Sphenix-calibration-l mailing list

[Hugo Pereira Da Costa <hugo.pereira-da-costa AT cea.fr>]

Hi all,

the notes from Tuesday's meeting are at https://indico.bnl.gov/event/9684/attachments/30677/48150/notes.txt and below.
As usual, comments/corrections are welcome,

Ross and Hugo

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1. Integration of the Micromegas to the TPC in CAD (Klaus)
There is in principle enough room to mount the Micromegas on top of the TPC in the free space below the EMCAL.
"Free" radius range from ~820mm to 890mm. Current outermost radius for the Micromegas is 10*167.6/2 = 838mm.

However:
- this does not include support structure for the Micromegas
- in the drawings, the space is marked Reserved (for a DIRC ? Is it for SPHENIX ?)

Comments:
- Depending on the implementation one could move the FEE to the side of the MM instead of the top to liberate some space
- The choice of connectors for the FEE is not final. Takao will send drawings of the FEE board and connectors to interested parties
- Keeping the FEE on the top one can center it more to slightly reduce the outermost radius
- rather than checking against the apparently available space in the current drawings, it might be better to check against the envelope allocated to the TPC. It would be much simpler for the integration if the Micromegas could fit in this envelope, rather than overlap to that allocated to the EMCAL (or others)

2. Status of the internal discussion concerning the MM project in Saclay:
- project presented to the Saclay heads of relevant departments. Will be discussed with head of the institute.
- ongoing discussions on anticipated discharge rates in the Micromegas, to decide on the technology (resistive or not)

3. Distortion Software (Ross)
- new items added to projects and milestones for September:
 "implement full 3D external fields and both TPC halves"
 "study short timescale distortion maps with long time-scale already subtracted"

slide 6:
New maps covering both sides of the TPC.
Q: is it correct/understood that the delta phi distortion has the same sign on both side of the TPC ? (electric field goes in opposite directions; magnetic field is ~ the same.
A: yes. will make a drawing to explain it (simpler than words)

Q: difference of magnitude between both sides is because Magnetic Field is not completely identical ?
A: yes.

Slide 8: estimation of time-averaged charge distribution and distortions still ongoing. In particular there remain some z structures on the current average that need to be understood and smoothed.  Newest, double-sided version has some coding issue, so continuing to use older 'rev2' map that is mirrored by hand.

4. Update on distortion reconstruction (Hugo)
Slide 4:
Q: Bottom right plot is with using reconstructed clusters in the TPC and track fit through reconstructed clusters in MVTX, INTT and MM ?
A: yes. The only place where truth information is used is for the track finding.

Slide 8:
- will need to commit the code for introducing the distortions in the reconstruction chain. Two versions exist, from Hugo and Henry. Should synchronize, cleanup and merge. In particular Henry implemented per/event map. Hugo uses the same map for all events.

Q: When will we have the required specifications for the Micromegas to match sPHENIX requirements ?
A: Several aspects to the question.

Concerning spacial resolution, current setup is somewhat standard (1mm/2mm pitch depending on the side, leading to 100um/200um resolutions), and it is enough.

Concerning efficiency: results on distortion reconstruction shown here correspond to 0.5s of data. If indeed one is interested in reconstructing time average maps on a timescale of several minutes (at least 10x longer time), one can tolerate large inefficiencies. However, the higher the efficiency, the shorter the timescale over which one can reconstruct a given map, which would allow more crosschecks against fluctuations thereof.

Concerning occupancy (number of fired strips per collisions including pileup), it is on the high side: ~16%, and it would be nice to reduce it to below 10% (smaller pitch, smaller amplification/drift space, different gas, or even cut the strips in half)

Concerning discharges: this is the critical part. From the number of particles per collision per tile Maxence estimated 4 discharges/second. In comparison, COMPASS Micromegas chambers have about one per minute.
Q: Will the electronic survive such a discharge rate ?
A: (Tom) can be tested in the lab with chip-killer device

Q: what dead time does this generate (depends for instance on the decoupling scheme of the electronic channels to the ground)
A: could be tested with FEE + Micromegas detector in the lab.

Q: is this rate acceptable or must one go to resistive layers (making the detector harder, longer to build) ?
Q: does this discharge rate include interaction of the particles with the detector material (e.g. the mesh) ?
Q: do the quoted particle rates include back splash from EMCAL ?
A: No. Should as a smaller HIJING sample that include the complete EMCAL.

5. Micromegas integration to the ACTS tracking (Tony)
- Discussion in how exactly Micromegas will be implemented as a detector ?
Likely as plane pieces that map the original cylinder, similar to what is done in the TPC.
Will need to pay attention to the bias issues created by using 1D measurement and approximated to a plane, but at the wrong location in the "other" direction (as was the case in GenFit). Only affects the z measurement.
- ultimately will use plane implementation, as in the real life. ACTS should be already setup to handle this properly as there are detector of such geometry in ATLAS.

6. Outer Tracker Elevator Pitch for sPHENIX management (Christof)
Agreed to go through it and improved. Suggestion to add a second page that describes the Micromegas detector briefly and illustrates that it "does the job".

On 9/28/20 8:32 AM, Hugo Pereira Da Costa via sPHENIX-calibration-l wrote:

      Dear All,

The next meeting on outer-tracker studies and spacecharge distortions in the TPC will take place tomorrow, Tuesday, Sept 29, at 11AM EDT

The indico page is at https://indico.bnl.gov/event/9684/ and connection details are below.

Contributions are welcome,

Best,

Hugo

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Meeting URL
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Meeting ID
676 999 731

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