Colin Yancey

Research Progress

May 8 - 9, 2018

Jonah, James and I worked on the poster for our scintillator group to present on May 10. Here's a picture of it below. I attached a PDF version at the bottom of this page.

May 2, 2018

Before the meeting we had today, I attempted to create the tyvek covering all 5 sides of the tile. The initial results I got were terrible, mainly because I discovered very soon that all my measurements were double the length of what they needed to be. Here was my revised code for covering the sides, when I fixed the actual sizes and placed in variables for easier manipulation:

Some of the repetition in this code may be reducible, but in order to avoid errors, I made it specific to each physical rectangular prism. The front shape is given a Wireframe value of true in order to actually see the photons bouncing inside the detection zone since that is the side the simulation faces when in presentation. Here is what the simulation looks like with the wrapping:

Keep in mind that despite not being set to be visible, there is a barrier in the front represented by a wireframe covered in tyvek, so the tile + photodetector combination is completely encased in tyvek.

This is what the simulation looks like when photons are generated inside the space within the borders:

The new commands being used are shown below, which uses half length half width and half height measurements to place photons randomly within a given volume space.

Ideally, we do not want any photons being generated inside the dimple space since those technically wouldn't occur due to there not being a scintillator there, so this simulation is somewhat erroneous in the data it is producing (it had an efficiency of .2). Despite this, one of our next steps will be to remove this issue and then create a heat map to look at how uniformly the photons are being absorbed across their generation in the tile.

April 25, 2018

We talked about the tyvek issues regarding the scintillator letting too many or too little photons through. In order to prevent this from occurring, we decided that before we made the heat maps for uniform photon detection, we would create tyvek bordering on all 5 sides (maybe even on the top layer everywhere except the dimple) in order to improve photon collection by the photodetector. This will hopefully allow for better uniform detection when this is actually tested.

April 24, 2018

I got quite a bit done today. After the initial creation of the geometry last week, and based off of the conversations going on in the Slack, it was clear that Tyvek was the reason for the downfall of the simulation's efficiency. We were attempting to get a non-trivial uniform efficiency (a uniform efficiency greater than 0) since an efficiency of 0 would be relatively useless for actual results in the real world. Based on the simulation, it was apparent that practically none of the photons could escape the geometry, but when the tyvek wrapping was removed, they could. The code below is the arbiter of whether the tyvek was on or off of the geometry, which was covering the entire constructive solid geometry (CSG) model of the tile with the impression.

Basically, if wrapping_toggle was on, the entire tile would be wrapped in tyvek. Once wrapping_toggle was turned off, the resulting simulation, with the wrapper being the air (or just the surrounding "physical world surface"), looked like this:

Now, clearly the photons are not very present in this image. 100 photons were simulated, but only four lines of photons are actually visible in this simulation. This is because there was a .96 efficiency, or 96 of the 100 photons were absorbed by the photodetector in front of the tile. This is versus the efficiency of 1 beforehand when the photons were generated in the same position and the tyvek was on, as every single photon was bouncing off the tyvek-coated material straight into the photodetector given that the impression is 2 mm deep and the tile is 4 mm in width, such that the photons being generated at 0, 0, 0 were painting the edge between the dimple's inside and outside positioning. Another major factor to consider is the initial direction of these photons. All photons being generated appear to be moving in the position width direction of the tile. This, I realized, was due to the direction 0 0 0 having a default along the width direction. In order to fix this, I used the iso command for direction which generated photons uniformly across all angular directions. This was the new command set:

Using iso, a lack of tyvek, and the new position that was 2/3 of the way from the center to the edge given that the tile is 3 cm by 3 cm, this was the new simulation result:

While the new simulation may look a bit crazier, this yielded an efficiency of .01, which meant that one of the one hundred generated photons actually hit the photodetector. Clearly, based on the simulation, the photons are now able to escape the tile while also still bouncing around if at angles parallel enough with the tile borders. We do not necessarily want the photons to be escaping if they exit through any area of the tile except the dimple, so may not yet be what the goal is, but it is progress towards what we want. Shown below are two other simulations of the same nature using the same commands, just with different photon origins.

5mm * 5 mm photon origin away from center, .04 efficiency

2 mm * 2 mm photon origin away from center, .09 efficiency

April 18, 2018

I built the tile impression after some tinkering and manipulating the events. The first try I had was using a sphere and placing it some distance away in order to create the subtraction necessary. However, this was unnecessarily complicated given that Geant has an ellipsoid geometry that I just have to reference in the includes at the top of the file which is must easier to implement in the tile impression. This is what I now have as my tile impression code:

This geometry led to the resulting simulation when run with photons:

The yellow lines coming from the sides are (as far as we can tell) just used by Geant4 to make the connections to the circle for triangular approximations of an actual ellipsoid since geometries by computers aren't actually perfectly spherical ellipsoids, so this is the approximation that is likely used to generate them. From what we notice, they seem to have no impact on the simulation and are just used to make sure the dimple is correctly shaped. The photons are still being generated from the base of the detector and sent directly upwards.

April 16, 2018

I looked over some of the background into actual geometric constructions for such a detector as I was not previously exposed to actually manipulating the geometry. This was a useful picture in helping me understand how the geometry actually was given its dimensions and properties.

Basically, the G4VSolid* type is what gives the actual geometry to its respective value. In this case, G4Box is being used, so a box with a half length of 1 meter, half width of 2 meters, and a half height of 3 meters is being constructed. G4LogicalVolume* then takes the G4VSolid* object and uses it give it a material as well as preparing it to be placed as a physical volume. The actual physical volume is then placed in the Geant4 "world" with G4VPhysicalVolume*, which under a specific mother volume decided earlier called pMotherLog. The physical volume also contains a G4ThreeVector which is used to position the object, in this case at the origin with a rotation given by pRotation. Any sort of geometry can be used, and I found http://geant4.cern.ch/G4UsersDocuments/UsersGuides/ForApplicationDeveloper/html/Detector/geometry.html to be useful in exploring the different geometries available.

April 10, 2018

With the actual files now available, I ran the initial simulation using ./LYSim and ran some photons to see what the tile currently looked like. This was the result:

Dr. Eno and Dr. Belloni requested that we remove the fiber in order to actually do the dimple simulation, so this was removed alongside the mirror (which was apparently part of the fiber used to reflect photons back in the correct direction).

As a result of deleting the fiber, the photodetector seemed to default to jumping to the center of the tile. I'm not sure if this is because of some sort of positional dependency on the fiber, but regardless, this will have to be changed since Geant4 is not going to like the awkward geometry, and seems to already be acting up as there appears to be an origin of photon generation that wasn't there before in the set up. Also, the fiber's existence for some reason made the photons red, and now they are green. Hopefully this isn't an issue.

March 28, 2018

Now that Spring Break is over, we got back to working on the project, but since it's already nearing the end of March, we thought it best to begin working on the actual code that will be relevant to the dimple geometry given that it may take awhile to figure out which geometry is best. These are the new files we are working with, which is a much more extensive library of code. The actual code is under UMDSRDGEStudy-Utils/src, build will just be the area where the events will actually need to take place since all the code in the src is manipulating the ./LYSim command in build. These files were cloned over from a repository available online at https://github.com/saraheno/AlanHorstGEANTTile

The first thing I noticed was how gruelingly long it took to run photontest.mac, and this was because it was attempting to run 100,000 photon events, something that would take half an hour to an hour. Because of this, I attempted to use condor to fix this issue.

Despite changing the pathing, it appeared to not work, so I will likely not be focusing on this and just make the event count smaller for now given that we are just testing the design. Condor may come in handy later though when we are testing uniformity of the photon detection.

March 18, 2018

In order to do the pion event, I had to readjust the geometry, but I only ended up running 5 events with 10 particles. This was likely not enough.This meant that my respective Eabs was low on data (energy absorbed histogram). This is what the event looks like below, which despite looking chaotic, is only the result of a few pions going through the scintillator-detector combo.

The event shown above gave the results here, which in the actual project may be data relevant to getting the uncertainty in our simulated measurements.

...and this was the Eabs, again not too impressive due to the low pion count despite the chaotic visualization. The reason the events are not uniform is because the actual geometry of the detector was still not thick enough to make the events more uniform, which they should have been if the pion was having its energy completely or mostly lost to the detector by passing through it (which would be what we want). Thus, we will probably have to make it thicker.

March 16, 2018

Condor successfully implemented and integrated for running software other than just the test file provided, will attempt to use later with the actual project implementation. Hopefully this will help us run multiple processes at once across multiple threads without getting our jobs cancelled on the cluster.

March 10, 2018

I attempted to get condor set up, placing it in the following repository and running it like this:

Unfortunately, as seen above, this first attempt was not successful because some of the new pathings were out of place due to retrieving this from Dr. Eno's software under her space in the cluster. After changing all of the directories carefully, I successfully got it working.

March 6, 2018

I finally simulated the question 2 graphs correctly, and these were the graphs I got. The actual event visual is not too interesting due to it being a massive culmination of a bunch of photons with little to no intelligible direction in pathing.

February 26, 2018

I looked over documents pertaining to the CMS detector upgrade, specifically dealing with the actual scintillation involved. The entire purpose of our project is to simulate uniform scintillation across a dimple-geometry based scintillator, so it is good to have a background pertaining to what is actually planned for the future CMS detector. The reason for this upgrade is to allow for higher-energy events, which will require improved logistics throughout the systems involved. This has been planned since its initial construction, which involves reducing the timing between bunches of events to 25 nanoseconds in order to allow for more data to be produced. As a result, there will have to be better methods to quickly sift through the data and figure out which parts are relevant to particle physicists, which is an area of major debate between departments looking for different signals for their proposed particle models.

Diagram above details the actual luminosity plans of the HL-LHC over the next 20 years or so as well as progress that has been made so far. We are on track to more than double the peak luminosity by 2025.

Increased degradation of detector is expected because of increased radiation exposure; means of reducing this damage are being looked into over the next few years in order to prevent major damage from occurring which could affect results if allowed to happen.

This picture shows the calorimeter radiation damage as distributed over the 2D surface. The scintillator tiles are expecting a dosage up to 300 kGy. The detector will have to improve its ability to distinguish between events given that the event frequency will be approximately doubled.

February 20, 2018

I continued work on the Geant tutorial, accessing histogram files utilizing the TBrowser new command. The one shown below is a result of the particle count (for electrons this time) being raised to 1000, which is why there are 1000 events in the histogram below.

I also spent some time looking through the multiple files downloaded from the origin of the cloned Geant data.

The actual 1000 electron simulation was run using this code:

....and this was the result! Not too informative, will likely be disabling these visuals in the future since they do not provide much utility for current tutorial activities.

February 19, 2018

I read through "Optimizations of light-collection efficiency and uniformity for liquid-scintillator tiles" (https://github.com/ZishuoYang/GEANT4-ScintillatorTile/blob/master/CMS_DN2015_009.pdf) and briefly summarized the key points. I have included a copy of this summary below.

• Radiation-hard scintillators are highly desirable to have a long life time while maintaining a good signal; liquid scintillators are a promising candidate

February 12, 2018

I was contacted by Dr. Eno about the issue with the code and she replied that the code likely needed a little updating before running it again. She posted revised code for me to try on Putty on Slack and told me for the future to use Slack's @ system in order to gain attention for issues more quickly so that the correct people are notified. I have included the revised code below for the GEANT4 trial run of the tutorial:

mkdir junk

cd junk

cp /data/users/eno/StandAlone/PFCal/PFCalEE/g4env.csh .

source g4env.csh

cp -r /data/users/eno/geant4.9.6.p04/examples/basic/B4/B4a .

mkdir B4-build

cd B4-build

cmake -DGeant4_DIR=$G4LIB ../B4a

make

./exampleB4a 

/tracking/verbose 1

/run/beamOn 1

exit

February 8, 2018

I continued from where I started on February 7th in terms of progress on the Geant4 Tutorial (https://sites.google.com/a/physics.umd.edu/physhonr268n/tutorials/geant4tutorial), but ran in to trouble immediately after cloning the repository when attempting to run source G4_setup.sh. It was unable to find the path necessary to set these specific preparatory procedures, so I contacted Dr. Eno in order to know how to proceed despite the error I received.

February 7, 2018

I talked with Dr. Eno alongside James and Jonah. We were given a brief introduction to plastic scintillators and the mechanics behind them, such as how they are used to create detectable events (photons/light from energetic particles). I asked about the specific interactions of a "collision" since the term has always seemed nebulous to me, and it was explained as just an exchange of photons between particles moving at different velocities in close proximity. We discussed what we had completed so far, which namely was just reading the articles given to us by Dr. Eno last week and attempting to understand them. I asked Dr. Eno about this graph in particular, which came from the first link listed for January 31, 2018 (Figure 27.8). She explained that the graph is demonstrating an initial change in mean energy loss range for lower energy states that are generally correlated with the silicon's thickness, but as the mean energy loss rate increases, the thickness matters less because the higher energy loss is likely due to direct impacts with silicon atoms in the material unlike the lower energy "collisions" which were not head-on, and therefore led to less energy loss.

I joined the group's Slack, which will allow us to easily communicate while also giving Dr. Eno the opportunity to provide important information to us easily without needing to go through email. From this, I obtained the link to the HONR Physics GEANT4 Tutorial (https://sites.google.com/a/physics.umd.edu/physhonr268n/tutorials/geant4tutorial), and began following the steps to get the GEANT4 software set up on my computer as its own repository. So far I've only cloned the repository for the sample, but ideally, this will be a useful library of tools to create the eventual simulation.

February 6, 2018

I continued my research into plastic scintillators, reading the remaining portions of information. Interesting notes include the fact that scintillators are somewhere around 3-15% efficient in terms of light energy that is actually recordable as a result of energetic loss through a scintillator (of the available energy).

February 1, 2018

I began reading through the first article sections as well as the second article section. They discuss the properties and aspects of plastic scintillators at such a high level of depth to the point where much of it is difficult to follow. I may require more lower-level background reading to fully understand what is going on.

January 31, 2018

I spoke with Dr. Sarah Eno and Dr. Alberto Belloni about potential projects that may be feasible for the Spring semester, and was given two options. One was about identifying ideal geometries of an impression in a structure to allow for a photodetector apparatus to obtain the most data available from incoming particles and their subsequent light emission when interacting with the structure. This project was identified as the more feasible one when compared to the other option, involving the detection of dark matter. This project would have been focusing on work that would revolve around theories of how dark matter may be detected in a high-energy interaction, with potentially dark matter particles being part of the resulting decays in energy. Unfortunately, many students in the past who have participated in this project have made "glacial progress" likely due to the depth of physics involved for an undergraduate, as well as the added complications of dealing with these highly theoretical models. I decided to go with the first project, and Dr. Eno sent readings as well as instructions to pursue a set-up as CMS users. The readings identified have been listed below and pertain to the selected first project.

http://pdg.lbl.gov/2011/reviews/rpp2011-rev-passage-particles-matter.pdf, Sections 27.2.1, 27.2.2, 27.2.7, 27.2.8

https://docs.google.com/file/d/0B_Ce2ncoxFYka2V5US1MR2xvbXM/, Chapter 8, Section 1

http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=04437293&tag=1

https://cds.cern.ch/record/2020886/files/LHCC-P-008.pdf Chapter 3.5.1, 3.5.9

https://sites.google.com/a/physics.umd.edu/physhonr268n/tutorials/geant4tutorial

January 25, 2018

I began looking into dark matter-based conclusions and theories in order to have a better grasp of the phenomenon when group work begins with our assigned projects/mentors.

- References -

http://releases.jhu.edu/2016/06/15/did-gravitational-wave-detector-find-dark-matter/

Informal Posts

Casually describes aspects of dark matter and a particular physicist's recent take on how a relationship between it and dark energy (spatial acceleration) may bear utility

https://arstechnica.com/features/2017/05/emergent-gravity-and-dark-matter-explained-by-excited-universe/

NASA post, also describing ideas of dark matter and dark energy

https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/