k. honscheid, wsu apr. 15, 2005 k. honscheid dept. of physics ohio state university new results...
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K. Honscheid, WSU Apr. 15, 2005
K. HonscheidDept. of Physics
Ohio State University
New Results from the BaBar Experiment
Part 1: Matter-Antimatter Asymmetry
Part 2: CP Violation and the SM
Part 3: Beyond the Standard Model
K. Honscheid, WSU Apr. 15, 2005
• Einstein showed us that matter and energy are equivalent
• When matter and antimatter meet, they annihilate into energy
• Energy can also materialize as particle-antiparticle pair
Matter, Energy and the Big Bang
Predict: nMatter/nPhoton~ 0
Exp: nb/n~ (6.1 +/- 0.3) x 10-10 (WMAP)
K. Honscheid, WSU Apr. 15, 2005
So how can this happen?
1. Baryon number violation(Proton Decay)
2. Thermal non-equilibrium
3. C and CP violation(Asymmetry between particle and anti-particle)
In 1967, A. Sakharov showed that the generation of the net baryon number in the universe requires:
Transition to broken electroweak symmetry provides these
conditions
K. Honscheid, WSU Apr. 15, 2005
• Get equal amounts ofmatter and anti-matter
• Wait…
• See what’s left(in anything)
Experimental Possibilities:
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
The Upsilon(4S) - a copious, clean source of B meson pairs1 of every 4 hadronic events is a BB pairNo other particles produced in Y(4S) decayEqual amounts of matter and anti-matter
Preparing the Matter – Antimatter Sample
28.0hadr
bb
Collect a few 108 B0 B0 pairs
B mesons contain a b quark and a light anti-quark.mB = 5.28 GeV (~5x mProton)
BB
Thre
shold
K. Honscheid, WSU Apr. 15, 2005
Threshold kinematics: we know the initial energy of the system
Analysis techniques
2*2*BbeamES pEm **
beamB EEE
Background Background
(spherical)
(jet-structure)
Event topology
Signal Signal
K. Honscheid, WSU Apr. 15, 2005
227 x 106 B0 Mesons
Count B0K+ Decays
227 x 106 B0 Mesons
Count B0K-+ Decays
Is N(B0K+ ) equal to N(B0K-+ )?
Searching for the Asymmetry
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
c
Particle
Quartz bar
Cherenkov light
Active Detector Surface
K. Honscheid, WSU Apr. 15, 2005
BABARB0K+
B0K+
BABARbackgroun
d subtracted
227 x 106 B0 Mesons
Count B0K+ Decays
227 x 106 B0 Mesons
Count B0K-+ Decays
Is N(B0K+ ) equal to N(B0K-+ )?
Searching for the Asymmetry
K. Honscheid, WSU Apr. 15, 2005
Using
We obtain
First confirmed observation of direct CP violation in B decays
Direct CP Violation in B Decays
CP
Br B f Br B fA
Br B f Br B f
0
0
9
696
10
n B K
n B K
K. Honscheid, WSU Apr. 15, 2005
CP( ) =
Part 2: CP Violation in the Standard Model
CP Operator:
q
q’
J
g
q
q’
J
g*
Mirror
coupling
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
• Mass eigenstates are not the weak eigenstates
• The CKM Matrix rotates the quarks from one basis to the other
Vcb Vub
d’Vu
d
Vus
Vu
b
d
s’ = Vcd Vcs Vcb s
b’ Vtd Vtd Vtb b
u
d
t
c
bs
3 2
2
3
=cos(c)=0.22
K. Honscheid, WSU Apr. 15, 2005
The Unitarity TriangleVisualizing 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
• Testing the Standard Model– Measure angles, sides in as many ways possible– SM predicts all angles are large
β
-i
-i
γ1 1
1 1 1
1 1
e
e
CKM phases (in Wolfenstein convention)
u
d
t
c
bs
Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb
K. Honscheid, WSU Apr. 15, 2005
Understanding CP Violation in B K
A1 = a1 e i1
B0 -+
B0 +-
A1 = a1 ei1 ei1
• include the strong phase (doesn’t change sign)• more than one amplitude with different weak phase; (A = A1+A2)
A1 = a1 e -i1A1 = a1 e-i1 ei1
Asymmetry = = ~ 2 sin() sin(2)= 0
A2 = a2 ei2 ei2
A2 = a2 e-i2 ei2
+
+
|A|2 – |A|2
|A|2 + |A|2
(B) – (B)(B) + (B)
s
u
dd0B
KubV
*usV
b u
Tree decay
ubusVVA *
s
u
dd
0BKg
b
utcu ,,
Penguin decay
tbtsVVA *
K. Honscheid, WSU Apr. 15, 2005
B0 B0 Mixing and CP Violation
A neutral B Meson
Mixing frequency md 0.5 ps-1
N(B
0)-
N(B
0)
N(B
0)+
N(B
0)
0B
fiCPA e
CPf
0B
12
2 Mi
M
ie
fiCPA e
CPV through interference between mixing and decay amplitudes
Interference between ‘B B fCP’ and ‘B fCP’
The SM allows B0 B0 oscillations
B0 fraction ~ sin(md t)
K. Honscheid, WSU Apr. 15, 2005
Time-Dependent CP Asymmetries
W+c
s
b c
d d
B0
0 0SK K
CP Eigenstate: CP = -1
0 0
0 0
( ( ) ) ( ( ) )( ) Im sin
( ( ) ) ( ( ) )CP CP CP
phys CP phys CPf f f d
phys CP phys CP
B t f B t fA t m t
B t f B t f
Quark subprocess
B0 mixing
K0 mixing
* * **
* * *I m I m I mcscs tbcb td cd tdb ccs
cs cscb tb td cd td
V V V V VV VV V V V V V V
Amplitude of CP asymmetry
sin2
/J
0 0
0 0
( ( ) ) ( ( ) )( ) Im sin
( ( ) ) ( ( ) )CP CP CP
phys CP phys CPf f f d
phys CP phys CP
B t f B t fA t m t
B t f B t f
sin2
K. Honscheid, WSU Apr. 15, 2005
t =0
Time-dependent analysis requires B0 flavor tagging
We need to know the flavour of the B at a reference t=0.
B 0
(4S)
The two mesons oscillate coherently : at any given
time, if one is a B0 the other is necessarily a B0
In this example, the tag-side meson decays first.
It decays semi-leptonically and the charge of the
lepton gives the flavour of the tag-side meson :
l = B 0 l = B 0. Kaon tags also used.
tagB 0l (e-, -) =0.56
z = t c rec
sK
t picoseconds later, the B 0 (or perhaps its now a B 0) decays.
B 0
ll
d0B b
W
At t=0 we know this
meson is B0
K. Honscheid, WSU Apr. 15, 2005
Step by Step Approach to CP Violation
1. Start with a few x 108 B0 B0
pairs (more is better)2. Reconstruct one B0 in a CP
eigenstate decay mode3. Tag the other B to make
the matter/antimatter distinction
4. Determine the time between the two B0 decays, t
5. Plot t distribution separately for B and B tagged events
6. Extract ACP and sin2
t (ps)
sin 2
sinmt
AC
P(
t)
B tagged
B tagged
t (ps)
K. Honscheid, WSU Apr. 15, 2005
Results: sin 2and the observation of CP
CP = -1•B J/ Ks
0, Ks0 +-, 00
•B (2S) Ks0
•B c1 Ks0
•B J/ K*0, K*0 Ks0
•B c Ks0
CP = +1•B J/ KL
0
J/Ks and otherb cc s final states
BaBar result: sin2 = 0.722 0.040 0.023
(12w) sin(2)
w = mis-tag fraction
7730 events
227 million BB pairs
K. Honscheid, WSU Apr. 15, 2005
(0,0) (0,1)
(,)
Vub Vud
Vcd Vcb
*
*
Vtd Vtb
Vcd Vcb
*
*
The Unitarity Triangle
[23.3 ± 1.5]o
K. Honscheid, WSU Apr. 15, 2005
Ks is not the only CP Eigenstate
Access to from the interference of a b→u decay () with B0B0 mixing ()
d
d
0B
*tbV
tdV
b
b
0Bt
t
*tdV
tbV** // tdtbtdtb VVVVpq
B0B0 mixing
du
dd0B
ubV
*udV
b u
Tree decay
ubudVVA *
222 iii eeeA
A
p
q
ACP(t)=sin(2)sin(mdt).
sin2
K. Honscheid, WSU Apr. 15, 2005
Time-dependent ACP of B→
Blue : Fit projectionRed : qq background + B0→K cross-feed
0B
0B
03.017.030.0")2sin(" 60 10)2.06.07.4()( BB
)M227(33467)( BBBN
BR result in fact obtained from 97MBB
K. Honscheid, WSU Apr. 15, 2005
Houston, we have a problem
KK
K
B0 +-
B0 K+-
B0+ 157 19 (4.7 0.6 0.2) x 10-6
B0K+ 589 30 (17.90.9 0.7) x 10-6
Penguin/Tree ~ 30%
q
q
K. Honscheid, WSU Apr. 15, 2005
The route to sinPenguin Pollution
• Access to from the interference of a b→u decay () with B0B0 mixing ()
d
d
0B
*tbV
tdV
b
b
0Bt
t
*tdV
tbV** // tdtbtdtb VVVVpq
B0B0 mixing
du
dd0B
ubV
*udV
b u
Tree decay
ubudVVA *
)cos()sin()( tmCtmStA dd
sin
)2sin(1 2
C
CS eff
ii
iii
CP eePT
eePTe
2
du
dd
0B
gb
utcu ,,
Penguin decay
tbtdVVA *
Inc. penguin contribution
0
)2sin(
C
S
222 iiiCP eee
A
A
p
q
How can we obtain α from αeff ?
Time-dep. asymmetry :
NB : T = "tree" amplitude P = "penguin" amplitude
K. Honscheid, WSU Apr. 15, 2005
How to estimate |eff| : Isospin analysis
• Use SU(2) to relate decay rates of different hh final states (h {})
• Need to measure several related B.F.s
Gronau, London : PRL65, 3381 (1990)Gronau, London : PRL65, 3381 (1990)
)( 0 BAΑ
)( 00000 BAΑ
)( 00 BAΑ
Difficult to reconstruct.Limiting factor in analysis
2| eff
|
)(~ 0 BAΑ
)(~ 00000 BAΑ
K. Honscheid, WSU Apr. 15, 2005
Now we need B→
• 61±17 events in signal peak (227MBB)– Signal significance = 5.0– Detection efficiency 25%
• Time-integrated result gives :
6000 10)10.032.017.1()( BB
06.056.012.000 C
B±→±0
• 3 B.F.s– B0– B
– B0
• 2 asymmetries– C
– C
Using isospin
relations and
• Large penguin pollution ( P/T )– Isospin analysis not currently viable in the B→ system
|eff |< 35°
K. Honscheid, WSU Apr. 15, 2005
B → Sometimes you have to be lucky
P → VV decaythree possible ang mom states:S wave (L=0, CP even)
P wave (L=1, CP odd)
D wave (L=2, CP even)
We are lucky:
helicity angle
~100% longitudinally polarized!Transverse component taken as zero in analysis
PRL 93 (2004) 231801
22
12
41
22
12
21
2
sinsin)1(coscoscoscos
LL ff
dd
Nd
K. Honscheid, WSU Apr. 15, 2005
very clean tags
Time dependent analysis of B→• Maximum likelihood fit in 8-D variable space
32133 events in fit sample
04.003.003.099.0
long
Lf60 10)5430()( BB
)M122( BB
52617)( BN
60 107.4)(.. BBfc
)( tACP
0B
0B
)M97( BB
08.014.0)(
24.033.0 long
S
09.018.003.0)(
longC
K. Honscheid, WSU Apr. 15, 2005
• Similar analysis used to search for – Dominant systematic stems from the potential interference from B→a1
±± (~22%)
Searching for B→
1233)( 2220
000 BN
C.L.%90101.1
10)19.054.0()(6
636.032.0
000
BB
)M227( BB
%27Eff.Rec.
c.f. B→B.F.= 4.7 x 106
and B→B.F.= 1.2 x 106
B (B→= 33 x 106
K. Honscheid, WSU Apr. 15, 2005
• The small rate of means
– |eff | is small[er]
– P/T is small in the B→ system
(…Relative to B→ system)
– No isospin violation (~1%)– No EW Penguins (~2%)
Isospin analysis using B→000 B
|eff |< 11°
)(11.)(4.)(8100 penguinsyststat
00A
2A
0 0A A
2A
00A2 peng
K. Honscheid, WSU Apr. 15, 2005
(0,0) (0,1)
(,)
Vub Vud
Vcd Vcb
*
*
Vtd Vtb
Vcd Vcb
*
*
[23.3 ± 1.5]o
The Unitarity Triangle
[103 ± 11]o
K. Honscheid, WSU Apr. 15, 2005
The 3rd Angle:
Color suppressed
*cb usA V V
*ub csA V V
cbV
*usV
ubV
*csV
3
3 2 2 ie
Basic Idea
0 0
0 0 Use interf erence between and
decays where the ( ) decay to a common fi nal state B D K B D K
D D f
(*)0(*)
(*)0
Size of CP asymmetry depends on | ( )|
~0.1 0.3| ( )|B
A B D Kr
A B D K
K. Honscheid, WSU Apr. 15, 2005
First Look at the Data
75 1318 7
K K
0 76 13SK CP CP
214 pairs M 214 pairs M
BABAR-CONF-04/039Only a loose bound on rB with current statistics: (rB)2 = 0.19±0.23
Several other methods are being investigated
More data would help a lot…
K. Honscheid, WSU Apr. 15, 2005
Combined Experimental Constraint on
o
indirect constraint
8fi t: 58 7
CKM
o
From combined
GLW and ADS fi t:
2051 34
BABAR & BABAR & Belle Belle
combinedcombined
BABAR & BABAR & Belle Belle
combinedcombined
K. Honscheid, WSU Apr. 15, 2005
(0,0)
Vub Vud
Vcd Vcb
*
*
Vtd Vtb
Vcd Vcb
*
*
The Unitarity Triangle
[23.3 ± 1.5]o
[103 ± 11]o
[51+20-34]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/n~ 10-20
• Experimentally we find nb/n~ (6.1±0.3) x 10-
10 (WMAP)
K. Honscheid, WSU Apr. 15, 2005
• FCNC transitions bs and bd are sensitive probes of new physics
• Precise Standard Model predictions.
• Experimental challenges for bd (B B)– Continuum background– Background from bs (BK*) (50-100x bigger)
Part 3: Consistency Checks
Ali et al hep-ph/0405075
Part 3: Beyond the Standard Model
0,1
2
3( ) 0,0
1( )
tb
cd cb
V
V V
tdV
K. Honscheid, WSU Apr. 15, 2005
Combined B00,B0,B-- results
• No signals observed
@90% CL
K. Honscheid, WSU Apr. 15, 2005
CKM constraints from B()
BABAR BF ratio upper limit < 0.029 → |Vtd/Vts| < 0.19 (90% CL)
Penguins are starting to provide meaningful CKM constraint
(2,R) = (0.85,0.10) Ali et al. hep-ph/0405075
no theory error
with theory error (2,R) = (0.75,0.00)
95% CL BABAR allowed region
(inside the blue arc)
K. Honscheid, WSU Apr. 15, 2005
New CP Violating Phases in Penguin Decays?
b
dd
W cbV
csV
c /J
s0K
c
+ mixing CP = -e-2
+ mixing CP = -e-2
+ mixing CP = -e-2
b st
ss
d
W
d 0 K
, ,...
b st
dd
d
W
d
0 K
0 , ,...
Vtb
Vts*
Vtb
Vts*
K. Honscheid, WSU Apr. 15, 2005
Update on BKo
0Bb s
s
sd
d
W
g
, ,u c t
0SK
0
0
0.070 50 0.25 0.040 00 0.23 0 05
CP K
K
S .
C . .
0 0LB K
98 ± 18 events
0 0SB K
hep-ex/0502019
prel
imin
ary
114 ± 12 events
SM
Belle[BELLE-CONF-0435]
K. Honscheid, WSU Apr. 15, 2005
Reaching for more statistics – B 0 K 0 revisited
• Analysis does not require that ss decays through 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
• But need to understand CP eigenvalue of K+K-KS: has well defined CP eigenvalue of +1, - CP of non-resonant KK depends angular momentum L of KK pair
• Perform partial wave analysis– Estimate fraction of S wave (CP even) and P wave (CP odd) and
calculate average CP eigenvalue from fitted composition
0K
b
dg
t
d
ss
s
W
0BK+K- Nsig = 452 ± 28
(excl. res.)
b
d
0BK
g
t
s
us
u
W 2~tb tsV V
0Kds
K b
d
0BK
s
us
u
W
0Kd
s
K
4~ iub us uV V R e
OK Not OK
K. Honscheid, WSU Apr. 15, 2005
CP analysis of B K+K- KS
• Result of angular analysis
– Result consistent with cross checkusing iso-spin analysis (Belle)
• Result of time dependent CP fit
2
-even 2 20.89 0.08 0.06s
CPs p
Af
A A
0 0
-even 0 0
2 ( )0.75 0.11
( )S S
CP
B K K Kf
B K K K
0
0
0.42 0.17 0.04
0.10 0.14 0.06S
S
K K K
K K K
S
C
fSK+K-KS/(2fCP-even-1)] =
+0.55 ±0.22 ± 0.04 ±0.11(stat) (syst) (fCP-even)
K. Honscheid, WSU Apr. 15, 2005
More penguin exercises – B0 KS KS KS
• Use beam line as constraint and acceptonly KS with sufficient number of SVXhits.
• 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
• Result consistent with SM
05.034.0
04.071.028.025.0
38.032.0
C
SK0
b
d
0BK
g
t
s
us
u
W 2~tb tsV V
0Kds
K sddssd
K0
K0
K0
hep-ex/0502013
Ger
shon
, Haz
umi
hep-p
h/04
0209
7
K. Honscheid, WSU Apr. 15, 2005
IP-Constrained Vertexing
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:
Constrain decay products to beam-spot in x-y:
beam
0
B0
+
inflated beam
4m
200m
KS
Same technique as Ks0
hep-ex/0503011
K. Honscheid, WSU Apr. 15, 2005
Combined “sin2” Results
sin2β
…but comparison ignores subleading diagrams !
sin 2 0.47 0.07penguin
sin2β
sin2βPenguin±
sin2β
+
K. Honscheid, WSU Apr. 15, 2005
Corrections: b→s Decay Amplitude ~ VubVus
*
• Decays involving Vub enter with decay phase • Doubly-CKM suppressed w.r.t dominant diagram
iufusub eAVV 4)(*
b u
d
uWs
d
bs
d
u
W
u
d
ss
color-allowed treecolor-suppressed tree
Contribute to ’Ks, f0Ks, Ks, but not Ks[in KKKs (requires ss popup from soft g)]
Contribute to non-resonant KKKs (requires ss popup from soft g)
Contributes to all b sss modes
b
dd
sW
u
sZ,g, s
penguin
K. Honscheid, WSU Apr. 15, 2005
• 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
– 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]
Adding Theoretical Uncertainties
2xΔ
sin2
β‘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 sin2. 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.