I've never heard of a branch of science called "scientism"
{Added in edit}That's because it's a philosophy or a point of view, not a branch of science.
quote:Scientism is usually used to mean the acceptance of scientific theory and scientific methods as applicable in all fields of inquiry about the world, including morality, ethics, art, and religion.
Here, 'science' is held to be the ultimate recourse in questions of public policy and even religion.
This viewpoint is typified by comments, such as 'Science demonstrates that it is useless (or useful) to use seatbelts in cars' or 'Science has shown that religion is wrong' or 'Science shows that capitalism (or communism or socialism) is correct.' In the case of such views as Marxism (and most types of totalitarian rationales) such views are also called historicism, relying on a 'scientific' analysis of inevitable historical patterns.