thanks. I asked for the right term not for the searching strategy, but I want to know what the english term for the "science of piano playing" is. In Germany I've sometimes red "Pianistik".
...and I thought I'd given you 3 terms for the price of 1

"piano pedagogy" "piano technique" "Piano method" - all are used.
There's a page here that discusses the various methods used historically -
https://www.cs.bsu.edu/homepages/kevinp/PnoTech1.htm Note he calls it "piano technique"
Your own "science of piano playing" is a 4th as it seems perfectly good English to me

Although I think the scientific aspects aren't really part of the methods to call them science - a page or two of justification for a technique based on human anatomy mebbe - and, if you include practise, a page or two justifying that based on the way we learn. But if you're interested in history, they make medicine look like a science, which is no mean feat

At the extreme, a book that attempts to combine 3rd world economics, the structure of crystals, Beethoven and the number 1000 for some light entertainment in the appendix.