Hello guys. I am studying the experiment conducted by Chamberlain, Segrè, Wiegand and Ypsilantis in 1955 at Berkeley (using the Bevatron) to observe antiprotons. Here is the article: http://escholarship.org/uc/item/46p0z8w7#page-3 I have some questions. 1) While the desired reaction of proton to copper-proton target was p p → p p p p' there is a strong background of Pion production. Why? And what is the reaction for the pion production? 2) You can read at the bottom of page 3, that negative particles scattered at 21° from the bevatron beam have a momentum of 1.19 Bev/c. Why? I can attempt to answer just question 1: Pions are lighter than proton, so the threshold is lower. The reaction I figured out was p n → π- p p Thanks!