This code does Geometric Reconstruction (GR) in npsim simulations of the ePIC hpDIRC. It is a standalone code that compiles and runs outside the eic-shell, after you've produced simulation rootfiles inside the shell. The code reads two TTrees, keeps them in sync, and loops through them to calculate thetaC (mrad) for every particle incident on hpDIRC bars. This code was developed to explore the hpDIRC PID performance and to inform about viable approaches for doing this same reconstruction inside eicrecon soon.

Once you have a working eic-shell, first install ddDircAction, the stepping action plugin that writes the "incidence tree." To compile ddDircAction:

cd eic
git clone git@github.com:eic/ddDircAction.git
cd ddDircAction
mkdir build install
#---- !!! inside eic-shell !!!
cmake -B build -S . -DCMAKE_INSTALL_PREFIX=install -DCMAKE_C_COMPILER=/usr/bin/cc -DCMAKE_CXX_COMPILER=/usr/bin/g++
cmake --build build -- install
cd .. 

Make sure that the ddDircAction location is added to LD_LIBRARY_PATH (update the path used to match your case):

export LD_LIBRARY_PATH=/Users/wjllope/eic/ddDircAction/install/lib:${LD_LIBRARY_PATH}

This line should be added to your local mysetup script.

To install dircGR:

cd ~/eic
git clone git@github.com:eic/dircGR.git
cd build
#---- !!! outside eic-shell !!!
cmake ..
cmake --build .

This will install the folder "dircGR" inside your "eic" subdirectory, and build the application "ddircGR_app" which will be found in ~/eic/dircGR/run/ when cmake completes.

Once the app is built, change directories to ../run/

You will notice the subdirectory named "LUT" there! Inside it are the ten look-up tables for the ten bars in each bar box. There is thus no need for you to generate LUTs. If you would like to do this anyway though, some helper files are also in dircGR/run, feel free to contact me for additional details.

Simulations are done inside the eic-shell, and we will run dircGR on the output of those outside the shell. One mode to run npsim is the "gun", where single particles with specific momenta and direction can be fired from the vertex.

You may need to install and build the epic geometry:

cd eic
git clone git@github.com:eic/epic.git
cd epic
mkdir build install
#---- !!! inside eic-shell !!!
cmake -B build -S . -DCMAKE_INSTALL_PREFIX=install
cmake --build build -- install
cd ..
source install/bin/thisepic.sh

Let's throw 3 GeV pions at a polar angle of 70 degrees. The azimuthal angle is chosen for this polar angle and momentum so that the particles strike the center (in azimuth) of bar "5", one of the "middle" bars in each bar box. For convenience in the subsequent steps, i am running npsim from within the dircGR/run/ directory:

cd dircGR/run
#---- !!! inside eic-shell !!!
npsim.py --runType batch \
--printLevel WARNING \
--action.step '{"name":"ddDIRCactionStep","parameter":{"OutputBase":"sim_dirconly_500evt_pi+3GeV70deg.incidence", "fileNumber":1, "DetailLevel":1}}' \
--compactFile $DETECTOR_PATH/epic.xml -G -N 500 --gun.particle "pi+" \
--gun.momentumMin 3*GeV --gun.momentumMax 3*GeV --gun.phiMin 354.73*deg --gun.phiMax 354.73*deg \
--gun.thetaMin 70*deg --gun.thetaMax 70*deg --gun.distribution uniform --gun.position 0*cm,0*cm,0*cm \
--outputFile sim_dirconly_500evt_pi+3GeV70deg.edm4hep.root

This will take a few minutes to complete. When it does, you should see these files in this same directory:

 24351777 Aug  7 14:57 sim_dirconly_500evt_pi+3GeV70deg.edm4hep.root
   529160 Aug  7 14:57 sim_dirconly_500evt_pi+3GeV70deg.incidence.root

Note these files have the same basename, and the extensions 'edm4hep.root' for the standard npsim output (large file) and 'incidence.root' for the charged particle incidence information (small file).

To do the PID, you then run the *.edm4hep.root file through dircGR.

#---- !!! outside eic-shell !!!
./dircGR_app sim_dirconly_500evt_pi+3GeV70deg.edm4hep.root epic

You will now see two new files in this same directory:

sim_dirconly_500evt_pi+3GeV70deg.gr.pdf
sim_dirconly_500evt_pi+3GeV70deg.gr.root

Note the basename is the same, and the extensions are ".gr.(pdf/root)".

Pick any existing event file (these have the extension hepmc3.tree.root), and put it into eic/dircGR/run. Run npsim using this file as input, and remove all the gun commands, for example:

#---- !!! inside eic-shell !!!
time npsim -N 5000 --runType batch --printLevel WARNING \
--action.step '{"name":"ddDIRCactionStep","parameter":{"OutputBase":"dis_eicBeam_hiDiv_18x275_1to10.incidence", "fileNumber":1, "DetailLevel":1}}' \
--inputFiles dis_eicBeam_hiDiv_18x275_1to10.hepmc3.tree.root \
--compactFile $DETECTOR_PATH/epic.xml \
--outputFile dis_eicBeam_hiDiv_18x275_1to10.edm4hep.root

and this will create two files:

dis_eicBeam_hiDiv_18x275_1to10.edm4hep.root
dis_eicBeam_hiDiv_18x275_1to10.incidence.root

and you can then run these through dircGR via:

#---- !!! outside eic-shell !!!
./dircGR_app dis_eicBeam_hiDiv_18x275_1to10.edm4hep.root epic

which will create:

dis_eicBeam_hiDiv_18x275_1to10.gr.pdf
dis_eicBeam_hiDiv_18x275_1to10.gr.root

The TH2D histogram hthetaC_ptot provides a decent overview of the PID performance by plotting the Cherenkov angle (in mrad) versus the track momentum, for all particles striking any hpDIRC bar anywhere along its length. The appropriate LUT is used for each bar-incident particle; 20M OPs were used to calculate each LUT. Tight timing cuts (~1ns wide) and OP polar angle cuts are implemented as a function of the Z-position of the incidence. The OP polar angles of prism paths are also required to be consistent with the allowed range of polar angles for hit-producing OPs created at this Z-position. Chromatic corrections are applied. The thetaC resolution in the present code is approximately 4-6 mrad, which is close to expectations. Some additional improvements to the chromatic corrections is likely possible.