1. CP Violation in B Decays
Vivek Sharma
University of California at San Diego
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Ringberg Workshop 2006

2. Task: Over Constrain The Unitarity Triangle
By Measurement of UT Sides
By Measurement of UT Angles  
CPV
B0+- , , +-
b d
B0B0
b u l 
B-  
CPV
BK0 (bccs)
BK0 (bsss 
CPV
B-DK-
B0 D0K0 
b c l 
Is CKM Matrix the (only) Source of CP Violation?

3. CP Violation
CP violation can be observed by comparing decay rates of particles and antiparticles
The difference in decay rates arises from a different interference term for the matter Vs. antimatter process.

4. CP Violation Due to Quantum Interference
Weak phase wk changes sign under CP, strong phase st does not
G(B ® f )
G(B ® f )

5. Direct CP Violation in B0 K
Classic example of Quantum Interference
Loop diagrams from New Physics (e.g. SUSY) can modify
SM asymmetry contributing to the Penguin (P) amplitude
Measurement is a simple “Counting Experiment”

6. Direct CP Violation in B0K+p-
Bkgd symmetric!
4.2, syst. included
BaBar
LARGE CP Violation !
unlike Kaon system
no  due to had. uncertain.

7. CPV In Interference Between Mixing and Decay

8. Peculiarities at (4S)BB
Ebeam= 5.29 GeV e+ e- e- e+ g
Under symmetric energy collisions, B mesons are slow (0.07)
travel only ~30m, not enough to measure their decay time

9. B0 B0 (4S) Spin = 1 With l = 1 B0 B0 are in coherent l=1 state
With l = 1
B0 B0 are in coherent l=1 state
Since production, each of the two particles evolve in time, may mix
BUT they evolve coherently (Bose statistics |> = |> flavor |>space is symmetric ) so that at any time, until one particle decays, there is exactly one B0 and one B0 present but never a B0 B0 or B0 B0 (quantum coherence)
However when one of the particles decays, the other continues to evolve
Now possible to have (4S) final state with 2 B0 or 2 B0,
probability is governed by the difference in time between the two B decays

10. When One B decay tags b flavor, Other decays to fCP
ttag
tfcp  K0 Dt
Tag
fCP

11. B Decays to CP Eigenstates

12. Time dependent CP Asymmetry in “Interference”

13. This is achieved by producing boosted (4S)BB
At (4S): integrated asymmetry is zero
must do a time-dependent analysis !
This is achieved by producing boosted (4S)BB

14. Asymmetric Energy Collider To Measure B Decay Time
Boost (4S) in lab frame by colliding beams of unequal energy but with same E2CM = 4.Elow Ehigh=M2
Daughter B mesons are boosted and the decay separation is large Z ~ 200m, distance scale measurable with Silicon detectors
Positron Beam
Electron Beam
(4S)

15. CP Violation Studies at Asymmetric Energy Colliders

16. Probing The CKM Angle 

17. CPV In B0 J/K0 (Platinum Mode)
dominated
by a single
decay amplitude
CP = -1 (+1)
for J/y K0S(L)
Same is true for a variety of B (cc) s final states

18. Time-Dependent CP Asymmetry with a Perfect Detector
Perfect measurement of time interval t=t
Perfect tagging of B0 and B0 meson flavors
For a B decay mode such as B0Ks with |f|=1
sin 2b B0
Asymmetry ACP
CPV

19. Steps in Time-Dependent CPV Measurementz
distinguish
B0 Vs B0 m- K-
bgU(4S) = 0.55
Coherent BB pair B0
B0  J/y Ks
Vivek Sharma , UCSD

20. Effect of Mis-measurements On Dt Distribution
perfect
flavor tagging & time resolution
realistic
mis-tagging & finite time resolution
CP PDF

21. B Charmonium Data Samples
4323
6028 signal
11000
non-CP
965

22. Sin(2b) Result From B Charmonium K0 Modes (2006)
0.040 (stat)
0.023 (syst)
BaBar 348M BB
(cc) KSmodes
(CP = -1)
sin2β = 0.642
0.031 (stat)
0.017 (syst)
Belle 535M BB
J/ψ KL mode
(CP = +1)
sin2β = 0.6740.026
Average

23. Breaking Ambiguities In Measurement of 

24. Angle  From B0 +-
Neglecting Penguin diagram (P) T P

25. Estimating Penguin Pollution in B0 +-, + -

26. B0 + - System As Probe of 
“Large” rate
615 ± 57
“Smaller” Penguin Pollution
mES
0f0
00
98 ± 22
N00 = ± 22
−31
2
A00
A+0

27. B0 + - System As Probe of 
Longitudinally polarized
 Helicity angle

28. TD CPV Measurement in B0 + -
615 57 signal events
CPV not yet observed here
but measurement constrains 

29. Discerning : Not Very Precise Yet

30. Probing The CKM Angle 

31. CP Asymmetry In B DK Decay  
Look for B decays with 2 amplitudes with relative weak phase 
Relative phase: (B– DK–), (B+ DK+)
includes weak (γ) and strong (δ) phase.

32.  from B±D0 K±: D0 KS + - Dalitz Analysis2
Schematic view of the interference

33. B Samples From Belle ( 357 fb-1)
BD*K
BDK
81±8 events
331±17 evnt
Clean signals but poor statistics
for a Dalitz analysis !
BDK*
54±8 evnt

34. The B->D0 K Dalitz Distributions: Belle
Direct CP Violation lies in in the dissimilarity between
the two Dalitz distributions: See any ?

35. Measurement Of CKM Angle /3
Belle ( 357 fb-1)
W.A. combining all  measurements
γ = (82 ± 19)o 95% CL γ = (-98 ± 19)0 95% CL

36. The Unitarity Triangle Defined By CPV Measurements
Precise Portrait of UT Triangle
from CPV Measurements

37. UT With CPV & CP Conserving Measurements
Incredible consistency between measurements
 Paradigm shift ! CKM Picture well describes observed CPV
 Look for NP as correction to the CKM picture
Inputs:

38. Searching For New Physics by Comparing pattern of CP asymmetry in bs Penguin decays With goldplated b ccs (Tree)

39. Comparing CP Asymmetries : Penguins Vs Tree
In SM both decays dominated
by a single amplitude with no
additional weak phase
Tree
New physics coupling to
Penguin decays can add
additional amplitudes with
different CPV phases
Penguin 3
New Physics

40. New Physics ?
Standard Model

41. Naïve Ranking Of Penguin Modes by SM “pollution”
Naive (dimensional) uncertainties on sin2
Decay amplitude of interest
SM Pollution f f
Supergold
Gold
Bronze
Note that within QCD Factorization these uncertainties turn out to be much smaller !

42. First Observation of TD CPV in B0  h’K0
Large statistics mode
BaBar 384M
5.5 measurement
’KS
1252 signal events
(Ks +KL mode)
similar result from Belle

43. Golden Penguin Mode : B0   K0
Belle: 535M BB
307  21 fKS signal
114  17 fKL signal
S K0 =  0.21(stat)  0.06(syst)
C  K0 =  0.15(stat)  0.05(syst)

44. Golden Penguin Mode : B0  K0 K0 K0
Belle 535M BB
SKsKsKs=  0.32(stat)  0.08(syst)
CKsKsKs=  0.20(stat)  0.07(syst)
background
　　subtracted
good tags
185  17
KSKSKS signal

45. Summary of sin2eff In b s Penguins
Individually, each decay mode in reasonable agreement with SM
But smaller than bgccs
in all 9 modes !
Naïve b  s penguin average
sin2eff = 0.52 0.05
Compared to Tree:
sin2eff = 0.68 0.03
 2.6s difference
Theoretical models predict
SM pollution to increase
sin2eff !!
Interesting ! Measurements statistically limited !

46. Theory Predictions, Accounting For subdominant SM Amplitudes
2-body:
Beneke, PLB 620 (2005) 143
Calculations within framework of QCD factorization
3-body:
Cheng, Chua & Soni,
hep-ph/
sin2eff > 0.68
points to an even
larger discrepancy !

47. What Are s-Penguins Telling Us ?
This could be one of the greatest discoveries of the century,
depending, of course, on how far down it goes…
2.6s?
discrepancy

48. Need More Data To Understand The Puzzle
Luminosity expectations:
K*g
2004=240 fb-1
2008=1.0 ab-1
f0KS
KSp0
jKS
h’KS
KKKS
4s discovery region if non-SM
physics is 0.19 effect
2004
2008
Individual modes reach 4-5 sigma level
Projections are statistical errors only;
but systematic errors at few percent level

49. Projected Data Sample Growth20
Double again from 2006 to 2008
ICHEP08
Integrated Luminosity [fb-1]
PEP-II: IR-2 vacuum, 2xrf stations, BPM work, feedback systems
BABAR: LST installation
4-month down for LCLS, PEP-II & BABAR 17
Double from 2004 to 2006
ICHEP06 12
Lpeak = 9x1033
Expect each experiment to accumulate 1000 fb-1 by 2008

50. Summary & Prospects
CP Violation in B decays systematically studied at BaBar & Belle. A Comprehensive picture emerging
Standard Model picture (3 generation CKM matrix) of CP Violation consistent will all observations
New Physics (in loops) can still contribute to observed CPV but is unlikely to be the dominant source
CPV violation in the clean bs Penguin Decays appears lower than SM predictions (> 2.6)
more data needed to reveal true nature of discrepancy
B-factories expect to triple data sets by 2008
LHC-B will probe the Bs sector…Super B-factories ?

51. Suggested Reading: A Partial List
Reviews of |Vub| & |Vcb|, CKM Matrix, B Mixing & CP Violation in the Particle Data Book
CP violation and the CKM matrix : A. Hocker & Z. Ligeti
hep-ph/
BaBar Physics Book available online at
Discovery Potential of a Super B factory:
B Physics at the Tevatron: Run II and Beyond :
hep-ph/
Textbooks:
Heavy Quark Physics: Manohar & Wise; Published by Cambridge
CP Violation: Branco,Lavoura,Silva; Published by Clarendon Press
CP Violation by Bigi & Sanda; Published by Cambridge Press

52. Backup Slides

53. Tree
Penguin:: u,c,t loops 

54. The Unitarity Triangle For B System
Angles of Unitarity Triangle
Specific forms of CP Violation in B decay provide clean
information about the angles of the UT triangle
Same triangle also defined by length of its sides (from CP conserving
B decay processes such as b u l nu )  Overconstrained triangle

55. Direct CP Violation in B0 K : Belle (386M BB)
Combined significance >> 6
Belle
Rules out Superweak model
Establishes CPV not just due
to phase of B Mixing
But hadronic uncertainties
preclude determination of
CKM angle 
 challenge to theory

57. The Unitarity Triangle Defined By CPV Measurements
New B Factory milestone: Comparable UT precision from CPV in B decays alone

58. Belle and Babar Detectors: Optimized For CP Studies
Enough energy to barely
produce 2 B mesons,
nothing else!
B mesons are entangled
 Need for Asymm energy collisions

59. B0 B0 (4S) Spin = 1 With l = 1 B0 B0 are in coherent l=1 state
With l = 1
B0 B0 are in coherent l=1 state
Each of the two particles evolve in time (can mix till decay)
BUT they evolve in tandem since Bose statistics requires overall symm. wavefn
So that at any time, until one particle decays, there is exactly one B0 and one B0 present  ( EPR !)
However after one of the particles decays, the other continues to evolve
Now possible to have a (4S) event final state with 2 B0 or 2 B0
probability is governed by the time difference t between the two B decays

60. Quantum Correlation at (4S)
B 0
ttag X Y
tflav Dt B0
(4S)
ttag
Decay of first B (B0) at time ttag ensures the other B is B0
End of Quantum entanglement ! Defines a ref. time (clock)
At t > ttag, B0 has some probability to oscillate into B0 before it decays at time tflav into a flavor specific state
Two possibilities in the (4S) event depending on whether the 2nd B mixed/oscillated or not:

61. Time Dependent B0 Oscillation (Or Mixing)

62. B0 Decays to CP Eigenstates
ttag
tfcp  K0 Dt
Tag
fCP

63. B0 Decays to CP Eigenstates

64. At (4S): integrated asymmetry is zero
must do a time-dependent analysis !
This is impossible to do in a conventional symmetric energy collider producing (4S)BB !!

65. Summary of |Vub| From Inclusive Measurements

66. Unitarity Triangle From Measurement of Sides
Put all these
measurements
together 
ρ = ± η = ± ± 0.031
UT Definition
from angles 

67. When One B decay tags b flavor, Other decays to fCP
ttag
tfcp  K0 Dt
Tag
fCP