A research paper is based on research (sorry to sound redundant). This is to say that a research paper should have a thesis and you seek to prove it. For this paper to be written in a responsible way, of course, you will have to dig through sources. The more serious the paper, the more thorough your research needs to be. In light of this, you will certainty need to go through primary and secondary sources.
When you work through the primary sources, you are essentially looking at the data and coming to a conclusion based on your observations. When you work through the secondary sources, you are seeing what other scholars in the field have said and done. You are seeing if they conducted responsible research based on the primary sources.
As to whether the paper is short or long really depend on what you are trying to achieve.
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