The Asymmetry Between Matter and Anti-Matter

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The Asymmetry Between Matter and Anti-Matter
Or How to Know if its Safe to Shake an Aliens
Hand
K. Honscheid Dept. of Physics Ohio State
University
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Anti Matter
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Anti-Matter and Homeland Security

• We are going back to the Moon
• We might go to Mars
• What if

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The Standard Model of Particle Physics

• Very few types of particles are needed to build
  CharlottesvilleProton uud Neutron udd
• Many more particles were discovered in cosmic
  rays and with particle accelerators
• The positron was the first anti-particle
• The anti-proton was discovered in 1955
• Quark-antiquark bound states
  are called mesons
• p ud K0 ds
• B0 bd B0 bd

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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 particle-antipartic
  le pair

Predict nMatter/nPhoton 0 Exp nb/ng
(6.1 /- 0.3) x 10-10 (WMAP)
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So how can this happen?
In 1967, A. Sakharov showed that the generation
of the net baryon number in the universe requires

• Baryon number violation(Proton Decay)
• Thermal non-equilibrium
• C and CP violation(Asymmetry between particle
  and anti-particle)

Transition to broken electroweak symmetry
provides these conditions
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Where is all the Antimatter?

• No matter antimatter annihilation radiation has
  been observed.
• No evidence for anti-nuclei in cosmic rays
• The AMS-02 experiment on the International Space
  Station will search for antimatter

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How to Distinguish Matter from Antimater

• Same mass and spin
• Equal but opposite charge, magnetic dipole
  moment, lepton/baryon number
• Hydrogen vs. Anti-Hydrogensame energy levels and
  spectroscopy

Hubble Time-Lapse Movie Of Crab Pulsar Wind (2000
2001, 24 observations)
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Experimental Possibilities

• Get equal amounts ofmatter and anti-matter
• Wait
• See whats left(in anything)

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PEP-II Asymmetric B Factory
Stanford Linear Accelerator Center, Stanford,
California
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The BaBar Experiment
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Preparing the Matter Antimatter Sample
B mesons contain a b quark and a light
anti-quark. mB 5.28 GeV (5x mProton)

• The Upsilon(4S) - a copious, clean source of B0
  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
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A B0B0 Event
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Analysis techniques
Threshold kinematics we know the initial energy
of the system

Background
Background
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Searching for the Asymmetry
227 x 106 B0 Mesons Count B0?K?? Decays
227 x 106 B0 Mesons Count B0?K-? Decays
Is N(B0?K?? ) equal to N(B0?K-? )?
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How to Tell a Pion from a Kaon

• Angle of Cherenkov light is related to particle
  velocity
• Transmitted by internal reflection
• Detected by10,000 PMTs

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Searching for the Asymmetry
227 x 106 B0 Mesons Count B0?K?? Decays
227 x 106 B0 Mesons Count B0?K-? Decays
Is N(B0?K?? ) equal to N(B0?K-? )?
B0?K??
BABAR
background subtracted
BABAR
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Direct CP Violation in B Decays
Using We obtain First confirmed
observation of direct CP violation in B
decays Tell the Alien we are made from the stuff
that decays less frequently to Kp
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Symmetries of Nature that usually work

• Parity, P
• Reflection a system through the origin, thereby
  converting right-handed into left-handed
  coordinate systems
• Vectors (momentum) change sign but axial vectors
  (spin) remain unchanged

• Time Reversal, T
• Reverse the arrow of time, reversing all
  time-dependent quantities, e.g. momentum

• Charge Conjugation, C
• Change all particles into anti-particles and vice
  versa

Good symmetries of strong and electromagnetic
forces
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Including Neutrinos
Does not exists
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CP Violation in the Standard Model
CP Operator
coupling
q
q
g
g
CP( )
q
q
J
J?
Mirror
To incorporate CP violation g ?
g (coupling has to be complex)
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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 Vud Vus Vub d
s Vcd Vcs Vcb s
b Vtd Vtd Vtb b
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The Unitarity TriangleVisualizing CKM
information from Bd decays
d
b
s

• The CKM matrix Vij is unitary with 4 independent
  fundamental parameters
• Unitarity constraint from 1st and 3rd columns
  ?i Vi3Vi10
• Testing the Standard Model
• Measure angles, sides in as many ways possible
• SM predicts all angles are large

u
Vud Vus Vub Vcd Vcs Vcb Vtd
Vts Vtb
c
t
CKM phases (in Wolfenstein convention)
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Understanding CP Violation in B ? Kp
A1 a1 eif1 eid1
A1 a1 e if1
B0 K-p

A2 a2 eif2 eid2
B0 Kp-

• include the strong phase (doesnt change sign)
• more than one amplitude with different weak
  phase (A A1A2)

2 sin(f1 - f2) sin(d1 - d2)
0
Asymmetry
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B0 B0 Mixing and CP Violation
A neutral B Meson
Mixing frequency Dmd ? 0.5 ps-1
B0 fraction sin(Dmd Dt)
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Time-Dependent CP Asymmetries
c
b
c
CP Eigenstate hCP -1
W
B0
s
d
d
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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
  mode
• 3. Tag the other B0 to make the
  matter/antimatter distinction
• 4. Determine the time between the two B0 decays,
  Dt
• 5. Plot Dt distribution separately for B and B
  tagged events
• 6. Plot time dependent asymmetry
• ACP(t)sin(2b)sin(DmdDt
  )

sin 2b
sinDmDt
Dt (ps)
Dt (ps)
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Time-dependent analysis requires B0 flavor tagging

• We need to know the flavour of the B at a
  reference t0.

At t0 we know this meson is B0
B 0
rec
B 0
B 0
tag
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Silicon Vertex Tracker (SVT)
5 layers of double-sided silicon strip detectors
( 1 m2), 150K channels of custom rad-hard IC
readout (2 Mrad)
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Results sin 2b and the observation of CP
J/yKs and otherb ? cc s final states
227 million BB pairs

• CP -1
• B ? J/? Ks0, Ks0 ? pp-, p0p0
• B ? ?(2S) Ks0
• B ? ?c1 Ks0
• B ? J/? K0, K0 ? Ks0??
• B ? ?c Ks0

7730 events

• CP 1
• B ? J/? KL0

BaBar result sin2b 0.722 ? 0.040 ? 0.023
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The Unitarity Triangle

• b

23.3 1.5o
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yKs is not the only CP Eigenstate
Access to a from the interference of a b?u decay
(g) with B0 mixing (b)
g
a p - b - g
sin2a
ACP(t)sin(2a)sin(DmdDt).
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Time-dependent ACP of B0?pp-
Blue Fit projection Red qq background
B0?Kp cross-feed
BR result in fact obtained from 97MBB
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Houston, we have a problem
B0 ? pp-
B0 ? Kp-
B0?pp- 157 ? 19 (4.7 ? 0.6 ? 0.2) x 10-6
B0?Kp- 589 ? 30 (17.9?0.9 ?0.7) x 10-6
Penguin/Tree 30
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The route to sin(2a) Penguin Pollution

• Access to a from the interference of a b?u decay
  (g) with B0B0 mixing (b)

g
Inc. penguin contribution
How can we obtain a from aeff ?
Time-dep. asymmetry
NB T "tree" amplitude P "penguin"
amplitude
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How to estimate a-aeff Isospin analysis

• Use SU(2) to relate decay rates of different hh
  final states (h ? p,r)
• Need to measure several related B.F.s

2?-?eff
Difficult to reconstruct. Limiting factor in
analysis
Gronau, London PRL65, 3381 (1990)
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Now we need B0?p0p0

• 6117 events in signal peak (227MBB)
• Signal significance 5.0s
• Detection efficiency 25

B?rp0

• Time-integrated result gives

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B ? rr Sometimes you have to be lucky
P ? VV decaythree possible ang mom states
S wave (L0, CP even) P wave (L1, CP odd) D wave
(L2, CP even)
r helicity angle
We are lucky
100 longitudinally polarized! Transverse
component taken as zero in analysis
PRL 93 (2004) 231801
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Time dependent analysis of B?rr-

• Maximum likelihood fit in 8-D variable space

32133 events in fit sample
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Searching for B?r0r0

• Similar analysis used to search for r0r0
• Dominant systematic stems from the potential
  interference from B?a1p (22)

c.f. B?pp- B.F. 4.7 x 10-6 and B?p0p0 B.F. 1.2
x 10-6
B (B?rr-) 33 x 10-6
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Isospin analysis using B?rr

• The small rate of means
• a-aeff is smaller
• P/T is small in the B?rr system
• (Relative to B?pp system)
• No isospin violation (1)
• No EW Penguins (2)

a-aeff lt 11
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The Unitarity Triangle
103 11o

• a

23.3 1.5o
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The 3rd Angle g
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First Look at the Data
Only a loose bound on rB with current statistics
(rB)2 0.190.23
BABAR-CONF-04/039
Several other methods are being
investigated More data would help a lot
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Combined Experimental Constraint on g
BABAR Belle combined
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The Unitarity Triangle

• g

103 11o
23.3 1.5o
5120-34o
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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
• Experimentally we find nb/ng (6.10.3) x 10-10
  (WMAP)

h
r
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New Physics in Penguin Decays?

• FCNC transitions b?sg and b?dg are sensitive
  probes of new physics
  
• Precise Standard Model predictions.
• Experimental challenges for b?dg (B?rg B?wg)
• Continuum background
• Background from b?sg (B?Kg) (50-100x bigger)

Ali et al hep-ph/0405075
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Combined B0?r0g,B0?wg,B-?r-g results

• No signals observed

_at_90
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CKM constraints from B?r(w)g
BABAR BF ratio upper limit lt 0.029 ? Vtd/Vts lt
0.19 (90 CL)
Ali et al. hep-ph/0405075
(z2,DR) (0.85,0.10)
no theory error
(z2,DR) (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)

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New CP Violating Phases in Penguin Decays?
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Reaching for more statistics B 0 ? ? K 0
revisited

• Analysis does not require that ss decays through
  f resonance, it works with non-resonant KK- 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 KK-KS
• - f 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

KK-
Nsig 452 28 (excl. ? res.)
OK
Not OK
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CP analysis of B ? KK- KS

• Result of angular analysis
• Result consistent with cross checkusing iso-spin
  analysis (Belle)
• Result of time dependent CP fit

hf?SKK-KS/(2fCP-even-1) 0.55 0.22 0.04
0.11
(stat)
(syst)
(fCP-even)
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More penguin exercises B0 ? KS KS KS
hep-ex/0502013

• 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
• Result consistent with SM

hfK0?
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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.

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Conclusions (now with numbers)

• PEP-II and BABAR (as well as BELLE) have
  performed beyond expectation
• CP violation in the B system is well established
• sin(2b) fast becoming a precision measurement
• As for the other two angles (the subject of this
  presentation)
• Many analysis strategies in progress
• The CKM angle a is measured but greater precision
  will come
• First experimental results on g are available
• Most of the results presented today are based on
  datasets up-to 227 MBB
• BABAR and PEP-II aim to achieve 550 MBB (500
  fb-1) by summer 2006