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Search for exclusive two body decays of B→D h at Belle. * S. Thesis Defense of Luminda Kulasiri Dept. of Physics, University of Cincinnati 05.09.2005. Motivation-. *. V cs. c. c. s. s. W -. W -. b. u. b. * -. * -. u. V ub. D S. D S. *. V ub. V cs. p 0. B 0.

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Thesis Defense of Luminda Kulasiri Dept. of Physics, University of Cincinnati 05.09.2005

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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

Thesis Defense of

Luminda Kulasiri

Dept. of Physics, University of Cincinnati

05.09.2005


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Motivation-

*

Vcs

c

c

s

s

W-

W-

b

u

b

*-

*-

u

Vub

DS

DS

*

Vub

Vcs

p0

B0

B-

p+

d

d

u

u

  • Decay via b → u spectator Diagram

  • Clean measurement for Vub -No penguin terms

  • Model independent

  • Not yet seen

  • Importantinput for measuring Sin(2β+γ)

CKM Matrix


Motivation

b

*+

DS

*

Vcb

Vud

s

W

s

K-

d

u

Motivation-

  • Evidence for W-exchange

  • First seen in B0→ Ds-K+decay

  • PRL 89, 231804(2002)

  • Not seen

  • Role of the final state interactions

  • Br can be as large as 10-4

  • D+-, D00 can turn out to beDs*-K+

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

c

B0


Past measurements theoretical predictions

Past Measurements & Theoretical Predictions

-PDG 2004

Theoretical predictions

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


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Theoretical predictions

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

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


Kekb accelerator

KEKB Accelerator

  • Asymmetric Collider with,

  • 8.0 GeV e- x 3.5 GeV e+

  • 22 mrad crossing angle

  • Lpeak = 15.33nb-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

Belle Detector

Aerogel Cherenkov cnt.

KL/µ Detector

CsI Calorimeter

3.5 GeV e+

TOF counter

SC solenoid

8GeV e-

Silicon Vertex

Detector (SVD)

Central Drift Chamber (CDC)


Belle detector1

Belle Detector

  • Silicon Vertex Detector (SVD)

  • Tracks low momentum particles with CDC

  • Vertex 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 ionization of 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 counter

K/ separation using timing of plastic scintillation counters

CsI Calorimeter

Measure energy of e’ns and  via detection of scintillation light from e.m. showers.

KL/µ Detector

Detect high mom.(>600 MeV) K/µ

SC Solenoid

Generates 1.5 T mag. field


Particle identification pid at belle

Particle Identification (PID) at Belle

  • Uses information from CDC, TOF, and ACC

  • Combine the information using Likelihood method

Pi – likelihood for signal species

Pj – likelihood for background species

Where i, j {e, , K, , p}


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

  • Used 250 fb-1 data at (4S) Center of Mass resonance

  • 274.8 million BB events

Decay Chain

B0→ Ds*+-,

B0→ Ds*-K+,

B+→ Ds*+0

Ds*+→ Ds+

Ds+ → {+, KSK+, K*K+}

→K+K-, KS→+-, K*→K+-

Conjugate modes are also assumed


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Data

Data

Reconstruction of  and, K*0

→K+K-

Kaon ID > 0.6

1.0116 < 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)


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Helicity Angle

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

  • Flat dist. for background events.

  • Cos2(θ) dist. for signal events.

  • Selection requirement,

  • |cos(θh)| > 0.3

Bg. evts.

Signal evts.


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Data

Reconstruction of K0s

K0s→+-

Pion ID > 0.6

0.4902 < 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 plane

d- angle betn. the momentum vector and decay vertex displacement vector in r- plane

Signal Events

Background Events

dr(cm)

dr(cm)

d(rad)

d(rad)


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Photon Energy (Eg)

Bg.

Signal

Reconstruction of DS+and DS*+

±3 of the nominal mass

(1968.5±0.6 MeV)

1.9539 < M() < 1.9833 GeV

1.9471 < M(KSK) < 1.9901 GeV

1.9495 < M(K*K) < 1.9877 GeV

momentum selection

1.7< 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 – reject if 0.12 < M() <0.15 GeV

GeV


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

GeV

GeV/c2

B→Ds*+- (Ds+→+)

Selection of the B Candidate

Two quantities M(B) and E

are defined as,

E vs. M(B)

Signal MC

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


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Largest background source is e+e-→ qq (q{u,d,s,c}) events

Fisher Discriminant is a powerful tool to discriminate signal and background

Background Suppression – Fisher Discriminant (FD)

  • A linear combination of 9 variables

  • Optimized to discriminate signal from background


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

  • Cos(θth) – Angle between thrust axis of the B candidate

  • and the thrust axis of the remaining particles.

  • Cos(B) – Angle between the B momentum & beam axis

  • qr x (QD) – qr contains flavor information of the other B;

  • q = ±1; 0<r<1; QD – charge of Ds

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

is the mom. of the ith particle in CM frame

s

s

Combine all 9 variables into F

Background Suppression – Fisher Discriminant (FD)

(cont.)


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Used Figure of Merit (FOM)

vs FD plots to decide the best

selection

Background Suppression – Fisher Discriminant (FD) (cont.)

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

continuum

Signal

Arbitrary units

s - Signal

b - background

FD


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

N - inclusive Ds* yield ;  - efficiency ;

Reconstruction Efficiencies

  • 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

Following relationships can be obtained


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Sideband Study

  • Sidebands of Ds and M used

  • 3 from lower and upper side of the signal region

  • used to compare data and MC

  • Background shapes were obtained

Observations:

  • Bkg. shapes of data and MC agree each other

  • Observed a disagreement in bkg. levels ~12% – 22%

  • Bkg. of Ds not random – real Ds but not from Ds*→Ds


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

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

    • Bkg. - linear shape, by fitting data excluding the signal region

      E-1D

    • Signal - Gaussian shape with mean &  fixed to sig. MC shape

    • Bkg. - sideband shapes of M

Lmax - max. likelihood

L(0) – max. likelihood if

signal is zero


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Simultaneous fitting - cont.

Ds*+-

Ds*-K+

E fit

Solid line (red) – total fit

dotted line (blue) - background

Ds*+0


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Simultaneous fitting - cont.

DS*+-

DS*+K-

  • M fit

  • Solid line (red) – total fit

  • dotted line (blue) - background

DS*+0


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Systematic Uncertainties

Since 3 Ds modes,

Total Syst. error = common syst. errors + indept. syst. errors

Common Errors (%)


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Systematic Uncertainties-cont.

Independent Errors


R d for sin 2 1 3

RD* for Sin(21+3)

D* - strong phase,c – Cabibbo angle

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

- good agreement with the expected result which is ~0.02


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

Estimation of Vub

-Good agreement with the world average for

|Vub| which is (3.67±0.47)x10-3


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

  • 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*

Summary


Yields and branching fractions

Yields and Branching fractions


M and e

M and E

DS*+-

DS*-K+

DS*+0

(2.14 0.81)x10-5

(2.43 1.11)x10-5

(1.64 0.66)x10-5

M

E


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

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

DS*+-

19.0±5.7 evts

DS*-K+

11.0±4.8 evts

DS*+0

9.4±5.5 evts


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

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

4.48.4

evts.

15.15.6

evts.

8.24.7

evts.


Thesis defense of luminda kulasiri dept of physics university of cincinnati 05 09 2005

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

DS*+-

21.4±5.9 evts.

DS*-K+

10.6±4.9 evts.

DS*+0

8.1±5.7 evts.


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