The Notch

The "notch" in pseudorapidity is pronounced, and fairly precisely centered on eta=0.88 --

Plot number of hits fit vs eta (zooming in on 0.83 to 0.93 now...).  We are missing tracks with N fit points > 40 entirely in this region.

We zoom in again, to 0.86 < eta < 0.90, and this time plot the radius of the last hit on the track (a.k.a. the first point on the seed) vs eta.  Here we see that there is a class of events which is depleted for Rlast > 190 or so.