Lets say I have a uniform line charge moving at a speed v. This will create the B field for our stern-gerlach experiment. Now I shoot neutrons or some other particle with spin that will be affected by the B field. Now lets say I am moving with this line charge at speed v. In my frame there is no B field just an E field. But I will still see the particle deflect based on its spin. Would i say the particle deflected in my frame because its B field is now and E field in my frame?