sPHENIX EMCal discussion

["Lajoie, John G [PHYSA]" <lajoie AT iastate.edu>]

Hi Anne, Gabor:

    Thanks for the information - I agree with Gabor that in principle we could study this in simulation. I'm guessing that because the denominator in the sampling fraction calculation is dominated by the absorber, a 10% variation in density would be approximately a 10% variation in sampling fraction.

     Some variation is inherent to this process and can't be avoided.  I guess all this just points out is the need to keep track of every module, it's measured parameters, and final location in the installation - something I'm sure you are already planning to do.  If we have the information I'm pretty sure we could make a module-by-module correction offline.
   
Regards,
John

On 2/26/2016 7:35 PM, Sickles, Anne M wrote:

Hi Dave, John & Gabor,

The Illinois modules are numbered according to the production sequence so, yes, in general we are getting higher density with time.  However there are a couple of features.  Between module 6 & 7 there was a change in the filling procedure for the tungsten and you can see a corresponding increase in density.  Additionally the final eight Illinois modules were produced with a different batch of tungsten powder from the prior modules and a slightly different mold.  These modules were all produced this week under essentially identical conditions and thus I think the observed density variation is inherent in the (current) procedure.  The effect of the tungsten powder batch is something we are looking into in more detail; at this point we can only say that not all tungsten powder is the same…

For the THP modules the numbers don’t mean anything about the production since the numbers were assigned in Illinois rather than at THP at production time.  The density variation is a point of concern, but I don’t have a quantitative number of the size of density variation we can tolerate.  Obviously we can take steps to correct for it or model it with simulation, but we also need to build a density range into our QA criteria for the modules themselves.  That is something I hope to understand better with the test beam.

Best,

Anne

On Feb 26, 2016, at 5:29 PM, Gabor David <david AT bnl.gov> wrote:

On Fri, 26 Feb 2016, Lajoie, John G [PHYSA] wrote:

Hi, John,

Hi Vera,
    Very nice plot!
    The THP points in particular had me wondering if there is a limit to the
variation of the density that you can tolerate?  I would expect that a
module-to-module variation in the density (of the absorber) would lead to a
variation in the effective sampling fraction, which could degrade the
effective energy resolution.  I suppose if you knew the density of each
module you could make a correction?

wild guess: yes, and two different ways.
1/ have the same density in each module in the simulation,
but at the end correct the visible signal in each tower (such a
"calibration of the simulation output" is not unheard of, actually
in some sense we are doing it even now)
2/ get different densities for different modules in GEANT4
(just kidding; nightmare!)

Maybe a first good question to ask would be to compare
the simulated response in two modules with densities corresponding
to the two ends of the current density distribution.

2 cents :-)

Gabor

John
On 2/26/2016 4:24 PM, Loggins, Vera wrote:
     Hi all,
I just wanted to share the density plot vs. module number that we have
at UIUC.  I have plotted this along with THP's numbers.
Have a good weekend,
Vera
--
John Lajoie
Professor of Physics
Iowa State University
 
(515) 294-6952
lajoie AT iastate.edu
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--
Gabor David  (david AT bnl.gov)
Brookhaven National Laboratory
Physics Department, Bldg 510/c
UPTON NY 11973
Tel: (631)344-3016
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--------------------------------------------------------------

Anne Sickles

Assistant Professor, Department of Physics

University of Illinois at Urbana-Champaign

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

John Lajoie

Professor of Physics

Iowa State University

 

(515) 294-6952

lajoie AT iastate.edu

Contact me: john.lajoie