Branching out into a new research area
Be sure you read the relevant articles you can find so that you know what has already been done. Then go to the relevant conferences and see if you can talk one of the senior people into giving you 15 minutes for a discussion of your ideas over a cup of coffee -- and if that turns out to be productive, see if they are interested in collaborating in a paper. You will likely do the majority of the work for the paper, but the senior co-author will make sure you stay on the right track, and point you at other papers that you may have missed by yourself. He or she may also introduce you to other researchers in the field who have thought about connections between fields such as the one you have in mind.
What do the rest of you do when you are preparing to do work in a new, unfamiliar research topic?
If you are at a university where there is some institute that roughly deals with the general field you are interested in, just pay them a visit. I have always used such opportunities to get in touch with people from (thematically) further-away institutes. Even if they cannot help you now, you have established a contact that may prove useful in the future, when there is another opportunity for collaboration - either directly with you, or by someone else in your group who is interested in a given topic.
In any case, if you do not actually know the other institute, it does not matter much who you talk to first - just pick any one of the researchers there whose general field seems to be related and ask them which one of their colleagues you'd best talk to about topic X. They will then either forward you to someone who is proficient about the topic, or recommend a way how to obtain some information from external sources.
In my opinion, it is only after you have established such a contact that it makes much sense to read papers about the new topic. Otherwise (at least if the new topic is truly in an unfamiliar (sub-)field), too many aspects are usually unknown to you to find a worthwhile selection of papers to read: You do not know the primary venues, nor the signs that a venue is highly-regarded in the unknown field, nor the conventions of what is considered "thorough" or "exciting" in that field etc.