vivek sharma university of california at san diego cp violation in b decays ringberg workshop 2006
Post on 13-Jan-2016
219 Views
Preview:
TRANSCRIPT
Vivek Sharma
University of California at San Diego
CP Violation in B DecaysCP Violation in B Decays
Ringberg Workshop 2006
2
Task: Over Constrain The Unitarity Triangle
CPVB-DK-
B0 D0K0
CPV
BK0 (bccs)BK0 (bsss
CPV B0+- , , +-
b u
l
B-
b c l
b dB 0B 0
By Measurement of UT Sides By Measurement of UT Angles
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.
1A
2A
1A
2A
CP Viola io( t) n) ( a f a f
4
CP Violation Due to Quantum Interference
Weak phase wk changes sign under CP, strong phase st does not
stwkCP Violation
( ) ( )f or 0 and 0B f B f
2
1 2( ) wk sti iB f A A e e
st 1A
2A
wk
(B
f ) wk
2
1 2( ) wk sti iB f A A e e(B f
)
1AB f
2
wk sti iAe e
5
Direct CP Violation in B0 K
2 iSM amplitude e T P
sinKA
TP
•Loop diagrams from New Physics (e.g. SUSY) can modify
SM asymmetry contributing to the Penguin (P) amplitude
• Measurement is a simple “Counting Experiment”
Classic example of Quantum Interference
6
Direct CP Violation in B0K+
0
0
9
696
10
n B K
n B K
Bkgd symmetric!
696 9100.133
696 910A
0.133 0.030 0.009KA
4.2, syst. includedBaBar
LARGE CP Violation !unlike Kaon system
7
CPV In Interference Between Mixing and Decay
0 0
CP asymm. can be very large and can be clean
Neutral B Decays into CP final state acces
ly related to CKM angles
when only a single
ible by both & de
dominant decay amplitud
ca s
e
yCPf B B
0B
fiCPA e
CPf
0B2iq
ep
fi
CPA e
8
Peculiarities at (4S)BB (4S)
Ebeam= 5.29 GeV
e+ e-
Ebeam= 5.29 GeV
e
e
b
b
(4 )S
0B0B
Under symmetric energy collisions, B mesons are slow (0.07) travel only ~30m, not enough to measure their decay time
9
• 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
0 0Quantum Entanglement (EPR) in Y(4S) B B
(4S) B0 B0
Spin = 1 0 0
With l = 1
10
When One B decay tags b flavor, Other decays to fCP
(4S)B0 B0
ttag ttagtfcp
K0t
0 0B B
Tag
fCP
0
0
1.When one B decays to
2.It identifies the other B particle as B at THAT time
3.Ultimate
state which t
ly the de
ags its flavor at time t (as a B
cays at tim
t= t
e into some CP final state B
)
CP
tag
g
f
ta
t CPf
11
B Decays to CP Eigenstates
CP CP
0 0f CP f
CP tag
tag CP
tag
1
1
C
2
P
2
Pr obability of observing a final state |f | f depends on :
1. decay time t and t
2. decay amplitude
3. Oscillation paramete
A f | H | B ;A
r
4. Flavor of B , wheth
q | M |
p
e
f
M
| H | B
r
C
C
P
P CP
CP
CP C
C
P
P CP CP
CP
f f f
f C0
CP
f ff
f
0 0tag g
f
f
a
P
t
A f |
B B or B B
Using property
Define a useful CP parameter
A A
where CP eigenva
AAq q=
p
lue of f &
A
| B
H
p A
12
Time dependent CP Asymmetry in “Interference”
0 0
0 0
2
2 2
Time dependent CP asymmetry in time
( ) ( )
( ) ( )
12 sin cos
1 1
= sinS
t =
CPCP
CP CP
phys CP phys CP
phys CP phys CP
ff
B B
f f
B
CPtagf
B t f B t f
f B t f B t fCP
m t m t
m
t t
a
Im
cosC Bt m t
CP
CP CP
CP
When is dominated by a single decay amplitude:
1 0
Asymme str iy n
f
f f
B f
C
m tB
a
Im
13
Decay Rates and CP Asymmetries at (4S)
At (4S): integrated asymmetry is zero must do a time-dependent analysis !
This is achieved by producing boosted (4S)BB
CPfa d t 0 !!
sin Δm ΔtBS
14
Asymmetric Energy Collider To Measure B Decay Time
Electron Beam Positron Beam
(4S)
Boost (4S) in lab frame by colliding beams of unequal energy but with same E2
CM = 4.Elow Ehigh=M2
Daughter B mesons are boosted and the decay separation is large Z ~ 200, distance scale measurable with Silicon detectors
15
CP Violation Studies at Asymmetric Energy Colliders
Probing The CKM Angle
17
CPV In B0 J/K0 (Platinum Mode)
1λ
β)sin(2)Im(λ
S
S
ψK
ψK
L SψK ψKλ λ
CP = -1 (+1)
for J/K0S(L)
0 /,/ 1 sin 2 sin( )t
S L CPB J K e mt
0 /,/ 1 sin 2 sin( )t
S L CPB J K e mt
0B
fiCPA e
CPf
0B
12
2i
M
ie
fiCPA e
Same is true for a variety of B (cc) s final states
S
S
S
*cb cs*cb cs
*cs cd*cs
*t
* *ψKB tb cbb td td
* *cd
ψK *B ψK tb cb cdtb td tdcd
Vq A V V Vλ =
V VV V
V V
V V
V=- = -
p A V VV V VV V
2ie
dominatedby a single
decay amplitude
18
Time-Dependent CP Asymmetry with a Perfect Detector
sin2( ) sin(ΔmΔβ )CPA t t sin2( ) sin(ΔmΔβ )CPA t t
• Perfect measurement of time interval t=t• Perfect tagging of B0 and B0 meson flavors•For a B decay mode such as B0Ks with |f|=1
sin 2
B0B0
Asy
mm
etry
AC
P
CP
V
Vivek Sharma , UCSD 19
+e-e
B0 J/ KsB0 J/ Ks
z
Δ zΔ tβγ c
Brec
Btag 4s
(4S) = 0.55
z-π
0sK
+π
+μ-μ
Coherent BB pair
B0
B0
distinguish
B0 Vs B0
distinguish
B0 Vs B0
Steps in Time-Dependent CPV Measurement
20
Effect of Mis-measurements On t Distribution
00tag BB 00
tag BB 00tag BB 00
tag BB
CP PDF
perfect flavor tagging & time
resolution
realistic mis-tagging & finite time
resolution
| |/
, ( ) 1 sin2 (1 2 )sin4
t
CP CPef t tw m
~ 1 ps 170 m
~ 6 ps 1000 m2
t
mixt
21
B Charmonium Data Samples (348M ) BB(348M ) BB
6028 signal
4323
965 11000 non-CP
22
Sin(2 Result From B Charmonium K0 Modes (2006)
(cc) KSmodes
(CP = 1)
J/ψ KL mode
(CP = +1)
sin2β = 0.7220.040 (stat) 0.023 (syst)
BaBar 348M BB
sin2β = 0.6420.031 (stat) 0.017 (syst)
Belle 535M BB
sin2β = 0.6740.026Average
23
Breaking Ambiguities In Measurement of
24
T
Angle From B0 +-
* *
-* *
sin(2 - 2 - 2 ) sin 2Imtb td ud ub
tb td ud ub
V V V VB
V V V V
Neglecting Penguin diagram (P)
2ie 2 ie
P
eff
*Weak Phase in Penguin term is arg( ) different from Tree, so modifies
and depending on its relative strength w.r.t Tree
td tb
peng
V V
Im
25
Estimating Penguin Pollution in B0 +-, + -
A2
1
A2
1
00 AA
00A
00A
peng2 00 0 0 0
00 0 0 0
0
0
0 0
0 0
( )
( )
( )
(
)
)
( )
(
A A B
A A
A A B
A A B
A A B
A
B
A B
0 0 0 +- +0 00
0
B states can have I=0 or
B , and related by SU(
2; Gluonic Penguins co
2) Isospin relation between amplitudes A ,
ntribute only to I=0 ( I=1/2 rule)
A and A
B has only tree ampli
+0 -0tude | A | = | A |
00 00penguin
+0 00
To constrain by isospin analysis requires A and A to be very small or
very large ! Measure and constrain A ,A by rate and asymmetry
measurements
26
B0 + - System As Probe of
0 6
0
Br(B ) (23.5 2.2 4.1) 10 !!
Five times larger than Br(B )
“Large” rate
615 ± 57
openg ef
0 0 0 6
0 6
f
0Substantially smaller (x25) than B !
Much more amenabl
Br(B ) 1.16 0.37 10 (3 )
Br(B ) 1
constraint on | | 18 @ 6
e to Isospin analysis
6.8 3.1 10
8% CL
“Smaller” Penguin Pollution
mES 0f0
00
98 ± 22
2A00
A+0
/ 2A
27
B0 + - System As Probe of
• Longitudinally polarized0
L
Angular analysis shows that B
is almost 100% longitudinally polarized !
Pure CP-even final state
This simpli
f 0.9
fies
77 0.
CPV analysis
024
Helicity angle
28
TD CPV Measurement in B0 + -
0.050.070.19 0.21
0.07 0.15 0.06
Long
Long
S
C
615 57 signal events
CPV not yet observed herebut measurement constrains
CP sin mA S Ccos tt m
29
Discerning : Not Very Precise Yet
119
Combining
B , , (93 )
Precise measurement
needs much more data
o
CPV
[74 117]
Dominant uncertainty
is the Penguin pollution
o
B
Probing The CKM Angle
31
CP Asymmetry In B DK Decay
0K
Look for B decays with 2 amplitudes with relative weak phase
iV eub
000~ DreDD i
Relative phase: (B– DK–), (B+ DK+)
includes weak (γ) and strong (δ) phase.
Relative strength of the two B decay amplitudes matters for interference
A(b u)r 0.1 0.3 , larger r larger CPV precise
A(b )c
32
from B±D0 K±: D0 KS + - Dalitz Analysis
2 2 2 ( ) 2 2 2 For : | | | ( , ) ( , )| i
bB A f m m r e f m m
2 2 2 ( ) 2 2 2 For : | | | ( , ) ( , )| ibB A f m m r e f m m
2 0 2 2 0 2 Defining ( ) ; ( ) S Sm M K m M K
2
( )ibr e
2
sKm
2
sKm
2
SKm
2
sKm
0 D 0 D
2A
Schematic view of the interference
0S
+ -B
Simultaneous fit to D K Dalitz distribution of
info on rB and , B data and strong phase gives
33
B Samples From Belle ( 357 fb-1)
Clean signals but poor statisticsfor a Dalitz analysis !
331±17 evnt
BDK
81±8 events
54±8 evnt
BD*K
BDK*
34
The B->D0 K Dalitz Distributions: Belle
B- B+B-DK- B+DK+
Direct CP Violation lies in in the dissimilarity betweenthe two Dalitz distributions: See any ?
35
Measurement Of CKM Angle /3
Belle ( 357 fb-1)
W.A. combining all measurementsγ = (82 ± 19)o [63,101] @ 95% CL γ = (-98 ± 19)0 [-118,-79] @ 95% CL
36
The Unitarity Triangle Defined By CPV Measurements
11993 , , 82 19 degrees
First time that all angles
22.2 1.0
measured + +
Precise Portrait of UT Triangle
from CPV Measurements
37
UT With CPV & CP Conserving Measurements
ub
cb
V
V
Inputs:
dm
sm
B
K
sin2
Incredible consistency between measurements Paradigm shift ! CKM Picture well describes observed CPV
Look for NP as correction to the CKM picture
38
Searching For New Physics by Comparing pattern of CP asymmetry in bs Penguin
decays With goldplated b ccs (Tree)
39
Tree
b
dd
W cbV
csV
c /J
s0K
c
Penguin
b s
, ,u c t, ,g Z
tb tsV V
s
dd
s
0K
3
New Physics
Comparing CP Asymmetries : Penguins Vs Tree
In SM both decays dominated by a single amplitude with no
additional weak phase
New physics coupling to Penguin decays can add additional amplitudes withdifferent CPV phases
S
Asymmetry must be same
[B K ] [penguin]sin2 sin2
Measured CPV
S
Asymmetries can be very differe
sinsi 2n2
nt
[B K ] [pengu in]eff
CPV
40
New Physics ?
Standard Model
S
experimentally observe
[B K ] [pesin2 nguisin2 n]
then ...
eff
If
41
Naïve Ranking Of Penguin Modes by SM “pollution”B
ron
zeG
old
Su
pe
rgo
ld
b
dg
t0B
d
ss
s
W 2~tb tsV V
0K
0', f
0K
b
dg
t
d
ss
s
W
0B
2~tb tsV V
b
dg
t0B
d
ds
d
W
2~tb tsV V 0 0, ,
0K
2( )
~ 5%
~ 5%
2( / )
~ 20%
2( (1 / ))qqf
b
dg
u0B
d
ss
W 4~ i
ub us uV V R e
4~ iub us uV V R e
W b
d
0B
d
uu 's 0K
0Ks
4~ iub us uV V R e
W b
d
0B
d
uu 0 0, ,
s 0K
Decay amplitude of interest SM PollutionNaive (dimensional) uncertainties on sin2
Note that within QCD Factorization these uncertainties turn out to be much smaller !
42
First Observation of TD CPV in B0 ’K0
• Large statistics mode
1252 signal events
(Ks +KL mode)
0 0 6BR( ) ~ 65.2 10B K 0 0 6
recBR( ) ~ 14.9 10SB K
0
0
0.58 0.03
0.16
0.10
0.07 0.03
K
K
S
C
5.5 measurement
BaBar 384M
’KS
similar result from Belle
43
Golden Penguin Mode : B0 K0
0K
b
dg
t
d
ss
s
W
[ ],
CPK K Belle: 535M BB
307 21 KS signal114 17 KL signal
307 21 KS signal114 17 KL signal S K0 = 0.50 0.21(stat) 0.06(syst)
C K0 = 0.07 0.15(stat) 0.05(syst) S K0 = 0.50 0.21(stat) 0.06(syst)
C K0 = 0.07 0.15(stat) 0.05(syst)
44
Golden Penguin Mode : B0 K0 K0 K0
Belle 535M BB
SKsKsKs= 0.30 0.32(stat) 0.08(syst)CKsKsKs= 0.31 0.20(stat) 0.07(syst)
SKsKsKs= 0.30 0.32(stat) 0.08(syst)CKsKsKs= 0.31 0.20(stat) 0.07(syst)
185 17 KSKSKS signal
185 17 KSKSKS signal
background subtracted good tags
45
Summary of sin2eff In b s Penguins
But smaller than bccs in all 9 modes !
But smaller than bccs in all 9 modes !
Interesting ! Measurements statistically limited !
Naïve b s penguin average sin2eff = 0.52 0.05Compared to Tree:sin2eff = 0.68 0.03 2.6 difference
Theoretical models predict SM pollution to increase sin2eff !!
Individually, each decay mode in reasonable agreement with SM
46
Theory Predictions, Accounting For subdominant SM Amplitudes
2-body:Beneke, PLB 620 (2005) 143
sin2 sin2 eff
3-body:Cheng, Chua & Soni,
hep-ph/0506268
Calculations within framework
of QCD factorization
greblu
y =e = 1
full s
ig ae
mrang
sin2eff > 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…
2.6
discrepancy
48
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40Ja
n-03
Jul-
03
Jan-
04
Jul-
04
Jan-
05
Jul-
05
Jan-
06
Jul-
06
Jan-
07
Jul-
07
Jan-
08
Jul-
08
Jan-
09
Jul-
09
Err
or
on
sin
e am
pli
tud
eNeed More Data To Understand The Puzzle
K*
4 discovery region if non-SM physics is 0.19 effect
2004=240 fb-1
2008=1.0 ab-1
Individual modes reach
4-5 sigma level
Projections are statistical errors only; but systematic errors at few percent
level
Luminosity expectation
s:
20082004
( ) 0.19S
f0KS
KS0
KS
’KS
KKKS
49
0
200
400
600
800
1000
1200
Ju
l-9
9
Ju
l-0
0
Ju
l-0
1
Ju
l-0
2
Ju
l-0
3
Ju
l-0
4
Ju
l-0
5
Ju
l-0
6
Ju
l-0
7
Ju
l-0
8
Projected Data Sample GrowthIn
teg
rate
d L
um
inosit
y [
fb-1]
12
17
20
Lpeak = 9x1033
o PEP-II: IR-2 vacuum, 2xrf stations, BPM work, feedback systems
o BABAR: LST installation
4-month down for LCLS, PEP-II &
BABAR
Double from 2004 to 2006
ICHEP06
Double again from 2006 to
2008 ICHEP08
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 bs 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
– http://pdg.lbl.gov/
• CP violation and the CKM matrix : A. Hocker & Z. Ligeti
– hep-ph/0605217
• BaBar Physics Book available online at
– http://www.slac.stanford.edu/pubs/slacreports/slac-r-504.html
• Discovery Potential of a Super B factory:
– http://www.slac.stanford.edu/pubs/slacreports/slac-r-709.html
• B Physics at the Tevatron: Run II and Beyond :
– hep-ph/0201071
• 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
Backup Slides
53
*c
*ub u
b cs
-2
s*
cb cs
(V V )
Aexpect -1
V V 1Since
V V 50
=10 A
T is the dominant amplitude
Hence "Platinum" mode !
0B K : The "Platinum" Final State Penguin:: u,c,t loops
* * *P tb ts cb cs ubt usc u A =V V +V V VP V + PP
Tree
*T cb cs ccsA V V T
T P c
* * *t
*cb cs
b ts
*cb
*u
cb
c
c
s c t u tb us
*ub
cs u s
us
b
s
u
V V
Use Unitarity
A A (T P P ) (P P )
relation V V V V V V
= (V
to rearrange terms
V V
(V VV
A
) +
T ) P
54
The Unitarity Triangle For B System
2
1
3
*arg
*
*arg
*
*arg
*
V Vtd tb
V Vud ub
V Vcd cb
V Vtd tb
V Vud ub
V Vcd cb
Angles of Unitarity Triangle† * *1 0 ud cd cb tbV V V V V VtdV *ubV
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 conservingB decay processes such as b u l nu ) Overconstrained triangle
2 6J A
55
Rules out Superweak model
Establishes CPV not just due
to phase of B Mixing
But hadronic uncertaintiespreclude determination ofCKM angle challenge to theory
Combined significance >> 6
Direct CP Violation in B0 K : Belle (386M BB)
Belle
56
57
The Unitarity Triangle Defined By CPV Measurements
159105 , , 59 19 degrees
First time that all angles
21.7 1.3
measured + +
New B Factory milestone: Comparable UT precision
from CPV in B decays alone
58
Belle and Babar Detectors: Optimized For CP Studies
e
e
b
b
(4 )S
0B0B
Enough energy to barely produce 2 B mesons, nothing else!
B mesons are entangled Need for Asymm energy collisions
59
• 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
0 0Quantum Entanglement in Y(4S) B B
(4S) B0 B0
Spin = 1 0 0
With l = 1
60
Quantum Correlation at (4S)
• 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:
(4S)B0
ttag
B 0
ttag
in final state
in final state
0 0no oscillation/mixing B B 0 0 oscillation/mixing B B
tflavt
0 0B BX
Y
61
Time Dependent B0 Oscillation (Or Mixing)
62
B0 Decays to CP Eigenstates
0 0CP
0
CP
CP t g
CP
a
B Decay products can't tell Flavor of d
CP eigenstates f accessible to both B & B mesons
ecaying B (B or B)
This is why Quantum coherence i
Examples : B K or B ,
n B B is useful at
0
tag tag CP
0tag
If B is a B at decay time t then B must have been
a B at that time
( !
t
4S)
(4S)B0 B0
ttag ttagtfcp
K0t
0 0B B
Tag
fCP
63
B0 Decays to CP Eigenstates
CP CP
0 0f CP f
CP tag
tag CP
12
1
CP
2
tag
Pr obability of observing the final state |f | f depends on :
1. decay time t and t
2. decay amplitude
3. Oscillation parameq | M |
p Mter
4. Fl
A f | H | B ;A f | H |
av
B
or of B , wheth
CP CP
CP
CP
CP CP CP
CP CP
CP
0CPf
f ff
f
f f f
f CP
0 0t
f
ag tag
A A
where CP eigenvalue of f
er B B or B B
Using property
Define a usefuAA
A f | H |
q q=
p A
&
l CP parameter
B
p A
64
Rates and CP Asymmetries at (4S)
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 !!
CPfa d t 0
sin Δm ΔtB
65
Summary of |Vub| From Inclusive Measurements
66
Unitarity Triangle From Measurement of Sides
ρ = 0.171 ± 0.041 η = ± 0.387 ± 0.031
Put all these measurementstogether
UT Definition from angles
67
When One B decay tags b flavor, Other decays to fCP
(4S)B0 B0
ttag ttagtfcp
K0t
0 0B B
Tag
fCP
0
0
1.When one B decays to
2.It identifies the other B particle as B at THAT time t= t
3.Ultimately
f
the decay
l
s
avor tagging state at ti
at time into some CP final s
me t (as
t
a
a e
t B
B)
CP
ta
P
ag
f
t
g
Ct f
2
f f2 2
f f
1 λ 2Im(λ )( ) exp( ) 1 cos( ) sin( )
1 λ 1 λ
F t t mt mt
0 0+ -Denoting rate of B by F (t) and B by F (t) CP CPf f
top related