Measurements of sin2Measurements of sin211 in processes at in processes at BelleBelle

CKM workshop at Nagoya 2006/12/13

Yu Nakahama (University of Tokyo)for the Belle Collaboration

•Analysis procedures •Results in 2006•Sensitivity of sin21 at Belle•Summary

Outline

sccb

2

Principle of Measurement

• Reconstruct B fCP(bccs) decays• Measure t and Determine flavor of Btag

• Evaluate CP asymmetry from the t and flavor information

e- e+e-: 8.0 GeVe+: 3.5 GeV

BCP

z

Btag

(4S) ~ 0.425

fCP(bccs)

z ctB ~ 200 m

Flavor tag ( )z

ct

3

BCP 　 J/K0 Reconstruction in 535M BB

2*/

2*KsJbeambc PEM

B0 J/ KS B0 J/ KL0 0

Beam energysubstituted B mass (GeV/c2)

B momentumin the cms (GeV/c)

Eve

nts /

50

MeV

/c

Eve

nts /

1 M

eV/c

2

+ data

MC: J KLX MC: signal

MC: J/ X MC: comb.

Nsig = 6512Purity 59 %

CP even

Nsig = 7482Purity 97%

CP odd

S→only)

pKL information is poor. lower purity

4

– IP (interaction point) tube constraint fit• IP profile

– Size:x~100m, y~5m.– Smearing due to B flight is taken into account by 21m in the x-y plane.

• No constraint in the beam direction (z-axis).

Measured track

Measured track

IP profileIP tube

t measurement -Vertex fit

CP side (J/ψ) Tag side

2-trk 1-trk Failed n-trk 1-trk Failed

Fraction (%) 93.7 0.9 5.4 82.5 10.3 7.2

Resolutionm) 52.5±0.2

108.9±3.2

107.5±1.0

256.4±4.3

z-axis

B decays vertices are reconstructed using the tracks coming from their decay particles using kinematical vertex fit.

5

Flavor Tagging• For the BCP-Btag coherency originated from Y(4S) decay,

Btag flavor determines BCP flavor (B0 or B0) at Btag decay time.

• Flavor information is determined from Btag decay products.

-1 0 +1-1 0 +1Btag=B0 B0B0 B0qr qr

Flavor information is parametrized using qr: q: MC determined discrete flavor (1 or -1) r: MC determined flavor ambiguity (0~1)

Even

t fra

ctio

n

6

Evaluation of CP asymmetries

0

1

sig 1

bkg

( , ;sin 2 , )1 [1 (1 2 ) (sin 2 sin cos )] ( )

4(1 ) ( )

d dB

sig

P t q A

f q w m t A m t R t

f P t

Btag = B0

Btag = B0

Btag = B0

Btag = B0Smeared by • Detector resolution• Wrong flavor tag effect

• (Bkg. contribution)

Signal

Background

Maximum Likelihood Fit

Wrong flavor tag effect Detector resolution

t (ps) t (ps)

Measured tTrue t

0)2(sin

),2sin;,(),2(sin.

1 111

ALLAqtPAL

Neve

iii

7

RCP RTag

We understand the following resolution components:– Detector resolution:

– Effect of non-primary particles:

– Kinematic approximation of B0 flight:

We determine the models and their parameters using control samples:

　　　 B0→D(*)-l+ D(*)-D*

　　　 B+→D0+, J/ψK+

Overview of Resolution function: R(t)

R(t) = RCP RTag RNP RK

RNP

RK

B

Bz

BD

lNon-primary particles

Brec

Ks

ll J/ψ

Residuals=Zrec ― Zgen

Bgen

[NIM A533: 370,2004]

8

Resolution functionUsing event-by-event vertex quality: z and , 　　　　　　　　　 (Vertex fit2 along the z direction only) Detector resolution is modeled using MC as:

- Event-by-event Double Gaussian- Sigma of Gaussian ~ Error z

- Scaled up according to

Entri

es

t (ps)

Neutral B

Lifetime fit

(B0 = 1.530 +/- 0.009ps 　 [PDG2006])

All resolution parameters aredetermined from fits to data/MC samples.

We verify the fitted lifetime usingthis model is self-consistent to the onewe used in the sin21,A fit. J/ψK0 DataB0 = 1.544 +/- 0.016(stat) ps

9

tmw d cos)21(

Wrong flavor tag effect

Wrong tag effect for each r binis estimated from time-dependent B0-B0 mixing fitusing self-tagged control samples:B0D(*)-l+ D(*)-D*

chg cosOF SFd

OF SF

P PA m tP P

Events are classified into 6 categories according to the r.

|t| (ps) |t| (ps)

Measured time-dependent flavor asymmetry

Dilution due to mis-flavor tagging

Wrong flavor tag effect

Time-dependent flavor asymmetry:

Measured asymmetry:

10

KEKB Integrated luminosityas a function of time

B0 J/ KS0

B0 J/ KL0

History of the measurements of sin21 at Belle

Results based on 535MBB

will be described.

andthe expected sensitivity in the future

11

2006 results with 535MBB0/CP SB J K 0/CP LB J K

Δt (ps)Δt (ps)

CP= -1 CP= +1

Raw

Asy

mm

etry

(=－

C

Psi

n2 1s

inm

t)

1sin2 0.643 0.0380.001 0.028A

1sin2 0.641 0.0570.045 0.033A

En

tries

/ 0.

5ps

Raw

Asy

mm

etry

0/CP SB J K 0/CP LB J K solesole

(total) (total)

Entri

es /

0.5p

s

12

Combined results with 535MBB

0 0/ ( )CP S LB J K K

1sin2 0.642 0.031 0.0170.018 0.021 0.014A

(stat.)

CombinedCombined

The other ccs processes are not included.

(syst.)

Entri

es /

0.5p

sR

aw A

sym

met

ry

-CPΔt (ps)

hep-ex/0608039, to appear in PRL

13

Prospect of sin21 uncertainty

Total Statistical Systematic

0.492/ab 0.035 0.031 0.0175/ab 0.017 0.010 0.014

50/ab 0.014 0.003 0.013

L /ab

Assumption:•Use the same analysis methods as of now.

•Use BJ/ψK0 only.

5/ab 50/ab535MBB↑0.492/ab

ー Total errorー Statistical errorー Systematic error

In L ~>2/ab region,the systematic error will be larger than the statistical one.

14

Systematic error of sin21

Categoriessin21)

with 535MBB

1.Vertexing 0.0122.Possible fit bias 　 0.007t Resolution function 0.0064. BG fractions (J/KL) 0.005

5.Wrong tag probability 0.0046.BG fractions (J/KS) 0.003

7.Fixed Physics parameters: md ,B0 0.001

8. BG t 0.0019.Tag-Side interference 0.001

Total 0.0170.017

sin21) with 5/ab

0.0120.002

0.0060.0020.0010.001

>0.000>0.000

0.001±0.013 ±0.003

Independent of the luminosity increase.

large

small

0.0140.014

15

Breakdown of the systematic error from Vertexingsin21) with 535MBB

1. IP tube constraint vertex fit 0.0072

2. Poor-quality vertex rejection 0.0064

3. Imperfect SVD alignment 0.0056

z bias 0.0050

5. Track error estimation 0.0033

6. Track rejection in Btag decay vertexing

0.0026

t fit range 0.0002

Total ±0.012

•Dominant

•Irreducible even with more data

1. IP tube constraint fit–Select only the events with the 2 tracks in CP side

2. Poor-quality vertex cut–Tighten a criteria for the vertex selection.

Limiting factor is imperfect SVD alignment.

Possible improvement ideaAs we have more data, we can reject the events with poorer quality to reduce the systematic error.

16

•With the current data set (492/fb),

Dominating source of the systematic error is vertexing, especially imperfect SVD alignment.

•In L ~>2/ab region, the systematic error will be larger than the statistical one.

•With 5/ab data,

• 50/ab data,

Summary

As we have more data, we can reject the events with poorer quality The systematic error could be reduced.

±0.010±0.014

±0.003±0.013(stat.) (syst.)

(stat.) (syst.)

Sensitivity of sin21 using BJ/ψK0 at Belle

17

Supporting Results• sin2 fit on non-CP eigenstate

– consistent to zero

• Lifetime fits – consistent to input lifetime for S, A fits

1 /

/

(sin 2 ) 0.018 0.020(stat)

0.003 0.014(stat)B J K

B J KA

0 0/

/

1.544 0.016(stat) ps

1.641 0.011(stat) psB J K

B J K

[tB0 = 1.530ps, md = 0.507/ps]

18

Systematic errors of B0J/K0

Sin21 A1.Vertexing 0.012 0.0092.Wrong tag probability 0.004 0.003t Resolution function 0.006 0.0014.Fixed Physics parameters 0.001 0.0015.Possible fit bias 0.007 0.0046.BG fractions (J/KS) 0.003 0.001 BG fractions (J/KL) 0.005 0.0027. BG t 0.001 0.0018.Tag-Side interference 0.001 0.009

total 0.017 0.014

19

More on Vertex errorsError of Imperfect SVD alignment• Misalign DSSDs in MC to reproduce IP resolution (15m shift an

d 0.15mrad rotation.)• Generate signal MC with and w/o misalignment • Obtain sin21 for two cases and take the difference.

Effect of Vertex section (cut poor quality vertices: (default : >250))• Obtain sin21 with andand take the larger variat

ion.

Error of IP tube constraint fit is obtained by changing the smearing effect due to B flight (default: 21m)

• Obtain sin21 with IP tube smearing by 11m and 41m and take the larger variation.

20

Flavor tagging

q: discrete flavor

Effective tagging efficiency:29.2+-1.4[%]

[NIM A 533, 516 (2004)]

21

Tag Side Interference• Interference between CKM-favored and CKM-

suppressed BD transitions in tag side.• Estimated by pseudo-experiments whose para

meters are obtained from B0D*l samples• No interference for semi-leptonic decay in tag

side (It was included till last year)

22

Prospects for less systematic errors

• IP tube constraint fit– Select only the events with the 2 tracks in CP side– Easy and little gain

• Poor-quality vertex cut– Select only the events with good vertex qualities.– Easy and effective but need data

• Imperfect SVD misalignment: – Difficult to improve and almost hopeless.– If better methods are found, need reprocess all data.

Vertexing

t Resolution function–Select only the events with good qualities

–We could model simply using less parameters.

–Potentially promising, but not so easy

23

Effect of non-primary particles• Most of tag-side B has

a secondary vertex coming from D decays.• The effects of these non-primary tracks

cannot be 100% eliminated in our vertexing algorythm.

• Modeled by – Gauss’sfunction : the effects of the tracks from the primary vertex. – Exponential function :the effects of Lifetime components of D

decaying into non-primary particles.

• A tagging lepton is expected to be from a primary vertex.– We determine the parameters of Gauss’sfunc.

for the events w/ tagging lepton w/o tagging lepton, separately.

.

BD

l

Non-primary particles

Tagging lepton

Entri

es (L

og)