Transcript hepweb.ucsd.edu

Experimental Aspects of CP
Violation in B Decays : Lecture IV
Vivek Sharma
University of California, San Diego
http://vsharma.ucsd.edu/prague/cpv.pdf
Outline of Lectures 3 & 4
• Lecture 3
• Three types of CP violation & SM expectations in B Decays
– Decay amplitude Weak phase structure
– Decay asymmetry prediction in SM
• General strategy for time-dependent CP asymmetry measurement
– Observables that probe angle 
• Time dependent CP asymmetry in B -> Charmonium KS modes Step-by-Step
• Other modes with subdominant or dominant Penguin
• Lecture 4
– Observables that probe angle
– Observables that probe angle 
– Summary of current measurements
– Future prospects
2
CP Asymmetries and Testing  against “”
Confronting Loop Decays with Tree Dominance
b  ccs decays are tree and penguin diagrams, with same dominant weak phases
b  sss decays are pure “internal” and “flavor-singlet” penguin diagrams
High virtual mass scales involved: believed to be sensitive to New Physics
Both decays dominated by single weak phase
Tree:
c
b

cb
V
W

Vcs
d
c J /
s
b  ccs
J / K
0
S ,L
b  sss
Penguin:
s
New Physics?
b
d
3
g, Z,

tb ts
VV
 q
2 i 
     J / KS0,L e
  p K
K0
d
u, c , t
 q   VcbVcs
 J /  K 0     
S ,L
 p B  VcbVcs
s

K
0
S ,L
 q   VtbVts   q 
 K 0          ~ K 0 e 2i 
S ,L
S ,L
 p B  VtbVts   p K
s
K0
d
?
sin2 [charmonium]  sin2 [s-penguin]
4
bs Penguin Observables
Naive (dimensional)
uncertainties on sin2
One may identify golden, silver and bronze-plated s-penguin modes:
Gold
W
B
0
 VubVus ~  4Ruei

u
b
g
d
Silver
Color-suppressed tree
B
0
W

Bronze
B
K0
W



[CP ]
B
0
b
u
 ', f0
s
d
s
B
0
W
0
B
0
b
d
, K  K 
( 2 )
K0
~ 5%
[CP ]
 VtbVts ~  2
t
s
g
s
 ', f0
s
d
K0
d
 ,  ,
K0
g

b
 VubVus ~  4Ruei
u
s
s
d
W
K0
0
t
d
 VubVus ~  4Ruei
u
b
d
s
d
s
d
Color-suppressed tree
0
, K K
u
b
d
s
s
W
 VtbVts ~  2

( 2 (1 fqq /  ))
~ 10%
 VtbVts ~  2

t
g
s
d
K0
d
d
 0 ,  0 ,
Note that within QCD Factorization these uncertainties turn out to be much smaller,
but you must believe in QCD Factorization !
( 2 /  )
~ 20%
5
Results on sin2 from s-penguin modes
All new!
All new!
2.7s from s-penguin
to sin2(cc)
2.4s from s-penguin
to sin2(cc)
6
World Averages for sin2 and s-penguin modes
3.6s from s-penguin
to sin2(cc)
No significant sign of Direct CP
Beginning to look suspicious but must wait for 5s/expt to get exciting
7
Comparison of Sin2 With “Sin2”
From Z. Ligeti
Upper limit
Some modes more clean for
Interpretation than others
8
Projections for Penguin Modes (BaBar)
0.40
f0 KS
KS0
jKS
’KS
KKKS
0.30
0.25
0.20
s (S )  0.30
Luminosity
expectations
:
2004=240 fb-1
2009=1.5 ab-1
K*
Similar
projections for
Belle as well
0.15
2009
Jul-09
Jan-09
Jan-08
Jul-07
Jan-07
Jul-06
Jan-06
Jul-05
Jan-05
Jan-04
Jul-03
0.00
5s discovery region if non-SM
physics is 30% effect
2004
Jul-04
0.05
Jul-08
0.10
Jan-03
Error on sine amplitude
0.35
Projections are statistical errors only;
but systematic errors at few percent level
9
PEP II Luminosity Projections
1200
30
Yearly Integrated Luminosity [fb-1]
Cumulative Integrated Luminosity [fb-1]
25
Peak Luminosity [10**33]
800
20
600
15
Peak Luminosity [10**33]
Integrated Luminosity ( fb-1)
1000
0.5 ab-1
400
10
200
5
0
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
Yearly Integrated Luminosity [fb-1]
3
23
41
39
62.6
66.1
120.1
151
160.1
217
216
Cumulative Integrated Luminosity [fb-1]
3
26
67
106
168.6
234.7
354.8
505.8
665.9
882.9
1098.9
Peak Luminosity [10**33]
1
2
4.4
5
7.5
10
13
16
20
22
25
0
Year
2004 2006
1.6 x 1034
10
Probing The CKM Angle 
Example of Class I (b u u d): B0 +Neglecting Penguin diagram
*
*



V
V
V
 
tb td
udVub
 B     

* 
* 
 VtbVtd  VudVub 
Im
 sin(2 )
Weak Phase in Penguin term is arg(Vtd*Vtb ) different from Tree so it will modify
Im and  depending on its relative strength w.r.t Tree. (Penguins are large!)
12
Reality in B0 +-, + Tree
, 
, 
, 
Penguin
, 
Ratio of amplitudes |P/T| and
strong phase difference d
can not be reliably calculated!
One can measure dpeng using isospin relation and bounds to get 
13
Measurement of  : Reality in B0 +-, + A 00
1 
A
2
2dpeng
A 00
1 
A
2
A0  A 0
3 such relations (one for each polarization)
A  A( B 0     )
A   A( B 0     )
Now need
to measure
A  A( B 0      )
A   A( B 0      )
A00  A( B 0   0 0 )
A00  A( B 0   0  0 )
A 00  A( B 0   0 0 )
A 00  A( B 0   0  0 )
A  A( B    )
0


0
A  A( B    )
0


0

A0  A( B      0 )
A 0  A( B      0 )
14
Time Dependent Asymmetry Measurement: B0 +-
B 0     (227M BB)
S  0.30  0.17  0.03
C  0.09  0.15  0.04
BABAR
B0
B0
15
Time Dependent Asymmetry Measurement: B0 +(372  32) +- signal
152M
152MBB
BB
good tag
C
S
Belle claim of direct and
= -0.58 0.15(stat) 0.07(syst)
= 1.00 0.21(stat) 0.07(syst) Indirect CPV not supported by
BaBar data
16
Comparison of Present and Past B0 +- results
Coefficients of time-dependent CP Asymmetry
With no penguins S  sin2, C  0
With large penguins
and |P/T| ~ 0.3
S  1  C2 sin 2eff
C  sin d
>3s discrepancy between
BABAR & Belle
3.2s
5.2s
Belle 3.2s evidence for Direct
CP violation not supported by
BABAR measurements
Caution When
averaging!
17
“One is too few and three is too many”
-Carlo Rubbia, CERN DG, 1990
Its essenstial for an independent & similarly capable
experiment to verify an experiment’s claims!
Constraining : B-  - 0 Rate Measurement
• B-  - 0 (I=2, I=1/2) has only tree amplitude, no penguin  Base of
Isospin triangle
B0
Bu
u
BaBar
19
Constraining  : B  00 Decay Diagrams
Difficult to calculate rates for such processes,
Smaller the better for constraining 
Grossman-Quinn bound:
20
B  00 : Rate and Flavor Tagged Rate Asymmetry
First measurements
B00 is large !
BF   (1.17  0.32  0.10)  10 6
4.9s
C   0.12  0.56  0.06
BaBar
0 0
0 0
Measured by flavor of the other B 
Btag
0.41
BF   (2.320.48
 0.22)  10 6 6.0s
0.16
C   0.43  0.510.17
Belle
0 0
0 0
Average
274M BB
Key ingredient for Isospin analysis
And constraints on angle 
21
Estimate of  From B Studies
Interpretation unclear because of inconsistency in B0 +-
Penguin pollution
 Not well constrained !
22
ACP(t) in B0 Decays
Run1-3 data (122M BB)
314±34 Signal Events (205 tagged)
fL=1.00±0.02
Fit: total
After cuts on
likelihood ratio
BaBar prelim
BaBar prelim
mES
Events with cleanest tags
E
Fit: bkgd
23
ACP(t) in B0 Decays
314±34 Signal Events B0+Distribution of ± helicity distributions in data
Clear demonstration of strong longitudinal polarization
fL=1.00±0.02
24
Results for sin2eff from B    decays
Extraction of  similar to , but with
advantage of larger rate ( 5) &
smaller Penguin pollution because
| A 00 | | A 00 |
,
much smaller:   eff smaller
| A 0 | | A  |
B 0      (122M BB pairs)
Signal: 314  34 events
BABAR
Potentially     could be mixed CP ,
but is observed to be almost pure CP  1
L
(fL 
  1.00 0.02  0.03)
Time-dependent CP Asymmetry
Slong  0.19  0.33  0.11
Clong  0.23  0.24  0.14
 eff
 S
1
long
 arcsin
2
2
1

C
long





25
Isospin Corrections for From Measurements
B 0   0  0 limit  Penguin Small
B 0  0
First result from Run 1-2 (89M BB pairs)
5.7
BF (B      0 )  (22.5 5.4  5.8)  10 6
Vs
B 0  00
Updated result from Run 1-4 (227M BB pairs)
BF (B 0   0  0 )  1.1  10 6 (90% CL)
A
A 
2
2 2d
A
00
peng
A00
A0  A0
Geometric limit on 2dpeng:
Grossman-Quinn bound
Can Measure 
more precisely
  96  10(stat )  4(sys )  11( peng ) 
o
Compare with 35o for 
26
B is an example of the fact that if you build a
good detector and take lots of data, people (with help
from nature) will find unpredictable & innovative ways
to surmount difficult sticky situations!
e.g: B for precise measurement of  was never
seriously discussed at conferences till last year
Summary Of Measurements of Angle 
Confidence level =1
 Favored result
28
Towards The Angle : The phase in Vub
Look for B decays with 2 amplitudes with relative weak phase 


K K


 
K 0
0


K  
V ei
ub
Direct CP Asymmetry
 Angle 
29
Angle  from B±DK±: Critical Requirement
• Relative size of the 2 B decay amplitudes matters for interference
Color suppression: Fcs  [0.2,0.5]
Left side U.T.: Ru  0.4
Expected range
• Want rb to be large to get more interference  Large CP asymmetry
– Diff. between rb=0.1 and rb=0.2 substantial for precision on 
– Theory cannot calculate r reliably must measure experimentally30
Angle  from B±D0 K±: Current Status
• Even with ~250 fb-1 data in hand for each experiment,
reconstructed samples of B±DK± events are too few for a
meaningful measurement of the angle  (and r, and strong phase d)
– E.g: Effective Br. Ratio for (B±D0 K±)(D0K+-) 10-7
N ([K  ]D K ) 4.74.0
3.2

2.1
N ([ K  ]D* K )  0.21.3
0.8 N ([ K  ]D* K )  1.21.4
D 0 0
D0
• The exception is the case when B±D0 K± and D0KS+- , a
Cabbibo favored decay accessible to both D0 and D0. Entire
resonant substructure can be used with Cabbibo-allowed and
suppressed modes in D0KS + - interfering directly
31
 from B±D0 K±: D0 KS + - Dalitz Analysis
KS+ For B  : | A |2 |f (m2, m2 )  rbe i (d  )f (m2, m2 ) |2
mK2  
s
For B  : | A |2 |f (m2, m2 )  rbe i (d  )f (m2, m2 ) |2
m2  M ( KS0  )2 ; m2  M ( KS0  )2
2
2
mK  
D0
s
D0
2
A 
rb e i (d  )
mK2  
S
Schematic
view of the
interference
mK2  
s
32
 from B±D0 K±: D0 KS + - Dalitz Analysis
Sensitivity to 
A functional form (model) for f(m2+ ,m2- )
obtained from high statistics D*+D0
sample can fix phase variation dD across
Dalitz plot.
Fit Dalitz distribution for B+ and Bsimultaneously using A- & A+ forms to
extract r, d and  simultaneously. No
additional assumptions necessary
=75,d=180,rB=0.125
Only two-fold ambiguity in  extraction
First and most precise such measurement from Belle 
33
D0 Dalitz Plot Model From High Statistics D*+ Sample
Characterize Dalitz distribution
with 15 two-body amplitudes
34
B+ D0K+ Samples
B+ D(*)0K+ signal
B+ D0K+
D0  Ksπ+π–
D0K
D0π
misID
146 events
112±12 signal
ΔE (GeV)
25% background
Mbc (GeV)
D*0K
D*0π
misID
B+ D*0K+
D*0 D0π0
D0  Ksπ+π–
39 events
33.6±6.2 signal
ΔE (GeV)
Mbc (GeV)
12% background
140 fb-1
35
  77o 17
 13  11( model )
19
26    126o [95% CL]
rB  0.26 0.10  0.03  0.04
0.14
rB*  0.20 0.19  0.02  0.04
0.17
73 events
M2(KS-) [GeV2]
B   D0 K 
M2(KS+) [GeV2]
B   D*0 K 
20 events
M2(KS+) [GeV2]
B   D0 K 
73 events
M2(KS+) [GeV2]
M2(KS-) [GeV2]
Visible asymmetry in Dalitz plots
M2(KS-) [GeV2]
Belle
140 fb1
M2(KS-) [GeV2]
 from B±D0 K±: D0 KS + - Dalitz Analysis
B   D*0 K 
19 events
M2(KS+) [GeV2]
Large !
Good start for direct measurement of  already, 2 data in hand
Ultimate sensitivity will depend on precise value of rb
36
 from B±D0 K±: D0 KS +- Dalitz Analysis
D0K
261 19
rB  0.17 (90% CL)
rB*  0.23 (90% CL)
d B  (130  45  8  10)o
d B*  (311  52  23  10)o
  (88  41  19  10)o
D*0(D00)K
83 11
D*0(D0)K
40 8
37
With measurement of CKM element
magnitudes and Angles , ,  in hand, Lets
Look at the - plane to see if all these
measurements hang together in 2004 !
Courtesy: The CKMfitter Group
Bd mixing
+ CPV in
K mixing
(K)
39
Add
|Vub/ Vcb|
40
+
BS Mixing
constraint
41
+ Sin2
42
+
constraint
43
All measurements consistent, apex of (,) well defined
+
measurement
44
Summary Of Results
• B factories producing data at record breaking pace !
• In just 4 years of data taking, CP Violation firmly established in
the B system by BaBar & Belle
– CPV in interference of Decay and Mixing: sin2=0.7260.037
– Direct CPV: ACP(B0K-+)= -0.110.02
– Limits on CPV in B mixing
• Unlike in the Kaon system, CPV in B system is O(1) effect
• “sin2”=0.300.08 from bs penguin decays 3.5s from sin2K
– Needs careful investigation
• B+- provides the best measurement of angle 
• First measurement of  from B±D0 K±, D0 + - Dalitz
analysis  the most promising technique with added statistics
– But precise & redundant measurements of  will be difficult
• All observables yield a consistent picture. The - plane is now
sharply defined
45
Limits of Future Explorations
46
PEP II Luminosity Projections
1200
30
Yearly Integrated Luminosity [fb-1]
Cumulative Integrated Luminosity [fb-1]
25
Peak Luminosity [10**33]
800
20
600
15
Peak Luminosity [10**33]
Integrated Luminosity ( fb-1)
1000
0.5 ab-1
400
10
200
5
0
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
Yearly Integrated Luminosity [fb-1]
3
23
41
39
62.6
66.1
120.1
151
160.1
217
216
Cumulative Integrated Luminosity [fb-1]
3
26
67
106
168.6
234.7
354.8
505.8
665.9
882.9
1098.9
Peak Luminosity [10**33]
1
2
4.4
5
7.5
10
13
16
20
22
25
0
Year
2004 2006
Similar projections for Belle
1.6 x 1034
47
Future Prognostications
• BaBar & Belle have just begun and have a long term and a rich program for B
physics (>2007) [I showed only 10% of results !]
– Most CP asymmetry measurements are statistics limited
• S-Penguins
• Alpha & Gamma measurements (multiple to be sure)
• CPV in B mixing remains to be discovered
–
Rare decays such as Radiative and Electroweak are a very clean probe of
new physics.
• e.g. F-B Asymmetry in b s l+ l• CPV in B  s  etc
• Tevatron is accumulating large B samples:
– They are the only current laboratory for studying Bs and b properties
• Immediate focus : Bs oscillation search till xs 20
• B Physics return to Europe in 2007 with LHC-B !!
– Will be the ultimate instrument for precision B physics
– Precise exploration of CPV in BS and Bd systems
48
LHC-b
• Reduced
material
• Improved
level-1 trigger
49
LHC-b: Example of CKM Physics Reach (107 s)
Reaction
Bo+BoJ/KS ,
J/l+ lBs Ds K-
Bs Ds -
Parameter
LHC
Yield
Asym
26,000
sin(2
Sensitivity†
>1.4
0.02
5,400 >1
14o
80,000
Reaction
3
<100†
B-Do (K+K-) K-

B0 D0CPbar K*0
B0 D0CP K*0bar

B-KS -

BoK+-

Parameter
Bo+-

Booo

BsJ/,
J/l+ l-

B0 D0(K)K*0
241,000 1.2
2c

xS
S/B
B-Do (K+-) K-
sin2c
BsJ/,
J/l+ lBsJ/
sin2c
BsJ/
S/S
50
Thank You & Best Wishes !
Backup Slides
Strategy for CP violation study in B0  + Helicity Frame
1
S
3
1
1
Transverse A1 
S
3
6
1
1
Transverse A1 
S
3
6
Longitudin al A0  
Pure
2
D
3 CP-eigenstate
1
D
P
2
1
D
P
2
 In a simultaneous fit we measure 4 quantities:
• +- yield and Polarization (fraction of longitudinal events)
• CLong and SLong CP parameters
 The additional parameters CTran and STran are fixed to zero
(vary within (-1.0 ; 1.0) in the study of the systematics) .
Longitudinal polarization
e |t|/
Long
Pure CP-eigenstate
f B 0 ( B 0 ) (t ) 
(1  S Long sin(mt )  C Long cos(mt ))
4
Transverse polarization
e |t|/
Tran
f B 0 ( B 0 ) (t ) 
(1  STran sin(mt )  CTran cos(mt ))
Mix of CP-eigenstate
4
(not useful…)
53
53
Ingredients of +- analysis
• Event selection:
 As the longitudinal polarization was expected to be large (>90%) we have optimized
our analysis to be able to treat the events with large values of |cos(H)|
(Longitudinal events have for the helicity distribution which is in ~cos(H)2).
 See details in BAD #634, #798.
• Rejection of continuum:
 NN approach.
 Combine discriminating variables:
• L0 and L2 monomials for
charged and neutral particles
• Sum of transverse momentum
• Cosine of the B thrust with z axis
• Cosine of the thrust of the r.o.e
with the B thrust
• Cosine of the B direction with z axis.
• 0 angular distribution.
• Choice of best candidate:
 Multiplicity per event ~ 1.8
 Choose one candidate per event with best c2.
54
transverse
longitudinal
qqbar
c2  
i
(mi 0  mPDG
)2
0
s
0
54
Likelihood Fit
• 8 discriminating variables
• mES , E, NN output and t
• Vector particle information (m1, m2, cos(1), cos(2)).
• 4 types of events:
 True Signal.
 Self Cross-Feed (~50% of the events
True
come from 0 mis-reconstruction):
Signal
 Longitudinal  (SCF fraction: 49%),
 Transverse  (SCF fraction: 25%).
 Continuum.
 floating parameters to model PDFs
 B backgrounds:
 Charmless B background (B0+-, B+0  +…. ).
 Charm B (bc) background.
 19 distinct PDFs!!!
Self
Cross-Feed
mES
mES
• Likelihood:
 The likelihood is the sum over the types of events of the terms :
Pdf(xNN)  Pdf( E)  Pdf( mB ),  Pdf( t)  Pdf( m1)  cos(1)  Pdf(m2)  cos(2)
 Minimization and Pdf modeling based on the RhoRhoTools package (RooFit technology).
55
55
Angle  from B±DK± : 3 Sets Of Observables
D decays to CP eigenstates (+, Ks0, …)
Interference term small
D decays to definite flavor states (K+)
Interference term large
D decays to 3-body states (Dalitz analysis of D0 decay)
Interference varies in 2-D Dalitz plot
Common parameters for all analyses :
56
B±DK± : D0 Decays to CP Eigenstates
Babar & Belle averages
(a.k.a. GLW technique)
• Note: rb and db different for each B mode (DK,DK*,D*K)
• No sign of large direct CP violation (rb is not anomalously large)
B±DK± : D0 decays to Definite Flavor
Favored (b c)
Babar
preliminary
Events / 10 MeV
Suppressed (b u)
suppressed
(a.k.a. ADS technique)
favored
Belle
Results for
• Hints of signals
• Rules out very optimistic
scenario (very large rb)
• Favors small rb
Belle
ICHEP 2004
Babar
hep-ex/0408028
58