Thesis Defense of

Luminda Kulasiri

Dept. of Physics, University of Cincinnati

05.09.2005

Search for exclusive two body decays of B→D h at Belle

*

S

Motivation-

*

*

)(

)(tan

*0

*0

*

sD

DscD f

f

DBBr

DBBrR

u

Vub

u

B-

u

s

c

W-

b Vcs*

DS

*-

0

Decay via b → u spectator Diagram

Clean measurement for Vub

No penguin terms

Model independent

No yet seen

Important input for measuring Sin(2β+γ)

Vub

d

B0

u

s

c

W-

b Vcs*

DS

* -

+

d

0*s

*s πD,πD

Motivation-

B0

Evidence for W-exchangeFirst seen in B0→ Ds

-+ decay -PRL 89, 231804(2002)

Not seen

Role of the final state interactionsBr can be as large as 10-4 D+-, D00 can turn out to be Ds*-K+

(B. Block et al. PRL 78, 3999, 1997)

cVcb*

Vudd

b DS

*+

K-

Ws

s

u

KD*s

Past Measurements & Theoretical Predictions

B B D 10S( ) .*0 54 1 @ 90% C.L.

B B D 3 3 10S0 4( ) .* @ 90% C.L.

B B D K 2 5 100S

3( ) .* @ 90% C.L.-PDG 2004

Theoretical predictions

( ) . | |* *B D 5 1a V V 10 s0S 1

2ub cs

2 12 1

A. Deandrea et al. Phy. Lett. B 318, 549(1993)

B B D 2 8 10

B B D 1 4 10

0S

5

S0 5

( ) .

( ) .

*

*

( ) .*B D 10 s0S

1 8 1 6 7

B B D 6 63 100S

5( ) . ( . )* B s1 5 6 1 0 1 2

→

→

a1~1.0, Vub~.003, Vcs~0.97

D. Choudhry et al. Phy. Rev. D, 45, 217(1992)

B B D 0 34 V V c 10 s

B B D 0 17 V V c 10 s

0S ub cb

21

2 10 1

S0

ub cb2

12 10 1

( ) . | / | ( )

( ) . | / | ( )

* '

* '

c 1 0 V 0 0411 cb' . , .

Theoretical predictions

KEKB Accelerator

•Asymmetric Collider with, 8.0 GeV e- x 3.5 GeV e+

•22 mrad crossing angle•Lpeak = 13.92 nb-1s-1

•∫Ldt ~400 fb-1

•Ecm = 10.58 GeV

operates at (4S) resonance

e+e- → (4S) →BB

(4S) center of mass frame

Belle Detector

Silicon VertexDetector(SVD)

Central Drift Chamber(CDC)

Aerogel Cherenkov cnt.KL/µ Detector

CsI Calorimeter

TOF counter

SC solenoid

8GeV e-

3.5 GeV e+

Belle Detector

Silicon Vertex Detector (SVD)Tracks low momentum particles with CDCVertex reconstruction, 18 µm

Central Drift Chamber (CDC)Mom. of charged particles is measured from the curvature of the track traversing in the magnetic field PID using dE/dx - energy loss by ionizationin the matter

Aerogel Cerenkov Counter (ACC)•Index of refraction ranges from 1.01 to 1.03•K/ ID between 1.2 – 4.0 GeV/c

TOF counterK/ seperation using timing of plastic scintillation counters

CsI CalorimeterMeasure energy of e’ns and via detection of scintillation light from e.m. showers.

KL/µ DetectorDetect high mom.(>600 MeV) K/µ

SC SolenoidGenerates 1.5 T mag. field

Particle ID at Belle

• Uses information from CDC, TOF, and ACC• Combine the information using Likelihood method

P rob(i: j)P

P P

P P P P

i

i j

i iC D C

iT O F

iA C C

Pi – likelihood for signal speciesPj – likelihood for background speciesWhere i, j {e, , K, , p}

• Used 250 fb-1 data at (4S) center of Mass resonance 274.8 million BB events

Decay Chain

Conjugate modes are also assumed

B0→ Ds*+ -,

B0→ Ds*- K+,

B+→ Ds*+ 0

Ds*+→ Ds

+

Ds+ → {+, KSK+, K*K+}

→K+K-, KS→+-, K*→K+-

Reconstruction of , K0s, and K*0

→K+K- Kaon ID>0.61.0116<M(KK)<1.0272 GeV(±3 of the nominal mass)

K*0→K+- K/ ID>0.6|M(KK) – 0.8961| < 0.060 GeV(±3 of the nominal mass)

Data

Data

Helicity Angle

Helicity angle(θh) – Angle between momentum of DS and momentum of K in (K*) frame.

Bg. evts.

Signal evts.

•Flat dist. for background evts.

•Cos2(θ) dist. for signal evts.

•Selection requirement, |cos(θh)| > 0.3

Reconstruction of , K0s, and K*0 - Cont.

K0s→+-

Pion ID>0.60.4902<M(+-)<0.5051 GeV(±3 of the nominal mass)2<30 (vertex reconstruction fit)Other cuts: dr>0.009 cm; d<0.2 rad

dr – smaller of dr1 and dr2, where dr1 and dr2 are the smallest approach from the IP to the two tracks in x-y planed- angle betn. the momentum vector and decay vertex displacement vector in r- plane

Background Events Signal Events

dr(cm) d(rad) dr(cm) d(rad)

Data

Reconstruction of DS+

and DS*+

±3 of the nominal mass (1968.5±0.6 MeV)

1.9539<M()<1.9833 GeV1.9471<M(KSK)<1.9901GeV1.9495<M(K*K)<1.9877GeV

momentum selection1.7<P(cms)<2.5 GeV

M=M(DS*)-M(DS)M has better resolution than mass.

0.124<M<0.164 GeV

A large portion of the background is accounted by photons that are not really coming from DS*.

E(cms)>110 MeV

0 veto

Photon Energy (E)

SignalBg.

GeV

D DS*

S },,{ 0*0 KKKKD ss

Selection of the B Candidate

B D B D K B DS S S0 0 0 * * *, ,

Two quantities M(B) and E are defined as,

M B E Pbeam ii

( ) 2 2

E E Ei beami

where Ebeam =5.29 GeV,

Pi – mom. of B, Ei – energy of B

Signal Region, –0.05<E<0.05 GeV for h {, K} –0.10<E<0.05 GeV for h {0}

5.27<M(B)<5.29 GeV/c2

GeV/c2

B→Ds*+- (Ds

+→+)G

eV

Sign

al M

C

E vs. M(B)

Background Suppression – Fisher Discriminant

Largest background source is e+e-→ qq eventsFisher Discriminant is a powerful tool to discriminate signal and background• A linear combination of 9 variables• Optimized to discriminate signal from background

r

P P P

P Pll

i jij

l ij

i jij

| | | | ( )

| | | |; , , ,

cos 1 2 3 4

RP P P

P Pll

i hi

l ih

i hi

| | | | ( )

| | | |; ,

cos 2 4

qq even ts

B B even ts

Background Suppression – Fisher Discriminant (cont.)

• Cos(θth) – Angle between thrust axis of the B cand., and the thrust axis of the remaining particles.

• Cos(B) – Angle between the B momentum & beam axis •qr x (QDS) – qr contains flavor information of the other B; q = ±1; 0<r<1;

TT p

pi

i

ii

| |

| |

Where is a unit vector s. t. it maximizes TT

is the mom. of the ith particle in CM framep i

F r R qr Ql l l l thll

B D s 1 2 3co s( ) co s( ) ( )Combine all 9 variables into F

Background Suppression – Fisher Discriminant (cont.)

All the parameters are optimized to get the maximum discrimination between signal and background

Used Figure of Merit (FOM) plots to decide the best selection

F O M s b /

FD

Arb

itrar

y un

its continuum Signal

S - SignalB - background

• First used Sig. MC – fitting M(B)• Observed inconsistency among the yields of DS sub modes• Minimized MC dependence by using inclusive M

•Efficiency for mode obtained using sig. MC•Total eff. obtained by multiplying by eff. of the other cuts

K S K K S K S

S S S

N

NB r D

B r D K K

B r K K

B r K

( )

( )

( )

( )0 0

K K K K S

S

N

NB r D

B r D K K

B r K K

B r K K

* *

* *

( )

( )

( )

( )

0 0

N – inclusive M yield ; - efficiency ;

Reconstruction Efficiencies

Following relationships can be obtained

Sideband Study

• Sidebands of Ds and M used • 3 from lower and upper side of the signal region• Can be used to compare data and MC• Background shapes and rates can be obtained

• Bg. shapes of data and MC agree each other• Observed a disagreement in bg. levels ~12% – 22%• Bg. of Ds not random – real Ds but not from Ds

*→Ds

Observations:

Simultaneous Fitting

Simultaneous fitting of 3 DS sub decay modes

Common branching fraction for all 3 DS sub-decay modes

M-1D• Signal-Gaussian shape with mean & fixed to sig. MC shape• Bg. – linear shape, by fitting data excluding the signal region

E-1D• Signal-Gaussian shape with mean & fixed to sig. MC shape• Bg. – sideband shapes of M

Significance))/L(L( max0ln2

Simultaneous fitting - cont.

E fitSolid line (red) – total fitdotted line (blue) - background

Ds*+- Ds*-K+

Ds*+0

)9.2(10)46.181.2()(

)5.2(10)65.097.0()(

)1.4(10)77.082.1()(

50*

5*0

5*0

s

s

s

DBBr

KDBBr

DBBr

DS*+-

DS*+K-

DS*+0

Simultaneous fitting - cont.

M fit•Solid line (red) – total fit•dotted line (blue) - background

)0.4(10)11.143.2()(

)5.4(10)66.064.1()(

)8.4(10)81.014.2()(

50*

5*0

5*0

s

s

s

DBBr

KDBBr

DBBr

Systematic Uncertainties

Since 3 Ds modes,Total Syst. error = common syst. errors + indept. syst. errors

Common Errors (%)

rcon.

0 recon.

Br(Ds*→Ds)

NBB

Total

Ds*+-

5

-

3

1

5.9

Ds*-K+

5

-

3

1

5.9

Ds*+0

5

5

3

1

7.7

Systematic Uncertainties-cont.

Independent Errors

Br(Ds) /Br(Ds→)

Br(sub Ds)

Ks

Fitting

MC stat.

Tracking

PID

Common

Total

Br(Ds→)

Ds*+-

+ KsK+ K*K+

0.00 22.2 9.1

1.4 0.4 0.2

- 3.0 -8.20

4.5

3.4

2.9

5.9

12.04

25.0

Ds*-K+

+ KsK+ K*K+

0.00 22.2 9.1

1.4 0.4 0.2

- 3.0 -

9.40

6.1

4.5

3.9

5.9

14.25

25.0

Ds*+0

+ KsK+ K*K+

0.00 22.2 9.1

1.4 0.4 0.2- 3.0 -

14.9

8.1

4.4

4.0

7.7

17.98

25.0

RD* for Sin(21+3)

s R

RB r B DB r B D

ff

D D

D cs D

Ds

2 2 1 3

0

0

* *

*

*

**

sin( )

tan(( ) *

ff

D

D s

*

*

. . 1 1 0 0 0 2

D* - strong phase, c – Cabibbo angle

D. Becirevic, Nucl. Phys. Proc. Suppl. 94, 337 (2001

0023.02286.0)tan(

10)21.076.2()( 3*0

c

DBBr

2

* 10)53.021.2( DR

- good agreement with the expected result which is ~0.02

Estimation of Vub

3

'1

12

1102'1

2*0

10)26.164.2(||

0.1)(;10)016.0542.1(;0015.00413.0||

10)]([|/|34.0)(

ub

BBcb

bcbubs

V

mCV

smCVVDB

-Good agreement with the world average for |Vub| which is (3.67±0.47)x10-3

Summary

Used 278.4 million events M fits give more consistent results Both M and E results agree within errors

Obtained estimates for Vub and RD*

B B

)9.2(10)61.042.011.143.2()(

)5.2(10)41.023.066.064.1()(

)1.4(10)54.026.081.014.2()(

50*

5*0

5*0

s

s

s

DBBr

KDBBr

DBBr

DS*+-

19.0±5.7 evts DS*-K+

11.0±4.8 evts

DS*+0

9.4±5.5 evts

Combined yields from M fit (274.8 m evts.) BB

Combined yields from M(B) fit (274.8 m evts.)

DS*+-

21.4±5.9 evts.

DS*+0

8.1±5.7 evts.

DS*-K+

10.6±4.9 evts.

BB

Combined yields from E fit (274.8 m evts.) BB

4.48.4 evts.

15.15.6 evts.

8.24.7 evts.