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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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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-

*

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)


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}


  • 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


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)


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.


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)


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


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


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


  • 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.)


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


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


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


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


Simultaneous fitting - cont.

Ds*+-

Ds*-K+

E fit

Solid line (red) – total fit

dotted line (blue) - background

Ds*+0


Simultaneous fitting - cont.

DS*+-

DS*+K-

  • M fit

  • Solid line (red) – total fit

  • dotted line (blue) - background

DS*+0


Systematic Uncertainties

Since 3 Ds modes,

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

Common Errors (%)


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


Estimation of Vub

-Good agreement with the world average for

|Vub| which is (3.67±0.47)x10-3


  • 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



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


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


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

4.48.4

evts.

15.15.6

evts.

8.24.7

evts.


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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