sPHENIX bulk physics topical group

[Hao-Ren Jheng <hrjheng AT mit.edu>]

Dear all,

I would like to give an update on the comments I received during the meeting before the end of the week. 

I've uploaded a set of slides to the indico page, https://indico.bnl.gov/event/16640/contributions/66845/attachments/42761/71968/BulkPhysicsTG_Followup_20220819.pdf.

Below I summarize the slides in a few items:

• S1: The “off-diagonal” events in the 2D plot (Truth PV Z position v.s Reco PV Z position) are all with very few number of clusters in the 1st MVTX layer, confirming my guess during the meeting.
• S4: The vertex resolution has a suspicious trend as a function of centrality bins (The number of clusters in the 1st MVTX layer is used as the centrality variable for now). From the 2D plot shown on the right hand side, there seems to be a discontinuity at Nclusters~1000, this reflects the fact that the resolution becomes higher after bin5. This should be carefully checked to understand whether the problem comes from simulation or the vertex finding algorithm.

Thanks again for all the clarification questions/comments/suggestions raised and given during the meeting. Further comments are welcome and appreciated.

Best,

Hao-Ren

Ron Belmont <belmonrj AT gmail.com> 於 2022年8月16日 13:15 寫道：

Hi All,

Many thanks for the very lively and engaging discussion today.  Meeting minutes are attached below; see also the agenda page.  Please feel free to send me any corrections if you find a mistake.

Regards,

Ron

Hao-Ren, multiplicity analysis with tracklets

Slide 2
Question: How is centrality categorized for these results?
Answer: Forward hadron multiplicity
Question: Is it possible to work around the autocorrelations and use the central barrel multiplicity as the centrality measure?
Answer: Possibly, but reluctant to make such a dramatic departure from previous measurements

Slide 5
Comment: Of order 10^4 events is sufficient for a measurement; 10^5 events as used by LHC experiments yields approximately zero statistical uncertainty

Slide 7
Clarification: rho_n is the radial distance from the beam pipe to the nth layer of the MVTX, so it's the same for all clusters in a given layer

Slide 9
Question: What is the cause of the off-diagonal events?
Answer: Unknown, will study.
Comment: Likely from very very low multiplicity events, not yet clear how far peripheral we want to go for this measurement
Question: Status of simulations with no pileup?
Answer: Request has been made to Chris
Question: Is the no pileup simulation less realistic?
Answer: There may some very low luminosity running initially. Alternately, it may be possible to request low luminosity running at the end of a store
Comment: Higher luminosity running would necessitate the use of the INTT to get vertex separation
Question: How are truth vertices counted? Use negative embed ID?
Answer: Just count the number of truth vertices in the tree.
Comment: Might be interesting to compare the negative embed ID to the simple count.

Slide 10
Comment: Would be nice to see the evolution of the width in eta as a function of multiplicity

Slide 12
Question: Why is the eta distribution asymmetric?
Answer: The z-vertex distribution in the simulation is asymmetric (see backups, slide 43)
Comment: There may be some bias in the z-vertex distribution during real data taking, corrections would need to be worked out

Slide 15
Question: Are the alignment offsets of 10um, 50um, 100um realistic?
Answer: Yes, realistic. A mis-alignment on the order of 1 mm or more would be a major problem

General discussion
Question: Can use off-center collisions to get large acceptance?
Answer: In principle yes, but planning to focus on consistency with previous measurements
Comment: Ideal analysis for day-1, as it demonstrates a lot of systems working correctly (MBD and MVTX timed in, DAQ operating, data can be reconstructed, etc) but is still a simpler analysis than something requiring e.g. full tracking.

-----------------------------------------------------------------------------
Ron Belmont (he/him/his)
Past Chair, RHIC/AGS Users' Executive Committee
Assistant Professor, Department of Physics & Astronomy
University of North Carolina at Greensboro
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On Aug 15, 2022, at 10:08 AM, Ron Belmont <belmonrj AT gmail.com> wrote:

Hi All,

A reminder that we’ll have a TG meeting tomorrow at 9am EDT.

Agenda page: https://indico.bnl.gov/event/16640/

Zoom room: https://bnl.zoomgov.com/j/1613525277?pwd=TExaWUJYUHJMcERCV2ZLQW1OajExZz09 

Regards,

Ron

-----------------------------------------------------------------------------
Ron Belmont (he/him/his)
Past Chair, RHIC/AGS Users' Executive Committee
Assistant Professor, Department of Physics & Astronomy
University of North Carolina at Greensboro
-----------------------------------------------------------------------------

On Aug 12, 2022, at 11:05 AM, Ron Belmont <belmonrj AT gmail.com> wrote:

Hi All,

We’ll have a Bulk TG meeting this coming Tuesday, August 16 at 9am EDT.  So far we are expecting an update on the multiplicity with tracklets analysis from Hao-Ren, and other updates are welcome.  Please let me know if you’d like to present.

Agenda page: https://indico.bnl.gov/event/16640/

Zoom room: https://bnl.zoomgov.com/j/1613525277?pwd=TExaWUJYUHJMcERCV2ZLQW1OajExZz09 

Regards,

Ron

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