On the observability of free quarks near their production thresholds
  It is proposed to search for free quarks near their production thresholds. If the current-quark masses for u, d quarks are smaller than the pion mass, $u\bar{u}$ and $d\bar{d}$ pairs produced below the pion pair threshold, would not have sufficient energy to hadronize and could be observable. In the case of large u,d quark masses and also for the heavy quarks, production near threshold may show hadronization probability $<1$, and lead to free quarks. Searches for fractional charges in stable matter could be more promising, through irradiation of samples at energies near the quark pair production thresholds. 
A. Markou