Sphenix-calibration-l mailing list

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

Hi all,

The notes from yesterday's meeting are at https://indico.bnl.gov/event/9195/attachments/30027/46854/notes.txt and bellow.

As usual, comments and corrections are welcome.

Hugo

--------------------------------------

Slide 3:

Q: what is meant by disabling the TPC ?

A: TPC is included in the track finding, but disabled from the track fit.

It is implicitly assumed that distortions in the TPC will not prevent the track finding to still work. Relying on the MVTX+INTT (and Micromegas) only for the track finding will not work.

Q: Do you use truth track finding or full algorithm

A: full algorithm. In details: PHTPCTracker (CA based seeding), PHGenFitTrkProp and PHGenFitTrkFitter, modified to disable TPC hits

Q: you require hits in MVTX and the INTT, in order to have a valid extrapolation in the TPC. Do you know the efficiency of this ? It is exepcted to be very low.

A: No. Will rerun the reconstruction, including the official evaluators, to look at matching efficiency as defined there. Will work on evaluating the same quantity using own evaluator

Q: did you look at the actual distribution of the residuals in the TPC. Are they Gaussian ? Centered on zero ?

A: double-checked: yes. Will look at centrality dependence. Indeed the track sample is small though.

Q: how will you proceed to study Micromegas configuration

A: 1/ look at how precise one can reconstruct the distortions in the fraction of the acceptance covered by Micromegas and using all the available data (=2sec)

2/ Following Christof's suggestion, see to which extend using the distortions evaluated in one sector of the TPC can be applied to the other sectors

Q: this is effectively a measure of the impact of GEM to GEM gain + IBF fluctuations, right ?

A: yes.

On SC distortion maps: 'suspicious' phi features discussed in past meetings are actually real. Time-averaged maps should become available in the coming days.

Slide 4:

Q: which threshold did you use ?

A: the one in the TPC digitizer (4xENC + pedestal)

Comment: so considering all hits instead of hits above threshold gives an increase of ~50% in occupancy. This sounds reasonable.

Q: quoted occupancies in the TPC appear smaller than what people remember. (up to 30%)

A: still double-checking. There have been many changes: used 200kHz PU in the past; the radial extend of the pads in the inner chambers have been divided by two; some studies focused on central collisions only. Difference in occupancy with respect to older files from Christof is understood. Detailed comparison with older studies from Jin are in progress. At first look numbers seem to agree reasonably well.

AOB: will contact Saclay team directly to discuss occupancy in the Micromegas with experts.