Present: Stepan, Maurik, FX, Tim, Takashi, John
Please send additions/corrections to whole EC.

1. News. Stepan mentioned that Kashy has little use for Hall B this week, but getting time for day shifts W-F is meeting opposition from the 12 GeV project. Management hasn't weighed in yet.

2. Should we move the SVT to 0.5 mm? If so, when? Major issues are:

a. How much data needed?

Present amount of data at 1.5 mm is 1.4 B triggers. If everything is working well, we expect 1/2 week to produce publishable physics results. That corresponds to roughly 3 B triggers. We all agreed that our first priority is to get to 3B triggers before moving. Unfortunately, we still haven't proved that we are writing the expected number of triggers to tape. So there is some uncertainty about whether 3B triggers is enough.

We may learn more from Matt or Rafo this week.

b. What happens if beam hits SVT?

Tim repeated that we don't know exactly what will happen if beam hits layer 1. Worst case is cracked si from thermal stresses, or sensor wide shorts that prevent operation. It's possible to lose the whole sensor, and therefore layer 1. We expect the rest of the system to be okay even if layer 1 were lost. Tim would like to better understand thermal loads on the Si. We'd also like to put T and SC halo counters into the FSD and set thresholds so that beam hitting si would generate a trip asap.

c. Has beam behaved so far?

Beam has been within limits on 2h02 consistently. Maurik is studying this systematically to see any evidence for aberrant beam behavior. On trips, excessive beam motion has been observed on restoring beams, but it is thought that this is due to low currents in the bpms and faulty readings.  So far evidence is that beam stability is okay for moving to 0.5 mm.

d. Consequences of moving in?

If we move the SVT in, we expect the event size to increase. We assume the DAQ can handle that without problems. Will the trigger rate change? Perhaps, because beam tail will now hit silicon, and could generate more triggers and Ecal backgrounds. This is not expected to be a big effect or a problem.

e. What if we lose layer 1?

 If we lose layer 1, the vertexing resolution will be significantly degraded, perhaps to the point of eliminating the vertexing  measurement. The beam constrained mass resolution will also be degraded, but the acceptance basically preserved by layers 2-6 of the SVT. The bump hunt will survive with degraded resolution.

3. Decision.

EC decided to first accumulate ~3B triggers. This number is expected to be enough for our students and for first publications.  If this can happen this week, and stable beams are restored by Sunday, we'd consider moving the SVT to 1/2 mm Sunday afternoon. EC will revisit the question on Friday at 9AM Pac to see how the event total is progressing and react to new developments.

Respectfully,

John

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