sin2?1 at Belle

1
sin2?1 at Belle
Masashi Hazumi (KEK) for the Belle
Collaboration
Outline

• Status of KEKB and Belle
• sin2?1 Winter 02 Update
• Conclusion

2
The Belle Collaboration
A World-Wide Activity Involving 50 Institutions
300 members
3
The Belle Collaboration
A World-Wide Activity Involving 50 Institutions
300 members
4
The Belle Collaboration
A World-Wide Activity Involving 50 Institutions
300 members
5
B Factory at KEK 1-page Introduction
8GeV electron
3.5GeV positron
KEKB Collider
6
B Factory at KEK 1-page Introduction
8GeV electron
3.5GeV positron
KEKB Collider
J/? Ks
B
flavor tagging
7
B Factory at KEK 1-page Introduction
8GeV electron
3.5GeV positron
Rate exp(-?t/?B)/2?B ? 1?(?q)sin2?1sin(?m?t)
? CP eigenvalue (e.g. ?1 for J/?Ks) q
Flavor tagging ( 1 for B0-bar(?t))
KEKB Collider
J/? Ks
B
flavor tagging
8
Experimental Challenges
1) Copious B pair production, efficient B
reconstruction 2) Efficient and correct flavor
tagging 3) Observation of time-dependent CP
asymmetry in B decays to a CP eigenstate
with good vertex resolution
?z ? cß??t (200?m at Belle)
9
July 2001 the Beginning of New Age
sin2?1 0.99 ? 0.14(stat) ? 0.06(sys) (Belle,
July 2001)
29.1fb-1 (31.3 million B pairs) PRL 87, 091802
(2001) hep-ex/0202027 (submitted to PRD)
World average (as of July 2001)
sin2?1 0.79 ? 0.10

• First CPV observed outside the kaon system
• Strongly support the KM machanism of CPV
• CP is not an approximate symmetry anymore

10
KEKB Luminosity the worlds best !

• Peak L 7.25?1033 cm-2s-1 (Mar. 28, 02)
• Daily Integrated L 387 pb-1/day (May. 11, 02)
• Weekly Integrated L 2.14 fb-1/week (Apr. 28, 02)

Daily Integrated luminosity history
76fb-1 recorded (May 13,02)
Integrated luminosity history
11
Belle Detector

• Silicon Vertex Detector (SVD)
• Impact parameter resolution
• ? 55?m for p1GeV/c at normal incidence
• Central Drift Chamber (CDC)
• (?Pt/Pt)2 (0.0019Pt)2 (0.0034)2 (Pt in
  GeV/c)2
• K/? separation with
• dE/dx in CDC (?dE/dx 6.9)
• TOF (?TOF 95ps)
• Aerogel Cerenkov (ACC)
• Efficiency 90,
• Fake rate 6 up to 3.5GeV/c
• ?, e? with CsI crystals (ECL)
• ?E/E 1.8 _at_ E1GeV
• e? efficiency gt 90
• (0.3 fake for p gt 1GeV/c)
• KL and ?? with KLM (RPC chambers)
• ?? efficiency gt 90
• (lt2 fake at p gt 1GeV/c)

Quite stable performance up to now
ACC
All components are importantfor the sin2?1
measurement.
12
Belle Detector

• Silicon Vertex Detector (SVD)
• Impact parameter resolution
• ? 55?m for p1GeV/c at normal incidence
• Central Drift Chamber (CDC)
• (?Pt/Pt)2 (0.0019Pt)2 (0.0034)2 (Pt in
  GeV/c)2
• K/? separation with
• dE/dx in CDC (?dE/dx 6.9)
• TOF (?TOF 95ps)
• Aerogel Cerenkov (ACC)
• Efficiency 90,
• Fake rate 6 up to 3.5GeV/c
• ?, e? with CsI crystals (ECL)
• ?E/E 1.8 _at_ E1GeV
• e? efficiency gt 90
• (0.3 fake for p gt 1GeV/c)
• KL and ?? with KLM (RPC chambers)
• ?? efficiency gt 90
• (lt2 fake at p gt 1GeV/c)

Quite stable performance up to now
ACC
All components are importantfor the sin2?1
measurement.
13
Mass Resolutions (1)
J/y ?mm- s9.6MeV/c2
J/y ?ee-(g) s10.7MeV/c2

• MKp(GeV/c2)

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Mass Resolutions (2)
?0??? ?4.8MeV/c2
???? ?12.1MeV/c2
Ks??0?0????? ?12.1MeV/c2
15
Fully-reconstructed Event Example
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sin2?1 Winter 02 Update
Major update ? Summer 2002 (90fb-1)
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Data Set
2002
Belle 20002001 (41.8fb-1)
(LP01 (published) 29.1fb-1)
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Reconstruction of CP Eigenstates
Mode of Ev. Purity
J/yKS(pp-) 636 0.95
J/yKS(p0p0) 102 0.80
y(2S)(ll-)KS 49 0.95
y(2S)(J/ypp-)KS 57 0.93
cc1(J/yg)KS 34 0.93
hc(KSKp-)KS 39 0.72
hc(KK-p0)KS 33 0.73
J/yK0(KSp0) 55 0.89
J/yKL 767 0.60
Total 1772
CP-odd (? ?1)
even/odd mix.
CP-even (? 1)
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All Modes (except B0 ? J/? KL)
B0 ? J/? Ks(???? )
1005 candidates
636 candidates 31 background (Purity 95)
102 cand.
106
34
72
55
B0 ? other modes
369 candidates 59 background (Purity 84)
(DE cut applied)
20
B0 ? J/? KL

• J/? ?ll? KL
• 2) Assume B?J/y KL
• compute PKL
• 3) Remove reconstructed
• B ? J/? K, J/? K,
• 4) Cut on a likelihood
• based on kinematical
• and shape quantities
• 5) Plot P P J/? PKL

B
KL direction 2-body decay kinematics
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B0 ? J/? KL



PB PJ/y PKL
Belle
run-dep. Ebeam correction
Nsig 462 events
B0 ? J/? KL
Nbkg 305 evts
767 total events 462 signal (Purity 60)
LP01 569 sig. 346 bkg
Total 1772 CP events
1316 LP01
PB(cms)
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Flavor Tagging (no change from LP01)
Use inclusive flavor-specific properties

• Inclusive Leptons
• high-p l? b? c l? n
• intermed-p l s l? n
• Inclusive Hadrons
• high-p p B0?D()? p, D()? r, etc.
• intermed-p K K X, p?p0
• low-p p? D0 p?

Also include correlations
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Belle Flavor Tagging Method
Look-up tables
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Wrong-tag Fraction Determination
Wrong tag fractions in 6
tagging categories
Flavor specific decays Tagging
B0 ? Dln, D()p/r
(?mixing)
OF - SF
Asym
OF SF
OF Opposite Flavor SF Same Flavor (i.e.
oscillated)
determined by data
Efficiency gt 99.5 e effective 27.0 ? 1.2
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Related topic Dmd (4 methods)
29.1fb-1 Preliminary (in ps-1)
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Event-by-event Likelihood
double Gaussian
Taken from data
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Improved Resolution Functions

• Separate response functions for vtx with 1-track
  IP constraint and other
• Outlier treatment
• Already adopted for the B lifetime analysis

More sensitive to R(Dt)
Simultaneous fit to B0,B-
t(B0) 1.554 0.030 0.019 (ps) t(B) 1.695
0.026 0.015 (ps) t(B) / t(B0) 1.091 0.023
0.014
PRL 88, 171801 (2002)
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sin2?1 Unbinned Maximum-likelihood Fit
1550 events
1137 LP01
Preliminary
sin2?1 0.82 ? 0.12 (stat) ? 0.05
(sys)

Raw data Asymmetry !
N(qxf-1) - N(qxf1)
N(qxf-1) N(qxf1)
29
sin2?1 Unbinned Maximum-likelihood Fit
1550 events
1137 LP01
Preliminary
sin2?1 0.82 ? 0.12 (stat) ? 0.05
(sys)

Raw data Asymmetry !
N(qxf-1) - N(qxf1)
N(qxf-1) N(qxf1)
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Raw Asymmetries
CP-1
sin2f1
0.69?
0.15 0.16

opposite!
CP1
1.14?
0.22 0.24
(statistical errors only)
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Test of Null Asymmetry
use B0?D()-p, D-r, J/yK(Kp-)
sin2f1

0.05?0.04
(statistical error only)
32
sin2?1 from various subsamples






q1 785 evts
q-1 765 evts
(statistical errors only)
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sin2?1 Systematic Errors
LP01
0.04 0.02 0.01 0.01 0.06
0.024 0.026
0.022 -0.025
0.022 0.019
0.022 -0.032
0.014 0.015
0.007 0.006
0.007 0.006
Preliminary
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Why better precision required ?

• sin2?1 in J/? Ks (and related)
• Insensitive to New Physics Boring ? No !
• Important as the Standard Model Anchoring Point
• Combination with other rare-decay CPV a
  promissing road to the Physics beyond the
  Standard Model
• Examples of rare decays
• B0??Ks New CPV phase search in penguin decays
• sin2?1(J/? Ks) sin2?1(?Ks ) ??
• Talk by K-F. Chen in the hot topics session
  with 73 signal events
• One of the most important inputs to the CKM fit

35
Conclusion

• KEKB Great Achievement !
• Lpeak 7.25 x 1033 cm-2s-1
• Belle Very Stable Operation
• sin2?1 0.82 ? 0.12 (stat) ? 0.05 (sys)
  (41.8fb-1)
• Summer update with 90fb-1 !
• Test the SM with other CPV in rare B decays !

Exciting time will yet to come !
36
Backup Slides
37
Kobayashi-Maskawa model of CPV
CPV due to the complex phase in CKM matrix

Vtd Vtb

?2
Vud Vub
?1
?3

Vcd Vcb
Unitarity triangle
Physics at Belle

• Discover CPV in B meson system (done !)
• Measure CKM elements (angles and lengths) with
  unprecedented precision to overconstrain
• Beyond the SM (e.g. a new CPV phase)

38
KEKB Luminosity
39
Control Samples
Semileptonic decays B0 ? D (?D0?)l ?
Hadronic decays B0? D()? ,D?
6 x 103 events
D0? K?
D0? K??0
D0? K? ? ?
Used to evaluate performance of flavor tagging
40
Vertex Reconstruction

• For CP-side, use J/y?ll-
• Reject poorly fit events.
• dzCP ? 75 mm (rms)
• For Tag-side
• use well fit tracks
• iterate discard worst track
• dztag ? 140 mm (rms)
• Require zCP - ztaglt2mm (10tB)
• s Dt ? 1.5 ps
• Tails ? 3 Effic. ? 85

41
J/?K Transversity Analysis
B ? VV usable !
(See BELLE-CONF-0105)
Psig(Dt, qtr ) (1-RT)PCP-1 (1cos2 qtr) 3/8
RT PCP1 (sin2 qtr) 3/4
42
B0??Ks Time-dependent CPV
Motivation
B0? J/? Ks
c
b
c
w
s
ACP(?t) ?f sin2?1sin(?md?t)

• Precise measurement of CPV in penguin decays a
  powerful tool to search for a new CPV phase
  beyond the Standard Model (SM)
• Large branching fractions for inclusive and
  exclusive B ? ? transition may be a hint.

43
B0??Ks Time-dependent CPV
Motivation
B0? J/? Ks
c
b
c
w
s
ACP(?t) ?f sin2?1sin(?md?t)

• Precise measurement of CPV in penguin decays a
  powerful tool to search for a new CPV phase
  beyond the Standard Model (SM)
• Large branching fractions for inclusive and
  exclusive B ? ? transition may be a hint.

44
B0??Ks Time-dependent CPV
Motivation
B0? J/? Ks
c
b
c
w
s
ACP(?t) ?f sin2?1sin(?md?t)

• Precise measurement of CPV in penguin decays a
  powerful tool to search for a new CPV phase
  beyond the Standard Model (SM)
• Large branching fractions for inclusive and
  exclusive B ? ? transition may be a hint.

45
Reconstruction
Belle 41.8fb-1
B
B0 Yields N(?? Ks) 45.5 N(???
Ks) 27.7
8.6 -7.9
???
6.2 -5.5
More will be given in the hot topic session
(K-F. Chen)
B0