The difference between a research paper and a regular essay isn't just length it's the type of intellectual work each requires. An essay demonstrates that you've understood material, can synthesise it, and can build a coherent argument from it. A research paper asks you to go further: to contribute something new to a field, investigate a question that hasn't been answered in quite this way before, and document your process thoroughly enough that another researcher could follow what you did and why.
Structurally, an academic research paper is formally organised typically introduction, literature review, methodology, results, discussion, and conclusion because the structure itself is part of the communication. Each section serves a specific function in the research argument, and readers familiar with the conventions expect to find specific information in each place. An essay is more flexible: the structure follows the argument, and the argument follows the thesis. A research paper's structure is, to a significant degree, predetermined by the discipline's conventions and departing from those conventions without reason draws negative attention from markers.
Academic versus non academic research writing
Academic research papers are written for a scholarly audience, maintain a formal and objective tone throughout, and depend heavily on peer reviewed sources for their credibility. Every claim that isn't common knowledge requires a citation not to demonstrate thoroughness but because academic knowledge is cumulative, and situating your claims within the existing literature is how your paper participates in the scholarly conversation rather than standing outside it. Non academic research writing (journalism, policy reports, market research) allows more flexible structure, draws on a wider range of sources, and aims at accessibility rather than scholarly precision. The conventions are different because the audiences and purposes are different and understanding which mode your assignment requires is the first thing worth clarifying in any brief.