has become less stringent


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BB00 →→ ((ρπρπ))00: : DalitzDalitz--plot analysisplot analysisBaBar-CONF-06/037 and references therein

0B

0B

−+πρ+−πρ

ρπ is not a CP eigenstateAn isospin-pentagon analysis method exists but is not fruitful

⇒ Time-dependent Dalitz-plot analysis assuming isospin symmetry,measuring 26 coefficients of the bilinear form factors

ρ0π0

ρ−π+

ρ+π−

The ρ(1450) and ρ(1700) resonances are also included in this analysis

Interference in the corners of the Dalitz plot provides information on strong phases between resonances

)(~)(~)(~)(~)()()()(

000

00

000

00

πρπρπρπππ

πρπρπρπππ

AfAfAfBA

AfAfAfBA

++=→

++=→+−

−−+

+−+

+−−

−++

−+

A. Snyder and H. Quinn, Phys. Rev. D, 48, 2139 (1993)

⊕ π0

π+

ρ−π−π− ρ0

π0

π+

Monte Carlo


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New New BaBarBaBar results: results: BB00 →→ ((ρπρπ))00 (1)

mES

∆t/σ(∆t)

BaBar-CONF-06/037

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m' θ'

data

projection of the fit result

signal misreconstructionexpected B backgroundcontinuum background

minimum of the three di-pion invariant masses


New New BaBarBaBar results: results: BB00 →→ ((ρπρπ))00 (2)

Sρπ = 0.01 ± 0.12 ± 0.028

Cρπ = 0.154 ± 0.090 ± 0.037

∆Sρπ = 0.06 ± 0.13 ± 0.029∆Cρπ = 0.377 ± 0.091 ± 0.021

parameters from the quasi-two-body description of B → ρπ :

a more physically intuitive way to represent direct-CP quantities:

Aρπ = −0.142 ± 0.041 ± 0.015

Aρπ = 0.03 ± 0.07 ± 0.03+−

Aρπ = −0.38+0.15 ± 0.07−0.16−+

BaBar-CONF-06/037

For results on Direct CP Violation, attend talk by Emanuele Di Marco at 12:12 today


An interpretation An interpretation of the new of the new BB00 →→ ((ρπρπ))00 resultsresults

0

0.25

0.5

0.75

1

-100 0 100

δ+- (deg)

C.L

.

B A B A RP R E L I M I N A R Y δδ++−−

[5, 63]ºat 68.3% C.L.

0

0.25

0.5

0.75

1

0 50 100 150

α (deg)

C.L

.

B A B A RP R E L I M I N A R Y

αα[75, 152]º

at 68.3% C.L.

no constraint at 2σ level

BaBar-CONF-06/037

δ+ − = arg(A+*A−) :the relative phase between the amplitudes of

B0 → ρ−π+ and B0 → ρ+π−

The constraint on α from B0 → (ρπ)0 is relatively weak – but free from ambiguities!


Recap of new resultsRecap of new results

Br (B0 → a± (1260)πm ) × Br (a± (1260) → πm π± π± ) = (16.6 ± 1.9 ± 1.5) × 10−61 1

Br (B0 → a±ρm ) × Br (a± → π+ π−π± ) < 30 × 10−6 (90% C.L.)1 1

Brρ0ρ0 = (1.16 +0.37 ± 0.27) × 10−6

First evidence, at 3.0σ−0.36 fL(B0 → ρ0ρ0)= 0.86+0.11 ± 0.05−0.13

Brρ±ρ0 = (16.8 ± 2.2 ± 2.3) × 10−6 fL(B± → ρ±ρ0) = 0.905 ± 0.042+0.023−0.027

Sππ = −0.53 ± 0.14 ± 0.02Cππ = −0.16 ± 0.11 ± 0.03

CP violation at 3.6σ

Brπ±π0 = (5.12 ± 0.47 ± 0.29) × 10−6

Brπ0π0 = (1.48 ± 0.26 ± 0.12) × 10−6

Cπ0π0 = −0.33 ± 0.36 ± 0.08

fL(B0 → ρ+ρ−) = 0.977 ± 0.024+0.015−0.013

Br ρ+ρ− = (23.5 ± 2.2 ± 4.1) × 10−6

BB00 →→ ((ρπρπ))00:: see page 18see page 18

Slong = −0.19 ± 0.21+0.05−0.07

ρρ

Clong = −0.07 ± 0.15 ± 0.06ρρ


(deg)α0 20 40 60 80 100 120 140 160 180

1 -

CL

(deg)α0 20 40 60 80 100 120 140 160 180

1 -

CL

CKM fit meas. in fitαno

BABARρ ρ →B π ρ →B

π π →B

Combined

0

0.2

0.4

0.6

0.8

1

ICHEP 2006

CKMf i t t e r

CKM fitno α in fit

169.7°

α ∈ [164, 176]º at 68.3% C.L.

Global fits for the value ofGlobal fits for the value of αα

CKMfitter Group (J. Charles et al.), Eur. Phys. J. C41, 1-131 (2005), [hep-ph/0406184], updated results and plots available at http://ckmfitter.in2p3.fr

M. Ciuchini, G. D'Agostini, E. Franco, V. Lubicz, G. Martinelli, F. Parodi, P. Roudeau, A. Stocchi, JHEP 0107 (2001) 013 [hep-ph/0012308],

updated results and plots available at http://utfit.roma1.infn.it

Please see talks by S. Please see talks by S. T'JampensT'Jampens ((CKMfitterCKMfitter) and V. ) and V. VagnoniVagnoni ((UTfitUTfit) for details) for details

97.5°

α ∈ [86, 114]ºat 68.3% C.L.

Two interpretations currently exist that convert the B → ππ, ρπ, ρρ measurements to constraints on α :

CKMfitter talk: 17:30 tomorrow UTfit talk: 17:48 tomorrow


Summary and outlookSummary and outlook

The ability of existing B-meson factories to measure the angle α with a precision

of a few degrees crucially depends on the developments in measuring the

branching fractions and CP parameters in B0 → ρ0ρ0 and B0 → π0π0

The BaBar experiment has observed evidence of

• Time-dependent CP violation in B0 → π+π−

• The decay process B0 → ρ0ρ0

and improved the precision of other measurements related to the extraction of α.

The extraction of α depends significantly on the statistical and theoretical treatment; The larger of the CKMfitter and UTfit 68.3% C.L. intervals is α ∈ [86, 114]º (CKMfitter)

measurements of the cp angle with the babar...

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