Space Charge Effect Analysis for ProtoDUNEs Michael Mooney, Arbin Timilsina Brookhaven National Laboratory ProtoDUNE Sim/Reco Meeting – July 12 th , 2017
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 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 2
Overview 3
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 D 3 , E -1.7 Ion Charge Density [nC/m 3 ] μBooNE K. McDonald Approximation! No Drift! 4
Impact on Track Reco. Impact on Track Reco. ♦ Two separate effects on reconstructed tracks : A • Reconstructed track shortens laterally (looks rotated) • B 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 Cathode A B Anode 5
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 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}) 6
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, 5 th /7 th 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) 7
ProtoDUNE-SP SCE Simulation 8
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) 9
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) 10
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) 11
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) 12
ProtoDUNE-DP SCE Simulation 13
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) 14
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) 15
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) 16
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) 17
SCE Calibration at ProtoDUNEs 18
SCE Calibration Overview SCE Calibration Overview ♦ 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 t 0 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) t 0 -tagged tracks using TPC/LCS information • • 4) Radioactive sources at fixed locations (inflexible) 5) Radioactive sources moving about cryostat (hard to get t 0 ) • ♦ ProtoDUNE-SP will utilize #2/#3 (no #1, #4/#5 not planned) ♦ ProtoDUNE-DP: #3 only? 19
ProtoDUNE-SP CRT ProtoDUNE-SP CRT ♦ 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 20
CRT-TPC Matching CRT-TPC Matching A. Timilsina ♦ 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) 21
Other t 0 -Tagging Methods Other t 0 -Tagging Methods C. Barnes, D. Caratelli, M. Mooney ♦ Can also tag track t 0 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
SCE Calibration w/ Tracks SCE Calibration w/ Tracks 23
SCE Calibration w/ Tracks SCE Calibration w/ Tracks Currently Being Tested at MicroBooNE 24
Discussion Discussion ♦ 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 t 0 -tagging using TPC information – Discussing state of simulation with Alex Himmel later today Infrastructure for creating t 0 -tagging “objects” or “associations” • that includes all possible t 0 -tagging methods Can export trajectory points of t 0 -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
BACKUP SLIDES 26
μBooNE SCE Data/MC Comp. BooNE SCE Data/MC Comp. μ 27
μBooNE UV Laser Coverage BooNE UV Laser Coverage μ ♦ 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 28
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