candidate: And here is a quote from de Sabbata and Gasperini : " With the word " matter " we denote , in this context , the sources of the interactions , that is spinor fields ( like quarks and leptons ) , which are believed to be the fundamental components of matter , or scalar fields , like the Higgs particles , which are used to introduced mass in a gauge theory ( and that , however , could be composed of more fundamental fermion fields ) .