§ Ind. Code § 3-10-8-7Vacancy in United States Senate; nominating candidates

A candidate for the office of United States Senator in a special election held to fill
a vacancy in accordance with IC 3-13-3-1 shall be nominated:
(1) at a primary election held under IC 3-10-1, if the vacancy occurs no later than noon
on the first date that a petition of nomination can be filed with a county voter
registration office under IC 3-8-2-10 before the primary election;