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The CLEO collaboration has made major contributions
to many aspects of 
, 
, 
, and 
physics
with precision unmatched anywhere in the world.
This has been made possible by the CLEO II detector, with its combination
of excellent tracking and CsI electromagnetic calorimetry,
and the large integrated luminosity provided by the CESR
accelerator. CESR is embarking on an upgrade program over the next five
years after which integrated luminosities up to
15 fb
/year-10 fb
on the 
resonance
and 5 fb
below the -will be provided.
CLEO data sets can be increased by up to an order of magnitude
which will allow further, significant strides forward in our
studies of heavy quarks and third generation leptons.
A central feature of the CESR upgrade, called Phase 3, is larger
focussing quadrupoles that
intrude into space now occupied by the CLEO II tracking detectors (see
Fig. 
), necessitating replacement of these aging devices.
It should be noted that the VD wire chamber is now 10 years old and the
main drift chamber is 6 years old. These elements need replacing
regardless of the accelerator upgrade and in addition the drift
chamber endplates and mounting structure compromise the performance
of the CsI calorimeter.
The other sub-detectors-CsI calorimeter, magnet coil, and
muon system-are compatible with the machine upgrade and our
future physics goals with only small
modifications, although higher data rates will require
more sophisticated readout electronics. The new tracking system design
compatible with the upgraded IR design will also provide the
space for a high-quality particle identification system
(see Fig. ) that will allow
separation up to 2.8 GeV/c. This upgrade program will
produce the CLEO III detector and will benefit all
areas of CLEO physics and will be particularly important for
the study of 
decays, especially rare decays as a window to observe
physics beyond the Standard Model.
The most important physics goals for CLEO remain those for physics.
While additional integrated luminosity would itself add to our knowledge,
greater detection and reconstruction efficiency from pion and kaon
identification up to momenta of 2.8 GeV/c will bring faster
rewards. This is analogous to the introduction of excellent photon
detection in the CLEO II detector which increased the number of
reconstructed 's per unit luminosity.
Other important topics which may become accessible include the measurement of
Cabibbo-suppressed ``penguin'' decays such as 
. A measurement of
the ratio of to 
, the latter recently measured by
CLEO II [1], is an excellent way to determine 
.
High momentum particle identification
coupled with the large CLEO III data sample will make it possible
to attempt the observation of CP violation in decays by, for example,
measuring the rate asymmetries in the decays
and 
[2]. In addition, direct measurement of one of the CP violating angles
can be attempted by measuring the branching ratios
for decays to 
where the decays
into a CP eigenstate.
CLEO III will also be able to address many new topics in the areas of
charm and tau physics.
For example, with high momentum particle identification,
the Cabibbo-suppressed semileptonic charm decays such as
can be measured even though there is a much larger rate from
.
For both charm physics and the study of fragmentation,
the momentum range for which such particle
separation is useful extends up to near the kinematic limit of approximately
5 GeV/c.
Also, the tau neutrino mass can best be limited
from studies of the decay 
due to the large
minimum hadronic mass in this channel (the present acceptance is <1%).
Again, particle identification is crucial.
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