CP Violation: la B epoque

1
CP Violation la B epoque
elle
CP studies using Beauty mesons

Stephen L.Olsen U. of Hawaii
U-Mass Colloquium Mar 12, 2003
2
CP Violation
Matter
anti- matter

Asymmetries
Big Bang
all matter no antimatter
matter- antimatter symmetric
3
Standard Model Symmetries
Weak
Strong EM
yes
violated (maximally)
yes
violated (small??)
violated (pretty badly)
yes
violated (20 level)
yes
4
WI the SMs industrial sector
matter-antimatter differences
CP violation
Flavor mixing
Flavor violations
flavor violations
gauge symm violations
Masses
5
Todays talk
level
CP violation
Flavor-mixing
Phys 100
B(eauty) mesons
B-meson primer (why are they interesting?)
CP-violation measurements
harder
Whats next?
6
Antimatter CP (a la Physics 100)
7
p mV
x
px mVx
2
2
(
)
E mc2
E mc2
if px is negative ? motion is backwards in x
if E is negative ? motion is backwards in time
!!!
8
backward time motion
-
B
-
-
-
t
-
-
-
-
when viewed forward in time
-
C
-

P
L
R
9
CP matter?
?antimatter
charge
CP operator
CP(
)
g
q?
q?
g
q
q
J
J
mirror
if g ? g (i.e. charge is complex)
CP symmetry is violated
(matter antimatter behave differently)
10
CP violation discovered in 1963
seen as a tiny (0.002) effect in certain K0
decays (not in p or nuclear b-decays)

• need a complex coupling specific to
  strangeness-changing processes

11
Flavor-mixing
12
Strangeness-changing weak decays circa 1963 eg
K?p e-n L?p e-n
(Flavor-mixing in the 3-quark era)
u d s
13
3 quarks
q2/3
s
Weak interactions
q-1/3
4 leptons
14
Strength of the Weak interaction
Problem 1 Different weak interaction charges
for m, n, and K decays
GF
m-
Gs
Gd
s
d
K-
n
u
u
p0
p
Gd? 0.98GF Gs? 0.2GF
15
Cabibbo soln flavors mix
Weak Int flavor state
Flavor mass eigenstates
d? a d b s
bGF
aGF
u
GF
u
u


s
d
d
W-
W-
W-
Unitarity a2 b2 1
Cabibbo angle
acos qc b sin qc
16
Missing neutral currents
Problem 2 no flavor-changing
neutral currents seen.
s
GN
OK
K-
d
d,u
d,u
p-
flavor-changing neutral currents (e.g. K?p ll-)
are strongly supressed
flavor-preserving neutral currents (e.g. nN?nX)
are allowed
17
GIM soln Introduce 4th quark
2 quark doublets
charmed quark
4-quark flavor-mixing matrix
Mass eigenstates
Weak eigenstates
Unitarity g a , d -b a2 b2 1
18
GIM cancellation of FCNC
Charged currents
u(c)
bGF
aGF
u(c)
s(d)
d(s)
W-
W-
forced to 0 by Unitarity
1
?0
Neutral currents
(a2b 2)GN
(abgd)GN
d(s)
d,(etc)
d,(etc)
s(d)
Z0
Z0
Flavor preserving
Flavor changing
OK
19
Incorporating CPV via flavor mixing
20
a complex flavor-mixing matrix?
a b -b a
Why not incorporate CPV by making ? complex?
not so simple a 2x2 matrix has 8 parameters
unitarity
4 conditions 4 quark
fields 3 free phases
of irreducible parameters 1
Cabibbo angle
21
2-generation flavor-mixing
cosqC sinqC -sinqC cosqC
a b -b a
?
Only 1 free parameter the Cabibbo angle
not enough degrees of freedom to incorporate a
complex number
qC?120
22
Enter Kobayashi Maskawa
suppose there are 3 quark generations
a 3x3 matrix has 18
parameters
unitarity 9 conditions
6 quark fields 5 free
phases
of irreducible parameters 4
one complex phase is possible!
three are needed for 3-dim rotation (e.g. Euler
angles)
23
KM (others) circa 1973 (Kyoto)
Makoto Kobayashi
Toshihide Maskawa
24
Original KM paper
From Prog. of Theor. Phys. Vol. 49 Feb. 2,
1973
CP-violating phase
3 Euler angles
25
A little history

• 1963 CP violation seen in K0 system
• 1973 KM 6-quark model proposed
• 1974 charm (4th ) quark discovered
• 1978 beauty/bottom (5th) quark discovered
• 1984 KM model makes it into PDG book
• 1995 truth/top (6th) quark discovered
• 2001 CPV in B-meson decays discovered

26
CKM matrix (in 2002)
CPV phases are in the corners

Vub
f3 (g)
u
b
W
f1 (b)
d
t
W
27
Unitarity




VcdVcb


VtdVtb
0
VudVub

Vtd Vtb

Vud Vub
?2
phase of Vtd
?1
?3
phase of Vub

Vcd Vcb
28
Testing the KM CPV mechanism
1st step show that at least one fi ? 0
QM phase measurement requires interference
29
Primer on B mesons
30
Lesson 1 Basic properties

• What are B mesons?
• B0 d b B0 b d
• B u b B- b u
• JPC 0-
• t 1.5 x 10-12 s (ct ? 450 mm)
• How do they decay?
• usually to charm b?c2 ? b?u2 ? 100
• How are they produced?
• ee- ?? (4S) ? B B is the cleanest process

31
Lesson 2 flavor-tagged B decays
In 99 of B0 decays B0 and B0 are
distinguishable by their decay products
semileptonic decays
X l n X l- n
B0
B0
hadronic decays
D X D X
B0
B0
32
Lesson 3 B ? CP eigenstate decays
In 1 of B0 decays final state is equally
accessible from B0 and B0
charmonium decays
J/yKS J/yKL
B0
B0
charmless decays
pp- KK-
B0
B0
33
Lesson 4 The ?(4S) resonance

• ?(ee-? BB) ? 1nb
• B0B0/BB- ? 50/50
• good S/N
• BB and nothing else
• EB Ecm/2
• coherent P-wave
• Bs ? at rest in CM

3S bb bound states
s(ee-)? hadrons
BB threshold
34
Lesson 5 Recurring question
What makes the b-quark interesting?

• CESR/CLEO
• PEPII/BaBar
• KEKB/Belle
• 50 of CDF D0
• BTeV
• LHCB
• ..

35
Lesson 5 Consider 2nd order b?d(s) FCNC
b?d



Vub
Vud
Vcb
Vcd
Vtb
Vtd


b
u
d
b
c
d
b
t
d



AVubVud f(mu) VcbVcd f(mc) VtbVtd f(mt)



GIM VubVud VcbVcd VtbVtd 0
same for b?s
a big if
? A 0 if mu mc mt
36
Lesson 6 Large mt overides GIM
but, mt gtgt mc mu
GIM cancellation is ineffective
V
td
V
td
B0 ? B0 mixing transition is strong
(and this accesses Vtd)
37
Lesson 7 loops are accessible
also, because mt gtgt mc mu
GIM-forbidden penguins are accessible
effects of massive virtual particles can show up
here
38
B-meson primer final exam
Q. What makes Bs interesting?
A. The large t-quark mass
mt174 GeV
39
Measuring KM phases
40
Sanda, Bigi Carter Technique
Proposed in 1981, before large t-quark mass B?B
mixing was discovered

• Use B ? CP eigenstate decays (fCP)
• eg B?J/? KS B?J/? KS
• Interfere B?fCP with B? B?fCP

Br(B?fCP) are small (lt10-3) need millions of B
mesons
41
Interfere B?fCP with B?B?fCP
J/y
Sanda, Bigi Carter
Vcb
B0

KS
?

?V2
td
J/y
sin2f1
V
Vtb
Vcb
td
B0
B0
B0
KS
V
td
Vtb
td
42
What do we measure?
Flavor-tag decay (B0 or B0 ?)
Asymmetric energies
J/?
e?
fCP
e?
KS
t0
?z
B - B B B
sin2?1
more B tags
t ? ?z/cß?
more B tags
(tags)
This is for CP-1 for CP1, the asymmetry is
opposite
43
Whats needed?

• Lots of B mesons (Br (B?fCP) 10?3)
• very high Luminosity ? KEKB
• Find CP eigenstate decays
• high quality ?? detector ? Belle
• Tag the other Bs flavor
• good particle id ? dE/dx, Aerogel, TOF
• Measure decay-time difference
• Asymmetric energies ? (_at_KEKB g b ct?200mm)
• good vertexing ? silicon strip vertex detector
• Extract results

44
Step 1 make B mesons ? KEKB
45
KEKB

• Two separate rings
• e (LER) 3.5 GeV
• e- (HER) 8.0 GeV
• ECM 10.58 GeV at ?(4S)
• Luminosity
• target 20 Bs /sec
• achieved 15 Bs/sec
• 11 mrad crossing angle
• Small beam sizes
• sy ?3 mm sx ? 100 mm

asymmetric ee- collider
46
world records
15 Bs/sec
800K Bs/day
140M Bs
47
The Belle Collaboration
A World-Wide Activity Involving 50 Institutions
48

la
elle
A magnetic spectrometer based on a huge
superconducting solenoid
49
The Belle Collaboration
250 Authors
50
Step 2 Select events
J/??????
KS?????
B0 ? J/? Ks event
51
B0 ? J/? KL in Belle
very important because this has opposite CP
and, thus, opposite asymmetry

• J/? ?ll? KL
• 2) Assume B?J/y KL
• compute PKL
• 3) Plot P P J/? PKL

B
52
Step3 determine the flavor of the other B
look at the remaining tracks in the event

• Inclusive Leptons
• high-p l? b? c l? n
• intermed-p l s l? n
• Inclusive Hadrons
• high-p p B0?D()? p, D()? r, etc.
• 
  p?p0
• low-p p? D0 p?
• intermed-p K
  K X

53
step 4 measure vertices
Ks????
7cm
54
y-z vertices
55
Step 5 extract results
Combine

• CP value (xf)
• Flavor-tag (q)
• Vertex info (Dt)

56
sin2f1 0.7190.0740.035
(B0 or B0 ?)
J/?
e?
fCP
e?
?z
KS
?z
more B tags
more B tags
t ? ?z/c ß?
Now an established well understood exptl
technique
57
Belle BaBar agree
CPV in K decays
sin2f1 (BaBar) 0.7410.0670.033
sin2f1 (Belle) 0.7190.0740.035
sin2f1 (World Av.) 0.7340.055
Agrees with SM
theory errors 1
58
Whats next?
1.) Measure other KM angles

Vtd Vtb

?2
Vud Vub
phase of Vtd
?1
?3
phase of Vub

Vcd Vcb
59
f2 (a) from B?pp-
V
p
ub

B0
p-

?V2 V2
? sin2f2
td
ub
V
V
p-
Vtb
ub
td
(aka sin2a)
B0
B0
p
V
Vtb
td
60
Must deal with Penguin Pollution i.e.
additional, non-tree amplitudes with different
strong weak phases

Vtb
Vtd

p-
B0
p
direct CPV
mixing-induced CPV
Rq(Dt) ?1q Appcos(DmDt) Sppsin(DmDt)
q1 ? B0 tag -1 ? B0 tag
61
pp- fit results
After background subtraction
Asymmetry with background subtracted
Still see a large CP Violation!
62
Constraints on f2
allowed regions
1580
f2
f2 (deg.)
780
?2
?1
?3
d (deg.)
63
Whats next (contd) ?
2. Are there non-SM CPV phases?
64
Measure sin2f1 using loop-dominated processes
eff
Example
no SM weak phases
, ?, KK-
SM sin2f1 sin2f1 from B?J/y KS unless there
are other, non-SM particles in the loop
eff
65
similar to m(g-2)
look for effects of heavy new particles in a well
understood SM loop process
m(g-2)
sin2f1eff

• well defined technique target
• theory exptl errors are well controlled
• errors on SM expectations are small (5)
• SM terms are highly suppressed
• SM loops contain t-quarks W-bosons
• ? effects of heavy non-SM particles can be large

lowest-order SM diagrams
SM loop particles t W
SM loop particle g

look for pp1 effects (i.e.100)
look for ppm effects
66
sin2f1eff results (SM sin2f10.72
0.05)
(hep-ex/0212062)?PRD(r)
78fb-1
B? fKS
B?hKS
B?KK-KS
-0.73 0.66
Spp
0.52 0.47
0.76 0.36
2.2s off!!
OK
OK
67
Summary

• CPV observed in B meson decays
• f1? 0 in agreement with KM expectations
• tests for non-KM-type CPV are underway
• does f1f2f3 180o ?
• f2 f3 measurement results soon
• are there non-SM new physics phases?
• investigate t-quark loop-processes
• stay tuned