I think their title is commitee clerks

"Senators and Senate committees operated with little or no staff assistance until the middle of the 19th century. In the 1850s, standing committees began to employ clerks on a case-by-case basis with the approval of the full Senate. These early clerks were typically hired only for a session and were paid on a per diem basis. On occasion, committees requested that their clerks be employed on a full-time basis with an annual salary."