1. A method for identifying peptides using tandem mass spectrometry, comprising: obtaining an experimental spectrum for a peptide to be analyzed, the experimental spectrum comprising a plurality of fragment peaks and having a parent mass, each fragment peak corresponding to a mass within the experimental spectrum; using a scoring function, scoring a match between the experimental spectrum and a spectrum corresponding to each candidate peptide of a plurality of candidate peptides to generate a match score for each candidate peptide, wherein the scoring function has a value corresponding to a number of fragment peaks in the experimental spectrum matching fragment peaks in a spectrum of the candidate peptide; using the match scores, computing, using a computer comprising a processor and a memory, a generating function of the experimental spectrum to determine a number of candidate peptides at each value of the scoring function, wherein the generating function is determined according to the relationship: ∑ all ⁢ ⁢ _ ⁢ ⁢ peptides ⁢ ⁢ _ ⁢ ⁢ P ⁢ ⅇ - Energy ⁡ ( P , S ) = ∑ t ⁢ x ⁡ ( t ) · ⅇ - t wherein Energy(P,S) is an energy score, x(t) is the number of peptides with energy t and S is the experimental spectrum; determining a score distribution of match scores of all candidate peptides for the experimental spectrum; using the score distribution, identifying a subset of the candidate peptides to be reported as possible explanations of the experimental spectrum; and generating a report for output to a display device or a memory device comprising a listing of the identified subset of candidate peptides and their score distributions.