I didn't know whether to put this in homework or in here because it is not homework but it is a question, so sorry in advance! I like to learn about quantum physics as a hobby, and I found this great link about working with actual particle accelerator data by an organization called Quarknet. Here is the link: http://quarknet.fnal.gov/projects/summer00/Main/student/index.shtml [Broken] I thought I would try and use this data(after clicking on "project context") to do what the site says and determine the mass and lifetime of the Z boson. I understand I need to use the E2 = m2c4 + pc2 formula, and I've found the energies, but the only problem is I don't know how to determine momentum. They give you the XY radius as well as the Z component of the particle's path, as I think it travels in a helical path because of the electromagnetic field. They also give you the cosine of the x, y, and z angles. I am totally lost on how to solve for momentum and I'd really like to understand how one would go about doing this. I know that momentum for relativistic particles is not simply mass times velocity, so could someone please help? Thank you!