Oct 14, 2003

1
Hot Topicsfrom the Belle Experiment
2
Contents

• Introduction to the Belle experiment
• CP violation in B 0 ? fKS
• Evidence of B 0 ? p 0p 0
• New resonance X(3872)
• Summary

3
Introduction to the Belle Experiment
4
KEKB Accelerator

• 3.5 GeV e ? 8.0 GeV e-
• ee- ? ?(4S) with bg 0.425.
• Crossing angle 11 mrad.

World Records
e
e-
3km circumference
L (1.06 ? 1034)/cm2/sec ? L dt 158
fb-1On-resonance 140 fb-1
History
1999 Jun
2003 Jul
5
Belle Detector
Aerogel Cherenkov Counter n 1.0151.030
Electromagnetic Calorimeter CsI(Tl) 16X0
3.5 GeV e
TOF counter
8.0 GeV e-
Central Drift Chamber Tracking dE/dx 50-layers
He/C2H5
KL m detector 14/15 layer RPCFe
Si Vertex Detector 3 layer DSSD
6
People
274 authors, 45 institutions
many nations
7
CP Violation in B 0 ? fKS
8
CP Violation by Kobayashi-Maskawa
KM ansatz CP violation is due to complex phase
in quark mixing matrix
h
unitarity triangle
CP violation parameters (f1, f2, f3) (b, a, g)
O
r
9
Time-Dependent CP Asymmetry
S -xfsin2f1 SM prediction
A 0 or l 1 ? No direct CPV
Inputs xf -1, S 0.6 A 0.0
10
New Physics Hunting in b ? sqq
SM predicts same CPV in b ? ccs and sqq.
New physics may deviate CPV in b ? ccs from sqq
New process w/ different CP phase
SM penguin
f

e.g.) squark penguin
Deviation from b ? ccs
Hint of new physics
11
b ? ccs Reconstruction
Detail by K.Miyabayashi
b ? ccs w/o J/?KL
140 fb-1, 152M BB pairs
Beam-energy constrained mass (GeV/c2)
B 0 ? J/?KL
J/? KL signal
5417 events are used in the fit.
pB (cms)
12
CP Violation in b ? ccs
Detail by K.Miyabayashi
5417 events _at_ 152M BB
poor flavor tag
Small systematic uncertainty ? Well controlled
analysis technique
fine flavor tag
consistent with no direct CPV
K. Abe et al. Belle collaboration,
BELLE-CONF-0353.
13
b ? sqq Reconstructions

• B0 ? fKS f ?KK?, KS ? pp?
• Minimal kaon-identification requirements.
• Belle standard KS selection.
• M(KK) ? M(f) lt 10MeV/c2 (mass resolution
  3.6 MeV/c2).
• pf in CMS gt 2.0 GeV/c.
• Belle standard continuum suppression (given
  later.)
• DE lt 60MeV, 5.27 lt Mbc lt 5.29 GeV/c2.

M(KK) GeV/c2

• Background is dominated by continuum
• CP in the background
• KK-KS (7.21.7)
• f 0(980)KS
• These effects are included in the systematic
  error.

14
b ? sqq Reconstructions - Contd

• B0 ? KK?KS
• More stringent kaon-identification requirements.
• Particle veto for f, D0, ?c0, and J/? ? KK? and
  D ? KKS.
• Belle standard continuum suppression.
• DE lt 40 MeV, 5.27 lt Mbc lt 5.29 GeV/c2.
• B0 ? hKS 1) h ? rg, r ? pp? 2) h ? hpp?,
  h ? gg
• Belle standard continuum suppression.
• DE lt 60MeV (h ? rg) ?100 lt DE lt 80 MeV (h ?
  hpp?)5.27 lt Mbc lt 5.29 GeV/c2

15
Beam-Energy Constrained Mass
68?11 signals 106 candidates for S and A
fit purity 0.64?0.10 efficiency 27.3
B 0 ? fKS
199?18 signals 361 candidates for S and A
fit purity 0.55?0.05 efficiency 15.7
B 0 ? KK-KS
B 0 ? h?KS
244?21 signals 421 candidates for S and A
fit purity 0.58?0.05 efficiency 17.7 (h?
hpp?) 15.7 (h? rg )
16
Unbinned Maximum Likelihood Fit
signal
background

• fsig Event by event signal probability

2. Psig
3. R Dt resolution function
4. Pbkg Background Dt distribution
17
CP Violation in b ? sqq
Fit sin2f1

_at_ 152M BB
B0 ? fKS
B0 ? KK-KS
B0 ? hKS
B ? fCP(sqq) decay vertices are reconstructed
using K- or p-track pair.
18
Consistency Checks

• CP violation parameters with A 0
• B0 ? fKS -xfS -0.99 0.50
• B0 ? KK-KS -xfS 0.54 0.24
• B0 ? h?KS -xfS 0.43 0.27
• Null asymmetry tests for S term
• B ? fK -xfS -0.09 0.26
• B ? h?K -xfS 0.10 0.14

Less correlation btw S and A
Consistent with S 0
19
Statistical Significance

• B0 ? KK-KS, hKS
• Consistent with sin2f1.
• B0 ? fKS
• 3.5s deviation (Feldman-Cousins).
• S(fKS) sin2f1 0.05 probability.

sin2f1
Hint of new physics? Need more data to establish
conclusion.
K. Abe et al. Belle collaboration,
hep-ex/0308035, submitted to Phys. Rev. Lett.
20
Evidence of B 0 ? p 0p 0
21
Disentangling f2
B0 ? p p - is one of promising decays to measure
f2
Two possible diagrams require measured f2
disentangled
u
u
P
T
d
u
W
t
b
u
d
b
W
Penguin-polluted CP violation
Br(B0 ? p 0p 0) measurement gives constraint on q.
22
B0 ? p0p0 Reconstruction

• B0 reconstruction
• 2 p 0s with 115 lt M(gg) lt 152 MeV/c2.
• Efficiency 9.90 0.03.
• Those MC-determined distributions are used in
  extraction of signal yield with calibration using
  B ? D0p decays in data.

Signal MC
Signal MC
DE GeV
Mbc GeV/c2
23
Continuum Suppression
Signal MC
Continuum
Fisher
Fisher
Construct likelihood
ee- ? BB
ee- ? qq
B flight direction
cosqB

• 1-cos2q for BB
• flat for qq

Multi-dimensionallikelihood ratio
Flavor tag quality
r

• r high ? well tagged? originated from B decay
• r low ? poorly tagged? originated from qq

24
B ? rp0 Contamination
According to MC study, other charmless decays
than B ? rp0 are negligible.
B ? rp0
pp0
DE GeV
Mbc GeV/c2
B ? rp0
charmless background incl. rp0

• DE-Mbc shape MC-determined 2-dimensional
  distribution.
• Yield Recent Br measurement with MC-determined
  efficiency.

Br(B ? rp0) measurement B. Aubert et al.
BaBar collaboration, hep-ex/0307087, submitted
to PRL.
25
Signal Extraction
_at_ 152 M BB
B ? rp 0 (modeled by MC)
Continuum
Mbc GeV/c2
DE GeV
Signal
Unbinned maximum likelihood fit
Signal shape is modeled by MC, and is calibrated
using B ? D0p decays in data.
Signal yield
Branching fraction
Significance incl. systematic error 3.4s
S.H.Lee, K.Suzuki et al. Belle collaboration,
hep-ex/0308040, submitted to Phys. Rev. Lett.
26
New Resonance X(3872)
27
New Narrow Resonance X ? pp-J/y

• Mass distribution

Data
MC
y(2S)
y(2S)

• g conversion elimination

Events / 0.010 GeV/c2
X
GeV/c2
GeV/c2
New resonance X is found.
28
B ? KX
_at_ 152M BB

• B ? KX reconstruction
• Add loosely identified kaon to X.

3-dim. unbinned likelihood fit.
MppJ/y
DE
Mbc
5.20
5.25
5.30
3.84
3.88
3.92
0.0
0.2
GeV/c2
GeV
GeV/c2
29
What is X?

• Hypothesis I 13D2
• M(X) 3872 MeV/c2 differs fromprediction
  M(13D2) 3810 MeV/c2.
• G(13D2 ? gcc1)/G(13D2 ? ppJ/y) 5, while G(X ?
  gcc1)/G(X ? ppJ/y) lt 1

Mbc
E.Eichten et al., Phys. Rev. D21, 203
(1980) W.Buchmüller and S.-H.H.Tye, Phys. Rev.
D24, 132 (1981).
M(gcc1)
No clear signal
30
What is X? - Contd

• Hypothesis II molecular charmonium
• M(X) 3872 0.6 0.5 MeV.
• M(D0) M(D0) 3871.2 1.0 MeV.
• Do above facts suggest loosely bound D0-D0
  state?
• Need more data to conclude.

q
q
D0-D0 molecule
Q
Q
S.-K.Choi, S.L.Olsen et al. Belle
collaboration, hep-ex/0309032, submitted to
Phys. Rev. Lett.
31
Summary
32
Summary

• 3.5s deviation is observed with Feldman-Cousins
  in CP violation in B 0 ? fKS from the SM. ?
  Hint of new physics?
• Br(B 0 ? p 0p 0) (1.70.60.2)106 is measured,
  which gives constraint on penguin uncertainty in
  f2.
• New resonance of X ? pp -J/y is observed at M(X)
  3872.00.60.5 MeV/c2 that does not look like
  cc state.

33
Backup Slides
34
Mixing-Induced CP Violation
Sanda, Bigi Carter
s
f
Vtb
Vts
W
b
s
t
B0
g
s
d
KS
d
?
s
V
f
Vtb
Vts
Vtb
td
W
b
t
b
s
t
B0
B0
g
W
W
s
d
t
d
KS
V
Vtb
d
td
35
How to Measure CP Violation?
Detail by K.Miyabayashi
e- 8.0 GeV e 3.5 GeV
fCP
BCP
e-
e
(4S)
bg 0.425
Btag
Dz ? cbgtB 200 mm
flavor tag
Dz

• Find B ? fCP decay
• Identify ( tag) flavor of B ? fCP
• Measure decay-time difference Dt
• Determine asymmetry in Dt distributions

36
Systematic Error of CPV in b ? ccs
Small uncertainty in analysis procedure
stat err. 0.057
37
B0 ? KK-KS CP ?1 Mixture
Since B0 ? KK-KS is 3-body decay, the final
state is a mixture of CP ?1. How can we
determine the mixing fraction?
CP ?1 fraction is equal to that of l even/odd
CP 1
CP 1
K
J0
J0
J0
decay
l
CP (-1)l
KS
B0
l
K-
J0
38
B0 ? KK-KS CP ?1 Mixture - Contd

• l-even fraction in K0K0gt can be determined by
  KSKSgt system

Using isospin symmetry,
CP 1
l odd
l even
CP even
39
Dt Distributions
B0 ? fKS
B0 ? KK-KS
B0 ? hKS
qxf -1
qxf -1
qxf -1
qxf 1
qxf 1
qxf 1
Dt ps
Dt ps
Dt ps
40
Systematic Errors of CPV in b ? sqq
fKS
h'KS
KKKS

• S A S A S A
• Wtag fractions 0.018 0.007 0.005 0.006 0.00
  5 0.007
• Physics parameters 0.033 0.002 0.006 0.002
  0.003 0.003
• Vertexing 0.022 0.046 0.016 0.027 0.044 0
  .024
• Background fraction 0.053 0.035 0.045 0.026
  0.029 0.036
• Background Dt 0.015 0.008 0.003 0.003 0.01
  0 0.006
• Resolution function 0.013 0.005 0.004 0.003
  0.007 0.004
• KKKs f0Ks bkg. 0.001 0.039
• -0.084
• Sum 0.09 0.07 0.05 0.04 0.05 0.04
• -0.11

Systematics are small and well understood from b
? ccs studies.
41
Systematic Uncertainty
42
M(pp-) Distribution
Fit to r-mass is pretty good
M(pp-) GeV/c2

• M(pp-) can be fitted by r-mass distribution
  well.
• 13D2 ? rJ/y is forbidden by isospin conservation
  rule.

43
Constraint on q
Belle Preliminary
M.Gronau et al., Phys. Lett. B 514, 315 (2001).
Using Our Results

• B0/B- 1.04
• B00/B- 0.39
• App 0.57