Measurements of sin2 1 in processes at Belle CKM workshop at Nagoya 2006/12/13 Yu Nakahama...
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Measurements of sin2Measurements of sin211 in processes at in processes at BelleBelle
CKM workshop at Nagoya 2006/12/13
Yu Nakahama (University of Tokyo)for the Belle Collaboration
•Analysis procedures •Results in 2006•Sensitivity of sin21 at Belle•Summary
Outline
sccb
2
Principle of Measurement
• Reconstruct B fCP(bccs) decays• Measure t and Determine flavor of Btag
• Evaluate CP asymmetry from the t and flavor information
e- e+e-: 8.0 GeVe+: 3.5 GeV
BCP
z
Btag
(4S) ~ 0.425
fCP(bccs)
z ctB ~ 200 m
Flavor tag ( )z
ct
3
BCP J/K0 Reconstruction in 535M BB
2*/
2*KsJbeambc PEM
B0 J/ KS B0 J/ KL0 0
Beam energysubstituted B mass (GeV/c2)
B momentumin the cms (GeV/c)
Eve
nts /
50
MeV
/c
Eve
nts /
1 M
eV/c
2
+ data
MC: J KLX MC: signal
MC: J/ X MC: comb.
Nsig = 6512Purity 59 %
CP even
Nsig = 7482Purity 97%
CP odd
S→only)
pKL information is poor. lower purity
4
– IP (interaction point) tube constraint fit• IP profile
– Size:x~100m, y~5m.– Smearing due to B flight is taken into account by 21m in the x-y plane.
• No constraint in the beam direction (z-axis).
Measured track
Measured track
IP profileIP tube
t measurement -Vertex fit
CP side (J/ψ) Tag side
2-trk 1-trk Failed n-trk 1-trk Failed
Fraction (%) 93.7 0.9 5.4 82.5 10.3 7.2
Resolutionm) 52.5±0.2
108.9±3.2
107.5±1.0
256.4±4.3
z-axis
B decays vertices are reconstructed using the tracks coming from their decay particles using kinematical vertex fit.
5
Flavor Tagging• For the BCP-Btag coherency originated from Y(4S) decay,
Btag flavor determines BCP flavor (B0 or B0) at Btag decay time.
• Flavor information is determined from Btag decay products.
-1 0 +1-1 0 +1Btag=B0 B0B0 B0qr qr
Flavor information is parametrized using qr: q: MC determined discrete flavor (1 or -1) r: MC determined flavor ambiguity (0~1)
Even
t fra
ctio
n
6
Evaluation of CP asymmetries
0
1
sig 1
bkg
( , ;sin 2 , )1 [1 (1 2 ) (sin 2 sin cos )] ( )
4(1 ) ( )
d dB
sig
P t q A
f q w m t A m t R t
f P t
Btag = B0
Btag = B0
Btag = B0
Btag = B0Smeared by • Detector resolution• Wrong flavor tag effect
• (Bkg. contribution)
Signal
Background
Maximum Likelihood Fit
Wrong flavor tag effect Detector resolution
t (ps) t (ps)
Measured tTrue t
0)2(sin
),2sin;,(),2(sin.
1 111
ALLAqtPAL
Neve
iii
7
RCP RTag
We understand the following resolution components:– Detector resolution:
– Effect of non-primary particles:
– Kinematic approximation of B0 flight:
We determine the models and their parameters using control samples:
B0→D(*)-l+ D(*)-D*
B+→D0+, J/ψK+
Overview of Resolution function: R(t)
R(t) = RCP RTag RNP RK
RNP
RK
B
Bz
BD
lNon-primary particles
Brec
Ks
ll J/ψ
Residuals=Zrec ― Zgen
Bgen
[NIM A533: 370,2004]
8
Resolution functionUsing event-by-event vertex quality: z and , (Vertex fit2 along the z direction only) Detector resolution is modeled using MC as:
- Event-by-event Double Gaussian- Sigma of Gaussian ~ Error z
- Scaled up according to
Entri
es
t (ps)
Neutral B
Lifetime fit
(B0 = 1.530 +/- 0.009ps [PDG2006])
All resolution parameters aredetermined from fits to data/MC samples.
We verify the fitted lifetime usingthis model is self-consistent to the onewe used in the sin21,A fit. J/ψK0 DataB0 = 1.544 +/- 0.016(stat) ps
9
tmw d cos)21(
Wrong flavor tag effect
Wrong tag effect for each r binis estimated from time-dependent B0-B0 mixing fitusing self-tagged control samples:B0D(*)-l+ D(*)-D*
chg cosOF SFd
OF SF
P PA m tP P
Events are classified into 6 categories according to the r.
|t| (ps) |t| (ps)
Measured time-dependent flavor asymmetry
Dilution due to mis-flavor tagging
Wrong flavor tag effect
Time-dependent flavor asymmetry:
Measured asymmetry:
10
KEKB Integrated luminosityas a function of time
B0 J/ KS0
B0 J/ KL0
History of the measurements of sin21 at Belle
Results based on 535MBB
will be described.
andthe expected sensitivity in the future
11
2006 results with 535MBB0/CP SB J K 0/CP LB J K
Δt (ps)Δt (ps)
CP= -1 CP= +1
Raw
Asy
mm
etry
(=-
C
Psi
n2 1s
inm
t)
1sin2 0.643 0.0380.001 0.028A
1sin2 0.641 0.0570.045 0.033A
En
tries
/ 0.
5ps
Raw
Asy
mm
etry
0/CP SB J K 0/CP LB J K solesole
(total) (total)
Entri
es /
0.5p
s
12
Combined results with 535MBB
0 0/ ( )CP S LB J K K
1sin2 0.642 0.031 0.0170.018 0.021 0.014A
(stat.)
CombinedCombined
The other ccs processes are not included.
(syst.)
Entri
es /
0.5p
sR
aw A
sym
met
ry
-CPΔt (ps)
hep-ex/0608039, to appear in PRL
13
Prospect of sin21 uncertainty
Total Statistical Systematic
0.492/ab 0.035 0.031 0.0175/ab 0.017 0.010 0.014
50/ab 0.014 0.003 0.013
L /ab
Assumption:•Use the same analysis methods as of now.
•Use BJ/ψK0 only.
5/ab 50/ab535MBB↑0.492/ab
ー Total errorー Statistical errorー Systematic error
In L ~>2/ab region,the systematic error will be larger than the statistical one.
14
Systematic error of sin21
Categoriessin21)
with 535MBB
1.Vertexing 0.0122.Possible fit bias 0.007t Resolution function 0.0064. BG fractions (J/KL) 0.005
5.Wrong tag probability 0.0046.BG fractions (J/KS) 0.003
7.Fixed Physics parameters: md ,B0 0.001
8. BG t 0.0019.Tag-Side interference 0.001
Total 0.0170.017
sin21) with 5/ab
0.0120.002
0.0060.0020.0010.001
>0.000>0.000
0.001±0.013 ±0.003
Independent of the luminosity increase.
large
small
0.0140.014
15
Breakdown of the systematic error from Vertexingsin21) with 535MBB
1. IP tube constraint vertex fit 0.0072
2. Poor-quality vertex rejection 0.0064
3. Imperfect SVD alignment 0.0056
z bias 0.0050
5. Track error estimation 0.0033
6. Track rejection in Btag decay vertexing
0.0026
t fit range 0.0002
Total ±0.012
•Dominant
•Irreducible even with more data
1. IP tube constraint fit–Select only the events with the 2 tracks in CP side
2. Poor-quality vertex cut–Tighten a criteria for the vertex selection.
Limiting factor is imperfect SVD alignment.
Possible improvement ideaAs we have more data, we can reject the events with poorer quality to reduce the systematic error.
16
•With the current data set (492/fb),
Dominating source of the systematic error is vertexing, especially imperfect SVD alignment.
•In L ~>2/ab region, the systematic error will be larger than the statistical one.
•With 5/ab data,
• 50/ab data,
Summary
As we have more data, we can reject the events with poorer quality The systematic error could be reduced.
±0.010±0.014
±0.003±0.013(stat.) (syst.)
(stat.) (syst.)
Sensitivity of sin21 using BJ/ψK0 at Belle
17
Supporting Results• sin2 fit on non-CP eigenstate
– consistent to zero
• Lifetime fits – consistent to input lifetime for S, A fits
1 /
/
(sin 2 ) 0.018 0.020(stat)
0.003 0.014(stat)B J K
B J KA
0 0/
/
1.544 0.016(stat) ps
1.641 0.011(stat) psB J K
B J K
[tB0 = 1.530ps, md = 0.507/ps]
18
Systematic errors of B0J/K0
Sin21 A1.Vertexing 0.012 0.0092.Wrong tag probability 0.004 0.003t Resolution function 0.006 0.0014.Fixed Physics parameters 0.001 0.0015.Possible fit bias 0.007 0.0046.BG fractions (J/KS) 0.003 0.001 BG fractions (J/KL) 0.005 0.0027. BG t 0.001 0.0018.Tag-Side interference 0.001 0.009
total 0.017 0.014
19
More on Vertex errorsError of Imperfect SVD alignment• Misalign DSSDs in MC to reproduce IP resolution (15m shift an
d 0.15mrad rotation.)• Generate signal MC with and w/o misalignment • Obtain sin21 for two cases and take the difference.
Effect of Vertex section (cut poor quality vertices: (default : >250))• Obtain sin21 with andand take the larger variat
ion.
Error of IP tube constraint fit is obtained by changing the smearing effect due to B flight (default: 21m)
• Obtain sin21 with IP tube smearing by 11m and 41m and take the larger variation.
20
Flavor tagging
q: discrete flavor
Effective tagging efficiency:29.2+-1.4[%]
[NIM A 533, 516 (2004)]
21
Tag Side Interference• Interference between CKM-favored and CKM-
suppressed BD transitions in tag side.• Estimated by pseudo-experiments whose para
meters are obtained from B0D*l samples• No interference for semi-leptonic decay in tag
side (It was included till last year)
22
Prospects for less systematic errors
• IP tube constraint fit– Select only the events with the 2 tracks in CP side– Easy and little gain
• Poor-quality vertex cut– Select only the events with good vertex qualities.– Easy and effective but need data
• Imperfect SVD misalignment: – Difficult to improve and almost hopeless.– If better methods are found, need reprocess all data.
Vertexing
t Resolution function–Select only the events with good qualities
–We could model simply using less parameters.
–Potentially promising, but not so easy
23
Effect of non-primary particles• Most of tag-side B has
a secondary vertex coming from D decays.• The effects of these non-primary tracks
cannot be 100% eliminated in our vertexing algorythm.
• Modeled by – Gauss’sfunction : the effects of the tracks from the primary vertex. – Exponential function :the effects of Lifetime components of D
decaying into non-primary particles.
• A tagging lepton is expected to be from a primary vertex.– We determine the parameters of Gauss’sfunc.
for the events w/ tagging lepton w/o tagging lepton, separately.
.
BD
l
Non-primary particles
Tagging lepton
Entri
es (L
og)