Wire Field Response Hanyu WEI Brookhaven National Lab Workshop on - - PowerPoint PPT Presentation

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Wire Field Response Hanyu WEI Brookhaven National Lab Workshop on - - PowerPoint PPT Presentation

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Wire Field Response Hanyu WEI Brookhaven National Lab Workshop on Calibration and Reconstruction for LArTPC detectors Dec 10-11, 2018 Fermilab Single-phase LArTPC detector C. Rubbia 1977 Fully active (space & time) detector with excellent

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Wire Field Response

Hanyu WEI Brookhaven National Lab

Workshop on Calibration and Reconstruction for LArTPC detectors Dec 10-11, 2018 Fermilab

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Charged particles Cathode Plane Incoming Neutrino Edrfit Ionization electrons

Single-phase LArTPC detector

Sense Wire Planes

ü Ionized electron drift along E-field ü Sense wire planes at anode as readout ü Photon sensor to record prompt light signals

Fully active (space & time) detector with excellent tracking and calorimetry capabilities

Wire readout

ü Cost & Power consumption in LAr ✗ Lose information: where the charge along the wire (pixel !" → 3 ⋅ ! wire)

  • C. Rubbia 1977

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What is this “transform”?

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Field Response

Induced current on a wire from a drifting ionized electron

! "#$ = &((

) *+, − ( ) ./01/)

Ramo’s theorem

" = −& 3) ⋅ ⃗ 67 Electron drift path (E field)

+

Weighting potential given a target wire U plane wires V plane wires Y plane wires

2D drift + 2D profile of wire planes Transparency condition: a set of bias voltages on three wire planes with which the ionized electrons are collected by the last wire plane. ü No amplification of ionization electrons in single-phase LArTPC ü More wire plane views, less ambiguity

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Induction & Collection plane

  • Collection plane
  • Electron collected by the wire
  • Big unipolar signal
  • Induction plane
  • Electron drift towards and past
  • Small bipolar signal

MicroBooNE

Normalization: collection plane integral=1e Field response ⊗ electronics response (2 us shaping)

LArTPC detector response ruled by field response!!

ü Shape ü Scale ü Smear

Kernel in signal processing (charge extraction)!

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Waveforms for various track topologies

s] µ Sample Time [ 150 − 100 − 50 − 50 100 150 ADC (Baseline Subtracted) 30 − 25 − 20 − 15 − 10 − 5 − 5 10

° ° 10 ° 20 ° 30 ° 40 ° 50 ° 60 ° 70 ° 80

U Plane

s] µ Sample Time [ 60 − 40 − 20 − 20 40 60 ADC (Baseline Subtracted) 15 − 10 − 5 − 5 10

V Plane

s] µ Sample Time [ 100 − 80 − 60 − 40 − 20 − 0 20 40 60 80 100 ADC (Baseline Subtracted) 5 10 15 20 25 30 35

Y Plane

Vary the angle relative to drift direction for tracks 0 degree: parallel to wire plane, isochronous track 90 degree: perpendicular to wire plane, the most extreme prolonged track

MicroBooNE Wire-Cell TPC full simulation for ideal tracks

Induction plane has significantly smaller signal for prolonged tracks even though more charge per wire pitch ß bipolar signal cancellation Field response makes quite a difference for different tracks and different wire planes!

JINST 13 P07006

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2D Field response (MicroBooNE)

  • 2D: Time (longitudinal) + Wire (transverse)
  • The residual 1D: Same along wire orientation

(Plot in log scale, arbitrary unit) Y-axis projection: Induced current on target wire given a drifting ionization electron at this transverse distance Target wire Collection

Long-range induction especially for induction planes!

Shielding from U plane

Difficulty in signal processing (charge extraction)!

JINST 13 P07006

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Long-range induction

inter-wire effect

  • Summation of responses over adjacent wires

= Signal on a single wire from an isochronous track (parallel to wire plane)

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Long-range induction

intra-wire effect

When an electron drifts at the wire “boundary” (center between two wires) Timing: ü Sizable delay (e.g. 4 us) for collection plane Amplitude: ü Considerable difference for induction plane 2D vs 3D model? [e.g. saddle point in the 2D model is not real …]

JINST 13 P07006

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Importance of field response

  • Rule the detector response (signal shape for various track topologies)
  • Long-range induction (inter- & intra-wire effect)
  • Induction vs collection planes
  • Kernel of the signal processing (charge extraction: conversion of raw waveforms to

number of electrons) which is the first step to all downstream event reconstructions

  • Specifically, the bipolar signal leads to difficulties for induction planes and to well

address this issue is extremely important to fully exploit LArTPC capabilities (all wire planes equally used to mitigate the wire readout ambiguity)

See my talk “Signal Processing & 2D deconvolution” tomorrow!

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How we get the field response?

✗So far we don’t have a good method to extract the field response in real data due to the complexity of the real signal (lose information …)

  • bipolar shape & long-range induction of field response, diffusion, track

topology dependency, sizable noise

✓Ab-initio analytic calculation of the field response

✓Garfield: a drift-chamber simulation program

✓ Geometry ✓ Electrostatic field ✓ Material in drift-chamber ✓ External table of the drift velocity vs E-field ✓ Drift-lines of electrons, current on sense wires ✓ Not support three-dimension structures

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Garfield calculation setup (MicroBooNE)

  • Well-aligned 2D profile of the wires for three wire planes (not a “real” but an

“average” cross section along the wire orientation)

  • The 2D setup is an approximation of the 3D wire structures

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Garfield calculation setup (MicroBooNE)

ü Fine-grained: 10 drift paths (per 0.3 mm) per wire pitch ü Long-range: 0 (central wire) ± 10 wires ü 126 (21 wires × 6) field responses are calculated (considering symmetry)

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Wire-Cell drift simulation (integrated in larsoft)

  • Kernel: 2D field response (long-range & fine-grained &

interpolation)

!"# $%&'()* = ,-./ ⊛ ,1234-1 ⊛ ,564/1 + 8/29- × ,2;242<-1

(x, y, z, t0, # of electrons)

ü Ionized electron absorption (electron lifetime in LAr) ü Gaussian diffusion (longitudinal / transverse) ü Fluctuation (for each gird of the discretized 2D Gaussian cloud) üField response (pre-calculated 2D Garfield calculation) üPre-amplifier electronic response (gain, shaping time) üAdditional response (RCRC filter, intermediate gain)

2 MHz sampling, max 2000 mV, 12- bit ADC Data-driven input + analytic method

Kernel:

=>?@ A ⋅ =>?@ C ⨂EFGHI C, A ⨂KLG>MN (A)⨂QR(A)⨂QR(A)

  • 1. Fine-grained: Gaussian diffusion + field

response (1/10 wire pitch)

  • 2. Long-range: 21 wires
  • 3. Two-dimensional

à Time & memory optimization

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Simulation vs Data

  • The elegant Wire-Cell simulation enables a direct comparison with the raw

waveforms in data

  • Validate the ab-initio calculation of field response
  • Comparison should be made for a certain track topology
  • Any inconsistency helps to re-tune the Garfield calculation by changing the setup

(generally not needed)

Tracks: angle between x-z plane projection and x axis, 5° < $%& < 15°

JINST 13 P07007

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Comparison across planes

  • Since the 2D field response is the kernel in signal processing, the good

matching of deconvolved charges from all three wire planes indicate the correctness of the field response.

ü ~10% smear originating from electronics noise ü Deviation due to the imperfection of detector

MicroBooNE Data MicroBooNE Data

Agreement in amplitude! Agreement in shape!

JINST 13 P07007 JINST 13 P07007

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Summary

  • The field response is the kernel in both simulation and signal

processing, of great importance to make “low-level” reconstruction right.

  • Obtained by analytic calculation, e.g. Garfield
  • Long-range induction (2D), fine-grained, proper interpolation
  • Several ways to validate the calculated field respones
  • Raw waveform comparison data vs simulation
  • Charge matching among all planes after signal processing

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Discussions – long range

  • Wire range in the 2D field response (e.g. MicroBoonE U plane

w/o shielding in front of it)

Isochronous track data vs. simulation

Wire geometry and track topology dependent

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Discussions – 3D calculation

  • Finite Element Method (FEM)
  • Garfield: not support three dimensional structures
  • Detector edge effect
  • CPU/RAM requirements scale with “volume” of the problem
  • “Impossible”? to do 3D at LArTPC wire readout (mm) scale
  • Leon Rochester @ slac is braving this challenge with custom FEM
  • Boundary Element Method (BEM) solves some problems
  • CPU/RAM requirements scale with “surface”
  • Fewer software implementations (compared to FEM)
  • Brett Viren @ BNL is exploring on this
  • A dedicated test-stand facility would greatly aid in validating the

residual 3D effect to a 2D field response calculation (LArFCS initiated

by Chao Zhang @ BNL).

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3D Field response (from B. Viren)

Qualitative agreement (preliminary). Subtle features will be smeared out by electronics.

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Back up

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DUNE-like field response from the Garfield calculation

DUNE like 4.71 mm wire pitch & gap

  • 665, -370, 0, +820V

U plane 2nd plane V plane 3rd plane Y plane 4th plane Collection plane G plane (not readout plane) 1st plane

Preliminary!

Unit: 0.1 us Summation of all field response over 0±10 wires

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Interpolation of fine-grained field response

  • Though fine-grained field response is employed, aliasing effect still shows

up especially for induction plane (bipolar shape signal)

Average field response for the two closest drift paths A simple linear interpolation

Induction Plane A prolonged track (large component along drift direction)

Improper bipolar cancellation (abrupt change) in the transition from one sub wire pitch to another

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