protodune-sp electron lifetime & drift time analysis · 3 protodune-sp electron lifetime &...

ProtoDUNE-SP Electron Lifetime & Drift Time Analysis

Justin Hugon

Louisiana State University

ProtoDUNE Sim/Reco Meeting

2018-08-15

Justin HugonLouisiana State UniversityProtoDUNE-SP Electron Lifetime & Drift Time2 Justin Hugon


Argon Purity & Electron Lifetime● Argon purity very important in LArTPCs

● Impurities catch electrons before they can drift to the anode readout plane● Extreme case: too little charge

makes it to anode to be reconstructed!

● We need to measure the purity of the argon to tell how much charge was lost

● Commercial purity monitors don’t have enough dynamic range, so we use the TPC

Drift TimeC

harg

e Good Purity

Bad Purity



Measuring Electron Lifetime

Bruce Baller wrote some code to extract electron lifetime

● Works even if lifetime is so bad you can’t reconstruct hits near the cathode

● Just fit ln(Q) versus t

Bruce’s talks:

Q=Q0exp(−t−t 0τ )

ln (Q)=ln (Q0)−t−t0

τ

ln (Q)=−t / τ+ConstantMeasured charge: Q

Charge before drift: Q0

Charge measurement time: t

Charge deposition time: t0

Electron lifetime: τ

https://indico.fnal.gov/event/14678/contribution/3/material/slides/0.pdf






Detailed Method & Selection

For each cluster:● Bin hits in 100 us wide bins

● Find the mean charge in each bin

● Find the truncated mean charge and drift time in each bin

● Fit ln(charge) versus drift time for the cluster to get electron lifetime estimate

● Use standard lineclusters● Only look at clusters with:

Drift time span >= 400 us

Number of hits >= 100● Only look at hits with charge between 0 & 10000

● Truncate to between 0.5 and 1.3 times mean charge

● Only use bin if it has 3 or more hits● Require histogram to have at least 5 bins with at least 4 hits

● Require the cluster lifetime estimate to be > 0

● Require cluster lifetime fit:● Chi2/NDF < 5



Out of the Box Electron Lifetime Results

● For the 3 ms electron lifetime datasets with and without space charge effect:

mcc10_protodune_beam_p2GeV_cosmics_3ms_(sce_)mcc10.0

● Using dunetpc v06_80_00 and the linecluster reconstruction from the MC production

● The electron lifetime is measured to be● 2.81 ± 0.027 ms for space charge effect● 2.46 ± 0.022 ms without space charge effect

● This is too low, just as Bruce found a year ago



Cathode to Anode or Anode to Cathode?

● Bruce thought the too low lifetime may be due to differences in how cathode to anode and anode to cathode tracks deposit energy

● Tagging direction using truth info, there doesn’t seem to be a difference



Cluster Reconstruction Quality

● Can match cluster hits back to sim::IDEs to truth particles to check how well reconstructed

● Almost all clusters only from one particle

● “Charge Efficiency” shows fraction of particle charge reconstructed & put in the cluster

● Electron lifetime consistent between high and low efficiency clusters



Look at Charge v. Drift Time in MC

● The next slides show example clusters from MCC10 with SCE

● These are all clusters we tried to analyze● The analyzer does some selection on goodness of fit, but I’m including all clusters here



Example Cluster

Lifetime fit looks fairly good

Black: Hits

Red: Not truncated mean +/- truncation region

Blue: Truncated mean +/- error on mean

Green: Lifetime Fit



Example Cluster

Lifetime fit looks good

Black: Hits



Green: Lifetime Fit



Example Cluster

Lifetime fit looks good besides the low outlier

Black: Hits



Green: Lifetime Fit



Example Cluster

Lifetime fit looks fairly good

Black: Hits



Green: Lifetime Fit



Example Cluster

This one had a lifetime < 0, so wasn’t included

Black: Hits



Green: Lifetime Fit



Example Cluster

Lifetime fit looks pretty good

Black: Hits



Green: Lifetime Fit



Fit Quality

● Those fits didn’t look stellar, but also not horrible either

● Chi2/NDF seems good, most < 2

● It seems like many of the plots had fewer histogram bins, maybe it would be interesting to look at the lifetime v. number of bins



Example Cluster

Clear dependence on both N hits

maybe N bins too



Toy Study of Lifetime Method

● Generate Landau distributed points with MPV=300 charge

● Hit time = evenly spaced within bins

● Reduce the charge assuming 3 ms lifetime

● Estimate the electron lifetime just like in analyzer

Magenta: True MPV*exp(-t/τ)

Black: Hits

Red: Not truncated mean


Green: Lifetime Fit



Toy Lifetime: Varying N Bins and Hits/Bin

● Lifetime depends on number of bins and hits/bin

● Low stats bins and low N bins seem to bias things

● Could fit a Landau instead of just truncated mean in each bin

● Also require clusters with lots of bins and hits/bin

Blue: Fitted cluster lifetimes

Green: True lifetime



Drift Time Monitoring

● Monitoring how long it takes for an electron to drift from the cathode to anode can help monitor the electric field and SCE

● Looking at the max – min time for each cluster should give an endpoint at the drift time

● There is a spike at the correct value: 2.25 ms

● There are some spurious clusters with larger times



Fine-grain Drift Time Monitoring

● It may take quite some events (or a CRT trigger) to reliably monitor the drift time per TPC

● What do we want this monitoring to look like?● Histograms for various

positions?

● Estimate the endpoint and report a number?



Conclusions & Next Steps

● Have a module to estimate electron lifetime● Estimate is too low, may be due to bias in taking mean of Landau distribution

● Drift time easy to monitor, but takes quite a few events to monitor well● Hopefully the CRT and halo muons will help

● Next steps:● Look into other methods of fitting the cluster lifetime

(fit Landaus, fit charge ratio versus delta t, unbinned fit)

● Refine drift time histograms and estimates



Backup Slides



Angular Dependence

Not much of an angular dependence



Cutting on Number of Hits

Cutting on N Hits is a smaller effect than in the toy study, maybe other correlations among cosmics?



SCE and No SCE

SCE widens the distribution, and the peak is at a little higher electron lifetime



Toy Lifetimes: Landau Distributed Charge



Toy Lifetimes: Gaussian Distributed Charge



Toy Lifetimes: Landau Distributed Charge—Mean of Log(Charge)



Toy Lifetimes: Gaussian Distributed Charge—Mean of Log(Charge)

protodune-sp electron lifetime & drift time analysis · 3 protodune-sp electron lifetime &...

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