Matter-Antimatter Asymmetries:
What have we learned?
Jeffrey D. Richman
University of California, Santa Barbara
MIT Physics Department Colloquium: May 5, 2005
PEP-II e+e- Ring and BABAR Detector
Linac
PEP-II ring: C=2.2 km
BABAR

1993: start of PEP-II
construction

1994: start of BABAR
construction

Spring 1999: BABAR moves
onto beamline

Oct 29, 2000 PEP-II
achieves design luminosity

Fall 2003: start trickle
injection of beams into PEPII (5 Hz)

Spring 2004: PEP-II
achieves 3X design
luminosity

Current data sample: about
230 M BB events.
BABAR Collaboration
The UCSB HEP Group in BABAR

Faculty: Claudio Campagnari,
J.D.R., (Michael Witherell).

Engineers and Technicians: Dave
Hale, Susanne Kyre, Sam Burke, Dan
Callahan, Julie May, Julie Stoner,
Andrea Allen, Lap-Yan Leung

Postdocs: Jeffrey Berryhill, Philip
Hart, Owen Long, Wouter Verkerke

Graduate Students: Adam Cunha,
Bryan Dahmes, Anton Eppich, TaeMin Hong, Natalia Kuznetsova,
Steven Levy, Michael Mazur.

Undergraduates: Aviva Shakell, Jeff
Flanigan, Oshin Nazarian.
BABAR/PEP-II
Experiment at SLAC
Antimatter and other radical ideas

Dirac relativistic wave eq’n
(1928): extra, “negative-energy”
solutions. Positron interpretation
confirmed by Anderson.

A radical idea: doubling the
number of kinds of particles!

Supersymmetry: doubles the
number of particles again!
Pb: 6 mm
thick
P.A.M. Dirac, Proc. Roy. Soc. (London), A117, 610 (1928);
ibid., A118, 351 (1928).
C.D. Anderson, Phys. Rev. 43, 491 (1933).
Discrete Symmetry Operators: C, P, T
C: a a
P: r  r
e

C
e

s
e

P
e

s  p reversed
e

incoming
T
e

outgoing
Discrete symmetry transformations: multiplicative (not additive)
quantum numbers. The weak interactions violate C, P, CP, T.
1st observation of CP violation

CP violation at a tiny level (10-3) was first discovered in 1964 in
the decays of neutral kaons (mesons with strange quarks).
B( K    )  (2.0  0.4) 10
0
L


3
CP ( K L0 )  1, CP (   , L  0)  1
Jim Cronin’s Nobel Prize lecture:
“...the effect is telling us that at some tiny level there is a
fundamental asymmetry between matter and antimatter, and it is
telling us that at some tiny level interactions will show an
asymmetry under the reversal of time. We know that
improvements in detector technology and quality of accelerators
will permit even more sensitive experiments in coming decades.
We are hopeful then, that at some epoch, perhaps distant, this
cryptic message from nature will be deciphered.”
Questions about antimatter
1.
Is the difference between matter and antimatter merely one of
convention, or do they behave differently?
CPT symmetry guarantees
m( a )  m( a )
 (a )   (a )
In contrast, SUSY is a badly
broken symmetry:
m(a )  m(a )
Compare corresponding processes
?
(a  f i )  (a  f i )  CP violation
rate (process)
rate (anti-process)
CP violation and alien civilizations
We can use our knowledge of CP violation to determine whether
alien civilizations are made of matter or antimatter without having
to touch them.
( B  K  )  ( B  K  )
ACP 
0
 
0
 
( B  K  )  ( B  K  )
0
bd


0


13%
bd
We have these inside of us.

K  us

  ud
Matter vs. antimatter: implications for cosmology
A. Sakharov (1967): How to generate an asymmetry between
N(baryons) and N(anti-baryons) in the universe (assuming
equal numbers initially)?

Baryon-number-violating process

Both C and CP violation (particle helicities
not relevant to particle populations)

Departure from thermal equilibrium
Bnet   ( X  Yi )  ( X  Yi )   Bi
i
We may well owe our existence to some form of CP violation at
work in the early universe.
2.
How are CP violating asymmetries produced?
The Standard Model predicts that, if CP violation occurs, it must
occur through specific kinds of quantum interference effects. In
the SM, CP violation is traced to a single parameter that is
connected with how quarks acquire their masses.
A1
source
A1
a
A2
a
A2
A1
A2
fi
fi
Two amplitudes with a CP violating relative phase

Suppose a decay can occur through two processes, with
amplitudes A1 and A2. Let A2 have a CP-violating phase
f2.
A  A1  a2e
i 2
A  A1  a2e
 i 2
No CP asymmetry!
(But the decay rate is different
from what it would be without the
phase.)
A  A1  A2
A2
A1  A1
A  A1  A2
2
A2
Two amplitudes with CP conserving & violating phases

Next, introduce a CP-conserving phase in addition to the
CP-violating phase.
A  A1  a2e
i (2  2 )
A  A1  a2e

i (  2  2 )
A  A1  A2
Now have a CP asymmetry
A A
A2
A1  A1
2 
2
2
A  A1  A2
A2
Evidence for “direct” CP violation in
B0K+ vs. B0K-
N ( BB )  227  106
B( B  K )  2  105
bkgd symmetric
n  B 0  K     910
n  B 0  K     696
696  910
A
 0.133
696  910
AK  0.133  0.030  0.009
hep-ex/0408057
Time-Dependent CP asymmetries
B0 mesons spontaneously oscillate into their own
antiparticles, providing a second path to final states
that are CP eigenstates. This provides an exactly
known CP conserving phase.
B0 ( bd )
fCP
B ( bd )
no net oscillation
no net oscillation
B
0
net oscillation
( B
0
phys
(t )  fCP )
fCP
0
B
0
B
0
net oscillation
( B
0
phys
B0
(t )  fCP )
3.
Can CP violation point to new physics?
source
A1
A2
ANP
Study processes in which there
can be extra amplitudes arising
from new physics (NP).
Must be sure that all SM
amplitudes are fully understood.
ANP from physics at high mass scales  small
 want to use processes in which A1,2 are small
KEK press release, 13 August 2003
(excerpt)
http://www.kek.jp/press/2003/belle3e.htmlh
Perspective on the b quark
u
 
d 
oscillations
c
t
 
 
s
b
loop

processes
The b-quark is relatively heavy, giving it many kinemetically
accessible final states.
All B decays are suppressed, because the b quark must decay
into quarks outside its own generation. This gives the b quark a
long lifetime (1.6 ps).

t

W
b
t-quark decays: very fast; overwhelmingly dominated by
Feynman diagrams for weak decay/oscillation amplitudes
e
Tree
W
b

d

e
b
c
d
d
Box
d
W

d
u
d
Penguin loop
d
u , c, t
b
W
Tree
u

u,c, t
W
W
b
s
u , c, t

b
d
g
d
Heavy particles (M>mb) are allowed in the intermediate state!
s
s
A few projects…
…the rest of them.
Blind Analysis
Nearly all CP and rare decay analyses in
BaBar are performed with a blind protocol.
Information that would reveal the result is hidden
until the full analysis procedure is defined.
Designed to avoid subconscious bias of the
experimenter. (E.g., desire to confirm a
an earlier result!)
When we are ready, we
have an unblinding party…..
Quark transitions and CP-violating phases
in the Standard Model
W
qj

gVij
W
qi
g
Lint  
( J W  J  †W )
2
qj

*
ij
gV
J    ui  12 (1   5 )Vij d j
i, j
LYukawa   (Y jk uLj uRk  Y jk d Lj d Rk  h.c.)
1
2
j ,k
v
m jk  
Y jk
2
Quark mass matrices
qi
(v  H ( x ))
Higgs field
v
mjk  
Y jk
2
The mysterious pattern of the CKM matrix V
1 2

V
V
V
1


 ud
us
ub 
2

V

1 2
V
V



1

cs
cb 
2

 cd
V
  A 3 (1    i )  A 2
V
V
ts
tb 
 td

 0.97 0.23 0.004 
 0.23 0.97 0.04 


 0.004 0.04

1


A 3 (   i ) 

2
4
A

O
(

)


1

(magnitudes only)
• The SM offers no explanation for this numerical pattern.
• But SM framework is highly predictive:
 Unitary matrix: (Col 1)(Col 3)* =0 etc.
 Only 4 independent parameters: A, , , 
 One CP violating phase parameter
The Standard Model “Unitarity Triangle”
[Col 1][Col 3]*=0
The structure of the CKM
matrix means that all terms in
(Col 1)(Col 3)* are of order 3.
If just 2 quark generations:
no CP phase allowed!
CP
Fat unitarity triangle  large angleslarge CP asymmetry
But only certain decays have interfering amplitudes!!
Possible new CP phases in bs from Supersymmetry
New source of flavor violation introduced by squark mass matrices
(not diagonalizable in same basis as quark mass matrices). Gluinos
can have flavor-changing couplings to quarks and squarks.
Standard Model
.
g=gluino
From S. Khalil and E. Kou, hep-ph/0212023
Production of B mesons in e+e- collisions
Since quarks have electric charge, they couple to the photon.
e-
TM
e+
b

b
0
B (bd )
d
d
b
(4 S )
strong
0
b
B (bd )
weak
t
10 23 s  ( B) 1.6  1012 s
B  (bu) B  (bu )
e e    bb  (4S )  B0 (bd ) B 0 (bd )
e e    uu , dd , ss , cc , bb , e e  ,     ,  
EM Calorimeter:
6580 CsI(Tl)
crystals (5% 
BaBar Event Display
(view normal to beams)
energy res.)
Cerenkov ring imaging
detectors: 144 quartz
bars (measure velocity)
Tracking volume:
B=1.5 T
Silicon Vertex Tracker
5 layers: 15-30 m res.
Rdrift chamber=80.9 cm
(40 measurement points, each with
100-200 m res. on charged tracks)
Identifying a decay process
a  1  2  ...
Ea  E1  E2  ...
pa  p1  p2  ...
m  E  ( pa )
2
a
2
a
2
2

 

   Ei     pi 
 i
  i

2
Peak at
m=mB
m
GeV/c2
 Ebeam 
2


   pi 
 i

2
Main parameters controlling the experimental design
mB  5.28 GeV
Mass/momentum scale
 (e e  (4S )) 1.1 nb
 
B( B  X CP )  103  106
 B 1.6 ps
m
0.5 ps
-1
Production cross section
Branching fractions to useful
final states.
B meson mean lifetime
2
(T=
m
12 ps)
B 0 B 0 oscillation frequency
Major issue: how can we observe an interference pattern that occurs
in time and whose variation occurs over about 1 ps?
PEP-II e+e- Ring
Two separate
storage rings
• unequal energies
• multibunch op.
• trickle injection
LER (3.1 GeV)
e+
I HER  1550 mA
I LER  2450 mA
N (bunches)  1588
e
HER (9.0 GeV)
Ee   Ee 

Ee   Ee 
0.49
Ee   Ee 
 
4 Ee  Ee 
0.56
Innermost Detector Subsystem: Silicon Vertex Tracker
Installed SVT Modules
Be beam pipe: R=2.79 cm
(B mesons move 0.25 mm along beam direction.)
Converting the interference pattern f(t) into f(z)
e

e

  4S   bb
  1023 s
10 s
B  bd
-1
0
B 0  bd
EPR correlated oscillations
B0
B0
B 0 decay (tag)
B 0 ( t  0)
z   c(t )
170 μm  1 ps
B 0  f CP
Ingredients of the CP Asymmetry
Measurement
  B (t )  f     B (t )  f 
0
ACP (t ) 
0
  B (t )  f     B (t )  f 
0
Determine initial state:
“tag” using other B.
Final state doesn’t tell
you whether its B0 or B0!
0
Measure t
dependence.
Reconstruct the
final-state system.
The magic
If there is just one direct decay amplitude in addition
to mixing, the poorly known hadronic matrix element
divides out!
For the modes BJ/ KS (J/ KL)
AJ / K 0
S ,L
 t   J / K
0
S ,L
 sin  2   sin  m  t 
If CP violation is due to interference between mixing
and one direct decay amp:
• Pure sin(m t) time dependence
• No dependence of asymmetry on hadronic physics
CP violation due to interference between mixing and
decay: non-exponential decay law
Final states for sin(2) “benchmark”

To obtain interference between direct decay and decay after
oscillation, must use final states that both B0 and B0 can decay to.
B 0 ( B 0 )  J / K S0
  (2 S ) K S0
  c1 K
 c K
0
S
0
S
 J / K L0
 J / K *0
Vcb
B
J /
0
K
0
K0 oscillates into a quantum
superposition of K0 and K0
Results on sin2 from charmonium modes
(cc) KS (CP odd) modes
J/ψ KL (CP even) mode
sin2 = 0.722  0.040 (stat)  0.023 (sys)
(2002 measurement: sin(2β) = 0.741±0.067±0.034)
Control samples

Many control samples are used in the measurement to calibrate resolutions
and errors in tagging.
Fit projections on the Δt
distributions of the J/ψK+
control sample
Summary of sin2 measurements with charm
or charmonium final states
Courtesy Heavy Flavors Averaging Group
An aside: progress on measuring a
The mode B  has nearly 100% longitudinal polarization and the
penguin contamination has been bounded by B0 0.
BABAR B+ -
a  [101 916 (1 )
29
18
(2 )]
Constraints on the Apex of the Unitarity Triangle
All constraints
Constraints from angles only




Combined BABAR and Belle data; plots courtesy of CKM fitter group.
Final states for sin(2) “penguin modes”
In the SM, these modes should also give a time-dependent CP
asymmetry with amplitude sin(2). [See later for caveats…]
B 0 ( B 0 )  f K S0
f
 K  K  K S0
 K S0 K S0 K S0
  K
0
S
 K
0
0
S
 f K
0
 K
0
S
B
0
K
0
S
K0 oscillates into a quantum
superposition of K0 and K0
0
Belle Results for BfKS
Summer 2003
BELLE
140 fb1
Signal


N f K S0        68  11
Sf K 0
S
0.09
 0.96  0.50(stat)
0.11
(syst)
Cf K 0  0.15  0.29(stat)  0.07(syst)
S
Summer 2004
BABAR B  f K
B fK
0
S


0
S


0
S
and B  K K K
BK K K
0
S
0
Btag
0
tag
B
0
Btag
0
Btag
Asymmetry
sin2  0.50  0.250.07
0.04
sin2 ~ SK K K 0 /(2fCP -even  1)
S


 0.55  0.22  0.04  0.11
Summer 2004
f K0
B0  f K0 : CPV Result
S = 0.73
fit
B  f K S0
Poor tags
S = +0.00  0.33
A = +0.06  0.22
Good tags
fKS + fKL : S (fK0) = +0.06  0.33  0.09
A (fK0) = +0.08  0.22  0.09
~2 away from SM
275M BB
BABAR vs. Belle in sin2 from bs loop processes
0.45  0.09
0.39  0.11
Combined BABAR & Belle Results for bs penguins
Theoretical issues for the penguin modes
Due to extra amplitudes, the Standard Model predictions for the
bs penguin modes are subject to some degree of uncertainty.
Mode
 f S  sin 2 
(Cheng,Chua,Soni)
 f S  sin 2  (Beneke & Neubert)
f K S0
0.029  0.037
[+0.01, 0.04]
 K S0
0.006  0.038
[-0.01, 0.03]
 0 K S0
0.048  0.038
[+0.02, 0.13]
 K S0
0.010 0.043
0.040
[+0.03, 0.19]
Projections for measurement uncertainties vs. time
Courtesy D. MacFarlane
0.40
f0KS
KS0
KS
’KS
KKKS
0.30
0.25
0.20
 (S )  0.30
K*
0.15
2009
Projections are statistical errors only;
but systematic errors at few percent level
Jul-09
Jan-09
Jan-08
Jul-07
Jan-07
Jul-06
Jan-06
Jul-05
Jan-05
Jan-04
Jul-03
0.00
5 discovery region if non-SM
physics is 0.30 effect
2004
Jul-04
0.05
Jul-08
0.10
Jan-03
Error on sine amplitude
0.35
Conclusions and Prospects

The B Factories at SLAC and KEK have far exceeded their design
specifications.

As expected from the SM, CP asymmetries in B meson decays can
be large--of O(1)-- in contrast to the O(10-3) effects observed in
the neutral-K system.

Agreement with the SM pattern of CP-violating and CPconserving observables indicates that the phase in the CKM matrix
is the dominant source of CP violation in quark processes.

However, there is still room for new physics effects. Additional
data and more theoretical work will be needed to resolve these
issues. Key information will also come from CDF/D0 at FNAL.

Major luminosity goals: 500 fb-1 by end of 2006; >1000 fb-1 by
end of 2008.
Backup slides
Measurement of Mixing Frequency
t  trec  ttag
T=2/m
m  0.516  0.016 (stat)  0.010 (sys) ps
-1
Time-dependent CP asymmetries from the
interference between mixing and decay
A1  e i D cos( 12 m  t )
B
0
fCP
no net oscillation
( B
0
phys
net oscillation
(t )  fCP )
0
B
A2  ie 2 i M sin( 12 m  t )e  i D

B A  e  i  cos( 1 m  t ) fCP
1
2
0
D
0
( Bphys
(t )  fCP )
B0
2 i M  i D
A2  ie
e
 sin( 12 m  t )
PEP-II and BABAR
P and C violation in the weak interactions
=spin direction
= momentum
direction
e



e
e


e


P
e

  

Allowed
Not Allowed
Allowed
e
C
P and C are each violated maximally in the weak interactions, but the
combined CP is a symmetry even for most weak processes!
A. Sakharov’s inscription
Out of S. Okubo’s effect
At high temperature
A fur coat is sewed for the Universe
Shaped for its crooked figure.
Measurement of Decay Time Distributions
τ( B  )
 1.082  0.026 (stat)  0.011 (sys)
0
τ( B )
B0 decay time
distribution
(linear scale)
background
Oscillations, the Einstein-Podolsky-Rosen
effect, and B tagging

A B0 meson spontaneously evolves into an anti-B0 meson!

The oscillations of the two B mesons are completed correlated
by their production mechanism (EPR). If one decays as a B0,
the other must have been a B0 at that instant!

Use the decay mode of the “tag” B meson to determine the
“flavor” of the other B meson at that “start” time.
Time-dependent CP asymmetries from the
interference between mixing and decay
A1  e i D cos( 12 m  t )
B
0
fCP
no net oscillation
( B
0
phys
net oscillation
(t )  fCP )
0
B
A2  ie 2 i M sin( 12 m  t )e  i D

B A  e  i  cos( 1 m  t ) fCP
1
2
0
D
0
( Bphys
(t )  fCP )
B0
2 i M  i D
A2  ie
e
 sin( 12 m  t )
Calculating the CP Asymmetry
AfCP (t )  S  sin( m  t ) - C  cos( m  t )
S
2  Im( )
1 
C
2
1 
2
If single direct-decay
amp, hadronic matrix
element divides out,
leaving pure phase.
Pure phase factor in B decays
since mixing is dominated by
M12 (off-shell intermediate
states).

1 
2
f CP H B 0
M  

M 12  12 f CP H B 0
*
12
i
2
i
2
*
12
Coverage of BABAR pentaquark searches
Expect pentaquarks  , 
are members of 10f  8f
Dedicated searches for
claimed states  5 , 5 , 50
Inclusive searches for
other states in the 10  8
(final states in red )
Dedicated searches for
selected states from
other multiplets , e . g .  *
5
5
5
5
5
Example pentaquark search:  5 (1540)
Compilation of positive signals
nK 
pK
0
S
BABAR
Lc2285
pKS0 (123fb-1 )
 5 (1540) ?
pKS0 (123fb-1 )
BABAR-CONF-04/036
Summary of Pentaquark Search Results
o Compare with
production of other
baryons resonances
o Λ(1520) may not be
most reliable guide
o Most positive results
at lower energies
o Different production
mechanisms for
exotic baryons?
BABAR-CONF-04/036
Measurement of the CKM angle a
BABAR & Belle
combined
Mirror
solutions
disfavored
From combined
 ,  ,  results:
9
a  100 10 


o
CKM indirect constraint
fit: a  98  16o
Z. Ligeti (LBNL)
Penguin Olympia
Andreas Hoecker
Naive (dimensional)
uncertainties on sin2
One may identify golden, silver and bronze-plated s-penguin modes:
Gold
W
B
0
b
 VubVus ~  4Ru e  i

u
s
g
s
s
d
d
Silver
Color-suppressed tree
B
0
b
d
W

Bronze
Color-suppressed tree
B
0
b
d
W

f, K K

W

[CP ]
B
0
 ', f0
W
B
0
 ,  ,
K0
t
b
g
W
0
B
0
b
d
s
s
s
d
f, K  K 
(  2 )
~ 5%
[CP ]
K0
 VtbVts ~  2

d
K0
0
g
d
K0
 VubVus ~  4Ru e  i
u
u
s
d
t
b
 VubVus ~  4Ru e  i
u
u
s
d
 VtbVts ~  2

s
s
s
d
 ', f0
( 2 (1 fqq /  ))
K0
~ 10%
 VtbVts ~  2

t
g
s
d
d
d
K0
 0 ,  0 ,
Note that within QCD Factorization these uncertainties turn out to be much smaller !
( 2 /  )
~ 20%
Direct CP Violation in BK
B 0  K  
BABAR
hep-ex/0408057,
to appear in PRL
ACP  0.133  0.030  0.009
4.2
Belle
Confirmation at ICHEP04
Signal (274M BB pairs): 2140  53
ACP  0.101  0.025  0.005
3.9
Average ACP  0.114  0.020
B   K  0
ACP  0.06  0.06  0.01 BABAR
ACP  0.04  0.05  0.02 Belle 3.6
Average
ACP  0.049  0.040
Signal (227M BB pairs): 1606  51
BABAR
B 0  K  
B 0  K  
Phenomenology of Oscillations

Effective Hamiltonian for the two-state system (not
Hermitian since particles decay!):
Quark masses, strong,
and EM interactions
 H11
H 
 H 21
B 0  f  B 0 transitions
f  off-shell f  on-shell
H12   M
 *
H 22   M 12
M12  i  
  *
M  2   12
12 

 
Decays
The Oscillation Frequency (m)

In the neutral B-meson system, the mixing amplitude is
completely dominated by off-shell intermediate states (m)
[contrast with the neutral kaon system].

Calculation of the mixing frequency
m  VtbVtd

 strong+weak interactions  0.5 ps
 2
-1
Time-dependent mixing probabilities and asymmetry
dN nomix 1

 et  1  cos(m  t ) 
dt
4τ B
dN mix
1
t

 e  1  cos(m  t ) 
dt
4τ B
NoMix(t) - Mix(t)
 Asym(t)=
 cos(m  t )
NoMix(t)  Mix(t)
Calculating the CP Asymmetry
0
AfCP (t ) 
f CP H B (t )
0
f CP H B (t )
2
 f CP H B (t )
2
2
 f CP H B (t )
2
0
0

  B 0 (t )  f CP     B 0 (t )  f CP 
  B 0 (t )  f CP     B 0 (t )  f CP 
AfCP (t )  S  sin( m  t ) - C  cos( m  t )
2
1 
2  Im(  )
S
C
2
2
1 
1 
Pure phase factor in B decays
since mixing is dominated by
M12 (off-shell intermediate
states).

If single direct-decay
amp, hadronic matrix
element divides out,
leaving pure phase.
f CP H B 0
M  

M 12  12 f CP H B 0
*
12
i
2
i
2
*
12
sin2 Signal and Control Samples
J/Y Ks
Bflav
J/Y Ks
(Ks  )
(Ks  +-)
mixing
sample
CP=-1
J/Y KL
CP=+1
J/Y Ks
(Ks Ks00)
J/Y
Y(2s) Ks
J/Y K*0
*0
J/Y
(K*0 KKs0)
c1 Ks
(Ks  00)
(K*0  Ks0)
Testing the assumptions in the extraction of sin2
extraction from charmonium modes


The extraction of sin(2) assumes

/=0 (no lifetime difference between neutral B mass eigenstates)

|q/p|=1 (checked with dilepton CP asymmetry measurement.)

CPT is conserved
We have performed a detailed study to check these assumptions:


submitted to PRL
PRD in final review
Quantity
/ sgn(Re 
|q/p|
(Re z)(Re()/||)
Im z
Measured value
Theory
The CKM angle a

The angle a enters into the CP asymmetries for bu
modes, such as
B   , B    , B   





Assuming the bu tree diagram dominates
d

+
B0
-

Time-dependent analysis would extract: S=sin2a, C=0

We now know that the penguin contribution is likely to
be sizeablehave two significant direct decay amplitudes
d
in addition to mixing.
+
B0
-
Effect of Mistagging and t Resolution
No mistagging and perfect t
w=Prob. for wrong tag
D=1-2w=0.5
Nomix
Mix
t
t
D=1-2w=0.5
t res: 99% at 1 ps; 1% at 8 ps
t
t
Stanford Linear Accelerator Center (SLAC)
Linear Accelerator
End station A:
fixed target expts
in 1970s found
nucleon
substructure (u, d
quarks).
SLC Experimental Hall:
Properties of Z boson were
measured here.
photograph by Steve Williams
SPEAR e+e- Ring
Discovery of 
same particle
discovered at
Brookhaven called J);
the J/ is the lowest
mass cc bound state.
Discovery of  lepton.
PEP-II Interaction
Region 2: home of the
BABAR; studies b
quarks & CP violation.
Linac/PEP-II layout
PEP-II beams and the interaction region
e
e


Luminosity
(x1034)
0.9 Units
e+
3.1 GeV
e-
9.0 GeV
I+
2.45 A
I-
1.55 A
(y*)
11 mm
(x*)
30 cm
Bunch length
10 mm
# bunches
Crossing angle
Need to avoid crossing between
outgoing bunch and next incoming bunch.
Tune shifts
(x/y)
rf frequency
Site power
1588
0 mrad
4.5/7 x100
476 MHz
40 MW
Current and projected performance of PEP-II
Luminosity
(x1034)
0.9
2.4 Units
e+
3.1
3.1 GeV
e-
9.0
9.0 GeV
I+
2.45
4.5 A
I-
1.55
2.2 A
(y*)
11
(x*)
30
30 cm
Bunch length
10
7.5 mm
# bunches
Crossing angle
Tune shifts (x/y)
rf frequency
Site power
1588
0
8 mm
1700
0 mrad
4.5/7
8/8 x100
476
476 MHz
40
40 MW
For 05 & 06 shutdowns:
Additional LER and HER rf
stations, vacuum chamber
upgrades, stronger B1
separation field,…
Best shift, no trickle
Nov 2003
Best shift, LER only trickle
Mar 2004
Best shift, double trickle
PEP-II: ~5 Hz continuous
KEKB: at ~5-10 min intervals
PEP-II Lumi
HER current
LER current
BABAR data sample

BABAR runs 24 hours/day
except during shutdowns
and machine development
periods.

BABAR operational
efficiency: 97%

Data processed in two
passes: (calibration and
reconstruction) within 2
days of acquisition.

1 fb-1  1.1 M BB events

Best instantaneous
luminosity: 10 BB/sec

Best month: 20 M BB

Total sample: 245 M BB
245 M BB
BaBar Detector
center line
DIRC:
quartz bars
standoff box
PM tubes
Superconducting
magnet (1.5 T)
Drift chamber
e
+
e
CsI crystals
Silicon Vertex
Tracker
Muon detector
& B-flux return
The BABAR Detector
1.5 T solenoid
DIRC
(particle ID)
CsI (Tl) Electromagnetic Calorimeter
e+ (3.1GeV)
Drift Chamber
Instrumented Flux Return
e- (9 GeV)
Silicon Vertex Tracker




SVT: 97% efficiency, 15m z resol. (inner layers, perpendicular tracks)
Tracking : pT)/pT = 0.13% PT  0.45%
DIRC : K- separation >3.4 for P<3.5GeV/c
EMC: E/E = 1.33% E-1/4  2.1%; 16.0-17.5 X/X0
BaBar Silicon Vertex Tracker (SVT)
• 5 concentric layers
• 340 Si sensors (wafers)
• Strips on both sides
• AC coupled
• 140 K readout chans.
• 10-40 m hit resol.
• about 70 cm long
50m
300m
80 e-/hole
pairs/m
BaBar DIRC (Cerenkov Particle ID System)
1
cos  C 
 n
Num. r.l.=0.19 X0
n  1.473
(C) = 3 mrad
Number of Cherenkov photons=20-60
BABAR DIRC
No. light bounces (typical)=300
Overall length (4 bars): 4.9 m
Roughness (r.m.s.)= 0.5 nm
3.5 cm  (typical) = 400 nm
The Electromagnetic Calorimeter
Design characteristics:
• 6580 crystals of CsI(Tl)
• Reconstruct  down to 10-20 MeV.
• Target resolution:
Performance:
• E/P width from bhabhas 2.4 %
• consistent with MC expectations.
• Correct  0 mass. A bit wider than
the MC.
• Significant improvements in noise.
• Energy cut per crystal now 0.8 MeV.
Drift Chamber Performance
• Momentum resolution:
• Measured with di-muon events. dPt / Pt = 2.9 % x Pt. Consistent with spec.
• Hit resolution:
• Measured to be 100 - 200 m, average value 125 m. Exceeds spec of 140 m.
• dE/dX resolution:
• Measured 7.5% with bhabha events.
• Hope to achieve 7% with further corrections.
DCH Hit Resolution
200 m
100 m
Signals for new states
*
0
0
D
(2458)

D
(2112)

DsJ (2317)  Ds
sJ
s
1022  50 events
195  26 events

Masses below DK threshold natural decay channel is forbidden.

Decay widths are within experimental resolution, about 10 MeV.

Pionic decays are I-spin violating, explaining the narrow observed widths.
PEP-II

Very high current, multibunch operation

2 rings helps avoid beam instabilities and parasitic
beam crossings (crossings not at the IP)

I(e+)=1.3 A (LER), I(e-)=0.7 A (HER)

Bunch spacing: 6.3-10.5 ns

Beam spot:

x=120 m y=5.6 m z=9 mm

Number bunches/beam: 553-829 (to 1658)

High-quality vacuum to keep beam-related
backgrounds tolerable for experiments
Quark Content of Mesons

Quark content of B mesons:
B 0  bd
B 0  bd

mB  5.28 GeV/c  5  mp

B  bu

all have: J  0, L  0, S  0
B  bu
2
Quark content of some lighter mesons
  ud  
_
0
1
2
(uu  dd )
K  us


c  K


c  K
1
0
0
K 
K  K
2
1
0
0
0
KL 
K  K
2
0
S

K  ds
0
0
S
  2.7 cm
CP=+1
0
L
  15.5 m
CP=-1
KEKB and Belle in Japan
Mt. Tsukuba
KEKB
Belle
~1 km in diameter
sin(2): summer 2003