publications - Alphabetical authorship order in graduate admissions (particularly high energy physics)

I would like to know how graduate admission committees at US Universities look at alphabetical authorship publications in a CV (particularly in high energy physics). Since the convention in high energy physics is to have authors in alphabetical order, how do the committees determine the contribution of the applicant (I guess recommendation letters is one way)? Also, do the committees actually read the papers (mentioned on the CV) on arXiv or the journal website to check the quality of the papers?

I am applying to US universities for a Ph.D. in high energy physics. Because my surname starts with one of the ending letters in the English alphabet, however, my name on all of my publications is last in the sequence. Could this create confusion in committee members about my contributions?