Identifying, Analyzing, and Using Discriminatory Variables for Classification of Neutrino Signal and Background Noise in Multivariate Analysis in the Askaryan Radio Array Experiment

Jesse Osborn Author

04/05/2021 Added

12 Plays

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Developing a noise filter for data in the Askaryan Radio Array Experiment by developing discriminatory variables based on the physical characteristics of the data.

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[00:00:01.940]Hi, my name is Jesse Osborn.
[00:00:03.990]And today I'm gonna be talking about my UCARE project,
[00:00:07.050]Identifying, Analyzing and Using Discriminatory Variables
[00:00:12.820]for Classification of Neutrino Signal
[00:00:15.190]and Background Noise and Multivariate Analysis
[00:00:17.570]in the Akaryan Radio Array Experiment.
[00:00:21.320]So the Askaryan Radio Array experiment
[00:00:23.750]is a neutrino detector built near the South Pole,
[00:00:28.640]which operates by trying to record radio wave signals
[00:00:35.110]that occur when high energy neutrinos come from outer space
[00:00:38.480]and interact with ice molecules at the South Pole.
[00:00:41.900]So the experiment is made up of five stations.
[00:00:46.380]Each of which has 16 radio wave antennas
[00:00:49.730]buried about 200 meters deep into the ice.
[00:00:53.860]So the Askryan Radio Array experiment or ARA for short,
[00:00:56.960]records, millions of events per year but only a handful
[00:01:02.180]of these events are expected to come from actual neutrinos
[00:01:06.250]from outer space that the experiment is trying to analyze.
[00:01:11.240]The rest of them are expected to come from background noise,
[00:01:16.910]from the instrumentation, electronics or construction
[00:01:20.560]going on at the South Pole, that sort of thing.
[00:01:24.000]So my goal with this research was to eliminate
[00:01:27.790]some of this background noise.
[00:01:29.810]Now, there currently exists three filters for the experiment
[00:01:34.450]that already work to get rid of background noise,
[00:01:37.490]based off of the physical characteristics
[00:01:40.510]of a actual neutrino signal that we're trying to measure.
[00:01:44.390]So the first filter is the hit filter
[00:01:47.620]which just requires that four of the 16 antennas
[00:01:50.800]for a given station record something for a given event.
[00:01:56.560]The second filter is the time sequence filter
[00:01:59.460]which just says these hits that these antennas
[00:02:02.640]are recording come in an order that resembles a planar wave
[00:02:08.580]moving across the antennas from a single point source.
[00:02:13.110]So wherever a neutrino would have interacted
[00:02:15.310]with an ice molecule.
[00:02:17.770]And the third filter is the arrival angle filter
[00:02:21.140]which restricts the stations to only recording stuff
[00:02:25.110]that comes from within the ice and not from above the ice.
[00:02:30.460]So these three filters get rid of about 99% of all the data
[00:02:39.180]that a given station might record for a single year.
[00:02:42.810]And for this particular experiment
[00:02:44.890]or for my particular research, I worked with 10% of the data
[00:02:49.770]taken by a single station for a given year
[00:02:52.590]which was about 10,400,000 events.
[00:02:55.730]And after these three filters had done their work
[00:02:58.610]on that number of events, we're down to about 2,700 events
[00:03:03.490]which I am taking for what I'm talking about today
[00:03:06.870]to be a background sample of events.
[00:03:09.980]And I'm comparing these background events
[00:03:13.470]because almost none of these are expected
[00:03:15.870]to be actual neutrino events with simulated neutrino events
[00:03:20.750]from a particular software package
[00:03:22.530]that another student developed.
[00:03:24.610]And I'm trying to draw distinctions
[00:03:27.530]between these two sets of events so I can get rid
[00:03:30.330]of all the remaining background events.
[00:03:34.720]So in particular, here's an example of an event
[00:03:38.750]that made it through all three of the existing filters.
[00:03:42.270]And here's an example of a simulated neutrino signal event.
[00:03:46.560]So, you know, looking at these two you can see
[00:03:48.790]there are a lot of fiscal characteristics
[00:03:51.240]that are different between them.
[00:03:53.550]And my goal was to try and build a collection of variables
[00:03:59.620]that can discriminate between these two different sets
[00:04:02.730]of data and plug these variables into a what's called TMVA
[00:04:08.370]which is just a computer algorithm that can take a bunch
[00:04:12.610]of input variables and turn them
[00:04:14.370]into a single output variable that's very good
[00:04:17.550]for distinguishing between actual signal
[00:04:21.040]and background noise.
[00:04:23.160]And then I wanted to see if discrimination
[00:04:26.010]on this new variable could be effectively used
[00:04:28.890]for a new filter for the ARA data.
[00:04:33.940]So for my research, instead of working directly
[00:04:38.250]with the radio wave forms as they exist,
[00:04:42.950]I would run an envelope over the wave forms
[00:04:45.960]which is defined up here in the top right.
[00:04:49.220]Just taking the data points and sort of smoothing them out
[00:04:52.390]and making them all positive as you can see here
[00:04:54.840]in this figure.
[00:04:56.260]And then by breaking the wave form up
[00:04:58.080]into four different quadrants and using
[00:05:00.650]the two smallest quadrants, which would be green
[00:05:04.090]and orange here, we can define a threshold level
[00:05:09.330]for interesting stuff in the wave form as I'll call it.
[00:05:14.190]So, as an example of this on an actual wave form,
[00:05:18.260]you can see here in red is an envelope that's been drawn
[00:05:21.560]and a line has been drawn at the level
[00:05:23.580]of what I call a threshold.
[00:05:26.090]And anything above this threshold is something interesting
[00:05:29.100]in the wave form that I wanna look at.
[00:05:31.860]So using this definition, I developed a bunch of variables
[00:05:36.850]some of which you can see here,
[00:05:39.770]and calculated these variables for both signal
[00:05:43.420]and background events to create these
[00:05:46.060]different distributions of the variables and their values
[00:05:50.610]for the two different samples,
[00:05:52.820]blue being the signal and red being the background samples.
[00:05:56.470]And you can see from these different plots
[00:05:58.550]that some of them have more or less disagreement
[00:06:03.550]between signal and background samples.
[00:06:06.810]But by using this TMVA computer algorithm,
[00:06:10.870]I can merge all of this information together
[00:06:13.930]into one very effective variable
[00:06:19.020]that I can use for discrimination.
[00:06:21.890]Here are some of the other variables that I worked with.
[00:06:24.960]So by taking all of these different distributions
[00:06:30.450]and plugging them into a computer algorithm,
[00:06:32.780]I can develop a single output variable which is seen here.
[00:06:37.840]Again with the background in red and the signal in blue.
[00:06:41.350]And here you can see there's a much wider separation
[00:06:44.720]between the two samples.
[00:06:46.440]So any simple restriction on this variable,
[00:06:49.920]say you want your events to have this variable
[00:06:55.500]be greater than zero, then you could cut all
[00:06:58.110]of this background in red over here on the left of the plot
[00:07:01.250]and keep what appears to be all of your signal in blue
[00:07:04.530]on the right of the plot.
[00:07:06.500]And to just quantify this a bit further,
[00:07:09.400]if you did perform these linear cuts
[00:07:12.390]on this distribution plot, you would see
[00:07:16.820]at one particular value, if you were willing to give up 4.9%
[00:07:22.000]of your total signal, you could remove upwards of 99.75%
[00:07:27.420]of all the background events.
[00:07:29.640]So it appears that by building a bunch of variables
[00:07:37.040]on individual wave forms for background and signal
[00:07:40.600]and plotting the distributions of these variables
[00:07:43.490]for a signal sample and a background sample,
[00:07:46.220]we can merge all these distributions into one
[00:07:49.310]very efficient variable to cut out a lot of background noise
[00:07:54.350]while keeping all of our good neutrino signal.
[00:07:58.590]So in essence, this was my research project for ARA.
[00:08:05.050]ARA already has three filters that have been developed
[00:08:07.710]to get rid of background noise,
[00:08:09.720]and they've done a lot of work,
[00:08:11.860]but there's still quite a bit of work left to be done.
[00:08:15.840]So I developed some discrimination variables
[00:08:18.550]and by using all of these variables
[00:08:21.210]and merging them together with a computer algorithm,
[00:08:25.280]I was able to create a single highly efficient variable
[00:08:30.950]for background rejection, greater than 90%
[00:08:34.690]background rejection in the samples that I looked at.
[00:08:39.230]And my hopes going forward are to develop this process
[00:08:44.410]into a fourth data filter for the ARA experiment.
[00:08:49.890]So I would like to thank my advisor, Dr. Ilya Kravchenko,
[00:08:53.640]who I've worked with for the past three years.
[00:08:57.810]I'd also like to thank you UCARE
[00:08:59.200]for funding all of this research.
[00:09:01.200]I'd like to thank a former UNL student Andrew Schultz,
[00:09:03.970]who helped develop some of the software for this project.
[00:09:07.080]And I'd also like to thank the ARA collaboration
[00:09:10.230]and the UNL Physics Department's High Energy Group
[00:09:13.020]for giving me valuable feedback
[00:09:15.520]during this research project.

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Identifying, Analyzing, and Using Discriminatory Variables for Classification of Neutrino Signal and Background Noise in Multivariate Analysis in the Askaryan Radio Array Experiment

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