sPHENIX HCal discussion

[Edouard Kistenev <kistenev AT bnl.gov>]

PS.    Sooorrry - it is ~1500 (24x64) channels not 3000 - my mistake.

Edward

On Aug 29, 2017, at 11:10 AM, Edouard Kistenev <kistenev AT bnl.gov> wrote:

John,

the e-id in sPHENIX is based on many things. Al HInner made with 30% (volume) of Scintillator will simply add 2X0 to the depth of EMC (from 18 to 20X0) and will make it longitudinally segmented. So eId is unlikely to suffer.  

I also tried but failed to find 25 years old note from Glenn Young explaining that PHENIX would be perfectly viable HI detector without EMC (Glenn was of strong opinions at a time). But both STAR and PHENIX made a lot of nice jet physics without hadronic calorimeters. LHC experiments have excellent hadronic calorimeters but no break-through results in HI physics, mostly helping to interpret what was already at least hinted at RHIC. It seems that actually measuring the jet energy serve at best checking conservation laws, jet finding and jet tagging is easier done with good tracking and good EMC next to the vertex and that we keep and even improving. Unless we are aiming for a major discovery - accounting for 0.5 Labs loss is just an extra 5% correction added in quadrature to the constant term in HCal - will matter but survivable. 

I think we first need to answer a simple question - are we modifying design today to still allow original design ideas implemented when money are available or we are getting creative under pressure and repositioning ourselves for better EMC while saving on the cost of HInner. Do we have enough resources to save 3000 readout channels of HInner. If answer is yes - are there cheap EMCOuter (still inside magnet)  solutions with 3k channels to replace HInner  (one we all know - it is on the floor in high bay). What’s about BaBar CsI (heresy but Haggerty is vacationing) - why not to test it in upcoming run at FNAL (are there anyone who is already working on such a plan - I will not be surprised - and I  would like to help if help if allowed). 

Edward

On Aug 29, 2017, at 9:46 AM, John Lajoie <lajoie AT iastate.edu> wrote:

Dear sPHENIX Simulators, 

    As many of you are aware, there has been a lot of discussion lately about ways to reduce the overall cost of sPHENIX, and making modifications to the inner HCAL design is a part of that discussion.  One of the things that we have been looking at is the possibility of making the inner HCAL from a cheaper non-magnetic material, like Al, as opposed to SS310 stainless steel.  Another option is replacing the inner HCAL with a frame to hold up the EMCal. 

    Sasha Lebedev and Abhisek have been looking at simulations of single-particle energy resolution and hadron rejection in embedded HIJING events for a Al inner HCAL, and they will present their results at next week's HCAL meeting.  At the risk of starting a discussion without most people having seen their results, I will say that the results are promising enough that I would like the simulations group and Jet ToG to start an effort to look at the jet energy resolution. As the timescale for some of these decisions is shortening, it would be helpful if there could be a discussion at this week's simulation meeting, and a start of the necessary production soon. 

    As a staring point for discussion, what I suggest is the following - repeat the pythia jets production that was used in the existing jets note with the standard configuration (inner HCAL made from SS310) and a modified inner HCAL with the material made from G4_Al.  I believe that both are necessary as there have been changes to the simulation code since the previous results, most notably the HCAL digitization has now been included in the standard macros. These simulations will be able to serve two purposes: 

-> Examine the effect of changing this inner HCAL material change on the jet energy resolution, and compare to the single-particle results from Abhisek. 

-> Examine the effect of no inner HCAL - just an Al frame.

I believe that the latter can be done by just ignoring the inner HCAL in calculating the jet energy in the Al inner HCAL simulations, but this takes some explanation. 

Let's assume that we want to replace the inner HCAL with just an Al frame. It will still need to support the weight of the EMCal. In talking with the engineers, it will still most likely be some sort of a box-beam structure (as it is now) as that is mechanically very strong.  In addition, we won't design the frame with large gaps as that would create non-uniformities and open areas that would allow the soft part of a jet to spread out in the magnetic field.  The combination of these two dictates that an Al frame would look very much like the existing inner HCAL mechanical structure, so, in the absence of a detailed frame design we can simulate the effect by just including and inner HCAL made from Al and ignoring the energy collected in the scintillator. 

Including a frame of dead material will have two effects - it will degrade the energy resolution, and it could spread out the shower.  What I'm suggesting is we take the approach that we won't design a frame that makes the latter any worse, and look at the effect on the former.  This has the advantage of being something we can do right now. 

Rather than doing the full pythia embedded in HIJING first, I would suggest that the jets ToG look at the energy for pythia jets first. Based on those results we could decide if a full embedded study is warranted.

Regards,
John Lajoie

On 8/28/2017 6:53 AM, Huang, Jin wrote:

Hello everyone,

 

We will have a regular sPHENIX simulation and software meeting, Tue Aug 29nd, 1PM EST @ 2-219

 

Following last week’s discussion, Tony will introduce new tunes for tracking simulation to reflect updated understanding of the TPC occupancy. Further contributions will be welcomed too.

 

The agenda page is at https://indico.bnl.gov/conferenceDisplay.py?confId=2708  , for which the common modification password is "1008"

•         For residents at BNL, we will meet at the 2-219 conference room if not closed for snow

•         To join the Meeting via phone bridge:  https://bluejeans.com/619960505  

•         To join via Phone:

1) Dial: 

        +1.408.740.7256

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2) Enter Conference ID: 619960505

 

Looking forward to talking to you,

 

Cheers,

 

Jin

 

 

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Brookhaven National Laboratory

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John Lajoie

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Iowa State University

 

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