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<title>China's Proposed tau cF Project</title>
<h1>China's Proposed tau cF Project</h1>
    From 1984 to 1988, China constructed  BEPC/BES on time and within 
the budget. Since then  have been obtained some important physics results, 
such as  precise tau lepton mass measurement;  
measurement of $D_{s}$ pure leptonic 
decay fraction and  the $f_{D_{s}}$; the observation of the $\theta(1720)$ 
complicated structure; the first measurement 
of $\psi\rightarrow\tau^{+}\tau^{-}$ branching 
fraction,  confirmation of the existence of $\xi(2230)$; etc. All these 
have given eloquent proof  of BEPC/BES's 
 success, and shown the ability of the Chinese 
scientists in high energy physics, 
 especially in the area of tau and charm physics.<p>
    But there are a lot of topics remains to be studied 
more thoroughly  in 
the energy region of tau-charm.  After a lot of detailed investigations 
and discussions, China's high energy community has drawn a decission  to 
construct  a  tau-Charm Factory ($\tau$cF) in Beijing, 
on the site of BEPC, while  
several attempts to build such a facility had  failed in 
other countries.<p>
    The proposed $\tau\cF composes a two-ring $e^{+}e^{-}$ 
collider at  energy 
range of 3 - 6GeV, with a normal luminosity of $10^{33}cm^{-2}s^{-1}$, 
and a high performance detector. This proposal has received good  remarks 
from the international high energy community, say, at  SLAC tau
-Charm Workshop held in August of 1994.<p>
    $\tau$cF has special  advantages in the studies of tau and charm physics. 
It  can be used to precisely test the Standard Model.  
$\tau$cF would   improve the measurement precision for most 
interesting physics topics by an order of magnitude,  search for and make 
detailed studies of glueball states and other exotic states,  search for 
possible CP violation in tau decay and $D^{0}D^{0}$ mixing. With $\tau$cF 
made, important physics results and surprising new discoveries may  be 
highly expected. This   $\tau$cF  will be one of the major high 
energy facilities in the world at the beginning of  next centrury. The 
$\tau$cF, 
 the Psi meson Factory (DA$\Psi$NIA) to be built in Italy, the two B factories 
to be built at KEK and SLAC,  Tevatron at Fermilab, HERA at DESY,  
RHIC at Brookhaven and the approved LHC at CERN  will run at different 
energies and   will be complementary. The  construction of the $\tau$cF
 will enable China to remain active 
in high energy physics for another one or two decades.<p>
    For China,  $\tau$cF is a big challenge both in terms of  
 technical difficulties  and in terms of financial investment. 
A plan to realize the project in three stages was put forward recently.  
The first stage is for the  feasibility study, the second  for a detailed 
engineering design or R&D and the third  for the construction.<p>
    Now the Proposal for  $\tau$cF Feasibility Study has been approved by the 
government and a special fund of 5 million Yuan has been allocated. In the 
proposal,   the necessity of building the 
$\tau$cF,  the prospective  physics results,  the measurement accuracy, 
 the requirements on the machine and detector performance, 
and  the technical difficulties and the possible solutions are 
discribed. <p>
    According to the schedule, the feasibility study will last to  
mid  1996, then  a  decision on the second stage's  R&D 
activities should be made. This second phase  may take   two 
to three years, if the government approves it. 
The    $\tau$cF  proposal has received positive 
responses from the Review Committee. And fortunately, the  $\tau$cF gains 
supports from  many scientists in China and receives favourite considerations 
from the government. <p>
    Meanwhile, the $\tau$cF  proposal    has also attracted much attentions 
from international high energy community, several major labs have expressed 
their intention to participate in China's  $\tau$cF construction.<p>
    BEPC News will henceforth open a special column to report the 
latest progresses in the $\tau$cF project, 
 and relevant informations on $\tau$cF will also be posted on 
IHEP WWW home page.<p>
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June 1995 BEPC News <p>