recently. For the next year or two, CLEO will return to the
Y
(1
S
,2
S
,3
S
) resonances, after which it is planned to opti-
mize CESR to run at the lower energies appropriate for
charm production.
289
This will permit a return to many inter-
esting questions with a vastly improved detector and statis-
tical sample.
5. DESY (Germany)
A circular electron accelerator at the Deutsches Elektronen
Synchrotron
~
DESY
!
laboratory was converted to an
electron–positron collider
~
DORIS
!
whose experimental pro-
gram paralleled that of CESR/CLEO for a number of years,
yielding important information about
Y
spectroscopy and
B
mesons, for example through work of the ARGUS Collabo-
ration. Subsequent machines included the larger
e
1
e
2
col-
lider PETRA
~
maximum c.m. energy 46 GeV
!
and the cur-
rently operating HERA lepton–proton collider, which has
studied both
e
2
p
and
e
1
p
interactions. HERA has extended
information on deep inelastic lepton scattering to new kine-
matic regimes and provided important information on the
gluon structure of the proton.
6. Fermilab (USA)
The Fermi National Accelerator Laboratory in Batavia, Il-
linois, USA, began operation in 1972 as a proton accelerator
with initial energy 200 GeV, rising to 400 GeV within a year.
With the addition of a ring of superconducting magnets in
1983 it was converted to an energy of 800 GeV capable of
providing protons to fixed targets and proton-antiproton col-
lisions with a center-of-mass energy of 1.8 TeV.
127,290
Its
energy has recently been upgraded to nearly 1 TeV per beam
with the addition of a new 150-GeV proton ring called the
Main Injector. Outstanding discoveries at Fermilab include
those of the bottom quark in 1977,
188,189
the top quark in
1994,
190–195
and the tau neutrino in 2000.
291
7. Frascati (Italy)
A major pioneer in the study of electron–positron colli-
sions has been the Laboratori Nazionali di Frascati
~
INFN
!
near Rome, Italy. Starting in the early 1960s with the ADA
collider and continuing through the ADONE storage ring,
which begain operation in the late 1960s, the laboratory has
now begun to operate a machine called DA
F
NE
~
DAFNE
!
,
which seeks to produce kaons and other particles through the
reaction
e
1
e
2
→
f
→
•••
at a center-of-mass energy of 1.02
GeV.
8. KEK (Japan)
In the early 1970s, a 12-GeV proton synchrotron was con-
structed in Japan near Tokyo at the National Laboratory for
High Energy Physics, for which KEK
~
Ko–Energi–
Kenkyujo
!
is the acronym in Japanese. The next major
project at KEK, the TRISTAN
e
1
e
2
collider, attained a
center-of-mass energy in excess of 60 GeV, the highest in the
world for such a machine at its debut in 1986. Among the
topics studied by TRISTAN included weak–electromagnetic
interference through the processes
e
1
e
2
→
(
g
*
,
Z
*
)
→
•••
,
where the asterisk denotes a virtual photon or
Z
. The latest
project at KEK is the KEK-
B e
1
e
2
collider, a lower-energy
machine built in the TRISTAN tunnel, which is designed to
produce pairs of
B
mesons with net motion on their center-
of-mass by using unequal electron and positron energies. In
this way the positions at which the
B
mesons decay can be
spread out longitudinally, permitting easier study of time-
dependences that are of particular interest in
CP
-violating
processes. The Belle detector operating at KEK-
B
200
is pro-
ducing significant results on
B
decays, as mentioned
above
203
!
, as is the BaBar detector operating at PEP-II
~
see
the description of SLAC, below
!
.
9. Novosibirsk (Russia)
A series of
e
1
e
2
colliders has operated at the Budker
Institute for High Energy Physics in Novosibirsk for a num-
ber of years. Indeed, work at this laboratory helped to pio-
neer the study of beam dynamics essential for achieving such
collisions. These colliders performed important measure-
ments at the center-of-mass energies of the
Y
(9.46) and
f
(1.02) resonances, where the numbers denote the mass in
GeV/
c
2
.
10. Protvino (Russia)
The largest accelerator at present in Russia is a 76-GeV
proton synchrotron at Serphukhov
~
Protvino
!
, which began
operation in the early 1970s. It was the first to detect rising
meson–baryon cross sections,
292
followed soon by the obser-
vation of a similar effect in proton–proton collisions at the
CERN ISR
~
see above
!
.
11. SLAC (USA)
The early program of the 30-GeV 2-mile-long linear elec-
tron accelerator at the Stanford Linear Accelerator Center
~
SLAC
!
included the discovery of pointlike constituents in-
side the proton through deep inelastic scattering.
96,152,153
In
the early 1970s the SPEAR electron–positron storage ring
was constructed with maximum center-of-mass energy equal
to 7.4 GeV. Late in 1973 this machine confirmed a surprising
enhancement of the
e
1
e
2
annihilation cross section starting
at a c.m. energy of 4 GeV seen earlier at the Cambridge
Electron Accelerator
~
CEA
!
, and in 1974 was one of two
sources of the discovery of the
J
/
c
particle,
186
the other
being a fixed-target experiment at Brookhaven National
Laboratory
185
~
see above
!
. In the mid-1970s construction
was begun on PEP, an electron–positron collider with c.m.
energy of about 30 GeV, which performed studies of the
elctroweak theory and was the first to measure the
b
quark
lifetime. The energy of the LINAC was then raised to 50
GeV, both electrons and positrons were accelerated, and
these were then bent in arcs to collide with one another at
energies equal to or greater than the mass of the
Z
boson.
This machine, the Stanford Linear Collider
~
SLC
!
,
124
pio-
neered in precision studies of the
Z
boson through its Mark II
and SLD detectors; its early measurement of the
Z
width was
a piece of evidence for three families of quarks and
leptons.
128
The latest SLAC project, the PEP-II asymmetric
e
1
e
2
collider, has seen evidence for
CP
violation in
B
de-
cays in its BaBar detector
199,202
~
see also KEK-
B
and Belle,
above
!
, and has achieved record luminosity for any collider.
By the middle of this decade both BaBar and Belle expect to
have produced and recorded several hundred million
BB¯
pairs.
316
316
Am. J. Phys., Vol. 71, No. 4, April 2003
Jonathan L. Rosner
