Thesis Defense of Luminda Kulasiri Dept. of Physics, University of Cincinnati 05.09.2005 Search for...
-
date post
20-Dec-2015 -
Category
Documents
-
view
215 -
download
0
Transcript of Thesis Defense of Luminda Kulasiri Dept. of Physics, University of Cincinnati 05.09.2005 Search for...
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.