a
Part 1: Matter-Antimatter Asymmetry
Part 2: CP Violation and the SM
g
b
Part 3: Beyond the Standard Model
New Results from the BaBar Experiment
K. Honscheid
Dept. of Physics
Ohio
State
University
K. Honscheid, WSU
Apr. 15,
2005
Matter, Energy and the Big Bang
• Einstein showed us that matter and energy are
equivalent
• When matter and antimatter meet, they
annihilate into energy
• Energy can also materialize as particleantiparticle pair
Predict:
Exp:
nMatter/nPhoton~ 0
nb/ng~ (6.1 +/- 0.3) x 10-10 (WMAP)
K. Honscheid, WSU Apr. 15, 2005
So how can this happen?
In 1967, A. Sakharov showed
that the generation of the net
baryon number in the universe
requires:
1.
Baryon number violation
(Proton Decay)
2.
Thermal non-equilibrium
3.
C and CP violation
(Asymmetry between
particle and anti-particle)
Transition to broken electroweak
symmetry provides these conditions
K. Honscheid, WSU Apr. 15, 2005
Experimental Possibilities:
• Get equal amounts of
matter and anti-matter
• Wait…
• See what’s left
(in anything)
K. Honscheid, WSU Apr. 15, 2005
PEP-II Asymmetric B Factory
Stanford Linear Accelerator Center,
Stanford, California
K. Honscheid, WSU Apr. 15, 2005
The BaBar Experiment
K. Honscheid, WSU Apr. 15, 2005
Preparing the Matter – Antimatter Sample
B mesons contain a b quark and a light anti-quark.
BB Threshold
mB = 5.28 GeV (~5x mProton)
 
 bb
 0.28
 hadr 
The Upsilon(4S) - a copious, clean source of B meson pairs
1 of every 4 hadronic events is a BB pair
No other particles produced in Y(4S) decay
Equal amounts of matter and anti-matter
Collect a few 108 B0 B0 pairs
K. Honscheid, WSU Apr. 15, 2005
Analysis techniques
Threshold kinematics: we know the initial energy of the system
*2
mES  Ebeam
 pB*2
Signal
*
E  EB*  Ebeam
Event topology
Signal
(spherical)
Background
Background
(jet-structure)
K. Honscheid, WSU Apr. 15, 2005
Searching for the Asymmetry
227 x 106 B0 Mesons
227 x 106 B0 Mesons
Count B0K+ Decays
Count B0K-+ Decays
Is N(B0K+ ) equal to N(B0K-+ )?
K. Honscheid, WSU Apr. 15, 2005
How to Tell a Pion from a Kaon
Angle of Cherenkov light is
related to particle velocity
– Transmitted by internal
reflection
– Detected by~10,000
PMTs
Quartz bar
Particle
c
Cherenkov light
K. Honscheid, WSU Apr. 15, 2005
Active
Detector
Surface
Searching for the Asymmetry
227 x 106 B0 Mesons
227 x 106 B0 Mesons
Count B0K+ Decays
Count B0K-+ Decays
Is N(B0K+ ) equal to N(B0K-+ )?
B0K+
B0K+
BABAR
BABAR
background
subtracted
K. Honscheid, WSU Apr. 15, 2005
Direct CP Violation in B Decays
nK  1606  51
Using
n  B 0  K     910
n  B 0  K     696
AK  0.133  0.030  0.009
ACP 
We obtain
Br  B  f   Br  B  f 
Br  B  f   Br  B  f 
nK  1606  51
AK  0.133  0.030  0.009
First confirmed observation of direct CP violation in B decays
K. Honscheid, WSU Apr. 15, 2005
Part 2: CP Violation in the Standard Model
CP Operator:
CP(
g
q
coupling
q’
J
) =
q’
g*
q
J
Mirror
To incorporate CP violation
g ≠ g*
(coupling has to be complex)
K. Honscheid, WSU Apr. 15, 2005
The Kobayashi-Maskawa Matrix
• The weak interaction can change
the favor of quarks and lepton
• Quarks couple across generation
boundaries
Vcb
Vub
• Mass eigenstates are not the
weak eigenstates
• The CKM Matrix rotates the
quarks from one basis to the
other
d’
s’
b’
d
u
s
b
Vud Vlus Vub
d
l
3
= c Vcdl Vcs Vcbl
2
t
l
Vtd
Vltd Vtb
3
2
l=cos(c)=0.22
K. Honscheid, WSU Apr. 15, 2005
s
b
The Unitarity Triangle
Visualizing CKM information from Bd decays
•
•
The CKM matrix Vij is unitary with 4
independent fundamental parameters
Unitarity constraint from 1st and 3rd
columns: i V*i3Vi1=0
d
s
b
u
Vud
Vus
Vub
c
Vcd
Vcs
Vcb
t
Vtd
Vts
Vtb
CKM phases
(in Wolfenstein convention)
 1 1 e-iγ 


 1 1 1 
 e-iβ 1 1 


•
Testing the Standard Model
– Measure angles, sides in as many ways possible
– SM predicts all angles are large
K. Honscheid, WSU Apr. 15, 2005
Understanding CP Violation in B  K
Tree decay
B0
K-+
A1 = a1
eifif11eid1
+
A2 = a2 eif2 eid2
Vus*
g
B
0 b
d
Vub
s
u
u
d
K

A  Vus*Vub
B0
K+-
A1 = a1 e-if-if11eid1
+
A2 = a2 e-if2 eid2
Penguin decay
B
b
0 u,c,t
g
d
s
u
u
d
K

A  Vts*Vtb
• include the strong phase (doesn’t change sign)
• more than one amplitude with different weak phase; (A = A1+A2)
|A|2 – |A|2
G(B) – G(B)
~2
sin(f1  f2) sin(d1  d2)
Asymmetry =
=
=
0
2
2
|A| + |A|
G(B) + G(B)
K. Honscheid, WSU Apr. 15, 2005
B0 B0 Mixing and CP Violation
fb
A neutral B Meson
fb

N(B0)-N(B0)
N(B0)+N(B0)
The SM allows B0 B0 oscillations
CPV through interference
between mixing and
decay amplitudes
B0
ACP e i f
M 12 
Mixing frequency md  0.5 ps-1
Interference between B0 fraction ~ sin(m t)
d
‘B  B  fCP’ and ‘B  fCP’
2i M
ie
B
0
fCP
ACP e i f
K. Honscheid, WSU Apr. 15, 2005
Time-Dependent CP Asymmetries
b
W+
B0
c
c
s
d
d
J /
CP Eigenstate:
hCP = -1
K 0  KS0
0
0
G(Bphys
(t )  fCP )  G(Bphys
(t )  fCP )
AfCP (t ) 
 sin2
hfCP Im lbfCP sin md t

0
0
G(Bphys (t )  fCP )  G(Bphys (t )  fCP )
Amplitude of CP asymmetry
Im lb ccs
VcsVcb* VtbVtd* VcsVcd* 
Vtd*
 sin2b
 Im  *  *  *   Im
Vtd
VcsVcb VtbVtd VcsVcd 
Quark
subprocess
B0
mixing
K0
mixing
K. Honscheid, WSU Apr. 15, 2005
Time-dependent analysis requires B0 flavor tagging
t =0
We need to know the flavour of the B at a reference t=0.
z = t gbc
0
At t=0 we
B0
know this
meson is B0
B
rec
K s
(4S)
bg =0.56
B0
The two mesons oscillate
coherently : at any given
time, if one is a B0 the
other is necessarily a B0
tag
W
l  (e-, m -)
In this example, the tagside meson decays first.
It decays semi-leptonically
and the charge of the
lepton gives the flavour of
the tag-side meson :
l = B0
l  = B 0.
Kaon tags also used.
B0

b
d
t picoseconds
later, the B 0 (or
perhaps its now
a B 0) decays.
K. Honscheid, WSU Apr. 15, 2005
l
l
Step by Step Approach to CP Violation
B tagged
1.
B tagged
2.
3.
t (ps)
4.
ACP(t)
5.
sin 2b
6.
Start with a few x 108 B0 B0
pairs (more is better)
Reconstruct one B0 in a CP
eigenstate decay mode
Tag the other B to make the
matter/antimatter distinction
Determine the time between
the two B0 decays, t
Plot t distribution separately
for B and B tagged events
Extract ACP and sin2b
sinmt
t (ps)
K. Honscheid, WSU Apr. 15, 2005
Results: sin 2b and the observation of CP
227 million BB pairs
J/Ks and other
b  cc s final states
CP = -1
7730 events
(12w) sin(2b)
w = mis-tag fraction
•B 
•B 
•B 
•B 
•B 
J/ Ks0, Ks0  +-, 00
(2S) Ks0
c1 Ks0
J/ K*0, K*0  Ks0
hc Ks0
CP = +1
•B  J/ KL0
BaBar result: sin2b = 0.722  0.040  0.023
K. Honscheid, WSU Apr. 15, 2005
The Unitarity Triangle
(r,h)
Vub* Vud
Vcd Vcb*
(0,0)
a
g
Vtd Vtb*
Vcd Vcb*
o
(0,1)
[23.3 ± 1.5]
K. Honscheid, WSU Apr. 15, 2005
Ks is not the only CP Eigenstate
Access to a from the interference of a b→u decay (g) with B0B0 mixing (b)
Tree decay
B0B0 mixing
b
B
0
d
Vtb*
Vtd*
t
t
Vud*
g
d
B
0
B
b
Vtb
Vtd
q / p  Vtb*Vtd / VtbVtd*
0 b
d
Vub
d
u
u
d


A  Vud* Vub
q A
l
 e i 2 b e i 2g  ei 2a
p A
abg
sin2a
ACP(t)=sin(2a)sin(mdt).
K. Honscheid, WSU Apr. 15, 2005
Time-dependent ACP of B→
Blue : Fit projection
Red : qq background + B0→K cross-feed
B0
B0
N ( B     )  467  33 (227M BB )
B( B    )  (4.7  0.6  0.2) 10
0


6
"sin( 2a ) "  0.30  0.17  0.03
BR result in fact
obtained from 97MBB
K. Honscheid, WSU Apr. 15, 2005
Houston, we have a problem


B0  +K
K
K
B0  K+-
q
q

B0+
157  19
(4.7  0.6  0.2) x 10-6
B0K+
589  30
(17.90.9 0.7) x
10-6
Penguin/Tree ~ 30%
K. Honscheid, WSU Apr. 15, 2005
The route to sin2a: Penguin Pollution
Access to a from the interference of a b→u decay (g) with B0B0 mixing (b)
•
Tree decay
B0B0 mixing
b
B
0
d
Vtb*
Vtd*
t
t
Vud*
g
d
B
0
B
b
Vtb
Vtd
q / p  Vtb*Vtd / VtbVtd*
Penguin decay
Vub
0 b
d
d
u
u
d



B
b
0 u,c,t
d
q A

 e i 2 b e i 2g  ei 2a
p A
lCP  e
i 2a
Inc. penguin contribution
S  sin( 2a )
C 0
Time-dep. asymmetry :
NB :

T  P e  ig eid
T  P e ig eid
S  1  C 2 sin( 2a eff )
C  sin d
A (t )  S sin( md t )  C cos(md t )
T = "tree" amplitude

A  Vtd*Vtb
A  Vud* Vub
lCP
g
d
u
u
d
How can we
obtain α
from αeff ?
P = "penguin" amplitude
K. Honscheid, WSU Apr. 15, 2005
How to estimate |aaeff| : Isospin analysis
•
Use SU(2) to relate decay rates of different hh final states (h  {,r})
•
Need to measure several related B.F.s
Α    A( B 0     )
~ 
Α  A( B 0     )
Α  A( B    )
0


0
Α 00  A( B 0   0 0 )
~ 00
Α  A( B 0   0 0 )
Difficult to reconstruct.
Limiting factor in analysis
Gronau, London : PRL65, 3381 (1990)
K. Honscheid, WSU Apr. 15, 2005
Now we need B→
•
61±17 events in signal peak (227MBB)
– Signal significance = 5.0
– Detection efficiency 25%
Using isospin
relations and
• 3 B.F.s
– B0
– B  
– B0  
2 asymmetries
–
–
C
C
|aaeff |< 35°
B±→r±0
•
•
Time-integrated result gives :
B( B    )  (1.17  0.32  0.10) 10
0
0
0
C 0 0  0.12  0.56  0.06
6
•
Large penguin pollution ( P/T )
– Isospin analysis not currently
viable in the B→ system
K. Honscheid, WSU Apr. 15, 2005
B → rr: Sometimes you have to be lucky
P → VV decay
three possible ang mom states:
S wave (L=0, CP even)
P wave (L=1, CP odd)
D wave (L=2, CP even)
d 2N
 f L cos 2 1 cos 2  2  14 (1  f L ) sin 2 1 sin 2  2
d cos1d cos 2
r helicity angle
We are lucky:
~100% longitudinally polarized!
Transverse component taken as zero in analysis
PRL 93 (2004) 231801
K. Honscheid, WSU Apr. 15, 2005
Time dependent analysis of B→rr
•
Maximum likelihood fit in 8-D variable space
very clean tags
B0
32133 events in fit sample
(122M BB )
N ( B  r  r  )  617  52
S r  r  ( long)  0.33  0.24 00..08
14
Cr  r  (long)  0.03  0.18  0.09
B0
ACP (t )
f L  Glong G  0.99  0.0300..04
03
(97M BB )
B( B 0  r  r  )  (30  4  5) 106
c. f . B( B 0     )  4.7 106
K. Honscheid, WSU Apr. 15, 2005
Searching for B→rr
• Similar analysis used to search for rr
– Dominant systematic stems from the potential interference from B→a1±±
(~22%)
N ( B 0  r 0 r 0 )  3322
20  12
(227 M BB )
Rec. Eff.  27%
c.f. B→
B.F.= 4.7 x 106
and B→
B.F.= 1.2 x 106
6
B( B 0  r 0 r 0 )  (0.5400..36
32  0.19) 10
B (B→rr = 33 x 106
 1.1106
90% C.L.
K. Honscheid, WSU Apr. 15, 2005
Isospin analysis using B→rr
0
0 0
• The small rate of B  r r
– |aaeff | is small[er]
means
– P/T is small in the B→rr system
(…Relative to B→ system)
– No isospin violation (~1%)
– No EW Penguins (~2%)
A
A
2 2da
A00 2
peng
A00
A0  A0
|aaeff |< 11°
a  100  8(stat.)  4(syst.)  11( penguin)
K. Honscheid, WSU Apr. 15, 2005
The Unitarity Triangle
[103 (r,h)
± 11]o
Vub* Vud
Vcd Vcb*
(0,0)
g
Vtd Vtb*
Vcd Vcb*
b
[23.3 ±(0,1)
1.5]o
K. Honscheid, WSU Apr. 15, 2005
The 3rd Angle: g
Basic Idea
Use interference between B   D 0K  and B   D 0K 
decays where the D 0 (D 0 ) decay to a common final state f
Vus*
A  VubVcs*  l 3 r 2  h 2 eig
Vub
Vcb
V
*
cs
A  VcbVus*  l 3
Color
suppressed
Size of CP asymmetry depends on
(*)0 

|
A
(
B

D
K )|
rB(*) 
~ 0.1  0.3

(*)0 
| A(B  D K ) |
K. Honscheid, WSU Apr. 15, 2005
First Look at the Data
214M pairs
CP 
K K  75  13
   18  7
CP 
Only a loose bound on rB with current statistics: (rB)2 = 0.19±0.23
KS  0 76  13
BABAR-CONF-04/039
Several other methods are being investigated
More data would help a lot…
K. Honscheid, WSU Apr. 15, 2005
Combined Experimental Constraint on g
BABAR & Belle
combined
From combined
GLW and ADS fit:
20
g  51 34 


o
CKM indirect constraint
o

8
fit: g  58 7 


K. Honscheid, WSU Apr. 15, 2005
The Unitarity Triangle
[103 ± 11]o
Vub* Vud
Vcd Vcb*
a
Vtd Vtb*
Vcd Vcb*
b
(0,0)+20 ]o
[51
-34
[23.3 ± 1.5]o
K. Honscheid, WSU Apr. 15, 2005
Putting it all together
• The complex phase in the
CKM matrix correctly
describes CPV in the B
meson system.
• Based on SM CPV the
baryon to photon ratio in
the universe should be
nb/ng~ 10-20
h
• Experimentally we find
nb/ng~ (6.1±0.3) x 10-10
(WMAP)
r
K. Honscheid, WSU Apr. 15, 2005
Part 3: Beyond
Consistency
the Standard
Checks Model
• FCNC transitions bsg and bdg are sensitive
probes of new physics h
a 2 
g (3 )
VtdVtb
VcdVcb
b (1 )
• Precise Standard Model predictions.
0, 0
1, 0 r
Ali et al hep-ph/0405075
• Experimental challenges for bdg (Brg Bwg)
– Continuum background
– Background from bsg (BK*g) (50-100x bigger)
K. Honscheid, WSU Apr. 15, 2005
Combined B0r0g,B0wg,B-r-g results
• No signals observed
@90% CL
K. Honscheid, WSU Apr. 15, 2005
CKM constraints from Br(w)g
BABAR BF ratio upper limit < 0.029 → |Vtd/Vts| < 0.19 (90% CL)
Ali et al. hep-ph/0405075
(z2,R) = (0.85,0.10)
no theory error
(z2,R) = (0.75,0.00)
with theory error
Penguins are
starting to provide
meaningful CKM
constraint
rg 95% CL BABAR
allowed region (inside
the blue arc)
K. Honscheid, WSU Apr. 15, 2005
New CP Violating Phases in Penguin Decays?
c
b

cb
V
W

c J /
Vcs
d
s
K
0
+ mixing
lCP = -e-2b
+ mixing
lCP = -e-2b
+ mixing
lCP = -e-2b
d
W
b
t
Vts*
Vtb
d
d
W
b
d
t
Vtb
s
s
s
Vts*
s
d
d
d
 f ,h,...
K
0
K
0
 w, 
0
,...
K. Honscheid, WSU Apr. 15, 2005
Update on BfKo
W
b
d
u , c ,t
B0g
B 0  fKS0
s
s
f
s
d
KS0
0.07
0.04
 0.00  0.23  0.05
hCP  SfK 0  0.50  0.25
C fK 0
hep-ex/0502019

114 ± 12 events
SM
Belle
B 0  [BELLE-CONF-0435]
fKL0
98 ± 18 events
K. Honscheid, WSU Apr. 15, 2005
Reaching for more statistics – B 0  f K 0 revisited
•
Analysis does not require that ss decays through f resonance, it works
with non-resonant K+K- as well
– 85% of KK is non-resonant – can select clean and high statistics sample
– But not ‘golden’ due to possible additional SM contribution with ss popping
W
B
0
b
t
s
s
s
d
g
d
b
B
t
g
0
d
OK
s
u
u
s
s
d
K0
K0
b
K
K
Nsig = 452 ± 28
(excl. f res.)
 VubVus ~ l 4Ru e  i g
 VtbVts ~ l 2
W
K+K-
B
0
W
d
u
s
s
u
s
d
K
K
K0
Not OK
•
But need to understand CP eigenvalue of K+K-KS:
•
Perform partial wave analysis
 f has well defined CP eigenvalue of +1,
- CP of non-resonant KK depends angular momentum L of KK pair
– Estimate fraction of S wave (CP even) and P wave (CP odd) and calculate
average CP eigenvalue from fitted composition
K. Honscheid, WSU Apr. 15, 2005
CP analysis of B  K+K- KS
• Result of angular analysis
fCP -even
As2
 2
 0.89  0.08  0.06
As  Ap2
– Result consistent with cross check
using iso-spin analysis (Belle)
fCP -even
2G(B   K KS0KS0 )

 0.75  0.11
G(B0  K K K 0 )
• Result of time dependent CP fit
SK K K 0  0.42  0.17  0.04
S
CK K K 0  0.10  0.14  0.06
S
hfSK+K-KS/(2fCP-even-1)] =
+0.55 ±0.22 ± 0.04 ±0.11
(stat)
(syst)
(fCP-even)
K. Honscheid, WSU Apr. 15, 2005
hep-ex/0502013
More penguin exercises – B0  KS KS KS
• Use beam line as constraint and accept
only KS with sufficient number of SVX
hits.
• Decay B0  KS KS KS is ‘golden’
penguin – little SM pollution expected
• Although 3-body decay, only L=even
partial waves allowed:
–
CP(KSKSKS) = CP(KS) = even
 VtbVts ~ l 2
W
b
t
g
B0
d
ss
ud
d
us
ss
sd
d
K0
K
K
K
0
K0
K
0
• Result consistent with SM
hfK0
S  0.71 00..38
32 0.04
C  0.34 00..28
25 0.05
K. Honscheid, WSU Apr. 15, 2005
IP-Constrained Vertexing
+
Same technique as Ks0
hep-ex/0503011

Constrain decay products
to beam-spot in x-y:
0
KS
4mm
B0
inflated beam
beam
200mm
Vertex precision depends on
number of hits in SVT
For 4 hits, t resolution as good as with
charged-tracks (60% events)
Crosscheck with J/KS:
K. Honscheid, WSU Apr. 15, 2005
Combined “sin2b” Results
sin2β ~ 2.9 
sin2β ~ 2.9 
+
sin2βPenguin  .43 ±.7
sin2β ~ 3.7 
…but comparison
ignores subleading
diagrams !
sin 2 b
penguin
K. Honscheid, WSU Apr. 15, 2005
 0.4
Corrections: b→s Decay Amplitude ~ VubVus*
*
ub us
(u )
f
V V A
W
4 ig
l e
b
• Decays involving Vub enter
with decay phase g
• Doubly-CKM suppressed
w.r.t dominant diagram
u
W
u
g, Z,g
d
d
Contributes to all b sss modes
b
u
s
d
s
s
s
color-allowed tree
color-suppressed tree
b
penguin
d
Contribute to h’Ks, f0Ks, wKs, but not fKs
[in KKKs (requires ss popup from soft g)]
d
W
s
s
s
u
u
d
Contribute to non-resonant KKKs
(requires ss popup from soft g)
K. Honscheid, WSU Apr. 15, 2005
Adding Theoretical Uncertainties
•
size of possible discrepancies
Δsin2β have been evaluated for
some modes:
– estimates of deviations based on
QCD-motivated specific models;
some have difficulties to reconcile
with measured B.R.
•
•
•
•
•
Beneke at al, NPB675
Ciuchini at al, hep-ph/0407073
Cheng et al, hep-ph/0502235
Buras et al, NPB697
Charles et al, hep-ph/0406184
2xΔsin2β
– model independent upper limits
based on SU(3) flavor symmetry
and measured b d,sqq B.R.
• [Grossman et al, PRD58;
Grossman et al, PRD68; Gronau,
Rosner, PLB564; Gronau et al,
PLB579; Gronau et al, PLB596;
Chiang et al, PRD70]
‘naive’ upper limit based on final state quark content,
CKM (λ2) and loop/tree (= 0.2-0.3) suppression factors
[Kirkby,Nir, PLB592; Hoecker, hep-ex/0410069]
K. Honscheid, WSU Apr. 15, 2005
Conclusion
• Almost 40 years after the discovery of CP violation in
the kaon system we are finally in a position to improve
our understanding of CP violation in the Standard
Model
• Belle and BaBar give consistent results for sin2b. Both
work extremely well
• The SM prediction of a single phase in the CKM matrix
as cause of CP violation appears to be correct.
• We now know how to distinguish between matter and
anti-matter aliens.
• New Physics will be needed to explain the baryon
asymmetry in the universe
• Will we find hints in CP phases and/or rare decays?
• Stay tuned as more data is coming in.
K. Honscheid, WSU Apr. 15, 2005