I don't think scores in Lucene are normalized, it just happens to be often a number between 0 and 1. The score depends on the query and if at all can only be used to compare the results of a single query. Trying to calculate a percentage on how well a document matches is actually discouraged. See also:

• http://stackoverflow.com/questions/5379176/how-to-normalize-lucene-scores
• http://wiki.apache.org/lucene-java/ScoresAsPercentages
• http://article.gmane.org/gmane.comp.jakarta.lucene.user/12076
• http://stackoverflow.com/questions/8918224/what-is-the-maximum-value-of-a-lucene-score

To get to the score you can use a projection query (that part is in place).