CPV measurements with Belle/KEKB

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CPV measurements with Belle/KEKB

• Stephen L. Olsen
• Univ. of Hawaii

Feb 17, 2003 LCPAC meeting at KEK
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f1 interfere B?fCP with B?B?fCP
(b)
J/y
Sanda, Bigi Carter
Vcb
B0

KS
?
?V2 ?sin2f1

td
J/y
V
Vtb
td
Vcb
(aka sin2b)
B0
B0
B0
KS
td
Vtb
V
td
theory errors 1
3
sin2f1 0.7190.0740.035
B - B B B
more B tags
(tags)
?z
more B tags
t ? ?z/c ß?
Now an established well understood exptl
technique
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Agree on value, not name!!
Belle BaBar agree
sin2f1 (BaBar) 0.7410.0670.033
sin2f1 (Belle) 0.7190.0740.035
sin2f1 (World Av.) 0.7340.055
Agrees with SM
theory errors 1
5
Whats next?

• sin2f1 ? shift to precision measurement mode
• high statistics
• better control of systematics
• measure other angles
• start with f2
• measure sin2f1 in non-ccs decay modes
• sensitive to new physics

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f2 (a) from B?pp-
V
p
ub

B0
p-

?V2 V2
? sin2f2
td
ub
V
V
p-
Vtb
ub
td
(aka sin2a)
B0
B0
p
V
Vtb
td
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Must deal with Penguin Pollution i.e.
additional, non-tree amplitudes with different
strong weak phases

Vtb
Vtd

p-
B0
p
direct CPV
mixing-induced CPV
Rq(Dt) ?1q Appcos(DmDt) Sppsin(DmDt)
q1 ? B0 tag -1 ? B0 tag
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First results from Belle (Mar 02)
Study of CPV Asymmetries in B0 ? pp Decays
PRL 89, 071801 (2002)

• 45 million B-meson pairs (42fb-1)
• 162 events in the signal region

Results indicate large CP asymmetries, outside of
A2S2?1 allowed region
-5 0 5
Dt (ps)
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Outside physical region some (2s) disagreement
with BaBar
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Changes since last March

• More data ! 85?106 B pairs (78 fb-1)
• Analysis improvements
• better track reconstruction algorithm
• more sophisticated Dt resolution function
• inclusion of additional signal candidates by
  optimizing event selection
• Thorough frequentist statistical analyses
• use of Monte Carlo (MC) pseudo-experiments based
  on control samples

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Event and time reconstruction (3)
Flavor tagging
Vertex and Dt
Continuum suppression
B0 ? pp Selection
Flow

• ee- ? qq (qu,d,s,c) continuum
• background suppression
• Event topology
• Modified Fox-Wolfram moments
• Fisher discriminants
• Angular distribution
• B flight direction
• Combined into a single likelihood ratio
• Select 2 regions for each flavor tag class
• LR gt 0.825
• LRmin lt LR ? 0.825

pp- (MC)
continuum
class 1
class 2
class 3
class 4
class 5
class 6
0.825
LRmin
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B0 ? pp- example
p
p-
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B0 ? pp candidates
LR gt 0.825
LRmin lt LR 0.825
pp- 57 Kp 22 qq 406 total 485
pp- 106 Kp 41 qq 128 total 275
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Event and time reconstruction (4)
Flavor tagging
Vertex and Dt
Continuum suppression
B0 ? pp Selection
Flow
Vertex reconstruction

• The same algorithm as that used for sin2f1 meas.
• Resolution mostly determined by the tag-side vtx.
• B lifetime demonstration with 85 million B pairs

B0gDp-, Dp-, Dr-, J/yKS and J/yK0
B0 lifetime 1.551?0.018(stat) ps
(PGD02 1.542?0.016 ps)
Example vertices
Time resolution (rms) 1.43ps
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Time-dependent fit
Unbinned maximum-likelihood fit (no
physical-region constraint)
2 free parameters (App , Spp) in the final fit
DE-Mbc dist.
B0gDp-, Dp-, Dr-, J/yKS and J/yK0
(single Gaussian outlier)
Lifetime fit
The fit program reproduces our sin2f1 results
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Reconstruction summary

• Established techniques for
• event selection
• background rejection
• flavor tagging
• vertexing
• time-difference (Dt) fit
• In particular, background well under control

Common techniques used for branching
fractions, Dmd, tB, sin2f1
Now we are able to obtain App and Spp.But lets
go through several crosschecksbefore opening the
box.
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B0 ? Kp control sample
Positively-identified kaons (reversed
particle-ID requirements w.r.t. pp selection)
LR gt 0.825
LRmin lt LR 0.825
total Kp yield 610 events
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Mixing fit using B0?Kp?
Consistent with the world average (0.489?0.008)
ps-1 PDG2002
(OF?SF)/(OFSF)
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Lifetime measurements
world average (PDG2002) (1.542 ? 0.016) ps
pp tB(1.42 ? 0.14) ps
Very different bkgnd fracs
Kp tB(1.46 ? 0.08) ps
BG shape fit
? background treatment is correct !
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CP fits to the B?Kp sample
q1
q-1
SKp 0.08 ? 0.16
AKp ?0.03 ? 0.11 (consistent with
counting analysis)
No asymmetry
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Null asymmetry tests
Null asymmetry
A ?0.015?0.022 S 0.045 ?0.033
Null asymmetry
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pp- fit results
After background subtraction
Asymmetry with background subtracted
Still see a large CP Violation!
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Fit results
App 0.77 ?0.27(stat) ?0.08(syst) Spp ?1.23
?0.41(stat) (syst)
0.08 ?0.07
After background subtraction
Asymmetry with background subtracted
data points with LR gt 0.825 curves from combined
fit result
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Likelihoods errors
The probability for such small Spp errors is
1.2
ln(L) is not parabolic

• we use most
• probable errors
• from toy-MC

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How often are we outside the physical region ?
App 0.77 ?0.27(stat) ?0.08(syst) Spp ?1.23
?0.41(stat) (syst)
Fit results
0.08 ?0.07
Probability that we have a fluctuation equal to
or larger than the fit to data (input values at
the physical boundary) 16.6
Physical region App2 Spp2 1
Note prob. outside the boundary
60.1 (independent of statistics)
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Cross-checks
Prev result App Spp 0.94 -1.21
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(App,Spp) CL regions
3.4s Evidence for CP violation in B0 ? pp
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Constraining f2
App
P/T 0. 276 ? 0.064 (Gronau-Rosner PRD65,
013004 (2002)
Spp
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Constraints on f2
allowed regions

• Input values for f1 and P/T
• f123.5? (sin2f10.73)
• P/T 0.3

• f2 constraint w/o isospin analysis !
• both App and Spp large
• less restrictive on d
• d lt 0 favored
• no constraint on d at 3s

f2 (deg.)
d (deg.)
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Constraints on f2 (contd)
( f1 23.5?)
P/T dependence
P/T 0.15
P/T 0.45
P/T 0.30
f2 (deg.)
d (deg.)

• Consistent with theoretical predictions
• Larger P/T favored

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Constraints on f2
78? f2 152?
(for 0.15?P/T?0.45)
f2
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(95.5 C.L.)
78? f2 152?
f1 dependence is small
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Strategies for f3
D0?CP
Gronau, London, Wyler
K?
?
Vub
Vcb
D0?CP
?3
?2
K?
Amax 2R 0.2
_at_ 78 fb 1 47 CP-even evts 50 CP-odd evts A
0.12 0.13
_at_500 fb 1 dA/Amax ?0.3
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Strategies for f3 (contd)
doubly Cabibbo-suppressed
Atwood, Dunietz, Soni
Vub
Vcb
Amax 1 but rate is small
Only 15 Dop evts, Cabibbo-suppressed DoK down
by 1/20
80 fb 1
B?Dop
Kp-
This strategy is very clean but requires lots
lots of data
Mbc
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Are there non-SM CPV phases?
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Measure sin2f1 using loop-dominated processes
eff
Example
no SM weak phases
, ?, KK-
SM sin2f1 sin2f1 from B?J/y KS unless there
are other, non-SM particles in the loop
eff
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similar to m(g-2)
look for effects of heavy new particles in a well
understood SM loop process
m(g-2)
sin2f1eff

• well defined technique target
• theory exptl errors are well controlled
• errors on SM expectations are small (5)
• SM terms are highly suppressed
• SM loops contain t-quarks W-bosons
• ? effects of heavy non-SM particles can be large

lowest-order SM diagrams
SM loop particles t W
SM loop particle g

look for pp1 effects (i.e.100)
look for ppm effects
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These channels are very clean the techniques
are understood
Wont reach experimental limits until 100 x more
data
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sin2f1eff results (SM sin2f10.72
0.05)
(hep-ex/0212062)?PRD(r)
78fb-1
B? fKS
B?hKS
B?KK-KS
-0.73 0.66
Spp
0.52 0.47
0.76 0.36
2.2soff
OK
OK
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CPV with Belle (summary)

• f1 well established
• next high precision measurements
• f2 1st exptl limits are established
• interesting near future
• f3 just beginning
• non-SM phases search has begun
• 2.2 s discrepancy seen in fKS
• BaBar has seen a similar discrepancy in fKS

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Conclusion

• Weve accomplished a lot in CPV
• There is still a lot more to be done
• KEKB Belle are up to the task