Not all research papers will require an explicitly stated thesis. Some research papers in some fields will simply require a strong focus. You can maintain a strong focus in your essay without an explicitly stated thesis by thinking about an implied thesis for your research paper. With an implied thesis, your point is never stated directly, but your paper does have a clear focus or point. Even if you’re not stating your thesis directly, you should keep your implied thesis in mind as you write. All papers require a specific focus, and a good research paper will maintain that focus throughout.
If you’re unsure about whether you should use an explicit thesis or simply maintain a clear focus without an explicit thesis, be sure to ask your instructor.