Noting posters/presentations (formal project titles/dates/locations) essential for statements of purpose in US PhD programs?
Don't confuse the purpose of the CV with that of the SoP. The former looks to the past, what you have already accomplished. The Statement of Purpose, on the other hand looks to your future and what you expect to do in the future, both in future schooling and beyond. Together they provide a more complete picture. 

So, I suggest that you only mention your past research in the SoP if it has research threads that you hope to follow in the future. And then, you only need to briefly mention the papers or projects (name, say) to create a link in the reader's mind. If you have work in progress, you can mention that. 

Don't leave the committee wondering how you view your future. "I've been great up to now but, .... (nothing)".