sPHENIX HCal discussion

[Edouard Kistenev <kistenev AT bnl.gov>]

Dear Aaron, thanks for absolutely perfect comments. And unfortunately they have no simple answers even in simulation. Jet is not a confluence of identical objects and calorimeter (sPHENIX like the others) is never (except if it is all built as a bolometer) will respond in similar ways even to the same object everywhere within its mechanical structure. It should be considered first and most a trigger device, sPHENIX will have a near perfect tracking which will never be equalled by calorimeter. Most of the particles in jets will be measured with precision which can never be matched in calorimeter (software cleanup). sPHENIX also have 1.5T field with cutoff for particles reaching calorimeters comparable to average transverse momenta suppressing underlying event (hardware cleanup).  The problem is how to share the energies seen in calorimeters into components already known from tracking and that one “yet to share”. This is when simulation is critical to account for the fact that the calorimeter is deeply structured longitudinally. In sPHENIX neighbor towers overlap ( due to the tilt of absorber plate) resulting in a double sampling along the same trajectory in a single calorimeter section. Simulation will predict the set of numbers for particle (energies in “sections”) distributed according currently non specified probability densities, it will be a job for calorimeter to reduce the uncertainties by offering linked measurements at different depths.

What’s left afterwards is the subject to a separate considerations - but at least it is a challenge. 

Note that I am not even talking about punchthroughs - they are just part of probability distribution and must be handled gracefully.

Edward

On Sep 11, 2017, at 12:26 PM, Aaron Angerami <angerami AT cern.ch> wrote:

Hi,

I didn’t make this comment during last week’s meeting, but I wanted to make sure the following is something that gets factored in when assessing the effects on performance. Obviously having punch-through will impact the jet energy resolution. However, it does it in a way which is dependent on how the jet fragments. We don’t want to be in a situation where the JER is degraded by an amount we deem to be tolerable, but end up with a nasty surprise when we try to do a measurement and there is a significant correlation between the jet’s properties and the calorimeter response. It would be useful to correlate the jet response with some of the jet’s properties. I recall Dennis had made such plots the last time this kind of descoping was studied extensively, and I think its important to include these in the list of jet studies. I think what was looked at then was the response for quark vs gluon jets and vs a jet property highest z value in the jet. 

Cheers,

Aaron

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

Aaron Angerami
LLNL, Staff Scientist
angerami AT cern.ch

Office:  1 925 423-7726
Moible: 1 925 495-7017
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On Sep 10, 2017, at 11:38 AM, John Lajoie <lajoie AT iastate.edu> wrote:

Dear Chris (copying your email to the lists):

    That's fantastic - thanks for taking the lead on this. I think we can get people to ramp up their time looking at simulations this coming week.

Regards,
John Lajoie

-------- Forwarded Message --------

Subject:	Re: inner HCAL action items
Date:	Sun, 10 Sep 2017 11:48:38 -0400
From:	pinkenburg <pinkenburg AT bnl.gov>
To:	John Lajoie <lajoie AT iastate.edu>, Dennis V. Perepelitsa <dvp AT bnl.gov>, Rosi Reed <rosijreed AT gmail.com>, Sasha Lebedev <LEBEDEV AT iastate.edu>
CC:	Lee Songkyo <songkyolee AT gmail.com>, 'Jamie Nagle' <jamie.nagle AT colorado.edu>, Jin Huang <jhuang AT bnl.gov>, Abhisek Sen <sen.abhisek AT gmail.com>, John Haggerty <haggerty AT bnl.gov>

Hello everyone,

the 0-4 fm hijing sims wit hthe al inner hcal  are finished (4 jobs crashed and I just restarted them). The files are under:

/sphenix/data/data02/rescope-2017-09-08/inner_hcal_al/sHijing/fm_0-4

I changed the setup of the sims so only successfully finished jobs copy their output there (so no more corrupt files, if you still find one - please let me know).

Our machines are idling - so I submitted the other hijing  b ranges (0-12, 5-9,  9-11) for processing. With a bit of luck most of them should be done by tomorrow,
They'll be under
/sphenix/data/data02/rescope-2017-09-08/inner_hcal_al/sHijing/fm_<b range>/

Chris

On 9/6/2017 8:07 PM, John Lajoie wrote:

Dear Dennis, Rosi, Sasha, Chris (and cc to a wider audience):

    First of all, let me thank everyone for the work that was presented at the HCAL meeting today. It's clear none of it is conclusive yet, but I think it is all helping to focus more clearly on the questions we should attempt to answer on a short timescale.

    Here are some notes on what I think the action items are from today - this is for discussion, so if you disagree, please speak up. If there is no discussion, then this is what I expect people will be working on and planning to report on at the next HCAL meeting (9/20) .

    One important note - Abhisek has modified the inner HCAL macro G4_HcalIn_ref.C so it includes a flag:

//Inner HCal absorber material selector:
//false - Default, absorber material is SS310
//true - Choose if you want Aluminum
const bool inner_hcal_material_Al = false;

and this is available in git. Setting this flag will modify both the inner HCAL material to Al *and* change the sampling fraction so the tower energies are properly calculated.  This should make it easier to swap between configurations without something being missed.

e/h rejection:
------------------

This is basically for Sasha:

(1) It would be good to repeat the 5GeV e/pi studies shown today to include the proper sampling fraction for the Al inner HCAL (use the new macro).  For the single particles, make an e/p cut and then estimate the *additional* rejection obtained from the E_IHCAL/E_CEMC ratio.

(2) Repeat the central HIJING embedded studies with the correct inner HCAL sampling fraction for Al, so we have the correct plots. Check to see if the conclusion still holds that in central HIJING the inner HCAL does not yield additional rejection.

(3) Move to the worst offender - antiprotons - and repeat the singles and embedded studies.

That's a fair amount of work. At this point I think we should take stock again, look at the results, and decide if we want to continue along the road of essentially reproducing Jin's earlier work to obtain a combined e/h rejection.

jet studies:
---------------

I personally think that at this point we have learned what we can learn from single particle studies, and we should ramp up more realistic jet studies. (If we need to go back and run some single particles as a crosscheck it's fairly quick to do so.)

(1) Run pythia jets with SS310 (already available from previous studies) and Al inner HCAL.

-> Fraction of jet energy leakage out the back as a function of jet energy (black hole)

-> Jet energy resolution (in this case with and without reading out the Al inner HCAL to see the effect)

-> Lateral size of the jets - something like this:  run the jet finder with a large jet radius, and then look at the tower energy distribution radially from the jet axis for the towers included in the jet for the inner and outer HCAL.  This is one quantitative way to look at how the calo jet shape/size is affected by the material change.  (I'm sure there are more things that can be looked at as well.)

I can contribute jet finding code that I used to do similar things for the forward calorimeters if that is helpful. The above would be a good start, and would undoubtedly lead to more questions.  I would like Rosi and Dennis to get Songkyo Lee involved in this as well (increasing the workforce by 50%).

(2) Lay the groundwork we need for HIJING embedded jets, since this might take some time to run. Dennis suggested that it would be good to have just a small sample of HIJING events to start with, and Rosi suggested starting with the a central selection.  Rosi, can you work with Chris to set up exactly what he should run to get started?

Once that is set, I would suggest starting production with the same centrality selections, etc., as done for the jet note studies with Al instead of SS310.  This will take a while, but in principle it will be available when we need it.  

Let me know what you think, but let's stay focused and not go crazy - getting complete, vetted answers that we are comfortable with to the above questions is a nontrivial amount of work for two weeks.

Regards,
John Lajoie

John Lajoie

Professor of Physics

Iowa State University

 

(515) 294-6952

lajoie AT iastate.edu

Contact me: john.lajoie

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-- 
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Christopher H. Pinkenburg	;    pinkenburg AT bnl.gov
				;    http://www.phenix.bnl.gov/~pinkenbu

Brookhaven National Laboratory	;    phone: (631) 344-5692
Physics Department Bldg 510 C	;    fax:   (631) 344-3253
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