Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field `vec(B)=B_(0)hat(K)`

Options

A. They have equal z-components of momenta
B. They must have equal charges.
C. They necessarily represent a particle, anti partile pair
D. The charge to mass ratio satisfty.

Answer

D

Explanation

For given pitch d correspond to charge particle, we have
`(q)/(m)=(2pivcostheta)/(qB)="constant"`
Since, charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field B, LHS for two particle should be same and of opposite dign, therefore.
`((e)/(m))_(1)+((e)/(m))_(2)=0`