There are a few errors in the solutions given in HM which I will try to point out, but they are generally correct. Problem solutions will be put on reserve in the library after the due date. I generally expect you and your study partners to have made a legitimate attempt at the problems before coming for hints so your questions are focussed.
Most particle physics is done in collaborations, some very large.
Joint work on, and discussion of, the problem assignments will give you practice in working in a collaborative setting whether or not you go into the field. Such experience is expected by most potential employers of physicists.