sPHENIX bulk physics topical group

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

Dear all,

This is Hao-Ren. I am a PhD student at MIT and am working on the charged particle multiplicity measurement with the tracklet method.

The following are my answers to the physics discussion questionnaire:

a) This analysis uses MVTX, possibly with information from INTT for the vertex reconstruction. Centrality information from the minimum bias detector (MBD) and sPHENIX event plane detector (sEPD) is also required.

b) The analysis strategy follows closely the one done in the CMS experiment with Pb-Pb collisions. Therefore, the sources of uncertainty are expected to be similar. Here I briefly describe the dominant uncertainties in the CMS analysis. The actual uncertainties and their magnitude will be estimated and carefully studied in the future.

1. Centrality determination: The determination of the centrality depends on the hadronic event selection efficiency, ultra-peripheral collisions contamination, and bin-by-bin migration of the centrality variable. The effect of this uncertainty on the final results was studied by repeating the analysis using various centrality tables derived by varying the event selection
2. Reconstruction efficiency: The simulation of the pT and multiplicity distributions influence the determination of the tracklet reconstruction efficiency. The effect was estimated by (1) varying the average of pT distribution and (2) changing the multiplicity variable.
3. Acceptance uncertainty: The positions of the CMS pixel detector barrel (BPIX) layers were not perfectly simulated. The effect was estimated from data by using the tracklets to map the active surface of the BPIX layers.

c) Centrality would be necessary. 

d) Simulation samples of HiJing Au-Au minimum bias without pile-up would be required. (The sample in the current study is HiJing Au-Au minimum bias with pile-up rate 50kHz)

e) O(10^4) events would be sufficient. 

Best,

Hao-Ren

Ron Belmont <belmonrj AT gmail.com> 於 2022年8月8日 00:11 寫道：

Hi All,

Following on the discussion at the general meeting, I’d like us to consider the following questions for some of the early Year-1 ("Day-1") analyses we’re interested in doing.

a) What detector subsystems are needed?

b) What are the expected dominant systematic uncertainties, and how will they be determined?
c) Which calibrations are needed (including centrality, event plane)?
d) What are the MC needs beyond that which is currently available?
e) What is the minimum luminosity necessary for the measurement to succeed?

You can reply to the list (encouraged) or to me privately, whichever you prefer.

*** To help out with an example, for Day-1 I’m interested in cumulant v2{2,4,6,8,10}.  Here are my answers: ***

a) For the final analysis, full tracking is needed, but as an intermediate step this analysis could possibly be done with tracklets, single layer hits, etc.

b) Typically the uniformity of the azimuthal acceptance, though sometimes the detector alignment.  Either can be checked with looking at the average Q-vector values as a function of centralty/multiplicity and z-vertex.

c) Centrality would be nice, but not required.  No event plane needed.  Properly calibrated tracks would necessary for a final result, but not for an early result with tracklets or hits.

d) No MC needs.

e) For just the v2{2,4,6,8} about 1 billion events is sufficient.  For accurate ratios like v2{6}/v2{4} and and v2{8}/v2{6} probably more like 20 billion.  No good answer for the v2{10}, we’ll just have to find out.

Cheers,

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