Relative representation of scientists and engineers on major experiments (especially particle physics)
I heard that postdocs and PhD students at CERN could volunteer for maintenance and similar tasks, and that those who did would have their names on the "Higgs paper" (hence the notoriously large author lists). Was this true and is it still the case?


There are a lot of maintenance and monitoring work performed by Ph.D candidates and postdocs at CERN and they may be entitled to have their names in a paper if they comply with the minimum requirements.

There are a minimum of night shifts and work hours in one of the experiments to be completed in order to participate as co-author in the papers produced due to work performed during the internship. If I am not in mistake, you need at least 6 months working in one of the experiments to comply with the minimum work hours demanded for co-authoring. 

Usually the ones attending internships at CERN are from experimental particles groups with collaboration to one of the experiments (CMS, ATLAS,etc). They are not purely experimentalists, but I am sure that they can not be purely theorists.