based its bending radius R in the magnetic field B along z direction in the tracking chamber according to the Lorentz force law, where P$_{xy}$ is the transverse component of the track momentum. The longitudinal component is measured by considering the polar angle θ of the track with respect to the e + beam direction, In other words, the radius is a measured value while the momentum is a derived value and dependent on the assumed charge q . In the CELOc and BESIII experiments [10 , 11] as well as others [3 − 6] q is a priori set to be 1 no matter how large charge it has. The momentum ⃗ P$_{n}$ measured in this way, we call it the nominal momentum, for the track equals to its real momentum ⃗ P$_{r}$ if q is 1. If q is not 1, its nominal momentum changes by a factor of 1 /q compared with its real momentum, i.e. ⃗ P$_{n}$ = 1 /q ⃗ P$_{r}$ . Hereafter q is assumed to be less than 1 for simplicity. For events with at least one particle of charge larger than 1, the similar analysis can be performed. Assuming there is a pair of quarks f and f with opposite charge qe in the event such as π $^{+}$π − uu , K $^{+}$K − dd and ppss , which is required to have even number of charged tracks. The total nominal momentum and energy are derived as If ⃗ P$_{n}$ (tot) = 0, there are two cases. One is that some tracks in the event are undetected for they are neutrinos or go beyond the coverage of the detector. Another is that q is not 1. For the latter case, q can be adjusted so that the real total momentum Then the mass m$_{f}$ of the quark (anti-quark) can be calculated by requiring the real total energy P$_{xy}$ = qeB/R, P$_{z}$ = P$_{xy}$ ctg( θ ) . ⃗ P$_{n}$ (tot) = ⃗ P$_{n}$ ( f ) + ⃗ P$_{n}$ ( f ) + others = 1 /q ⃗ P$_{r}$ ( f ) + 1 /q ⃗ P$_{r}$ ( f ) + others , E$_{n}$ (tot) = √ P$_{n}$ 2 ( f ) + m 2 f + √ P$_{n}$ 2 ( f ) + m 2 f + others = √ (1 /qP$_{r}$ ) $^{2}$( f ) + m 2 f + √ (1 /qP$_{r}$ ) $^{2}$( f ) + m 2 f + others . ⃗ P$_{r}$ (tot) = q ⃗ P$_{n}$ ( f ) + q ⃗ P$_{n}$ ( f ) + others = 0 . E$_{r}$ (tot) = √ ( qP$_{n}$ ) $^{2}$( f ) + m 2 f + √ ( qP$_{n}$ ) $^{2}$( f ) + m 2 f + others = √$_{s,}$ 3