Hi Mike, Concerning the possibility that this was due to the OTR screens, the inelastic interaction probability for a 450 GeV going through 0.01 cm of Titanium is about 3.4e-4, which would mean that about 7e5 protons of a 2e9 bunch would interact. I do not know the actual thickness of the OTR screens, nor their positions, but it could well explain the large rates seen by ALICE. Worth checking, at least, because that would be a simple and relieving explanation. cheers Massi

BTVSS Screen Status during second test:

Point 8:
Fri 22/8/2008
20:09 : Beam onto TDI - Alumina screen IN
20:49 : TDI Out - Screen changed to Ti
21:51 : Ti Screen taken OUT

Sat 23/8/2008
00:11 : Ti screen put IN
03:22 : TED IN
Only a few shots on Saturday all with Ti screen IN

Sun 24/8/2008
02:41 Beam back on TED
02:44 Beam on TDI
02:45 TDI OUT & Ti Screen IN

Mon 25/6/2008
03:31 TDI IN & Screens OUT


Point 2:
Sun 24/8/2008
14:19 Beam onto TDI. Ti Screen IN
14:20 TDI OUT
15:41 TED IN
16:05 TED & TDI Out. Ti Screen IN
20:47 Screens OUT & TDI IN
22:32 TED IN