Two changed particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field $\overrightarrow{B} =B_0 \hat k$

Question

$\begin{array}{1 1} \text{they have z- components of momenta} \\\text{They must have equal charges} \\ \text{They necessarily represent a particle - anti particle pair } \\ \text{The changes to mass ratio satisfy } \bigg(\large\frac{e}{m}\bigg)_1 +\bigg(\frac{e}{m}\bigg)_0= 0 \end{array}$