Space Charge Effect Analysis for ProtoDUNEs Michael Mooney, Arbin - - PowerPoint PPT Presentation

Space Charge Effect Analysis for ProtoDUNEs

Michael Mooney, Arbin Timilsina

Brookhaven National Laboratory ProtoDUNE Sim/Reco Meeting – July 12th, 2017

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Introduction Introduction

♦ 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

• f 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 Overview SCE 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
• f detector)

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

A B A B Cathode Anode

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SpaCE: Space Charge Estimator SpaCE: 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
• btain 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 Simulation SCE 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/cm E Field Distortions @ 500 V/cm

Central Z Slice (Max Effect) Cathode In Middle (Two Drift Volumes) Drift Coordinate: X Beam Direction: +Z (Into Page)

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

Central Z Slice (Max Effect) Cathode In Middle (Two Drift Volumes) Drift Coordinate: X Beam Direction: +Z (Into Page)

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

Central Z Slice (Max Effect) Cathode In Middle (Two Drift Volumes) Drift Coordinate: X Beam Direction: +Z (Into Page)

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

Central Z Slice (Max Effect) Cathode In Middle (Two Drift Volumes) Drift Coordinate: X Beam Direction: +Z (Into Page)

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ProtoDUNE-DP SCE Simulation

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

Central Z Slice (Max Effect) Cathode On Right (One Drift Volume) Drift Coordinate: X Beam Direction: +Z (Into Page)

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

Central Z Slice (Max Effect) Cathode On Right (One Drift Volume) Drift Coordinate: X Beam Direction: +Z (Into Page)

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

Central Z Slice (Max Effect) Cathode On Right (One Drift Volume) Drift Coordinate: X Beam Direction: +Z (Into Page)

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

Central Z Slice (Max Effect) Cathode On Right (One Drift Volume) Drift Coordinate: X Beam 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?

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SCE Calibration Overview SCE 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 CRT ProtoDUNE-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 Matching CRT-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

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Other t Other t0

0-Tagging Methods

• Tagging Methods
• C. Barnes,
• D. Caratelli,
• M. Mooney

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SCE Calibration w/ Tracks SCE Calibration w/ Tracks

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SCE Calibration w/ Tracks SCE Calibration w/ Tracks

Currently Being Tested at 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

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Discussion Discussion

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BACKUP SLIDES

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μ μBooNE SCE Data/MC Comp. BooNE SCE Data/MC Comp.

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μ μBooNE UV Laser Coverage BooNE 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