Edinburgh Seminar

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CP violation studies at BABAR
Philip Clark
University of Colorado
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Talk overview
Introduction to CP violation
PEPII and the BABAR experiment
The charmonium system
Various ?c results
BABAR CP violation results
Summary
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The Standard Model
Two types of fundamental particle
1) fermions which experience the forces quarks
confined eg. ?(ud), p(uud) leptons dont
experience strong force
2) bosons which transmit the forces
Four fundamental forces

• Gravitational, weak, EM and strong

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Symmetries and conservation laws
Relation between symmetry and conservation laws
Noethers theorem Symmetries ? conservation
laws

• C Charge Conjugation
• particle ? antiparticle

P Parity x ? -x
T time reversal run the film backwards
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C and P symmetry and the weak interaction
C and P are violated maximally
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CP symmetry
Is CP, a good symmetry for all interactions
including the weak interaction?
CosmologyCP violation is one of the three
necessary conditions to produce aglobal excess
of matter in the Universe (Andreï Sakharov, 1967)
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Matter-antimatter asymmetry
Perhaps the answer to why the Universe looks
like this not that???
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The CKM model
1973 M. Kobayashi and T. Maskawa made the
connection CP violation ? third
generation of quarks
quark doublets
l ? 0.22 A ? 0.83
CP violation in the Standard Model ? h ? 0
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The Unitarity Triangle
The CKM Matrix is complex
and unitary
9 unitarity relations
The Rescaled Unitarity Triangle
The Unitarity Triangle
Experimentally constraints on the coordinates
of the apex of the Rescaled Triangle in the
complex plane
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Precision test of the CKM model
Main experimental constraints on the
apex of the UT
BABAR
Phys. Rev. Lett. 89 (2002) 201802
World average (BABARBelle)
Heavy Flavor Averaging Group 2003
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Is the CKM mechanism sufficient?
What can we do?
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PEP II/BABAR at SLAC
Started construction in1994 Completed in 1999
Reached design luminosity in 2000
PEP II Asymmetric B Factory
Luminosity records
PEP-II/BABAR at SLAC
design peak best peak total recorded
3.0 x 1033 cm-2s-1
6.6 x 1033 cm-2s-1
130.4 fb-1
9 GeV e- on 3.1 GeV e
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The BABAR detector
DCH
DIRC
EMC
IFR
SVT
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B Mixing

• Certain mesons can do a neat little trick (K0,
  D0, B0)
• A B0 meson can change into an anti B0 meson (B0)
• This is called mixing. It means these
  particles can (and do) oscillate into their
  anti-particles and back again
• The oscillation frequency is about 0.5 ps-1!

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Measurement of sin2b
0
B
tag
Coherent BB production
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Observable CP Asymmetry
Dt spectrum of CP eigenstates
(perfect experiment with sin2b 0.6)
Different Dt spectrum for B0 and B0 Positive and
negative Dt
Visible asymmetry ACP nB0-nB0/(nB0nB0)
sin 2b
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CP asymmetry
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The new mode- B0 ? ?cKs

• In the ?c analysis group we have studied
• B? ? ?cK? and B0 ? ?cKs in the ?c decay modes

The two dominant modes measured have the
following branching fractions BR(B0? ?cK0) x
BR(?c ?K0K???) 36.8 ? 11.6 ? 6.0 x10-6
BR(B0? ?cK0) x BR(?c ?KK-?0) 11.3 ? 5.1 ?
2.4 x10-6
Combining gives us our CP sample
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CP asymmetry using B?hcK
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Sin2b per Charmonium mode
Good consistency between the measurements
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Summary of sin2b results
0.741
sin2b
reference sin2b
pure penguin
mostly penguin?
heavily supressed tree with competing penguin
suppressed treepenguin pollution
The other BABAR measurements agree with the
reference sin2b
Statistical conspiracy or hint of unexpected
physics effect?
within two standard deviations, or better
but consistently on the low side
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The Charmonium system
The ?c meson consists of a charm and anti-charm
quark
Bound state of two spin ½ particles (fermions)
J J1 J2
The combined angular momenta
J j1-j2, j1-j21, , (j1j2)-1 , (j1j2
) and m m1m2
gives
the singlet state
the triplet state
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Striking similarity
charmonium (cc)
positronium (ee-)
triplet
J/?(2S) triplet
singlet
triplet
J/? triplet
?c singlet
singlet
Introduction to High Energy Physics D. Perkins
4th edition April 2000
Missing singlet state ??c(2S)
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hc at BABAR
?
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Charming, but strange mesons
Ds cs Ds- cs mass 1968.5 MeV
Ds
D
DsJ(2317) ?Ds?0
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Large amount of theoretical interest
32 new preprints
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Summary
What we have covered

• Prequisites
• The Standard Model
• The discrete symmetries C P and T
• C and P violated maximally in weak interation
• CP violation in the kaon system
• Cosmological implications
• Formalism
• The Standard Model mechanism for CP violation
• Testing the unitarity of the CKM matrix
• Measurement of Sin2?
• General methodology
• Manifestation of CP violation by BaBar
• Comparison to other measurements
• Charmonium
• B ? ?c K transitions and branching fractions
• Using the ?c to measure sin2?
• Charmonium system and measurement of ?c(2S)
• New particle
• DsJ resonance

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The hc and the Charmonium System
In the ?c group we are studying the following
decay modes
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Resonant structure
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B physics at hadron machines
What next?
Advantages LHC cross-section 500 mb
1012 bb pairs/year at 2x1032 cm-2s-1
(down by 5 at Tevatron ) Challenges Even
t complexity Triggering Bunch spacing
25 ns (LHC) 132 ns (Tevatron)
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Comparison of yield and purity
Sample Ntagged Purity
J/? Ks (??-) 974 97
J/? Ks (?0?0) 170 89
?(2S) Ks 150 97
?c1Ks 80 95
?cKs 132 73
Total 1506 92
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At 1036
SLAC-PUB-8970
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Mixing and Sin2b analysis procedure

• Reconstruct one B fully in CP eigenstate or
  flavour eigenstate
• Other B partially reconstructed and flavour
  tagged
• Measure D z
• Fit for D t D z/cg b g

B Mixing-
PDF(Dt)?? exp(Dt/tB) ( 1 (1-2w) cos(DmDt)
)?R(Dt)
CP violation-
PDF(Dt)?? exp(Dt/tB) ( 1 (1-2w) sin2b
sin(DmDt) ) ?R(Dt)
(1-2w) is the dilution due to mistag R(Dt) is
the vertex resolution function
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Silicon Vertex Tracker (SVT)
580 mm

• Five layer double-sided Si
• Very low mass
• Stand-alone tracking device for PT lt 120 MeV/c
• Radiation hard
• z-resolution of 70?m on CP vertex

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Drift Chamber
Tracking resolution
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Detector of Internally Reflected Cherenkov Light
(DIRC)

Qc resolution
cosQc1/nb
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Cherenkov angles for p and K from D D0p, D0
K-p
p
K
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Electromagnetic calorimeter
Radiation length 1.85 cm (16 -18X0)
Moliere radius 3.8 cm
Peak emission 565 nm
Density 4.53 g/cm3
Time constant 940 ns
Light yield 40-50k photons/MeV
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Time-Dependent Asymmetries
Mixing using the Bflav sample
CP-violating asymmetry using the BCP sample
for example
Use the large statistics Bflav data sample to
determine the mis-tagging probabilities and the
parameters of the time-resolution function
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Instrumented Flux Return (IFR)
? ID efficiency and ? fake rate
Barrel section of IFR
Large solid angle coverage for muon id (Pgt1
GeV/c) and to detect neutral hadrons (K0L )
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Speaking of Direct CP violation
Uncertainty 5!
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Separating Signal from Background (II)

• The other powerful thing we can do is to exploit
  the event shape
• In the CM, the decay products of the B are
  distributed roughly spherically. This is because
  the pair of B mesons weigh only slightly less
  than the ?. They are essentially produced at
  rest
• The continuum is light quark pair production, so
  there is lots of extra energy. All the decay
  products bunch into jets
• We define variables that measure the degree of
  jettiness of the decay to tell us how more or
  less likely it is to be signal or background