1. “sin2f1” measurement with bs penguin decays at Belle
Koji Hara (Nagoya University)
for the Belle Collaboration

2. Measurement of time-dependent CP violation (tCPV) in B0h’K0
Introduction
Measurement of time-dependent CP violation (tCPV) in B0h’K0
tCPV result for B0KSp0
2018/12/8

3. Introduction J/ B0 B0 K0 K0 tCPV measurements in B0 decays /
b→ccs tree
b→sqq penguin _ d b c s w d b _ _ w
J/ s
η’,φ… B0 t g B0 s _ K0 s K0
Check if d
S=sin21 , A ~ 0 /
“sin21” ≡-ξfS= sin21, A ~ 0
Extra CPV phase
“sin2φ1“≠sin2φ1
Hint of New Physics
SM Anchor

4. SM Contamination
It is essential to estimate possible deviation from sin2f1within the SM to claim new physics.
bu Tree contamination
Final state rescattering T’ P 2 P’ T 4
color-allowed   +1
KsKsKs 1
Ks P’ T P T’ 
Ks
Ks 
f0Ks
Ks
~+1
K+KKs
CP
mode
color-suppresed _
sdd penguin _
sss penguin
2018/12/8

5. Theoretical Estimation
h’K0, fK0, KSKSKS are the “Golden modes” with the smallest expected difference from sin2f1 in SM
Expected differences are mostly positive.
For example,
[Chua, talk at FPCP06, hep-ph/ ]
2018/12/8

6. 2018/12/8

7. New tCPV result for B0h’KS+h’KL
2018/12/8

8. Event Selection Dominant Background is e+e-  qq continuum
 Distinguished from signal by the Likelihood Ratio made with event shape variables.
Bkg
signal
Likelihood Ratio
Event Shape
(Jet-like)
(Spherical)
2018/12/8

9. B0h’KS Signal
Event-by-event signal fractions extracted from 3D Mbc-DE-LR fit.
LR0.5
LR<0.5 LR fs
h’ rg Ks(p+p-) 794  36
 h(2g)pp Ks(p+p-) 363  21
 h(3p)pp Ks(p+p-) 100  11
rg Ks(p0p0) 103  15
h(2g)pp Ks(p0p0) 62  9
Total  46
2018/12/8

10. B0h’KL Signal Signals are extracted from PB*-LR 2D fit
Background subtracted
h’h(2g)pp KL 392  37
h(3p)pp KL  13
Total  39 LR
PB*(GeV/c)
2018/12/8

11. B0h’K0 Result Consistent with sin2f1
Background subtracted
“sin2f1”=  0.10  0.04
A =  0.07  0.05
Consistent with sin2f1
5.6s First observation of tCPV in bsqq penguin
good tag
2018/12/8

12. CP Fit Results for B0h’KS, KL
h’KS Background subtracted
“sin2f1”
good tag
h’KL Background subtracted
good tag A
2018/12/8
errors are statistical only

13. New tCPV result for B0KSp0
2018/12/8

14. tCPV in KSp0 bs penguin dominant mode
S  sin2f1 (Possible deviation within SM ~O(0.1) )
A Member of Kp Family
A is important to check the sum rule
A(K+p-)+A(K0p+)=A(K+p0)+A(K0p0)
No primary tracks from B vertex
Vertex reconstruction with KS trajectory
[Gronau, Phys. Lett. B627, 82 (2005)]
2018/12/8

15. B0KSp0 Signal
LR<0.7
LR0.7
Signal yield: 515  32
2018/12/8

16. Vertex Reconstruction with KS
Ks track
p+ p-
Extrapolate KS track to the Interaction Point
Vertex reconstruction efficiency ~33%
Events without the vertex can still be used for A measurement.
IP profile
BCP vertex
The validity is confirmed with the J/yKS as control sample.
B0 Lifetime / ps
sin2f1=+0.68+/-0.06
J/yKS with the KS Vertexing
Raw asymmetry
good tag
2018/12/8

17. B0KSp0 tCPV Result “sin2f1”= + 0.33  0.35  0.08
A =  0.14  0.05
Consistent with
sin2f1 from bc
the sum rule expectation
A = -0.150.06
using Belle 532M A, Br and
PDG2006 t+/t0
good tag
2018/12/8

18. Summary tCPV in bsqq modes are sensitive to the new physics
“Golden modes” are fK0, h’K0, KSKSKS
New Results from Belle with 532 M BB
Other tCPV results will be reported in the Plenary Talk by M. Hazumi.
B0h’K0
“sin2f1”=  0.10  0.04
A =  0.07  0.05
5.6s tCPV observation
B0KSp0
“sin2f1”=  0.35  0.08
A =  0.14  0.05
2018/12/8

19. 2018/12/8

20. B0h’KS DE distribution
2018/12/8

21. B0h’KS,h’KL Results “sin2f1”= + 0.67  0.11 A = - 0.03  0.07
2018/12/8
errors are statistical only

22. “sin2f1” A
2018/12/8

23. Systematic Errors h’K0 KSp0 dS dA dS dA
Vertexing
Flavor tagging
Resolution
Physics
Possible Fit bias
BG fraction
BG dt shape
Tag-side interference
Total
2018/12/8