Branching Ratios and Angular Distribution of B D* Decays

István Dankó

Rensselaer Polytechnic Institute

(CLEO Collaboration)

July 17, 2003

EPS Int. Europhysics Conference on HEP

Aachen, Germany

CESR CLEO

Outline

• Motivation

• CLEO detector and data

• Event Selection

• Maximum Likelihood Fit

• Results:

– Branching Fractions

– Helicity Amplitudes

• Conclusion

EPS Abstract: 119CLEO Collaboration, S. E. Csorna et al., Phys. Rev. D. 67, 112002 (2003)

Hadronic decays are complicated by final-state interactions. Factorization hypothesis (FH): the products of two-body B meson decays

hadronize independently. The validity of the FH has to be tested experimentally. If FH is valid then certain 2-body hadronic decays are analogous to similar

semileptonic decays:

Experimental tests:• Comparing decay rates,• Comparing the polarization of the B0D*+ decay to that of the B0D*+l

decay at the same momentum transfer (q2=M2=Ml

2 ).

J. Körner and G. Goldstein, Phys. Lett 89B, 105 (1979)

Motivation

0b d

uW

dd

cD*+

0

d

bc

W

l

d D*+

B D* Decay

• Color-enhanced diagram (a1)• Color-suppressed diagram (a2)

Color-allowed Color-suppressed

0*DB

*0 DB

• Color-enhanced diagram (a1)

Relative effective coupling strength in BSW model:

212*0

0*

)/75.01()()(

aaDBBrDBBr

M. Bauer, B. Stech, and M. Wirbel, Z. Phys. C 34, 103 (1987)

Color-allowed

B D* : Angular Distribution Three possible helicity final states

(P VV decay):

Angular distribution is described by the coherent sum of the three helicity states:

i

D

i

D

D

e

e

sinsin24

3~1,1

sinsin24

3~1,1

coscos22

3~0,0

*

*

*

),,(1,11,10,0coscos

*

*

2

0

3

D

D

HHHddd

d

H0, H+, H- : complex helicity amplitudes (H=|H|ei) Previous CLEO measurements:

Phys. Rev. D 50, 43 (1994): 0.89 fb-1 data, (cosD*,cos) CLEO CONF 98: 3.1 fb-1 data, (cosD*,cos, )

CLEO detector and data sample

The data were collected by the CLEO II/II.V detector at the Cornell Electron Storage Ring (CESR).

CLEO II:

– Tracking Chambers (1.5T B, 95% 4),– TOF,

– CsI EM Calorimeter (98% 4),

– Muon detectors (85% 4) CLEO II.V:

– Si Vertex Detector,

– He-Propane DR gas.

9.1 fb-1

(9.7 million BB pairs)

4.6 fb-1

to study background

BBSee )4(

qqee ),,,( scduq

Off-res.On-res.

BB threshold

Event reconstruction and selection criteria

• Charge track selection:– If p > 250 MeV:

• Originate from interaction point and well measured

• dE/dx consistent with K or hypothesis within 2.5

• No lepton– If p < 250 MeV (from D* and D0)

• Only loose requirement of consistency with originating from interaction point

0 selection:– Photon pair in barrel calorimeter– E > 30-65 MeV (mode dependent)– | M - M0 | < 2.5

• D0 selection:– | MK(n) – MD0 | < 2.5– D0K+0 : densely populated

region of the Dalitz plot• D*0 and D*+ selection:

– | M MPDG | < 2.5 (M = MD* MD0)

- selection:– | M M | < 150 MeV/c2

• B selection:–

• Background suppression:– Fox-Wolfram moment R2 < 0.5– | cos S | < 0.7-0.9– | cos B | < 0.95

0*DB

%)62(00D

*0 DB

%)68(0 D

0

0%)5.7(

%)13(

%)8.3(00

K

K

K

D

Ebeami EE 5.2

Maximum Likelihood Fit

Unbinned maximum likelihood fit: j = nj

S + njB number of signal and background events in the jth D0 decay mode,

– Probability density function (pdf):

jjj n

iBj

Sj

DBji

BjD

Sji

Sj

j j

n

j

nn

mMPnmMPn

n

e

1

**3

1

,cos,cos,,,cos,cos,,

!

),cos,(cos)()(),cos,cos,,( ** DBD mMmMP

Signal pdf: MB: Gaussian distribution for M: Breit-Wigner with Blatt-Weiskopf form-factor A: angular distribution corrected by detector acceptance

Background pdf: MB: ARGUS-type function M: flat distribution A : 2nd order polynomials in cosD*

and cos,1st order polynomial of cos(+0))

22Bbeam pEM

Two-step fit:

– For signal and background and mass distribution parameters (no angular part);

– For helicity amplitudes (signal, background and mass parameters are fixed).

Branching Ratio

)%02.009.003.068.0()*(

)%05.016.006.098.0()*(0

0

DBBr

DBBr

• NBB 2%• background shape 3%• efficiency 10 18%

• D* and D0

Br ratio error

To extract number of signal and background events: maximum likelihood fit to all events with 5.2 < MB < 5.3 GeV/c2 (angular distribution ignored)

1st Syst. Error 2nd Syst. Error

D0 decay mode, j njS (%)

BK+ 148.913.8 6.560.04

K+0 177.416.6 2.200.02

K++ 136.015.2 3.040.03

B0

K+ 196.314.6 10.880.05

K+0 196.116.4 3.670.03

K++ 170.613.9 4.460.03

Branching Ratio

Comparison with

previous results:

BSW effective couplings:2

12*0

0*

)/75.01()()(

aaDBBrDBBr

04.004.005.003.021.0/ 12 aa

3rd syst. error is from f+-/f00=1.0720.0450.0270.024 (PDG 02)

0*DB *0 DB

Helicity Amplitudes

Maximum likelihood fit including events with 5.27 < M < 5.30 GeV/c2 only:

– njS , nj

B (scaled) and mass distribution parameters are fixed,

– helicity parameters (|H+|, |H|, +-0, -0) are allowed to float in the fit

(|H0|2+|H+|2+|H|2=1, and 0=0),

Detector acceptance depends on the polarization (angular distribution) due to detector smearing needs iteration until helicity amplitudes converge.

Helicity Amplitudes

Systematic uncertainties:• Acceptance parametrization• Detector smearing• Background level/shape

(dominant)• Non-resonant 0 contribution• Polarization dependence on m

B D*0 B0 D*+

|H0| 0.9440.0090.009

0.9410.0090.006

|H+| 0.1220.0400.010

0.1070.0310.011

+ 1.020.280.11 1.420.270.04

|H| 0.3060.0300.025

0.3220.0250.016

0.650.160.06 0.310.120.04

Helicity amplitudes (H=|H|ei) |H0|2+|H+|2+|H|2=1

Non-trivial helicity amplitude phases (+ , ) Significance:

• Indication of FSI• Important for direct CPV in B decay

75.2:*

19.3:*0

0

DB

DB

Longitudinal Polarization

Longitudinal polarization:

222

0

2

0

HHH

HL

016.0018.0892.0

012.0016.0885.0

0*

*0

DB

DB

L

L

HQET with factorization:

019.0895.0*0 DBL

Previous CLEO measurements of long. polarization in B0D*+ :

030.0034.0878.0

05.005.093.0

L

L (1994)

(1998)

Consistent with measurement!

B0D*+’: CLEO Coll., PRD 64, 092001 (2001); B0 D*+DS*: CLEO Coll., PRD 62, 112003 (2000)

Conclusion

CLEO has measured the branching ratio and helicity amplitudes of the decays BD*0 and B0D*+.

Calculated the the ratio of effective coupling constants a2/a1 and the degree of longitudinal polarization.

The fraction of longitudinal polarization for B0D*+ decay confirms the validity of the factorization hypothesis at relatively low q2:

Measurement of the helicity amplitudes indicates a strong possibility of non-trivial helicity amplitude phases which would arise from final-state interactions

(indication of FSI has been reported in BJ/K* by CDF (PRL 85, 4668 (2000) and BD by CLEO (PRL 88, 062001 (2002) )

CLEO Collaboration, Phys. Rev. D 67, 112002 (2003)

22)*()*( 00

MqLL DBDB