A versatile lattice for a tau-charm factory that includes a monochromatization scheme (low-emittance) and a standard scheme (high-emittance)

A versatile lattice for a tau-charm factory working at 4 GeV center of mass energy with 10³³ cm^-2 s^-1 luminosity is considered. The main goal of this study is the possibility to easily use the same lattice for either a monochromatization (low-emittance) scheme or a standard (high-emittance) scheme. This monochromatization scheme permits one to reduce the spread of collision energies at the interaction point to 0.1 MeV. We consider a low-emittance arc (10^-8 m rad) typical from synchrotron radiation lattices and the passage from low-emittance to high-emittance (10^-7 m rad) is obtained by detuning the low-emittance arc