Text search exclude removing documents with unrelated keywords

I am running a text search in aggregation:

            $search:"dummy_text -investigating"

Document compound text Index field has value Gamma Delta CAR T Investigational Cell Therapy Monday . I do not understand why this document is getting missed with above text search. Clearly string holds a different word. And I cannot use a phrase since there can be multiple keywords in search string.

This is the esult of explain query. Now I don’t want to use stem word investig rather entire keyword investigating without the use of phrase search