Okay, your going to make me dust off the old particle physics book; I'll get a better answer for you before the end of the day. But, for all practical purposes a positron is just and electron with a positive charge. You can make them in a laboratory and you can control them just as you would control an electron, its not something strange to deal with. The theory that governs their behavior says they travel backwards in time, but if the theory didn't say it did, you could never tell they did in a laboratory, since they behave exactly like electrons except positively charge.