The source of truth for the R&D org structure and team membership is this spreadsheet. For an overview of all teams and areas of responsibility please see this document (*note that some data may be out-of-date between this doc and the handbook, the handbook is considered our official listing).
R&D is split into three different divisions: Product, Cloud, and Security. Under each division, there are teams with specific areas of ownership.
Each vertical team is responsible for a single product.