CPV measurements with Belle/KEKB
Stephen L. OlsenUniv. of Hawai’i
Feb 17, 2003 LCPAC meeting at KEK
B0
td
td
B0
Vtb
Vcb
KS
J/
J/
KS
V*2
sin21
Vtb
V*td
Vcb
B0B0
Sanda, Bigi & Carter:
+
1 : interfere BfCP with BBfCP ()
V*td
theory errors ~1%
(aka sin2
z
more B tags B - B
B + B (tags)
t z/c βγ
more B tags
Now an established & well understood expt’l technique
sin21 = 0.719±0.074±0.035
Belle & BaBar agree
sin21 (Belle)
=0.719±0.074±0.035
sin21 (BaBar)
=0.741±0.067±0.033
sin21 (World Av.)
=0.734±0.055
theory errors ~1%
Agree on value,not name!!
Agrees with SM
What’s next?
•sin2 shift to precision measurement mode•high statistics•better control of systematics
•measure other angles•start with
•measure sin2 in non-ccs decay modes•sensitive to new physics
2 () from B+
B0
B0
V*
V*
td
td
Vtb
Vtb
V
V
+
+
B0
+ V*2 V2
td ub sin22
ub
ub
(aka sin2
Must deal with “Penguin Pollution”i.e. additional, non-tree amplitudes
with different strong & weak phases
B0
+
Vtb Vtd
*
Rq(t) 1+q [Acos(mt) + Ssin(mt)]q=+1 B0 tag
1 B0 tag
direct CPV mixing-induced CPV
t (ps)
First results from Belle (Mar 02)
+0.38 +0.160.27 0.13
+0.250.31
(stat.) (syst.)
S = 1.21
A = +0.94 0.09
• 45 million B-meson pairs (42fb-1)• 162 events in the signal region
“Study of CPV Asymmetries in B0 +– Decays” PRL 89, 071801 (2002)
Results indicate large CP asymmetries, outside of A2+S21 allowed region
-5 0 5
Outside physical region & some (~2) disagreement with
BaBar
Changes since last March
• More data ! [85106 B pairs (78 fb-1)]
• Analysis improvements:• better track reconstruction algorithm
• more sophisticated t 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
e+e- qq (q=u,d,s,c) continuum background suppression
Event topologyModified Fox-Wolfram momentsFisher discriminants
Angular distributionB flight direction
Combined into a single likelihood ratio
Select 2 regions for each flavor tag classLR > 0.825LRmin < LR 0.825
Event and time reconstruction (3)
S
S qq
LLR
L L
FlowFlavortagging
Vertexand t
Continuumsuppression
LRmin 0.825
continuum (MC)
class 1 class 2
class 3 class 4
class 5 class 6
B0 +–
Selection
B0 example
+
B0 +– candidatesLR > 0.825
+- : 57K : 22qq : 406total : 485
LRmin < LR ≤ 0.825
+- : 106K : 41qq : 128total : 275
Event and time reconstruction (4)
FlowFlavortagging
Vertexand t
Continuumsuppression
• The same algorithm as that used for sin21 meas.• Resolution mostly determined by the tag-side vtx.• B lifetime demonstration with 85 million B pairs
Example vertices
Vertex reconstruction
B0D, D*, D*, J/KS and J/K*0
B0 lifetime1.5510.018(stat) ps
Time resolution (rms)1.43ps
(PGD02: 1.5420.016 ps)
B0 +–
Selection
Time-dependent fit
Unbinned maximum-likelihood fit (no physical-region constraint)
2 free parameters (A , Sin the final fit
(1 ) {( ) }
( )
i i
m q m mi ol K K sig qq qq qq
ol ol i
L P
P f f P f P R f P R d t
f P t
E-Mbc dist.
B0D, D*, D*, J/KS and J/K*0
Lifetime fit
(single Gaussianoutlier)
The fit program reproduces our sin21 results
Reconstruction summary
Now we are able to obtain A and SBut let’s go through several crosschecks
before opening the box.
• Established techniques for• event selection
• background rejection
• flavor tagging
• vertexing
• time-difference (t) fit
• In particular, background well under control
Common techniques used forbranching fractions,md, B, sin21
B0 K+– control samplePositively-identified kaons
(reversed particle-ID requirements w.r.t. selection)
total K yield: 610 events
LR > 0.825LRmin < LR ≤ 0.825
Mixing fit using B0K+
md=0.55 ps-1+0.050.07
Consistent withthe world average(0.4890.008) ps-1
PDG2002
(OF
SF)/
(OF+
SF)
: B=(1.42 0.14) ps
K : B=(1.46 0.08) ps
BG shape fit
Lifetime measurementsworld average (PDG2002)(1.542 0.016) ps
background treatment is correct !
Very different bkgnd fracs
CP fits to the BK sample
q=+1 q=1
SK = 0.08 0.16
AK =0.03 0.11 (consistent with counting analysis)
No asymmetry
Null asymmetry tests
A = 0.0150.022S = 0.045 0.033
Null asymmetry
Null asymmetry
fit results
Afterbackgroundsubtraction
5-5 0
Still see a large CP Violation!
5-5 0
Asymmetrywith background
subtracted
Fit results
Afterbackgroundsubtraction
Asymmetrywith backgroundsubtracted
5-5 0
A = +0.77 0.27(stat) 0.08(syst) S = 1.23 0.41(stat) (syst)+0.08
0.07
data points with LR > 0.825curves from combined fit result
Likelihoods & errors
The probability for such small S errors is ~1.2%
we use most probable errors
from toy-MC
ln(L) is not parabolic
Physical region A2 + S2 ≤ 1
Probability that we have a fluctuation equal to or larger than the fit to data(input values at the physical boundary)
16.6%
[Note] prob. outside the boundary 60.1%(~independent of statistics)
How often are we outside the physical region ?
A = +0.77 0.27(stat) 0.08(syst) S= 1.23 0.41(stat) (syst)+0.08
0.07
Fit results:
Cross-checks Prev result
A S
0.94 -1.21
3.4Evidence for CP violationin B0 +–
(A,S) CL regions
2
21
21
12
212
|/|cos)cos(|/|21
,/]sin)sin(|/|2[
,/]2sin|/|
cos)sin(|/|22[sin
TPTPR
RTPA
RTP
TPS
TP
Constraining 2
| P/T| = 0. 276 0.064(Gronau-Rosner
PRD65, 013004 (2002)
S
A
2 (d
eg.)
(deg.)
allowed regions• Input values for 1 and |P/T|
1=23.5 (sin21=0.73) |P/T| = 0.3
2 constraint w/o isospin analysis !
both A and S large
• less restrictive on < 0 favored no constraint on at 3
Constraints on 2
2 (d
eg.)
(deg.)
|P/T| = 0.15 |P/T| = 0.30 |P/T| = 0.45
Consistent with theoretical predictions Larger |P/T| favored
( 1 = 23.5)|P/T| dependence
Constraints on 2 (cont’d)
Constraints on 2
78 ≤ 2 ≤ 152
2
(for: 0.15|P/T|0.45)
1 dependence is small
78 ≤ 2 ≤ 152
(95.5% C.L.)
Strategies for 3
D0CPVub
Amax ~ 2R ~ 0.2
@ 78 fb –1
47 CP-even evts
50 CP-odd evts
A = 0.12 ± 0.13
@500 fb –1: A/Amax ~0.3
Gronau,London,Wyler D0CP
Vcb
32 K
K
Strategies for 3 (cont’d)doubly Cabibbo-suppressed
Amax ~ 1; but rate is small
80 fb –1:K+
Mbc
Only ~ 15 Do evts, Cabibbo-suppressed Dodown by ~1/20
Vub
Atwood,Dunietz, Soni
Vcb
BDo
This strategy is very clean but requires lots & lots of data
Are there non-SM CPV phases?
Measure sin21 using loop-dominated processes:
Example:
, ’, KK
no SM weak phases
SM: sin21 = sin21 from BJ/ KS
unless there are other, non-SM particles in the loop
eff
eff
similar to (g-2)
• well defined technique & target
– theory & expt’l errors are well controlled
– errors on SM expectationsare small (~5%)
• SM terms are highly suppressed
– SM loops contain t-quarks & W-bosons
– effects of heavy non-SM particles can be large
look for ppm effects look for pp1 effects
(i.e.~100%)
(g-2): sin21eff
:
SM loop particle: SM loop particles: t & W
lowest-order SM diagrams
look for effects of heavy new particles in a well understood SM
loop process
These channels are very clean& the techniques are
understood
Won’t reach experimental limits until ~100 x more data
sin21eff results: (SM: sin2=+0.72± 0.05)
2.2σoff
(hep-ex/0212062)PRD(r)78fb-1
0.73 ± 0.66
B KS
S +0.52 ± 0.47 +0.76 ± 0.36
B’KSBK+KKS
OKOK
CPV with Belle (summary)
• 1 well established
– next: high precision measurements
• 2 1st expt’l limits are established– interesting near future
• 3 just beginning
• non-SM phases search has begun –
– 2.2 discrepancy seen in KS – BaBar has seen a similar discrepancy in KS
Conclusion
• We’ve accomplished a lot in CPV
• There is still a lot more to be done
• KEKB & Belle are up to the task
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