Many papers about research studies and industry experience about agile software development have been presented at the various conference series devoted to this topic. The papers are available online, and I give the links to tables of contents below. Note that the full text of the papers is typically not available free, but requires some kind of individual or institutional subscription.
There is the "Agile200X" conference series
This conference series came from the union of two earlier series.
One was the
"Agile Development Conference"
One was the "XP Agile Universe Conference", or more formally,
"Extreme Programming and Agile Methods"
There is also the "XP200X" conference series, which, despite that name, is not only about XP. The formal name is