Haskall et al., The effects of L-theanine, caffeine and their
combination on cognition and mood, Biol Psych (2008); 77: 113–22.
Here's some of the detective work I've done:
The principal investigator of this study is listed on your link on ClinicalTrials.gov as Andrew Scholey of Northumbria University.
Looking on Google Scholar, and ...