Max Baak 1

Impact of Tag-side Interference onImpact of Tag-side Interference onMeasurement of sin(2Measurement of sin(2++) with ) with

Fully Reconstructed BFully Reconstructed B0 0 D D(*)(*) Decays Decays

Max BaakNIKHEF, Amsterdam

For the BaBar Collaboration

APS MeetingPhiladelphia, 8 April 2003

Max Baak 2

CP Violation in BCP Violation in B0 0 DD(*)(*)

• Four final states: D-+, D+- ; D*-+, D*+- (not CP eigenstates)

• Each pair accessible to B0 and B0 CP violation through interference

• Expected CP violation small (2%)

Suppressed amplitudethrough

bu transition

d

bc

d

0B

u

*D

* i iub cd rV V A e e

Dominant amplitude

c0B

d

bu

d

*D

*cb udV V A

strong phasedifference

(3)

CKM Unitarity Triangle

Max Baak 3

Time-Dependent sin(2Time-Dependent sin(2++) Measurement: Old ) Measurement: Old SchoolSchool

• Time evolution for B0 decays (Runmix) and B0 decays (Rmix) to D-+

2

2

1

1

rC

r

2

2sin 2

1

rS

r

+

+

cosπ ,Δ 1

π ,

sΔ Δ

cos

in Δ Δ

sin Δ ΔΔ 1 Δ Δ

tunmix d

d

d

dt

mix

S m tC m t

C

R D t N e

R D t N me m S tt

• For D+- : sin(2+-) sin(2++)

u m

u m

R RA

R R

r = 0.0

r = 0.1, = 0

• Simultaneous determination of r and challenging Estimate (and fix) r from B0 Ds

+- [1]

r(D) = 0.021 0.005 r(D*) = 0.017 0.007

1 [ 0.04,0.04] Similar for D*

[1] hep-ex/0211053 – submitted to PRL

Max Baak 4

Common Analysis Technique in BaBarCommon Analysis Technique in BaBar

Fully reconstruct one Bin state D or D*

Determine flavor of other B meson BTAG

(“tagging”)

Reconstruct vertex of BTAG and compute proper time difference

t

(4s)

Tag B

Reco B

K+

+

z

K+

t z/c = 0.55

At time of BTAG decay,the 2 B’s are in opposite

flavor states

z

Coherent B0B0

production

1.

2.

-s

-

Max Baak 5

Subtlety of B Flavor TaggingSubtlety of B Flavor Tagging

• Many B0DX modes (X a hadron) ‘kaon tag modes’

• At BR levels of O(10-4) intrinsic mistagging because of bu transitions in B0 decays

• Effect always assumed tiny, and accounted for by mistag fractions.

b c s

W W

,l

K

• Hidden assumption: Individual tagging states dominated

• Use charge correlation between final state and B flavor

by single B0 decay amplitudes

Not True!

Works well for lepton

tags!

Max Baak 6

B0

B0

Doubly-Cabibbo suppressed decays on the tag sideDoubly-Cabibbo suppressed decays on the tag side

1. (4s) B0 B0 system symmetric in two B’s

2. System evolves coherently in time

3. On reco-side bu interference is used for sin(2 + ) measurement. Induced time-dependent effects of order VubVcd/VcbVud = 0.02

bu Interference at tag-side B induces time-dependent effect, just like reco-side!

• Lepton tags unaffected. Kaon tags have problems.

Change the time-dependent pdf’s!

Long, Baak, Cahn, Kirkby

hep-ex/0303030

2% for sin2 with J/ Ks

100% effect for D(*) !

0B 0B(4s)

Max Baak 7

How the decay distributions change for How the decay distributions change for DD(*)(*)

• For sin(2+ ) measement (bu transition) tag-side problem of similar size compared to signal, cannot be ignored!

How do the time-dependent decay distributions change? • One kaon tag mode with (unknown!) amplitude ratio r’ and strong phase ’

Similar for D+-

r=0.1, =0, r’=0

r=0.1, r’=0.1, =0, ’=

r=0, r’=0

Equations pick up sine terms

Max Baak 8

Change of VariablesChange of Variables

Flavor-tag symmetric

lepton tags

Handle on phase

- Only 3 independent parts- The b parameter does not dilute in mistagging!

• Split off the strong phases and ’ for better parametrization set Reco side Tag side (`primed’)

r’ unknown

Max Baak 9

Fit TechniqueFit Technique

• Unbinned maximum likelihood fit to t spectra of D and D* samples.

Fit Parameters #

a,b,c parameters 13

Resolution Function 8

Mistag fractions 12

Background modelling

15

md and B fixed (PDG)

-

Free arameters 48

2 a(D) and a(D*) common for all tag. cats.

2 cLEP(D) and cLEP(D*)

3 b pars. : for each kaon tag. category,

common to D and D*

6 c pars. : for each kaon tagging cat. of D and

D*

Most sensitive to 2+

BaBar uses 1 lepton and 3 kaon tag. categories!

Similar to other

mixing

measurements

• In practice numerous kaon tag-modes

• No reason tag-side parameters r’ and ’ to be identical for each tag category

Use different b and c tag-parameters for each kaon tag. category

Max Baak 10

a(0)=0.0000.002

c(0)=0.0010.003

r’(generated)

r’(generated)

c LE

P(fi

t) –

cLE

P(g

en)

r’(generated)

r’(generated)

(c L

EP)

(a)

D*

a(fi

t) –

a(g

en)

Toy MC ValidationToy MC Validation

No observed biases in signal parameters!

• r = 0.02, , ’ = 0.00 a=0.04, c=0.00

• Toys correspond to 82 /fb of data+background (D plus D*)

Max Baak 11

Data Sample [1999-2002]: 82 fbData Sample [1999-2002]: 82 fb-1-1 on on (4s) (4s) ResonanceResonance

N(D) = 5207 87Purity = 85 %

N(D*) = 4746 78Purity= 94 %

Lepton KaonI KaonII Other

D 704 27

1328 39

1682 44

1550 44

D* 644 26

1197 36

1427 40

1492 40

breakdown in tagging categories

2 2cm cmES beam Bm E p

• Fully reconstructed BD(*) normally used for mistag fractions in sin2 analysis

Max Baak 12

Sensitivity to Sensitivity to after tag-side effect after tag-side effect

• Analysis not yet finished • With current D(*) data set,

what is loss & sensitivity to ?

2 sin 2 cos

2 cos 2 sinLEP

a r

c r

No tag-side interference(c cLEP)

With tag-side interference

Signal parameters:

(a[D]) 0.04

(c[D]) 0.04

(a[D]) 0.04

(cLEP[D])

0.07

Stat. sensitivity

(sin(2+)) ~ 0.Xloss due

to kaon tags

Identical errorsfor D* sample

BBAABBARAR82 fb82 fb

BBAABBARAR82 fb82 fb

Dominant Systematic uncertainties:

1) Uncertainty in r 3) Detector effects

2) Monte Carlo 4) Background

Systematics (sin(2+)) ~

0.5 x stat.

Max Baak 13

ConclusionConclusion

• Tag-side Doubly-Cabibbo-Suppressed decays sofar neglected in most time-dependent analyses (using coherent B-decays)

• Complications for sin(2+) measurements using D(*)

//a1 Effect cannot be ignored!

• Using correct parametrization, can work around problem.

Some loss in sensitivity to

First BaBar Result coming soon!

2% for sin2 with J/ Ks

100% effect for D(*)

(stay tuned)

Long, Baak, Cahn, Kirkby

hep-ex/0303030

Max Baak 14

Backup SlidesBackup Slides

Max Baak 15

B Flavor Tagging MethodsB Flavor Tagging Methods

• In BaBar tagging is handled with Neural Nets

• Information used:Primary lepton

Secondary lepton

Kaon(s)

Soft pions from D* decays

Fast charged tracks

0

0 *

0

0 0

,

,

, s

B D l

B D D K l

B DX D K X

B D X D D

l ,

K b c s

W W

l

Tagging category

Fraction of tagged events(%)

Wrong tag fraction w (%)

Q =

(1-2w)2 (%)

Lepton 9.1 0.2 3.3 0.6 7.9 0.3

Kaon+Kpi 16.7 0.2 9.9 0.7 10.7 0.4

Kaon+Spi 19.8 0.3 20.9 0.8 6.7 0.4

Inclusive 20.0 0.3 31.6 0.9 0.9 0.2

ALL 65.6 0.5 28.1 0.7

Smallest mistag fraction

The errors on a,cLEP

scale with quality Q 1

Q

Mistag fraction w determined from cosine coefficients

Max Baak 16

Multiple tag-side final statesMultiple tag-side final states

• In practice there are numerous tag-modes

• Combining these leads to average, effective r’eff and ’eff

• No reason to expect r’ and ’ to be identical for each tag category Use different b and c parameters for each category

• Hardly anything known about values of r’i or ’i

Uncertainty on r’eff : 0 – r’max

No sensitivity to 2+ from kaon tag-side parameters b and c

2 ' sin 2 cos '

2 cos 2 sin 'sin '

b r

c r r