sPHENIX tracking discussion

["Frawley, Anthony" <afrawley AT fsu.edu>]

Hi All,

The minutes of today's tracking meeting are below.

Cheers
Tony


sPHENIX tracking meeting, November 6, 2105
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We will have biweekly meetings at 9:00 am on Friday, the next one will be on November 20.

Gaku Mitsuka - update on HDI R&D:
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Outline for production of the HDI prototype and tests with the FPHX chip.

Prototype HDI and FPHX wire bonding could be done at BNL, still need to discuss that with them.
SIDET at FNAL would be the best place to do the mass production wire bonding (FVTX wedges were done there).

Plan is to test the HDI and FPHX without a connection to sensor, then add the sensor connection later (next year).

Any progress on how to stack the HDI strips on a ladder with multiple sensors? Still discussing.
Can bend HDI, or make HDI larger and use for multiple sensor outputs
For the moment, the focus is on demonstrating that a silicon module (HDI, FPHX chips, sensor) with 40 cm bus will work.

For sims we can assume that the HDI can be represented by a stack of long strips for now.

Will make prototypes from four 320 micron sensors and four 240 micron sensors

The silicon strip grant proposal has been submitted - will get feedback in January or February. The interview would be in March, around the 24th, if selected for that.

Discussed a few issues related to configuration testing:
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1) Can we make dead pixels estimates for the option to reuse the pixels?
Yasuyuki: We have 30 ladders + 6 new ones, would like to replace some of the old ones
The radius has to shrink to make 2*pi coverage - still have to settle on a radius.
The inner layer radius is limited by the beam pipe. Need 12 ladders there.
We can shrink the outer layer, but we will still need 32 ladders.
Yasuyuki will try to make some estimates of resulting dead areas.
Should try to put the worst ladders where they do the least harm. Will have to think about where that is.

2) Can we get a realistic G4 model of the reused pixels?
Mike: The G3 silicon model was ported into G4 by Matt Snowball. Mike will talk to him.

2) How about a realistic model of the MAPS pixels for configuration testing in simulations?
Mike: Best to re-utilize the G4 MAPS ladder geometries from ALICE. Mike has asked Leo for that.
Also, the cluster size is bigger than the pixel size due to diffusion, which is good. Want to add that to the simulations
There was an LDRD town meeting at LANL early this week. Mike thinks the MAPS proposal looks pretty good, but will not know about the LDRD results until June.

3) Another question for the MAPS pixels:
The pixels can be read out at up to 200 KHz. The integration time is such that a hit within a few microsecs can be included in the next event.
We could sort this out in software if we record every event - but we can not count on that. Even in a MB triggered data stream we will miss recording some events when running at high rates.
Or, we could subtract the previous event in the front end electronics using a buffering scheme.

4) We need a realistic G4 model of the silicon ladders:
We agreed that this did not need to wait for engineering details such as how to stack the HDI cards to be resolved.
We can add the HDI cards as a stack of layers in G4 to just get the mass correct for now, tidy it up later.

5) Material budgets: Yasuyuki commented that we have more certainty about some material budgets than others:
Reused pixels: we know the material budget because the ladders exist.
Strips: We are starting to make modules, so we will know .
MAPS pixels - how much uncertainty is there in the 0.3% / layer estimate?
TPC - uncertainty in field cage mass?
The question is whether the uncertainties in the mass budgets should be allowed for in configuration testing.
Editorial comment: We should certainly try varying the mass of material where we do not yet have final designs to see if we can tolerate increases. But the mass of the inner TPC field cage will not critically affect the mass resolution of the Upsilon, and a moderate increase in the mass of the MAPS pixels would not affect momentum resolution to first order, although it would cause an increase in radiative tails for electrons.

6) We did not have any TPC experts called in, so we deferred TPC questions until next time.
One question we would like to get feedback on early is whether we will need assistance (say an intermediate tracking layer, or an extended outer radius on the pixels) to match tracks from the TPC to the pixels in central collisions.

Mike suggested that we make 4 simulations macros that model the 4 possible combinations of detectors, and let them diverge. Agreed. This would allow us to explore the weaknesses of each option starting from an agreed upn configuration.
We should modularize the parts of the tracker as much as possible (for example the reused pixels geometry will be the same).

Ed: Future meetings:
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We should be trying to focus in on timescales, create a schedule, argue for resources based on a need to meet schedule.
At the next meeting Ed will reiterate for us where the hard points are in the schedule.