Transcript Edinburgh Seminar - University of Edinburgh

CP violation studies at BABAR
Philip Clark
University of Colorado
Talk overview
Introduction to CP violation
PEPII and the BABAR experiment
The charmonium system
Various c results
BABAR CP violation results
Summary
Philip J. Clark
CP violation studies at BaBar
Page 2
The Standard Model
Two types of fundamental particle:
1) fermions which experience the forces
quarks “confined” eg. +(ud), p(uud)
leptons don’t experience strong force
2) bosons which transmit the forces
Four fundamental forces:
Gravitational, weak, EM and strong
Philip J. Clark
CP violation studies at BaBar
Page 3
Symmetries and conservation laws
Relation between symmetry and conservation laws
Noether’s theorem
Symmetries  conservation laws
q
C = Charge Conjugation
particle  antiparticle
P = Parity: x  -x
q
y
z
-x
T = time reversal
x
“run the film backwards”
-z
-y
CP =
B. Cahn
Philip J. Clark
CP violation studies at BaBar
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C and P symmetry and the weak interaction
  






    

P  0,   0



 P,   1 P,   1
P
C
P  0,   0



 P,   1
P,   1





P  0,   0



 P,   1 P,   1
P  0,   0



 P,   1
P,   1
C and P are violated maximally
Philip J. Clark
CP violation studies at BaBar
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CP symmetry
Is CP, a good symmetry for all interactions
including the weak interaction?
CPLEAR
1964 : Christenson, Cronin, Fitch and Turlay
CP violation in the decay
of neutral kaons
A CP-violating process offers
an absolute way of distinguishing
a world of anti-matter
from a world of matter
Cosmology:
CP violation is one of the three necessary conditions to produce a
global excess of matter in the Universe (Andreï Sakharov, 1967)
Philip J. Clark
CP violation studies at BaBar
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Matter-antimatter asymmetry
Perhaps the answer to why the Universe looks like
this
not
that???
Philip J. Clark
CP violation studies at BaBar
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The CKM model
u c t
d s b
1973 : M. Kobayashi and T. Maskawa made the connection
CP violation  third generation of quarks
Cabibbo-Kobayashi-Maskawa matrix
d u
d
V:
quark doublets
W
b u
b
Vud
W
Vub
u
u
Complex matrix described by 4 independent real parameters
(e.g. three angles, one phase)
Wolfenstein parametrization:
  0.22 A  0.83
d s b
u
c
t
u
c
t
CP violation in the Standard Model 
Philip J. Clark
CP violation studies at BaBar
d s b
 ≠0
Page 8
The Unitarity Triangle
The CKM Matrix is complex and unitary
* V* V*
Vud
cd
td
Vud Vus
Vub
Vus*
Vcd Vcs
Vcb
Vtd
Vtb
*
Vcs
V*ts
* Vcb
* V*tb
Vub
Vts
1 0 0
0 1 0
=
9 unitarity
relations
0 0 1
 Vud Vub* + Vcd Vcb*+ Vtd Vtb *= 0
The Unitarity
Rescaled Triangle
Unitarity Triangle
The

CP Violation
area of the Triangle
Experimentally: constraints
on the coordinates of the apex
of the Rescaled Triangle
in the complex plane
Philip J. Clark
CP violation studies at BaBar
Page 9
Precision test of the CKM model
Main experimental constraints
on the apex of the UT
CP violation in the kaon system
Measurements of |Vub|
(b → u transitions)
B0 and Bs mixing frequencies

BABAR
Phys. Rev. Lett. 89 (2002) 201802
World average (BABAR+Belle+…)
Heavy Flavor Averaging Group 2003
Philip J. Clark
CP violation studies at BaBar
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Is the CKM mechanism sufficient?
Antimatter
in the
Universe
CP violation in the quark sector
is not enough to generate
the baryon asymmetry
of our Universe
?
What can we do?
Understand the origin of CP violation in the Standard Model
The Kobayashi & Maskawa mechanism
can it account for all the effects of CP violation
that are observed in the quark sector?
and if possible, reveal inconsistencies
between experimental data and theoretical predictions
Possible manifestations of New Physics?
Evidence for new sources of CP violation?
Philip J. Clark
CP violation studies at BaBar
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PEP II/BABAR at SLAC
PEP II
Asymmetric
B Factory
Started construction in1994
Completed in 1999
Reached design luminosity in 2000
Luminosity records
PEP-II/BABAR at SLAC
design peak: 3.0 x 1033 cm2s1
best peak:
6.6 x 1033 cm2s1
total recorded: 130.4 fb1
9 GeV e on 3.1 GeV e+
Philip J. Clark
CP violation studies at BaBar
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The BABAR detector
DCH
DIRC
EMC
SVT
Philip J. Clark
CP violation studies at BaBar
IFR
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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!
Philip J. Clark
CP violation studies at BaBar
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Measurement of sin2
y
Identify
B or anti-B

z
x
0
4S
Coherent BB
production
e
e
K-
Btag
B0rec
Dz
K S0

K+
  c


0
K
 S

D t  D z/cg  g
Philip J. Clark
CP violation studies at BaBar
Full reconstruction of
B   c Ks 0
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Observable CP Asymmetry
Dt spectrum of CP eigenstates
(perfect experiment with sin2 = 0.6)
Different Dt spectrum for B0 and B0
Positive and negative Dt
sin 2
Visible asymmetry
ACP= nB0-nB0/(nB0+nB0)
ACP (Dt )  sin(2 )  sin( Δmd Δt )
Philip J. Clark
CP violation studies at BaBar
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CP asymmetry
Philip J. Clark
CP violation studies at BaBar
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_
b
B0
The new mode:- B0  cKs
W
d
_
c 
c c
_
s K0
d
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 K+K-0)
11.3  5.1  2.4 x10-6
Combining gives us our CP sample:
Philip J. Clark
CP violation studies at BaBar
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CP asymmetry using B→cK
Philip J. Clark
CP violation studies at BaBar
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Sin2 per Charmonium mode
Good consistency
between the
measurements
Philip J. Clark
CP violation studies at BaBar
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Summary of “sin2” results
“sin2”
“reference” sin2
pure penguin
mostly penguin?
heavily supressed tree
with competing penguin
suppressed tree
penguin pollution
The other BABAR measurements
agree with the reference sin2
within two standard deviations, or better
Statistical conspiracy or
hint of unexpected
physics effect?
but… consistently on the low side
Philip J. Clark
CP violation studies at BaBar
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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-j2|+1, … , (j1+j2)-1 , (j1+j2 ) and m =m1+m2
gives:
J = 0 (½ - ½ )
J = 1 (½ + ½)
m=0
m = -1, 0, 1
the singlet state
the triplet state
Other examples are the:
hydrogen atom (e-p)
positronium
(e+e-)
Discrete energy levels and splittings exist and
can give information on the strong force
En
triplet
hyperfine splitting
singlet
Philip J. Clark
CP violation studies at BaBar
Page 22
Striking similarity
positronium (e+e-)
charmonium (cc)
triplet
J/(2S) triplet
singlet
triplet
J/ triplet
singlet
Missing singlet state
c(2S)
Philip J. Clark
c singlet
“Introduction to High Energy Physics”
D. Perkins 4th edition April 2000
CP violation studies at BaBar
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c at BABAR
c
mass and total width
c mass
c width
mass and total decay width
?
photon-photon
production
c(2S) mass and total width
Philip J. Clark
CP violation studies at BaBar
Page 24
Charming, but strange mesons
Ds+= cs
Ds- = cs
mass = 1968.5 MeV
D +s
D+
D+sJ(2317) D+s0
Philip J. Clark
CP violation studies at BaBar
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Large amount of theoretical interest
32 new preprints
Philip J. Clark
CP violation studies at BaBar
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What we have covered:

Summary
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
New
Philip J. Clark
B  c K transitions and branching fractions
Using the c to measure sin2
Charmonium system and measurement of c(2S)
particle
 DsJ+ resonance
CP violation studies at BaBar
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The c and the Charmonium System
: fundamental scalar state of the charmonium system,
hyperfine partner of the
In the c group we are studying
the following decay modes:
to hadrons
through virtual photon
radiative
Philip J. Clark
CP violation studies at BaBar
Page 28
Resonant structure
c  (KsK) resonant structure
M(K± ±)
resonant structure
– c  a0980) ?
– Should look for c  )
Branching fraction large
4.9 ± 1.8 % (c  )
1.28% (gg , ±±)
cf. 1.26% (c  KsK± ±)
No result from Belle
Philip J. Clark
M(K0s±)
c
Dalitz analysis
and
CP violation studies at BaBar
Page 29
B physicsWhat
at hadron
next?machines
Geant3 LHCb event display
Advantages:
LHC cross-section 500 mb
1012 bb pairs/year at 2x1032 cm-2s-1
(down by 5 at Tevatron )
Challenges:
Event complexity
Triggering
Bunch spacing:
25 ns (LHC)
132 ns (Tevatron)
Philip J. Clark
CP violation studies at BaBar
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Comparison of yield and purity
Philip J. Clark
Sample
Ntagged
Purity
J/ Ks (+-)
974
97%
J/ Ks (00)
170
89%
(2S) Ks
150
97%
c1Ks
80
95%
 cK s
132
73%
Total
1506
92%
CP violation studies at BaBar
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At 1036
SLAC-PUB-8970
Philip J. Clark
CP violation studies at BaBar
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Mixing and Sin2 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  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) sin2 sin(DmDt) ) R(Dt)
(1-2w) is the “dilution” due to mistag
R(Dt) is the vertex resolution function
Philip J. Clark
CP violation studies at BaBar
Page 33
Silicon Vertex Tracker (SVT)
580 mm
• Five layer double-sided Si
• Very low mass
• Stand-alone tracking device for PT < 120 MeV/c
• Radiation hard
• z-resolution of 70m on CP vertex
Philip J. Clark
CP violation studies at BaBar
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Drift Chamber
Tracking resolution
Philip J. Clark
CP violation studies at BaBar
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Detector of Internally Reflected Cherenkov
Light (DIRC):
Qc resolution:
cosQc=1/n
Philip J. Clark
CP violation studies at BaBar
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Cherenkov angles for  and K from D*
D0, D0 K-

K
Philip J. Clark
CP violation studies at BaBar
Page 37
Electromagnetic calorimeter
E
1%
 4  1.2%
E
E
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
Philip J. Clark
CP violation studies at BaBar
Page 38
Time-Dependent Asymmetries
B0 B 0 Mixing using the Bflav sample:
Amixing (Dt ) 
N(unm ixed) N(m ixed)
 1  2w .cos(ΔmBd Δt )
N(unm ixed) N(m ixed)
CP-violating asymmetry using the BCP sample
for example B0CP  J/  K S0
ACP (Dt ) 
N(Btag  B0 )  N(Btag  B 0 )
N(Btag  B0 )  N(Btag  B 0 )
 1  2w.sin 2 β. sin(ΔmBd Δt )
Use the large statistics Bflav data sample
to determine the mis-tagging probabilities and the
parameters of the time-resolution function
Philip J. Clark
CP violation studies at BaBar
Page 39
Instrumented Flux Return (IFR)
 ID efficiency and  fake rate
Barrel section of IFR
Large solid angle coverage for muon id (P>1 GeV/c) and to detect neutral
hadrons (K0L )
Philip J. Clark
CP violation studies at BaBar
Page 40
Speaking of Direct CP violation …
Uncertainty ~5%!
Philip J. Clark
CP violation studies at BaBar
Page 41
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
Philip J. Clark
CP violation studies at BaBar
e+
qq
e+
Signal
B
e-
eOther
B
Page 42