Hi guys. This is my first post here. Here it goes. I'm attending an introductory course on particle physics. By now, I'm supposed to know how to find out if a given reaction, say νμ+p→μ++n (for example) is possible or not. Unfortunately, the rules by which a reaction must abide are still foggy for me. I can't find anywhere a complete set of steps which I can follow to find out if a reaction is allowed or not. This is what I'm asking: I'm asking for a method which leads me to the answer to the question: "Is the reaction possible?". Ideally, the method should be written in the form: Are the quantities A, B and C conserved? If they are not, skip to point 5. If they are, go to the next point. Are the quantities D and E conserved? If not, the reaction is impossible. If they are, go to the next point. ........ ..... .... .... And so on. Thank you in advance! EDIT: I also want to know what type of interaction (strong, weak or EM) is predominant.