1) Psychology of pleasure 2) Study of pleasure 
part of ethics or psychology dealing with pleasure
He·don'ics noun (Philos.) That branch of moral philosophy which treats of the relation of duty to pleasure; the science of practical, positive enjoyment or pleasure. J. Grote. 
hedonics (used with a singular verb) 1. The branch of psychology that studies pleasant and unpleasant sensations and states of mind. 2. In philosophy, the branch of ethics that deals with the relation of pleasure to duty.