Solid Forward Calorimeter

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general design ideas

from Eugene Chudakov

a brief explanation is given in the proposal to PAC34, page 57-58.

A preshower I simulated gave a factor of 3 in e/pi rejection, which is important.

The resolution I used was 10/sqrt(E). With the shashlyk technology one can get 10% at 1 Gev easily, with a rad. hard scintillator. A better resolution of about 3-4%/sqrt(E) was obtained (KOPIO) with a high Sc/Pb ratio, but also with a rad. soft scintillator (there is a brief discussion in the proposal).

In order to make sure which resolution is enough one has to consider all the aspects including the pattern reconstruction. A poor reconstruction may lead to a more stringent requirement on the calorimeter resolution. The coordinate resolution is also very important, since tracking should start with the hit in the calorimeter.

I would suggest to assume 10%/sqrt(E) with a preshower, take some cell size to provide about 1 cm window for the shower center, and develop an algorithm for track reconstruction (Richard Holmes made some preliminary calculations). This is a critical issue, since the background in GEMs will be very high, and the calorimeter tagging is important. I used some assumptions on the GEM X-Y matching and resolutions, based on the SBB proposal in Hall A, which might be optimistic (Bogdan told me that they were concerned about it).

from Paul Souder

The Ecal has the following functions:

1. Provide a trigger.

2. Provide an energy for tracking.

3. Reject pions.

4. Study systematic errors.

Effect of resolution:

Pion rejection: the rejection factor is inversely proportional to the resolution. The asymmetry of the pions cn be measured, so the correction due to pion contamination can be made. However, if it is too big, complex systematic errors enter and the statistics is degraded.

Energy for tracking: The idea is that given a hit and an Ecal energy, one can compute where other possible hist are. This is the key to the tracking algorithm. We need a tracking Monte Carlo to determine which resolution dominates: multiple scattering, detector resolution, or Ecal resolution.

Trigger: Poor resolution may increase trigger rate.

Systematic errors: If the tracking and Ecal both have good resolution, the comparison is useful for minimizing systematic errors such as Q2.

Summary: The excellent resolution available with the sashlyk Ecal is useful. How much poorer resolution we can tolerate requires the Monte Carlo.

Task list

From Paul Reimer:

As I see it, the problem is how do we read out a segmented calorimeter if it is located completely inside the iron of the endcap flux return of the solenoid. There are three answers that I can think of:

  1. Use rather expensive APD's and if we need to service them, we need to open up the entire detector. This is the solution from our proposal, I think.
  2. Figure some way to get the light outside of the flux return iron, using wave shifters and fibers. The problem here is that you loose a lot of light in the process.
  3. Make the calorimeter part of the flux return iron so that the light naturally ends up at the downstream end of the flux return iron.

Zhiwen is looking at option 3. The first question to answer is what does the magnetic field do to the shower? To do this, I wanted to start with a simulation code that has been tested against measurements in a test beam. Thus we started with Hertzog et al's code which agrees with their test beam results (the code is called */SciFi, what a cool name!). My thought is that we need to do the following:

  1. Get the W/SciFi code from Hertzog running and show that we get similar results to what they got in their paper (complete)
  2. Add a magnetic field and study the changes in shower shape, transverse and longitudinal (in progress, near done)
  3. Switch from tungsten to iron and repeat step 2 (in progress, near complete)
  4. Change geometry from "fiber ribbons" to fibers on equilateral triangles and repeat 2 (starting, could be done in a week)
  5. Do 3d magnetic field simulation of calorimeter's Fe/SciFi geometry to get field correct. I don't have access to TOSCA easily at Argonne, but I do have access to another 3d field program. Here Zhiwen could start working with Juliette and learn TOSCA. It is a very marketable skill (many university professors do not know how to do it).
  6. Repeat step 4 (will be completed a week or less after step 5)
  7. Design calorimeter based on results of step 6. This is optimizing resolution as a function of iron to scintillating fiber ratio, determining the number of radiation lengths needed to contain the shower to the extend that we feel it needs to be contained and optimizing segmentation.
  8. Cost calorimeter
  9. Build prototype
  10. . . .

Work through step 6 will completely the question of will it work. From what Zhiwen's shown me, the answer will clearly be yes, but I would like him at the end of step 6 to write a tech note on this to document it, and that will take some time. Then we move on to designing and building. At some point around step 7/8 we need to present this to the collaboration and get their approval. There is also an issue of getting the preshower to work (to get the light out). This would be an issue with any choice of calorimeter. When I was at JLab last week (week of March 7), I think that Zhiwen and I figured out a cost effective solution, but it depends on the segmentation required by the experiment.

Shashlyk Ecal

Fe/SciFi Ecal

Pb/SciFi NIM paper 1990

W/SciFi NIM paper 2009

SoLID Magnet Options (and unstudied calorimeter thoughts)(Paul Reimer)

how to run code

  • 0. get all files from
  • 1. have a standard build of geant4 and setup its environment. (I used version 4.9.3.p02 with instruction
  • 2. have compat-gcc-*-c++* package installed (I use compat-gcc-34-c++-3.4.6-20.fc14.x86_64 on my fedora 14 x64 system)
  • 3. use my version GNUmakefile to replace GNUmakefile in the individual packages because the old ones are not clean and won't work.
  • 4. go to each package and compile by "make", you shoudl have the executable in bin directory.
  • 5. use my vis.mac to replace vis.mac in the individual packages to use OpenGL viewer instead of the author suggested HepRepXML
  • 6. read the CaloSim.pdf to know more about the program.

Note from the author, Noah Schroeder (,

"I'm pretty sure Calosim1 was just a copy of calosim that i used to experiment with new things, so you should start from the basic CaloSim program. As for the lightguide and fiber sims, optimization of the lightguides was largely a separate issue from the calorimeter itself, so it was easiest to deal with that on its own. In order to do that, we needed a good simulation for the distribution of the photons coming out of each fiber, hence the fiber sim. How we did the alorimeter was just measuring the energy deposit of a shower in a given calorimeter chunk, rather than simulating the actual transit of the photons through a fiber, then to a lightguide, then to a PMT. As for putting them together, we never got that far, so i'm not sure the easiest way to go."

"As far as the geometry goes, I think those dimensions weren't of any particular significance, we weren't that close to doing full scale sims yet. As far as the 5 degree angle, The calorimeter face will be angled 5 degrees away from directly at the incoming high energy incident particles to prevent channeling, where a particle travels down a single fiber"

shower calculation

To understand shower size for Fe and W

formula refer to Eugene's calorimeter talk (p18-22)
* Critical Energy Ec = 670MeV/(Z+1.24)
* Shower width    R  = 2*X0*21MeV/Ec/d
* Shower peak     Dmax = x0*(ln(E/Ec)-0.5)/d
* Shower depth    D  = Dmax+X0*(0.08*Z+9.6)/d
    Z       X0(g/cm2)  d(g/cm3)   Ec(MeV)      R(cm)        Dmax(cm)(1.5,2.0,2.5,3.0,3.5,11GeV)     D(cm)(1.5,2.0,2.5,3.0,3.5,11GeV)
Fe  26      13.84      7.87       23           3.24         6.48 6.95 7.36 7.67 7.95 9.97           27.01 27.50 27.90 28.22 28.50 30.51
W   74      6.76       19.3       8.3          1.75         1.65 1.75 1.82 1.89 1.94 2.34           7.08  7.18  7.26  7.32  7.38  7.78
For pure material, shower R_Fe/R_W = 1.85 , Dmax_Fe/Dmax_W = about 4, D_Fe/D_W = about 3.6
For absorber/fiber sandwich, shower size should be enlarged somewhat and the ratio will shifted toward 1


resolution is taken as σE/E in fiber by gaus fit.

simulation condition:

e- beam, 1mm wide, 5 degree in XZ plane, energy 1.5,2.0,2.5,3.0,3.5GeV
Calorimeter 20cm in X (width), 10cm in Y(height), 40cm in Z(depth)
0.5mm absorber/0.5mm diameter fiber sandwich, the rest is glue. plane along Y, fiber along Z.
fiber and glue are both assumed to be scintillator BC404
field is uniform 2T along Y

more plots


preshower segmentation


if preshower has no radio segmentation, only azimuthal segmentation, we can have lightguide on side. So what's rate?


According to rate estimated in PVDIS proposal (p40, For PVDIS with baffle, pion rate is 140MHz. this gives 5MHz(200ns) in 10deg. If beam bucket interval is 2ns, we have one pion every 100 buckets.

According to rate estimted in SIDIS proposal (p49, For SIDIS, pion rate is below 3Mz, this gives 100KHz(10us)

(are they correct?)

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