Solid Forward Calorimeter
Contents
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
So can I say the list of tasks is:
1) To figure out whether the EC can be used as flux return?
what is the advantage of that? saving space for other detectors? save material?
What is the disadvantage of it? What if the simulation shwos fine and after we made all detectors and put them together with the solenoid, we find there *IS* a problem with using EC as the flux return? Will it be too late to change?
2) To simulate the size, fragmentation, and what fiber to use;
3) To buy some propotype and run some test?
Wouldn't it be fatastic if we can put the prototype in the beam and see if it works? Then put it in som estrong magnetic field (is there a place like that in the hall?) and see if the reponse is not distorted?
If we canot do thse tests before the 12 GeV shutdown, will it be possible to run the tests elsewhere?
Xiaochao
Shashlyk Ecal
Fe/SciFi Ecal
SoLID Magnet Options (and unstudied calorimeter thoughts)(Paul Reimer)
how to run code
- 0. get all files from http://hallaweb.jlab.org/12GeV/SoLID/download/ec_SciFi/
- 1. have a standard build of geant4 and setup its environment. (I used version 4.9.3.p02 with instruction http://geant4.slac.stanford.edu/installation/)
- 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 (schroe16@illinois.edu, noschroeder@gmail.com)
"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) http://www.jlab.org/div_dept/consortium/08series/calor_lect.pdf * 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
resolution is taken as σE/E in fiber.
more plots
http://www.jlab.org/~zwzhao/ec_SciFi/
geometry
preshower segmentation
question:
if preshower has no radio segmentation, only azimuthal segmentation, we can have lightguide on side. So what's rate?
answer:
According to rate estimated in PVDIS proposal (p40 http://hallaweb.jlab.org/collab/PAC/PAC34/PR-09-012-pvdis.pdf), 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 http://hallaweb.jlab.org/collab/PAC/PAC35/PR-10-006-SoLID-Transversity.pdf), For SIDIS, pion rate is below 3Mz, this gives 100KHz(10us)
(are they correct?)
