Lifetimes of B Mesons CP Violation, Mixing and BaBar ... · BaBar Measurements of CP Violation, Mixing and Lifetimes of B Mesons Sören Prell UC San Diego On Behalf of the BaBar Collaboration

BaBar Measurements of CP Violation, Mixing and Lifetimes of B Mesons

Sören PrellUC San Diego

On Behalf of the BaBar Collaboration

9th International Symposium on Heavy Flavor PhysicsSeptember 10-13, 2001

Caltech, Pasadena

Sept. 10, 2001 S. Prell - Heavy Flavor 9 2

CP violation arises from single phase in CKM matrix

Unitarity of V implies eg. VudV*ub + VcdV*

cb + VtdV*tb =0

� represented as ‘unitary triangle’ in complex plane

CP violation in the Standard Model

)(O

1A)i1(A

A211

)i(A211

VVVVVVVVV

V 4

23

22

32

tbtstd

cbcscd

ubusud

λλλλ++++

λλλλ−−−−ηηηη−−−−ρρρρ−−−−λλλλ

λλλλλλλλ−−−−λλλλ−−−−

ηηηη−−−−ρρρρλλλλλλλλλλλλ−−−−

====

====

CP asymmetries in B0 decays give information on angles α,α,α,α,

β,β,β,β,

γγγγ

!!!!


The Unitarity Triangle without CP Violation Measurements

ββββ

Method described in Höcker et al,

hep-ex/0104062

�Test SM by over-constraining Unitarity Triangle with measurements of sides and angles


0 0

0 0

( ( ) ) ( ( ) )( )

( ( ) ) ( ( ) )cos ( ) sin ( )

CP

CP CP

CP CPphys physf

CP CPphys phys

f d f d

B t f B t fA t

B t f B t fC m t S m t

Γ → −Γ →=

Γ → +Γ →= ∆ + ∆

Time-dependent CP asymmetry:

CP violation results from interference between decays with and without mixing

CP violation results from interference between decays with and without mixing

)f)t(B(obPr)f)t(B(obPr1 CP0physCP

0physfCP →≠→⇒±≠λ

= | | 2

CP

CP

CP

CP

ff

f

fCPλ

Aqλp A

ie

= ⋅

− ϕ��

2f

2f

f ||1

||1C

CP

CPCP λ+

λ−=

2f

ff ||1

Im2S

CP

CPCP λ+

λ−=

CP from Interference of Mixing and Decay

2~ ie− β

0B

0B

CPf

mixing

decay

CPfA

CPfA

decay


0 0, ,/ /

( ) sin 2 sin( )S L S L

dJ K J KA t m t

ψ ψη β= − ∆

0,/| | 1

S LJ Kψλ =Single weak phase = no direct CP

00

00

K/JBK/JB

ψ→ψ→

0 01

0 01

/

/CP S

LCP

B J K

B J K

ψ

ψ=−

=+

→

→0Kb

c

sc

d0B

ψ/J

d

K0 mixing

Theoretically clean way to measure sin2βClear experimental signatureRelatively large branching fraction

Golden Channel: B0 →→→→

J/ψψψψ

K0S

ηCP = -1 (+1) for J/ψ K0

S(L)


• 9 GeV e- on 3.1 GeV e+ :

• ΥΥΥΥ(4S) boost in lab frame : βγβγβγβγ = 0.56

-e e Y(4S) BB+ → →

PEP-II Asymmetric B Factory


SLAC B Factory Performance

PEP-II delivered : 46.3 fb-1

BABAR recorded : 43.8 fb-1 (incl.4.5 fb-1 off peak)

•PEP-II top luminosity: 3.9 x 1033cm-2s-1

(design 3.0 x 1033)

•Top recorded L/24h: 240 pb-1

•BABAR logging efficiency: > 96%

October 99 September 7, 2001

30/fb analysedfor CP


DIRC ((((PID)144 quartz bars

11000 PMs

1.5 T solenoidEMC

6580 CsI(Tl) crystals

Drift Chamber40 stereo layers

Instrumented Flux Returniron / RPCs (muon / neutral hadrons)

Silicon Vertex Tracker5 layers, double sided strips

e+ (3.1 GeV)

e- (9 GeV)

SVT: 97% efficiency, 15 µm z hit resolution (inner layers, perp. tracks)SVT+DCH:σ(pT)/pT = 0.13 % ×××× pT + 0.45 %, σ(z0) = 65 @ 1 GeV/c DIRC: K-π separation 4.2 σ @ 3.0 GeV/c � 2.5 σ @ 4.0 GeV/c EMC: σE/E = 2.3 %⋅E-1/4 ⊕⊕⊕⊕ 1.9 %

The BABAR Detector


Measurement Analysis Technique1. B±/B0 Lifetimes a. B reconstruction of

flavor eigenstates b. B vertexing

2. B0B0-Mixing c. Flavor tagging + a. + b.3. CP-Asymmetries d. B reconstruction of CP

• sin (2β) eigenstates + a. + b. + c.• sin (2α)

CP Analysis StrategyHig h er p re c isi on

I nc re a si ng c omp le x ity

Factorizing the Analysis�understand techniques where most sensitive


Measurement of B+ and B0 Lifetimes

z∆

−e

( )S4Υ

Brec

Tag B vertex reconstructionTag B vertex

reconstruction

K −

0Dπ +

+e

z

∆t ∆z / βγ c≈ < >

π −

Btag

Exclusive B Meson and Vertex ReconstructionExclusive B Meson and Vertex Reconstruction

1. Exclusive Brec reconstruction eg. B-��D0ππππ-

2. Brec vertex reconstruction3. Inclusive Btag vertex reconstruction4.4.4.4. ∆∆∆∆t computation and fit to ∆∆∆∆t spectra

((((βγβγβγβγ))))Υ(4Υ(4Υ(4Υ(4S)))) = 0.56


)2Beam-Energy Substituted Mass (MeV/c5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300

2Ev

ents

/ 1

MeV

/c

0

200

400

600

800

1000

1200

1400 BABAR


2Ev

ents

/ 1

MeV

/c

0

200

400

600

800

1000

1200

1400 BABAR

Neutral BMesons

Charged BMesons

%38purity 9400N 00 B/B

≈

%85purity 8500N

B/B≈−+

Samples of Fully-Reconstructed B Decays

� Cabibbo-favored hadronic decays“Open Charm” decays

� Charmonium Decays

ducb→

s)cc(b→0 *0/ ( )B J K Kψ π+ −→

Flavor eigenstates Bflav for lifetime and mixing measurements

0( )B D π− ∗ −→

/ , (2 )B J K S Kψ ψ+ + +→

[GeV]

30 fb-1

01

( )B D π /ρ /a +∗ − + +→

cm 2 cm 2ES beam Bm = (E ) - (p )


Vertex and ∆t Reconstruction• Reconstruct Brec vertex from

– charged Brec daughters (σz(BRec)=65 µm)• Determine BTag vertex

from – charged tracks not

belonging to Brec– Brec vertex and

momentum– beam spot and

Υ(4S) momentum

• High efficiency (97%) through inclusion of 1-prong tags• Average ∆t resolution is 180 µm (<|∆z|> = βγcτ = 260 µm)• ∆t resolution function measured from data (Bflav sample)

Beam spot

Interaction Point

BREC VertexBREC daughters

BREC direction

BTAG direction

TAG Vertex

TAG tracks, V0s

z


τB Measurement at BaBar∆∆∆∆t resolution

~e-||||∆∆∆∆t||||/ττττ

~e-t/ττττ

measured ∆∆∆∆ttrue ∆∆∆∆t

B production point known eg. from beam spot

Either Brecor Btag can decay first (this analysis)

Need to disentangle resolution function from physics !

Resolutionfunction lifetime

Resolution Function + Lifetime

=

=BaBar

LEP/SLD


∆t Signal Resolution

(1 ) ( , ) ( , ) ( , )

tail outlier core t core

tail tail t tail

outlier outlier outlier

R f f G Sf G S

f G

σ µσ µ

σ µ

∆

∆

= − −++

(1 ) ( , 0) ( , 0) exp( / ) ( , )

tail outlier t core

tail t bias

outlier outlier outlier

R f f G Sf G S t Sf G

σ µσ µ τσ µ

∆

∆

= − − =+ = ⊗ −∆+

high flexibility

small correlation with τ(τ(τ(τ(B)

σσσσ∆∆∆∆z

Signal MC (B0)

∆t (meas-true)/σ∆t

tracks from long-lived D’s

in tag vertex�asymmetric RF

• event-by-event σ(∆t) from vertex errors• Resolution Function (RF) – 2 models:

– Sum of 3 Gaussians (mixing + CP analyses)

– Lifetime-like bias (lifetime analysis)

~0.6 ps


• Simultaneous unbinned maximum likelihood fit to B0/B+ samples

• 19 free parameters– τ(B+) and τ(B0) 2– ∆t signal resolution 5– empirical background 12

description• Background parameters

determined from mES sideband

Lifetime Likelihood Fit


2Ev

ents

/ 1

MeV

/c

0

200

400

600

800

1000

1200

1400 BABARB0 mES

B0 Bkgd ∆∆∆∆t

∆∆∆∆t characteristics determined from data


Neutral and Charged B Lifetimes• Precision measurements:

B0/ B0

B±

∆∆∆∆t (ps)

τ0 = 1.546 ± 0.032 ± 0.022 ps

τ± = 1.673 ± 0.032 ± 0.022 ps

τ ± /τ 0 = 1.082 ± 0.026 ± 0.011

∆t RF parameterization, ∆t outlier description

Common resolution function for B+ and B0

20 fb-1

Submitted to PRL

•2 % statistical error•1.5 % systematic error

∆t distribution well described out to ±12 ps

bkgd

signal +bkgd


comparison of lifetime resultsComparison of Lifetime Ratio MeasurementsComparison of Lifetime Ratio Measurements

Single most precise measurement

Systematic error 1% in B+/B0

lifetime ratio


Measurement of B0B0 Mixing

0tagB

−e

( )S4Υ

0recB

−�

-KB-Flavor TaggingB-Flavor Tagging

+eCoherent BB production (p-wave)

z

∆t ∆z / βγ c≈ < >

K −

0D π +π −

π +z∆

•B0 reconstruction and ∆∆∆∆t measurement same as in lifetime analysis•flavor of Btag determines if Brec has mixed �� study ∆∆∆∆t spectra of unmixed and mixed events

Exclusive B Meson and Vertex ReconstructionExclusive B Meson and Vertex Reconstruction


Decay Time Difference (reco-tag) (ps)

UnMixedMixed

0

10

20

30

40

50

60

-8 -6 -4 -2 0 2 4 6 8Decay Time Difference (reco-tag) (ps)

UnMixedMixed

0

10

20

30

40

50

60

-8 -6 -4 -2 0 2 4 6 8

∆∆tt Distributions in Mixing Analysis Distributions in Mixing Analysis perfect

flavor tagging & time resolutionrealistic

mis-tagging & finite time resolution

( )( )0 0 0 0

0 0 0 0

1 1 2 cos( )4

unmixed

mixed

Bd

d

|∆ t |/τ

mixing, dB

tag tagmixing, flav flav

tag tagmixing, flav flav

ef (∆t) ω ∆m ∆t Rτ

"f " (B B or B B )

"f " (B B or B B )

−

±

+

−

= × ± − ⊗

⇔

⇔


b sc

e- , µµµµ-

K-

Hierarchical Tagging CategoriesHierarchical Tagging CategoriesLepton Charge of fastest electron (muon) with

p* > 1.0 (1.1) GeV/cKaon Net charge of identified kaons ≠ 0NT1 Neural Network discriminants which exploit informationNT2 carried by non-identified leptons and kaons, soft pions

from D*’s, etc

B Flavor Tagging

Lepton, Kaon tagging

NN tagging

No tagging information � not used !


35.1 ± 1.922.0 ± 2.117.6 ± 1.08.9 ±±±± 1.3

Wrong tag fraction w (%)

68.4 ±0.713.8 ±0.37.8 ±0.3

35.8 ±±±±0.510.9 ±0.3

Fraction of tagged events ε (%)

26.1 ±±±± 1.2ALL1.2 ± 0.3NT22.5 ± 0.4NT1

15.0 ± 0.9Kaon7.4 ± 0.5Lepton

Q = ε(1-2w)2 (%)Tagging category

Flavor Tagging PerformanceLarge Bflav sample of events fully reconstructed, vertexed and tagged on other side provide tagging performance measurement:

Quality factor Q: σσσσ(sin2ββββ) ∝ 1/√√√√Q


• Unbinned maximum likelihood fit to flavor-tagged B0 sample:

Mixing Likelihood Fit

τB = 1.548 ps fixed

∆md 1Mistag rates for B0 and B0 tags 8Signal resolution function 9Empirical description of background ∆t 16

34 free parameters total �� determine ∆∆∆∆t characteristics from data

0

01 cos( )4

B|∆t|/τ

Mixing,B

d∆mef (∆t) ∆tτ

� ��

�

��

��

��

�

−

± = × ± ⊗1-2w RMixing PDF

Fit Parameters


|∆t| (ps)

Asy

mm

etry BABAR

-1-0.8-0.6-0.4-0.2

00.20.40.60.8

1

0 2 4 6 8 10 12

dm/π ∆

~ 1 2 w−

∆∆∆∆md= 0.519 ± 0.020 (stat) ± 0.016 (syst) h ps-1 (Preliminary)

BABARUnmixed Events

Eve

nts/

0.4

ps

∆t (ps)

Mixed Events0

100

200

300

400

0

100

200

300

400

-10 -5 0 5 10

( )mixingunmixed mixed( ) 1 2 cos( )unmixed mixed d

N( ) N( )A t w ∆m ∆tN( ) N( )

−∆ = ≈ − ×+

Mixing with FlavorMixing with Flavor EigenstateEigenstate SampleSample

20 fb-1

C.L. 28 %


preliminarypreliminary

∆m Measurement in Comparison

• Precision ∆md measurement (4%) with Bflav sample statistically limited

• Systematic error under control (3%, dominated by MC correction) � can be reduced to ~2%

• theoretical hadr. uncertaintieshamper precise extraction of Vtd

222 2 2

022(

6ˆ/ ) ddd

Fd W B t W BBB td

Gm m S m m V Bm fηπ

∆ =

(PDG2000)

See Brandt’s talk at 4:00 pm

2 2(210 40 MeV)ˆdd

BBB f = ±


(CP eigenstates) sin 2ββββ

Measurement of sin2β

z∆

0tagB

−e

( )S4Υ

0recB

−�

-KB-Flavor Tagging

B-Flavor Tagging

Reconstruction of B decays to CP eigenstates

Reconstruction of B decays to CP eigenstates

+µ

−π0SK

ψ/J

+π

00CPrec BB ====

(flavor eigenstates) resolution, mistag rates00flavrec BB ====

+eCoherent BB production (p-wave)

z

∆t ∆z / βγ c≈ < >

µ−

Flavor tagging and ∆t reconstruction same as

for mixing analysis

1999-2001 data32 x 106 BB pairs, 29 fb-1 on peak


2Ev

ents

/ 2.

5 M

eV/c

0

5

10

15

20

25 BABAR


2Ev

ents

/ 2.

5 M

eV/c

0

2

4

6

8

10

12

14

16

18

20 BABAR


2Ev

ents

/ 2.

5 M

eV/c

0

5

10

15

20

25

30

35

40

BABAR


2Ev

ents

/ 2.

5 M

eV/c

0

5

10

15

20

25

30

35 BABAR


2Ev

ents

/ 2.

5 M

eV/c

0

20

40

60

80

100

120

140

160

180

BABARThe CP Sample

ψ(2S) KS χc1 KS

J/ψ K* J/ψ KL

J/ψ KSKS→π+ π-

J/ψ KSKS → π0 π0

Before tagging:

After tagging: 80%74%51%

96%

Purity

803Full CP samplemixed50J/ψ K*0(KSπ0)

+1273J/ψ KL

-1480[J/ψ, ψ(2S), χc1] KS

CPtagged events

Sample


Observable CP Asymmetry

(perfect experiment with sin2β = 0.6)

Different ∆∆∆∆t spectrum for

• B0 and B0

• positive and negative ∆∆∆∆t

Note: time-integrated asymmetry is 0

Visible asymmetry ACP

∆t spectrum of CP eigenstates

sin 2β

( ) sin(2 ) sin( )CP dA t ∆m ∆tβ∆ = ×


CP Analysis: ∆t Distributions

1 cos( )4Bd

d

|∆t|/τ

mixing, dB

ef (∆t) ∆m ∆tτ� ��

� ��

� ��

� � ��

�

�

−

± = × ± ⊗1-2ω R

00tag BB = 00

tag BB =

realistic mis-tagging & finite time resolution

00tag BB = 00

tag BB =

perfectflavor tagging & time resolution

Measure mis-taggingprobability w and ∆t resolution function Rwith flavor eigenstate sample �known mixing amplitude (=1) and large statistics

1 sin2 sin( )4Bd

d

|∆t|/τ

CP, f dB

ef (∆t) η β ∆m ∆tτ� ��

� �

� � � � � � ��

� � �

−

± = × ⊗1-2ω� R

Mixing PDF

CP PDF


• Global unbinned maximum likelihood fit to data:• Mistag rates,

∆∆∆∆t resolutions• sin(2β)

Fit Parameterssin2β 1Mistag rates for B0/B0 tags 8Signal resolution function 16Empirical description 20of background ∆t

45 free parameters total �� determine ∆∆∆∆t characteristics from data

sin(2β) Likelihood Fit

Separate ∆t resolutions for 2 data taking periods

τB = 1.548 ps and∆md = 0.472 ps-1 fixed

tagged flavor sample

tagged CP samples

Global correlation coefficient for sin(2β) ρ = 13%


sin2ββββ=0.56 ± 0.15sin2ββββ=0.59 ± 0.20

Kaon tags

(Q=15%)

( )( ) 1 2 sin(2 ) sin( )CP dA t w ∆m ∆tβ∆ ≈ − × × Raw AsymmetriesAll tags

Raw ACP

ηf = −1events


J/Ψ KL ∆t Distributions

sin2ββββ=0.70±0.34

Fit projections are from global fit to all CP samples

Raw ACP


sin2β Fit Results

Consistency of CP channels P(χχχχ2) = 8%

sin(2ββββ) = 0.59 ± 0.14

Cross-checks:Null result in flavor samples

Goodness-of-fit: P(Lmax>Lobs) > 27%

Phys. Rev. Lett. 87091801 (2001)

All modes


0

0.5

1

1.5

-5 0 5

B A B A R

∆t (ps)si

n2β

all CP modes

sin2β in various Sub-Samples

sin(2β) measured in several ∆t bins

sin(2β) vs. J/ψ decay mode and tagging category and flavor for

η = −1 events


Large sin2β in B0 � χC1KS

• fit for B0/B0 ∆t PDFs, not for ACP

• accommodate large asymmetry with negative signal PDF (at -(+)π/2∆mdfor B0(B0) tagged events)

• Possible , because – No events at these ∆t

(eg. lepton tags)– Sum of signal + background PDFs

positive (eg. Kaon tags)• Note: a single lepton B0-tag at ∆t =

-π/2∆m would bring sin2β from 2.6 to ~1/(1-2wlep) ≈ 1.1

• Measure sin2β unbiased for low stat. samples and probability to obtain sin2β�2.6 when true value 0.7 is 1-2%

Lepton tags Kaon tags

∆∆∆∆t [ps]

B0 tags

B0 tags

1 ± sin2 sin( )4CP,B|∆t|/τ

dB

f (∆t) e β ∆m ∆tτ� �

� ��

� �

±

−×= 1-2ω


Run1�Run2 Changes/Results

• First publication in March 2001

• Changes since then:– More data (run 2): 23 ��32 BB pairs– Improved reconstruction efficiency– Optimized selection criteria takes into

account CP asymmetry of background in J/ψKL– Additional decay modes χC1KS and J/ψK*0

– Improved vertex resolution for reconstructed and tag B

sin(2β) = 0.34 ± 0.20 ± 0.05 PRL 86 (2001) 2515


Run 1 / Run 2 ResultsRun 1 Run 2

Difference for PRLmodes: 1.8 σσσσ

sin2β

Average 0.45±0.18

JΨKs 0.23±0.24

J/ΨKs2π0 0.13±0.65

Ψ(2S)Ks 0.40±0.49

χcKs 3.20+0.43.20 -0.7

J/ΨK*0 1.26±1.22

J/ΨKL 0.71±0.42

PRL modes 0.32±0.18

-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5

sin2β

Average 0.82±0.22

JΨKs 0.72±0.27

J/ΨKs2π0 1.62±0.74

Ψ(2S)Ks 1.85±1.21

χcKs 1.14±1.25

J/ΨK*0 0.15±1.62

J/ΨKL 0.68±0.58

PRL modes 0.83±0.23

-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5


Systematic Errors

• Signal resolution and vertex reconstruction 0.03– Resolution model, outliers, SVT residual misalignment

• Tagging 0.03– possible differences between BCP and Bflavor samples

• Backgrounds 0.02 (overall)– Signal probability, peaking background, CP content of

background– Total 0.09 for J/Ψ KL channel; 0.11 for J/Ψ K*0

• Total = 0.05 for total sample

0.161.01

K*0

0.050.14

Total

0.100.34

KL

0.05Systematic0.15Statistic

KSError


Interpretation of the Results

Method as in Höcker et al, hepex/0104062(also other recent global CKM matrix analyses)

BaBar sin2ββββ

(with 30/fb)

Error on sin2β is dominatedby statistics � will decrease~1/√Luminosity

One solution for β

is consistent with measurements of sides of Unitarity

Triangle


Search for Direct CP

Probing new physics (only use ηCP=-1 sample that contains no CP background)

|λ| = 0.93 ± 0.09 (stat.) ± 0.03 (syst.)

No evidence of direct CP violation due to decay amplitude interference (coefficient of the “sine” term unchanged)

2f

2f

f ||1

||1C

CP

CPCP λ+

λ−=

2f

ff ||1

Im2S

CP

CPCP λ+

λ−=

tmStmCA dfdfCP CPCP∆∆+∆∆= sincos

If at least 2 amplitudes with a weak phase difference contribute

|λ| might be different from 1(tree amplitude and leading penguin amplitude for B� J/ψ KS have same weak phase in SM)


u

u

d

bd

ub

u

| λλλλ | ≠≠≠≠ 1 ⇒⇒⇒⇒ must fit for direct CPIm (λλλλ) ≠≠≠≠ sin2αααα ⇒⇒⇒⇒ need to relate asymmetry to αααα

/( ) [1 sin( ) cos( )]4t

d def t S m t C m tτ

ππ ππτ−∆

± ∆ = ± ∆ ∆ ∆ ∆∓

Decay distributions f+(f-) when tag = B0(B0)

Cππππππππ ====

0, Sππππππππ = sin2αααα

αγ+β− η=η=≡λ i2f

)(i2f

f

f eeAA

pq

Cππππππππ ≠≠≠≠ 0, Sππππππππ = sin2ααααeff

Weak phase (only tree diagram) Additional phase from penguin diagram

penguin diagramtree diagramCP Violation in B0 → ππππ++++ππππ−−−− Decays


mES (NT2)

0

20

40

60

5.2 5.225 5.25 5.275 5.3

BABAR

GeV/c2

Can

dida

tes p

er 2

.0 M

eV/c2

mES (Kaon)

0

20

40

60

80

5.2 5.225 5.25 5.275 5.3

BABAR

GeV/c2

Can

dida

tes p

er 2

.0 M

eV/c2

mES (NT1)

0

10

20

30

5.2 5.225 5.25 5.275 5.3

BABAR

GeV/c2

Can

dida

tes p

er 2

.0 M

eV/c2

mES (Lepton)

0

5

10

15

20

5.2 5.225 5.25 5.275 5.3

BABAR

GeV/c2

Can

dida

tes p

er 2

.0 M

eV/c2

Lepton

Kaon

NT1 NT2

Likelihood Analyis with high reconstruction efficiency:Loose selection criteria yield 9741 two-prong candidates in 30.4 fb-1

(includes 97% background,almost entirely from continuum)

sum of π+π-/K+π- mESdistributions by tagging category (particle ID used in likelihood fit for ππ/Kπseparation)

B�π+π−,K+π−,K+K− Data Sample


Β � π+π−/K+π− Likelihood Fit• Simultaneous extended ML fit to the BRs and CP

asymmetries:– 8 event types (Sig and Bkg: π+π- , K+π− , K-π+ , K+K-

� measure also direct CP violation in charge asymmetry

– Discriminating variables (mES, ∆E , Fisher, Cherenkov angles, ∆t)

– Mistag rates and ∆t signal resolution function same as in sin2β fit (uses also untagged events to improve BR measurements)

– ∆md, B0 lifetime fixed – Empirical background parameters determined from mES

sidebandsFor BR measurementssee Dallapiccola’s talk

tomorrow

A = N(K-ππππ+)-N(K+ππππ−−−−)/N(K-ππππ+)+N(K+ππππ−−−−)


mES

π+π-

(GeV/c2)Ev

ents

/2 M

eV/c

2

mES

BABA R

∆E

π+π-

(GeV)

Even

ts/2

0 M

eV

∆E

BABAR

mES

K+π-

(GeV/c2)

Even

ts/2

MeV

/c2

mES

BABA R

∆E

K+π-

(GeV)Ev

ents

/20

MeV

∆E

BABAR

0

5

10

15

5.2 5 .30

5

10

15

-0.1 0 0.1

0

20

40

60

5.2 5 .30

20

40

60

-0.1 0 0.1

L = 30.4 fb-1

Total Yields:

3.63.4

1211

3.4 KK18217K

65

±±±±

±±±±ππππ

±±±±ππππππππ

−−−−++++

−−−−++++

−−−−++++

Events after likelihood ratio cuts

20 ππππππππ1 Kπ

23 ππππππππ2 Kπ

126 Kππππ3 ππ139 Kππππ

3 ππ

CP Sample: π+π−/K+π− Candidates


B0 � π+π− Asymmetry Result

• Measurement compatible with no CP in B0 � π+π−

• Statistically limited due to small branching fraction

• Need ~500/fb for σ(Sππ) ~ 0.10-0.15

PreliminaryPreliminary0.530.560.450.47

( ) 0.03 ( ) 0.11 ( )

( ) 0.25 ( ) 0.14 ( )

( ) 0.07 0.08 ( ) 0.02 ( )CP

S stat syst

C stat syst

A K stat syst

π π

π π

π

+ − +−

+ − +−

±

= ±

= − ±

= − ± ±∓


Summary and Outlook• New precision measurements of B0/B+ lifetimes and

B0B0 mixing frequency ∆md

• Measurement of flavor-tagged, time-dependent B decays at asymmetric B factory has become established technique

• BaBar observes CP violation in the B0 system at 4σ level

– Probability is < 3 x 10-5 to observe an equal or larger value if no CP violation exists

– Corresponding probability for only the ηCP = -1 modes is 2 x 10-4

sin(2ββββ) = 0.59 ± 0.14 ± 0.05

τ0 = 1.546 ± 0.032 ± 0.022 psτ± = 1.673 ± 0.032 ± 0.022 ps

τ0 /τ± = 1.082 ± 0.026 ± 0.011∆md = 0.519 ± 0.020 ± 0.016 h ps-1


Summary and Outlook (cont.)• First measurement of time-dependent CP asymmetry in

rare B decay mode B � π+π−

• The study of CP violation in the B system has started:– sin(2β) will very soon become precision measurement (� unitarity

triangle constraints will be limited by other CKM parameters) – Need to compare sin(2β) from different decay modes to test

standard model• With anticipated 100 fb-1 by next summer, error in

sin(2β) will be 0.08 and for the asymmetry in B � π+π−

error will be ~0.3

0.530.56

0.450.47

( ) 0.03 ( ) 0.11( )

( ) 0.25 ( ) 0.14( )

S stat systC stat syst

π ππ π

+ − +−

+ − +−

= ±

= − ±

Documents

Lifetimes of B Mesons CP Violation, Mixing and BaBar ... · BaBar Measurements of CP Violation, Mixing and Lifetimes of B Mesons Sören Prell UC San Diego On Behalf of the BaBar Collaboration