Space Charge Effect Analysis for ProtoDUNEs

Michael Mooney, Arbin TimilsinaBrookhaven National Laboratory

ProtoDUNE Sim/Reco Meeting – July 12th, 2017

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IntroductionIntroduction

♦ ProtoDUNEs are LArTPC detectors on the surface...• … so we expect non-negligible space charge effects (SCE)

♦ Space charge: excess electric charge (slow-moving ions) distributed over region of space due to cosmic muons passing through the liquid argon• Electrons drift in milliseconds, ions drift in minutes

♦ Can significantly impact calorimetry (dQ/dx), directionality of reconstructed tracks and showers• SCE distorts bulk E field, leads to spatial distortions of ionization

♦ Previously investigated space charge effects at MicroBooNE, including comparison to simulation• This talk: show expected impact for ProtoDUNE-SP and

ProtoDUNE-DP, calibration ideas, and Sim/Reco Group requests

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Overview

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SCE OverviewSCE Overview

♦ Space charge will pull drifting ionization electrons inward toward the center of the drift volume• Modifies E field in TPC, thus recombination level (dQ/dx)

• Modifies spatial information, thus track/shower direction, dQ/dx

• Approximately linear space charge profile w.r.t. drift coordinate

• Magnitude of spatial distortions scales with D3, E-1.7

Ion Charge Density [nC/m3]

K. McDonald

Approximation!No Drift!

μBooNE

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Impact on Track Reco.Impact on Track Reco.

♦ Two separate effects on reconstructed tracks:• Reconstructed track shortens laterally (looks rotated)

• Reconstructed track bows toward cathode (greater effect near center of detector)

♦ Can obtain straight track (or multiple-scattering track) by applying corrections derived from data-driven calibration

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SpaCE: Space Charge EstimatorSpaCE: Space Charge Estimator

♦ Code written in C++ with ROOT libraries

♦ Also makes use of external libraries (ALGLIB)

♦ Primary features:• Obtain E fields analytically (on 3D grid) via Fourier series

• Use interpolation scheme (RBF – radial basis functions) to obtain E fields in between solution points on grid

• Generate tracks in volume – line of uniformly-spaced points

• Employ ray-tracing to “read out” reconstructed {x,y,z} point for each track point – RKF45 method

♦ Can simulate arbitrary ion charge density profile if desired• Linear space charge density approximation for now

♦ Output: E field and spatial distortion maps (vs. {x,y,z})

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SCE SimulationSCE Simulation

♦ Can use SpaCE to produce displacement maps• Forward transportation: e.g. {x, y, z}

true → {x, y, z}

reco

– Use to simulate effect in MC

– Uncertainties describe accuracy of simulation

• Backward transportation: e.g. {x, y, z}reco

→ {x, y, z}true

– Derive from calibration and use in data or MC to correct reconstruction bias

– Uncertainties describe remainder systematic after bias-correction

♦ Two principal methods to encode displacement maps:• Parametric representation (for now, 5th/7th order polynomials) –

fewer parameters (thanks to Xin Qian for parametrization)

• Matrix representation – more generic/flexible

♦ Module in LArSoft ready to utilize maps (E field, spatial)

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ProtoDUNE-SP SCE Simulation

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E Field Distortions @ 500 V/cmE Field Distortions @ 500 V/cm

Central Z Slice (Max Effect)Cathode In Middle (Two Drift Volumes)

Drift Coordinate: XBeam Direction: +Z (Into Page)

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E Field Distortions @ 250 V/cmE Field Distortions @ 250 V/cm

Central Z Slice (Max Effect)Cathode In Middle (Two Drift Volumes)

Drift Coordinate: XBeam Direction: +Z (Into Page)

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Spatial Distortions @ 500 V/cmSpatial Distortions @ 500 V/cm

Central Z Slice (Max Effect)Cathode In Middle (Two Drift Volumes)

Drift Coordinate: XBeam Direction: +Z (Into Page)

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Spatial Distortions @ 250 V/cmSpatial Distortions @ 250 V/cm

Central Z Slice (Max Effect)Cathode In Middle (Two Drift Volumes)

Drift Coordinate: XBeam Direction: +Z (Into Page)

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ProtoDUNE-DP SCE Simulation

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E Field Distortions @ 500 V/cmE Field Distortions @ 500 V/cm

Central Z Slice (Max Effect)Cathode On Right (One Drift Volume)

Drift Coordinate: XBeam Direction: +Z (Into Page)

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E Field Distortions @ 1000 V/cmE Field Distortions @ 1000 V/cm

Central Z Slice (Max Effect)Cathode On Right (One Drift Volume)

Drift Coordinate: XBeam Direction: +Z (Into Page)

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Spatial Distortions @ 500 V/cmSpatial Distortions @ 500 V/cm

Central Z Slice (Max Effect)Cathode On Right (One Drift Volume)

Drift Coordinate: XBeam Direction: +Z (Into Page)

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Spatial Distortions @ 1000 V/cmSpatial Distortions @ 1000 V/cm

Central Z Slice (Max Effect)Cathode On Right (One Drift Volume)

Drift Coordinate: XBeam Direction: +Z (Into Page)

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SCE Calibration at ProtoDUNEs

♦ Basic need for space charge effect calibration: reconstructed space point (3D) with known true origin in 3D, covering entire active TPC volume• This requires knowing t0 of deposited charge

♦ Possibilities:• 1) Laser system (best option since true track truly known)

• 2) Cosmic ray tagger (cosmic muons and/or beam muon halo)

• 3) t0-tagged tracks using TPC/LCS information

• 4) Radioactive sources at fixed locations (inflexible)

• 5) Radioactive sources moving about cryostat (hard to get t0)

♦ ProtoDUNE-SP will utilize #2/#3 (no #1, #4/#5 not planned)

♦ ProtoDUNE-DP: #3 only?19

SCE Calibration OverviewSCE Calibration Overview

♦ 32 modules in total covering upstream and downstream faces of ProtoDUNE

♦ 8 H + 8 V modules on each side• 3.2 m × 1.6 m for

each module

• 2.5 × 2.5 cm pitch

♦ Can tag:• Cosmics

• Beam halo muons

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ProtoDUNE-SP CRTProtoDUNE-SP CRT

♦ ProtoDUNE-SP CRT-TPC matching algorithm has been developed by Arbin• Robust against presence of space charge effects

• Plan to tweak algorithm and utilize LCS to further improve purity

♦ No “proper” CRT geometry in simulation yet, so mocking CRT planes in simulation (w/ spatial smearing of hits)

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CRT-TPC MatchingCRT-TPC Matching

A. Timilsina

♦ Can also tag track t0 with strictly TPC info (purify with LCS)

• Side-piercing tracks: assume through-going, use geometry

• Cathode-anode crossers: projected x distance is full drift length

• Not pictured: cathode crossers (ProtoDUNEs only)

♦ Public note from MicroBooNE coming out on this soon 22

Other tOther t00-Tagging Methods-Tagging MethodsC. Barnes,D. Caratelli,M. Mooney

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SCE Calibration w/ TracksSCE Calibration w/ Tracks

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SCE Calibration w/ TracksSCE Calibration w/ Tracks

Currently Being Testedat MicroBooNE

♦ So, the big question which I've saved for the very last slide: what are our needs from the Sim/Reco group to help facilitate these measurements?

♦ Short term needs:• Light collection information (“flashes”): use to enhance purity of

t0-tagging using TPC information

– Discussing state of simulation with Alex Himmel later today

• Infrastructure for creating t0-tagging “objects” or “associations”

that includes all possible t0-tagging methods

– Can export trajectory points of t0-tagged tracks into flat ROOT

ntuple, perform calibration using stand-alone code

♦ Long term needs:• Include CRT “properly” in simulation (borrow from μBooNE?)

• Possibly: means for iterative tracking after SCE calibration done 25

DiscussionDiscussion

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BACKUPSLIDES

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μμBooNE SCE Data/MC Comp.BooNE SCE Data/MC Comp.

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μμBooNE UV Laser CoverageBooNE UV Laser Coverage

♦ Can use laser system to calibrate out space charge effect• Given true laser track and reconstructed track, can use an algorithm to

measure backward transportation displacement map

♦ Complications:• Can't address time-dependencies of LAr flow, if non-negligible

• Laser system can only target part of TPC

μBooNE