CP violation and the Belle Experiment
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Transcript CP violation and the Belle Experiment
CP violation and the Belle
Experiment
Jin Li
USTC
2010
1
What is a symmetry?
• Invariants of the system. (Space, time, rotation)
Momentum, Energy, Angular Momentum.
• Discrete symmetry.
2
Parity violation
Experiment
Parity inversion
C.S.Wu et. al.,
Phys. Rev. 105,
1413 (1957)
Observed
Not observed
3
Pion decay
Weak interaction: C and P are violated maximally.
4
1964: Discovery of CP violation
B(K2 ) (2.0 0.4) 10
Phys. Rev. Lett. 13, 138 (1964)
3
K2
1
( K 0 K 0 ) CP( K 2 ) 1
2
L 0 CP( ) (1) L 1
1999: Direct CP violation in kaon decay (KTeV and NA48)
2001: CP violation in B meson (Belle and Babar)
5
Matter and Antimatter in 1st 10−3s
10−35
second
#quark=#anti-quark
10−32-10−4 second
Slight excess of quark
10−3 second - NOW
~109 photons per quark
Sakhalov’s 3 conditions (1967):
1. Both C and CP violation
2. baryon number violating process
3. existence of non-equiblium
6
Quark mixing
Flavor is not conserved in the weak interaction.
u
c
t
The weak eigenstates are not flavor eigenstates:
d s b
7
CKM matrix
d ' Vud Vus Vub d
s ' Vcd Vcs Vcb s
b ' V V V b
td ts tb
V †V
1 0 0
0
1
0
0 0 1
6 quark phases
− 1 overall phase
VCKM
3x3 complex matrix
# free parameters = 18 − 9 − 5 = 4
3 Euler angles
(3-D rotation)
+1 complex
phase
8
Unitary Triangle
Wolfenstein’s parameterization
d
= (12/2)
= (12/2)
Vud Vub* +Vcd Vcb*+Vtd Vtb* = 0
Vtd Vtb
(b) 1
3 (g)
Vcd Vcb
*
A
*
(,)
__
2 (a)
_
Vud Vub
*
3 A(1 i )
_
3 A( i )
(g)
Normalized
(a)
(b)
(1,0)
_
e
i
/ 2
A ( i )
2
4
/ 2
A
O
(
)
A (1 i ) A 2
_
VCKM
e
b
i
3
9
Feynman diagrams
CP
Vij Vij*
necessary for CP violation
Two amplitudes needed to account for phase redefinition.
Direct CP violation as an example.
10
Direct CP violation
Af A ( P f )
Amplitudes for CP conjugates
Af A ( P f )
CP conservation: Af Af
a CP
f
Define
( P f ) ( P f )
( P f ) ( P f ) A
f
Af
Af a j e j e
i
i j
j
CP
Af a j e j e
i
i j
j
Af
2
Af
2
j
j
2
2
Af
2
Af
2
Changes sign under CP
“weak” phase
Does not change sign under CP
“strong” phase
2 a j ak sin( j k ) sin( j k )
j ,k
11
CP violation mechanism
Two contributions to the amplitude
aCP
f
2a1a2 sin(2 1 )sin( 2 1 )
a12 a22 a1a2 cos(2 1 ) cos( 2 1 )
•At least two interfering amplitudes with comparable size
•Different weak phases.
•Different strong phases.
12
An excellent example of direct CPV
Tree
Penguin
Vub* ei3
(World Average)
Interference between T & P
13
The B meson
¯ 0= b d,
¯ B+=u b,
¯ B−=b u¯
B0=d b¯ , B
Heaviest quark with bound states.
Long lifetime because of must decay outside of third family.
Decay through “b→c” dominant, |b→c|2/|b→u|2 ≈100 .
“penguin” in “b→s” transition.
Flavor oscillation through “b↔t” box diagram.
In e+e− collider, can be produced by (4S) resonance.
¯ ≈1nb
•σ(e+e− →BB)
¯ 0/B+B− = 50/50
•B0B
•Coherent 1− − P-wave
14
Flavor Oscillation
mass eigenstates:
BL p B0 q B 0
BH p B0 q B 0
m mH mL
H L
1
2
2
2
(m) () 4 M 12 12
4
*
m 4 Re(12
M 12 )
2
0
B
d (t )
i
dt B 0 (t )
0
B
(t )
i
M
2 B 0 (t )
M 11
*
M 12
M 12 i 11
*
M 22 2 12
12
22
15
Parameters in B0 mixing
12
M 12
m
m 2 M12
*
M12* 2i 12
q
2
p
m 2i
M12* VtdVtb*
* e2i1
M12 VtdVtb
m 0
q
m 0
B0 (t ) ei ( mi /2) cos
t B i sin
t B
p 2
2
m 0
p m 0
B 0 (t ) ei ( mi /2) cos
t B i sin
t B
q
2
2
Define
f
qAf
pAf
f e2i1
if final state f = CP eigenstate
16
Time-dependent CP violation
cos
B0
t
m
2
q
i sin
p
B0
Af
cos
B0
fcp
t
m
2
Af
B0
t
m
2
p
i sin
q
t
B0
f
A B 0 (t ) f
Arg( f )
A B 0 (t ) f
cos
t
m
2
sin
t
2
m
2
qAf
pAf
Af
fcp
m
2
Same “strong” phase
Case |λf| = 1
B0
Af
f e2i1
( B 0 (t ) f ) ( B 0 (t ) f )
ACP (t )
( B 0 (t ) f ) ( B 0 (t ) f )
Im( f ) sin(mt )
17
B0→J/Ψ KS
f
J / K
0
S ,L
q VcbVcs*
*
p d VcbVcs
q
p K
VtbVtd* VcbVcs* VcsVcd*
* * *
VtbVtd VcbVcs VcsVcd
B 0 mixing
K 0 mixing
Decay
J / K
0
S ,L
qAf
pAf
f e2i1
e 2i1
Theoretically clean
Clear experimental signatures
Relatively large BF
AJCP/ K 0 (t ) Im(J / K 0 ) sin(mt ) sin 21 sin(mt )
S ,L
S ,L
18
Now: Precise measurement
535M BB
BJ/Ks
_
465M BB
14000
signals
B
_ 0 tag
B0 tag
_
(cc)K(*)0
12000
signals
CP-odd
BJ/KL
CP-even
Av. 0.670 0.023: 3.4% error !
0.687 0.028 0.012
sin2= 0.650 0.029 0.018
19
+(2S)KS
[PRL 98,031802(07)+PRD77 091103(08)]
[PRD 79,072009(2009)]
19
Comparison to Kaon system
, I 0
K
qA( K 0 , I 0) 1
0
pA( K , I 0) 1
1 2
A( K L0 , I 0)
A( K S0 , I 0)
Re( ,I 0 ) 1 2Re( ) (3.31 0.04) 103
Im( ,I 0 ) 2Im( ) (3.14 0.04) 103
Im(J / KS ) sin 21 0.670 0.023
CP violation in B0 system far greater than in K0 system.
•In B physics, the physical states cannot be isolated.
One startes with pure B0 or B0 initial states. Parameter λf is natural.
•In K physics, the physical states are well-isolated,
thanks to very different lifeimes. Parameter ε is natural.
20
CPV meas. at B-factories
Inclusive info.
(lepton, K etc.)
Flavor-tag
(B0 or B0 ?)
eff ~30%
e
Prob.
e
t=0
Vertexing
Reconstruction
J/
fCP
z
KS
st~1.4ps
B0
B0-tag
B0
B0-tag
t z/cbg
fit
Extract
CPV
bg=0.425 (KEKB)
0.56 (PEP-II)
21
21
The KEKB Collider (Tsukuba, Japan)
SCC RF(HER)
Belle detector
8 x 3.5 GeV
22 mrad crossing angle
World record:
L = 1.7 x 1034/cm2/sec
ARES(LER)
Ares RF cavity
e+ source
22
The Belle Detector
23
Measuring the sub-picosecond time dependence of CPV
4 layers, radiation hard
readout, r = 1.5 cm
50m
Beam spot: 110 μm x
5 μm x 0.35 cm
Belle uses double-sided silicon strip detectors
to measure Δz.
Decay distance
increased by x 10
KEKB/Belle: βγ = 0.425
Vertex resolutions(Belle): (σ(zcp) = 75μm; σ(ztag) =140μm)24
New Physics in CP violation
Selected topics:
•Direct CP violation in B0 system.
•The penguin b→sss process.
•CP violation in exclusive b →sγ process.
25
Revisit Direct CP violation in B→K
Belle Results: Nature 452, 332
(2008)
Recent Update
0.07± 0.06 0.006
0.004
0.094± 0.08 ± 0.008
Acp(K) =
0.086± 0.0 ± 0.009
0.04± 0.6 ± 0.0
0.0 @ 8.s
0.098 0.0
{
Acp(K0) =
{
BaBar
Belle
CDF
CLEO
AVG
0.00± 0.09± 0.00 BaBar
0.07± 0.0± 0.0
Belle
0.9± 0.± 0.0
CLEO
0.050± 0.05 @2.0s
AK = Acp(K-
Acp(K0)
= 0.47±
0.08 @ 5.3s
AVG
26
The Kπ “puzzle”
Expectation from current theory
T & P are dominant AK ~ 0
C.-W.Chaing, et al., PRD 70, 034020
Enhancement of C ?
H.-n.Li,et al.,
C>T is needed
PRD 72, 114005
(C/T = 0.3–0.6 in SM)
breakdown of theoretical understanding
Y.-Y.Charng, et al., PRD 71, 014036
W.-S.Hou, et al.,
PRL 95, 141601
Enhancement of PEW ?
S.Baek, et al.,
PRD 71, 057502
Would indicate new physics.
Baek & London
PLB 653, 249
Feldmann, Jung & Mannel, JHEP 0808,066
27
Due to poor understanding of strong interactions?
Isospin sum rule for ACP in BK
M. Gronau, PLB 627, 82 (2005); D. Atwood & A. Soni, Phys. Rev. D 58, 036005(1998).
B →K
HFAG, ICHEP08
A(K00)
A(K0+)=0.009 ±0.025
A(K+0)=0.050 ±0.025
A(K+-)=-0.098 ±0.012
A(K00)=-0.01 ±0.10
measured (HFAG)
A(K0+)
expected (sum rule)
28
Non-KM CP violation in penguins
Vts : no KM phase
Decay amplitude does not bring
new phase.
q
f e 2i1 holds
p
In SM: sin2Φ1eff=sin2Φ1 in B0→ J/ΨKS
29
New Physics may enter b→s loops
O(1) effect allowed
even if SUSY scale is
above 2TeV.
b
B
s
s
0
d
s
d
KS0
Many new phases
are possible in SUSY
Large effects, O(0.1-0.2), are
also possible in extra
dimensional models e.g.with a 3
TeV Kaluza-Klein (K.K) particle.
e.g. K. Agashe, G. Perez, A. Soni,
PRD 71, 016002 (2005)
b
B
s
s
0
d
s
d
KS0
30
Summary of sin2Φ1eff measurements
sin2Φ1=0.67±0.02
0.44±0.17
0.18
0.59±0.07
0.74±0.17
Need more data to clarify
If there’s deviation.
31
Right-handed currents in exclusive bsγ processes
D.Atwood, M.Gronau, A.Soni, PRL79, 185 (1997)
D.Atwood, T.Gershon, M.Hazumi, A.Soni, PRD71, 076003 (2005)
b
mb
ms
b
sg L
ms
mb
sg R
• Time dependent CPV in B0 (KS0)K*γ
– SM: γis polarized, the final state almost flavor-specific.
S(KS0γ) ~ -2ms/mbsin21
– mheavy/mb enhancement for right-handed currents in many new
physics models (left-right symmetric, extra dimensions etc)
– No need for a new CPV phase (right handed currents
suffice)
32
Right handed currents ? e.g. new mode BKS 0 γ
Use the 0+ - decay for the
vertex in the silicon. Does not
Good tags:
require KS vertexing in the
silicon c.f BKS0 γ
BKS+- γ
Effective CP parameters in the
0 region
Require M() consistent
with a 0 meson
33
SCP mesurement in exclusive b→sγ
Opposite
C
34
Crab crossing
New IR
b*y = σz = 3 mm
3.5 GeV
SuperKEKB
Crab cavities installed and
undergoing testing in beam
e+ 9.4 A
e- 4.1 A
8 GeV
The superconducting cavities
will be upgraded to absorb
more higher-order mode power
up to 50 kW.
The state-of-art ARES
copper cavities will be
upgraded with higher energy
storage ratio to support
higher current.
Higher current
More RF
New vacuum system
+ Linac upgrade
The beam pipes and all
vacuum components will be
replaced with higher-current
design.
Damping ring
s *y I y RL
L
1
2ere s *x b*y Ry
-2s-1
Aiming 8 × 1035 cm
g
35
3535
New Physics in Super B factory
Now
CKM UT triangle
NP effect
50ab-1
36
Summary
• CP violation is caused by two amplitudes
and a common phase.
• Mixing-induced CP violation in B0 system
is much larger than in K0 system.
• New Physics in CP violation will be probed
by Belle-II.
37
BACKUP
38
Flavor Oscillations
39
Δm and ΔΓ
40
D0 mixing
41
NP in D0 mixing
~
2A
2 5
~ O(103 ) CPV in D system
negligible in SM
D0-mixing
CPV in interf. mix./decay:
q Af
A
Im
(1 M )ei 0; 0
p Af
2
Currently ~±200
50 ab-1 go below 20
1, 2, 3 s @ 50 ab-1
42 !
LFV, CPV in D/t : Clear Indication of New Physics