Post on 13-Dec-2015
transcript
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