  In the Standard Model of particle physics, the quarks and anti-quarks have
fractional charge equal to $\pm1/3$ or $\pm2/3$ of the electron's charge. There
has been a large number of experiments searching for fractional charge,
isolatable, elementary particles using a variety of methods, including $e^+e^-$
collisions using dE/dx ionization energy loss measurements, but no evidence has
been found to confirm existence of free fractional charge particles, which
leads to the quark confinement theory. In this paper, a proposal to search for
this kind particles is presented, which is based on the conservation law of
four-momentum. Thanks to the CLEOc and BESIII detectors' large coverage, good
particle identification, precision measurements of tracks' momenta and their
large recorded data samples, these features make the scheme feasible in
practice. The advantage of the scheme is independent of any theoretical models
and sensitive for a small fraction of the quarks transitioning to the
unconfinement phase from the confinement phase.
