I don't think there is a fixed pass score. There are a lot of theories floating out there. This discussion has taken place in another post for part 2 so you can check out the link I've provided below. In future, try using the search engine in the upper right corner of the "Forum" page to see if the matter you're interested in has already been discussed (whether questions or any inquiry); I use it all the time and it's very useful.
To my knowledge, @ShaktiRathore 's links above still apply (although we can confirm this week with GARP) and the exam methodology has not changed: the top 5% quantile (ie, the top ventile) score is determined from the overall score then a ratio is applied to that score. But the ventile cannot be known ex ante, and further the ratio varies; this amounts to a sophisticated version of "grading on a curve." @ShaktiRathore illustrates with an example (in links above) for P2 which seems plausible as an illustration of the mechanics: he assumes that the top ventile score is 75 out of 80, and the passing ratio is 70%, such that the passing score is 75 * 70% = 52.5. But it's just an illustration, GARP has certainly never guaranteed to us a fixed passing rate. It's my understanding that the intention is more along the lines of maintaining (eg) the P2 pass rate above 50%. Thanks!