Raw hit finding for dual phase Christoph Alt July 12 th , 2017 / - - PowerPoint PPT Presentation

Raw hit finding for dual phase

Christoph Alt July 12th, 2017 / protoDUNEs sim & reco meeting

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Overview

Raw hit finding for dual phase is ready to use:

• 1. Explaining the algorithm and the fcl parameters
• 2. Plans for further improvements
• 3. Where to find the code and .fcl’s
• 4. Performance check

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Explaining the algorithm

Goal: develop a hit finding algorithm for raw waveforms Data preparation: remove pedestal no deconvolution no noise filtering (for now) → In this presentation: white noise with RMS = 2.4 ADC total gain of 20 (= 10 per channel) Algorithm can be divided into 5 steps:

• 1. Peak finding
• 2. Peak grouping and merging and noise peak removal
• 3. Fitting
• 4. Re-fitting
• 5. Create a hit

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• 1. Peak finding
• 1. Find bin with highest ADC count above MinSig (8 ADC)
• 2. Define tini and tfin: walk along time axis until:

a bin with ADC 0 is found

• r a bin followed by TicksToStopPeakFinder consecutive bins

with same/higher ADC count is found (default for TicksToStopPeakFinder is 4, which is the rise time of elec. response function)

• 3. Repeat step 1 and 2 for remaining region

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2.1 Peak grouping

Group nearby peaks (...to fit the group instead of single peaks) if no bin with ADC 0 is found between the peaks and if distance between the peaks GroupMaxDistance (5) (this is mainly to catch low frequency noise which can ”connect” two seperated hits) and if number of peaks in this group MaxMultiHit (6) (fitting long multi peaks is slow, ∽1s for 10 peaks, growing exponentially) example below: grouped the two peaks on the left, but not the one

• n the right

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2.2 Peak merging

example below: one peak misidentified as two peaks due to noise Solution: merge two peaks of a group into one peak before fitting if DoMergePeaks = true and if ADC sum peak 2 < MergeADCSumThreshold · ADC sum peak 1 and if height peak 2 < MergeMaxADCThreshold · height peak 1 → This reduces fake noise peaks in the tails of the waveform default values for both parameters: 0.2

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2.3 Removing noise peaks

Want to get rid of noise peaks before fitting (see example below) Do not fit and remove peak if the width of a single peak/group of peaks is < MinWidth (10)

• r if ADC sum over width of this single peak/group of peaks is <

MinADCSumOverWidth (4.8 = 2·noise RMS) → MinWidth shouldn’t be larger than the width of elec. response (≈ 20 ticks) and MinADCSumOverWidth should scale with noise RMS

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3.1 Fitting: single peak

Fit single peak from tini to tfin (inclusive):

fit function f (t) = A ·

e

t−t0 τ1

1+e

t−t0 τ2

t0: seed = tmax - 2 ticks, limit: seed ± 5 ticks A: seed = 1.65·maxADC, limit: 0.1·seed to 2·seed

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3.2 fitting: grouped peaks

Perform single fit for a group of peaks (black) Each summand of the fit function corresponds to a single peak (blue) τ1 and τ2 are identical for all peaks, amplitude and mean vary seeds same as for single peaks, ranges for t0,i do not overlap

fit function f (t) =

• i Ai ·

e

t−t0,i τ1

1+e

t−t0,i τ2

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• 4. Re-fitting: check requirements

Why re-fitting? Two overlapping peaks misidentified as one: ⇓ re-fit ⇓ Do re-fit if TryNplus1Fits = true and χ2/NDF > Chi2NDFRetry (25) and number of peaks < 2· MaxMultiHit (2·6) → challenge: need good seeds for re-fit! Try to add a new peak

• r split an existing one.

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4.1 Re-fitting: Add peak

• 1. Sort all peaks in a group by their χ2/NDF, start with highest
• 2. Determine the bin with the highest positive derivation between

signal and fit for this peak. This bin is tmax,2 of the new peak.

• 3. Split peak halfway between tmax,1 and tmax,2.
• 4. Group peaks by default and re-fit
• 5. If χ2/NDF improved with re-fit, keep added peak and check

requirements for re-fitting again (previous slide)

• 6. Otherwise, start over with step 2 for peak with second highest

χ2/NDF etc. ⇓ add (and split) peak ⇓

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4.2 Re-fitting: Split peak

If adding a new peak didn’t work, do the following:

• 1. Sort all peaks in a group by their χ2/NDF, start with highest
• 2. Split this peak in the middle. tmax,1 and tmax,2 are in the

center of their respective peaks.

• 3. Group peaks by default and re-fit
• 4. If χ2/NDF improved with re-fit, keep added peak and check

requirements for re-fitting again (previous slide)

• 5. Otherwise, start over with step 2 for peak with second highest

χ2/NDF etc. ⇓ split (and add) peak ⇓

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• 5. Creating a hit

Save fit parameters for each peak: amplitude: A from fit mean: max of fit (see plot) → causes problem for BackTracker (working on it) width: calculate FWHM (full width at half maximum) from τ1 save FWHM/(2 ·

• 2 · ln(2)) as width

→ corresponds to sigma of a Gaussian fit: σ = FWHM/(2 ·

• 2 · ln(2))

energy: integral of fit from −∞ to +∞

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Plans for further improvements

• 1. Re-fitting sometimes deliver unreasonably small hits

→ remove hits with an integral < threshold → only accept re-fit when chi2/NDF is e.g. 10% better than before

• 2. When re-fitting, hits sometimes get split into two hits with

almost the same t0 → merge hits with e.g. ∆t0 < 1 tick after fitting (clustering?)

• 3. very long hits are split into several groups because of

MaxMultiHit threshold → substract fit of first group from waveform before fitting second group → try to implement this in the event display

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Where to find the code

Module: larreco/HitFinder/DPRawHitFinder module.cc table: "dpraw hitfinder" in larreco/HitFinder/hitfindermodules.fcl protodune dual phase reco .fcl: dunetpc/fcl/protodunedp/reco/ rawhitfinding reco protodunedp.fcl 3x1x1 reco .fcl (not tuned): dunetpc/fcl/3x1x1dp/reco/ rawhitfinding reco 3x1x1dp.fcl For easier tuning, the .fcl parameters for ptotodune dp and 3x1x1 are in the respective reco. fcl’s. Once tuning is fnished, will move them to: srcs/dunetpc/dune/HitFinderDUNE/hitfindermodules dune.fcl

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Performance of raw hit finding: data set

100 single µ− with Pµ− = 500 MeV in protoDUNE dp geo isotropic distribution within 45◦ in both planes Top view: Side view:

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Performance of raw hit finding: before re-fitting

gauss hit finding raw hit finding Average χ2/NDF: 34 (deconvoluted) vs. 13 (raw) Number of hits:

raw deconvoluted = 102 %

You get these histograms when you run the raw hit finding/gauss hit finding. Useful for tuning of Chi2NDFRetry.

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Performance of raw hit finding: re-fitting

after re-fitting (raw) zoom Reminder: Chi2NDFRetry is set to 25 Re-fitting fails only for a few hits → will look at these and see if algorithm can be further improved

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Performance of raw hit finding: tracking efficiency

Efficiency definition for track reconstruction:

• 1. Completeness 50 %
• 2. Purity 50 %
• 3. 75% Lreco

Ltruth 125%

more details: https: //indico.fnal.gov/getFile.py/access?contribId=57& sessionId=16&resId=0&materialId=slides&confId=10641 Results: Gauss: 97 % Raw: 100 % (standard linecluster or trajcluster, pmtrack) → check with higher statistics → will probably not be that good for tracks in drift direction

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Summary and outlook

Raw hit finding and fitting for dual phase is ready to use! (pushed one hour ago) Track reconstruction works well, shower reconstruction not tested yet Further improvements will only have a small impact Will tune it for 3x1x1 data next As usual: many thanks to Robert and Dorota (got many ideas from their hit fitting algorithm for ICARUS)

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