Measurements of sin2 a from B-Factories

Measurements of sin2from B-Factories

Masahiro MoriiHarvard University

The BABAR Collaboration

BEACH 2002, Vancouver, June 25-29, 2002

BEACH 2002, May 25-29, 2002 M. Morii, Harvard University 2

Introduction CP violation in B0 decays gives access to the angles

of the Unitarity Triangle

sin2 measured to ±0.08 dominated by B0 J/KS

Where does this leave us?

*

2 *

*

1 *

*

3 *

arg

arg

arg

td tb

ud ub

cd cb

td tb

ud ub

cd cb

V VV V

V VV V

V VV V

1

See D. Marlow’s talk


Unitarity Triangle and sin2 Measured sin2 agrees with indirect constraints

Shrinking (sin2) alonemay not reveal new physics

Must measure the sidesand the other angles

*

*ud ub

cd cb

V VV V

*

*td tb

cd cb

V VV V

Next possibility at the B Factories?


Measuring sin2 Time-dependent CP asymmetry in B0 fCP is

0 0

0 0

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

( ( ) ) ( ( ) ) CP CP

phys CP phys CPf d f d

phys CP phys CP

B t f B t fS m t C m t

B t f B t f

2

2 2

12Im1 1

CP

CP CP

CP

ff f

f

AqS Cp A

CKM phase appears here

b cc

s

W

cbVb u

u

d

W

ubV

0SB J K 0B

sin 2 sin 2

Easy!


Penguin Pollution Unlike J/ KS, mode suffers from significant

pollution from the penguin diagrams with a different weak phase

To estimate eff – , we need: P/T ratio – about 1/3 from BR(B K)/BR(B ) = strong phase difference between P and T

b uu

d

W

ubV

effsin 2b u

u

d

W

T = Tree P = Penguin

gtbV *

tdV


Mode BABAR BR106

Belle BR106

0

0 1.11.0

0 0 0

2 0 2 5.4 0.7 0.5 5.1 1.1 0.41 1 0 4.1 0.8 7.0 2.2 0.80 1 1 3.3 5.6

T C P

BBB

Taming Penguins Take advantage of the isospin symmetry

T C PT C P A

b uu

d

ddb u

u

d

dd

b u

u

d

dd

All preliminary


B0 00 Branching Ratio BABAR: Preliminary 54 fb-1

BR(00) < 3.3×10–6 (90% CL) Belle: Preliminary 31.7 M BB

2.2“bump” in the signal Fitted BR= (2.9 ± 1.5 ± 0.6)×10–6 BR(00) < 5.6×10–6 (90% CL)

CLEO: 9.13 fb-1

BR(00) < 5.7×10–6 (90% CL)

BELLE

Expect first observation in the near future


0 0

0 0

( ) ( )sin( ) cos( )

( ) ( )tag tag

d dtag tag

N B N BS m t C m t

N B N B

z c t

CP Asymmetry in B0

Same method as sin2 measurements Difference: the direct CP term cannot be neglected

9 GeV3.1 GeV4S

Btag

BCP

Tagusing l±, K±

Moving with = 0.55

e e

0 0orB B

CP final

state

# of events with 0 0 tagB B


Challenges Specific to B0 +

Topology B0 hh simple to reconstruct Particle ID must separate ± from K±

DIRC (BABAR) and Aerogel (Belle) Significant background from continuum

Event-shape variables Fisher discriminant Common with other CP measurements

Flavor tagging Vertex reconstruction

And, of course, as much as possibledtL

( ) ( )BR BR K


B0 Reconstruction

mbc (or mES) and E peak cleanly for the two-body signal K and KK peaks shifted in E Additional discrimination

2 2ES bm E p

CME E E

bE

MC

off-resonance data

MC

MC

BELLE BELLE

2 2( 2) ( )bc CMm E p p 2CME E E E


Whole event is jettyThe other B decays spherically

Continuum Background Most of the background come from continuum

Use event shape variables that represent “jettiness” to suppress them

Signal udsc background

Examples


Sphericity Angle Angle S between the sphericity axes of the B candidate and

the rest of the event

Cut at 0.8 removes 83% ofthe continuum background

SBABAR

MC

cos S

background

0.8

reject


Fisher Discriminant BABAR uses the “CLEO” Fisher

Momentum flow in 9 cones around the candidate axis

Output of Fisher goes into the likelihood fit

MC

D0data

Bkg MC

mES sideband data


Bkg MC

off-res. data

Fisher Discriminant Belle’s Fisher discriminant uses:

Modified Fox-Wolfram moments B flight direction

Output is turned intoa likelihood ratio R Cut at 0.825 removes

95% of continuumbackground

MC

D0data

reject


Event Sample – BABAR BABAR 55.6 fb-1 preliminary

enhanced for these plots with a cut on Fisher

Kcontinuum

16 715 9( ) 124N


Event Sample – Belle Belle 41.8 fb-1

K

Continuum

( ) 78.5 13.8(stat)N


Maximum Likelihood Fit Start from the physics function:

Fold in t resolution and mis-tag probabilities Multiply by PDFs for mES, E BABAR uses particle ID and Fisher in the fit

Belle uses these variables in event selection Add PDFs for background (K, KK, continuum)

Feed the candidates and turn the crank…

( ) 1 sin( ) cos( )4

t

d def t m C m tS t

0

0

tagtag

BB


BABAR

BELLE

CP Fit Results

BABAR and Belle disagree by >2 Belle 1.2 outside the physical

boundary Is there any problem?

Crosscheck systematics

BABAR (preliminary) Belle (hep-ex/0204002)

S –0.01 ± 0.37 ± 0.07

C –0.02 ± 0.29 ± 0.07

0.38+0.161.21 0.27 0.13

0.310.94 0.090.25

Belle usesA C

2 2 1S C


CP Asymmetries – BABAR

enhanced for these plots with a cut on Fisher No significant asymmetry


CP Asymmetries – Belle

Rate difference (= C) t-dependent asymmetry (= S and C)

Subtract bkg0 tagB0 tagB


Crosschecks Both experiment made extensive crosschecks, e.g.

Asymmetry in background? Look for asymmetries

in K or mass sideband Vertex resolution of the

2-body decays? Measure B lifetime with , K Measure mixing with K

Likelihood values and errors? Toy Monte Carlo studies

BELLE


Monte Carlo Fit Test Generate ~1000 “toy” experiments

Belle used (0.7, 0.7)for the central values

Fit and compare: Likelihood values Pull distributions Errors

Lowest probability: 5.4%

BABARS C

(S) (C)

MC

Measured

S C

BABAR

BELLEBELLE

Measured

Everything looks reasonable


BABAR

BELLE

Interpretation

How well do we know ?(*Gronau and Rosner, PRD65, 093012) Average BABAR and Belle Assume = 26°, P/T = 0.28

BABAR (preliminary) Belle (hep-ex/0204002) Average*

S –0.01 ± 0.37 ± 0.07 –0.66 ± 0.26

C –0.02 ± 0.29 ± 0.07 –0.49 ± 0.21

0.38+0.161.21 0.27 0.13

0.310.94 0.090.25

NB: Large uncertainty


Measured S ±1 corresponds to

Interpretation

Gronau and RosnerPRD65, 093012

[89 ,138 ]

Indirect:

BABAR + Belle

3021(97 )

Accuracy comparableto the indirect constraints

We are starting to measure


Summary BABAR and Belle measured sin2eff using B0 +

Direct constraint on is reaching useful accuracy Things to watch out for:

sin2eff with higher statistics Resolve “discrepancy” BR(B0 0 ) Better bound on eff –

BABAR (preliminary) Belle (hep-ex/0204002)

S –0.01 ± 0.37 ± 0.07

C –0.02 ± 0.29 ± 0.07

0.38+0.161.21 0.27 0.13

0.310.94 0.090.25


Bound on eff – Full isospin analysis (Gronau & London, 1990) requires

and separately Too hard for BABAR/Belle Upper limits on average BR

Use BR(00) to put upper bound on eff – Grossman and Quinn, 1998; Charles, 1998

0 0 0( )BR B 0 0 0( )BR B

Gronau, London, Sinha, SinhaPLB 514:315-320, 2001

0 0( ) ( )BR BR

eff2( ) Allowed

was assumed

0( ) 1.3( )

BRBR


GLSS Bound on eff – If I use and

GLSS bound weakerfor smaller BR()

Better measurements ofBR() and BR() will give us a betterhandle on the penguinsin the near future

0( ) 0.91 0.25( )

BRBR

6( ) 5.3 10BR

0 0 6( ) 10BR

eff2( )

BABAR90% CL

Small

Large


B Flight Direction Angle B of the B candidate momentum relative to the beam

axis

Signal Background ~flat

eeB

Bp BELLE

cos B

21 cos B


Systematic Errors BABAR:

Dominated by the shape of the particle ID variable Belle:

Uncertainties of the background fractions Fit bias near the physical boundary for S Wrong tag fraction for C

All measurements are statistically limited


Interpretation Measurements favor

maximally negative C

Corresponds to = 90° Maybe a good news

No discrete ambiguity! Time will tell

Gronau and RosnerPRD65, 093012

105120 90 75 60

90

90

= 26°, P/T = 0.28

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Measurements of sin2 a from B-Factories