Simulation of the ILD TPC with pixel readout Kees Ligtenberg LCTPC Collaboration meeting January 14, 2020 Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 1 / 12
Introduction In order to study the tracking performance of a large pixelised TPC, the pixel readout was imple- mented in the full ILD DD4HEP (Geant4) simu- lation Pixel readout simulation was build upon the pad readout simulation in ILCSoft version 02-01 Tiling of the ILD TPC with a quad module Outline Summary of pad and pixel TPC simulations (see also last year’s presentation) Changes since last year Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 2 / 12
Simulation of pad hits compared to pixel hits 6 mm 55 µ m 18 rows 990 µ m Pad hits Pixel hits 6 mm × 1 mm 55 µ m × 55 µ m Exactly one hit per layer Multiple or no hits per layer 22 electrons per hit 1 electron per hit Only diffusion in r φ and z Diffusion in x , y and z ∼ 200 hits per track ∼ 10 000 hits per track Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 3 / 12
Diffusion and hit resolution for pads and pixels As found in the latest code of DDTPCDigiProcessor Diffusion and hit resolution are simulated by smearing the hits by the expected resolution � � 6 mm � � 4 . 0 T D 2 � � 2 σ pads � r φ φ 0 sin 2 ( φ pad ) + � σ 2 r φ 0 + σ 2 = sin( θ pad ) L r φ N Eff h pad B � 4 . 0 T � � 2 σ pixels σ 2 r φ 0 + D 2 = L r φ r φ B � σ 2 z 0 + D 2 σ z = z L , Pads Pixels σ r φ 0 0.05 mm 0.016 mm σ z 0 0.4 mm 0.17 mm σ φ 0 0.9 mm 0.025 mm / √ cm 0.025 mm / √ cm D r φ 0.08 mm / √ cm 0.226 mm / √ cm D z 22 N Eff Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 4 / 12
Tiling of ILD end plate with GridPix quads Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 5 / 12
ILD end plate mask in simulation Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 6 / 12
Delta hit removal Before removal Remove hits if local density is more than 100 per 1 . 5 2 mm 2 Track digitisation with delta electron Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 7 / 12
Delta hit removal After removal Remove hits if local density is more than 100 per 1 . 5 2 mm 2 Track reconstruction without delta electron Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 8 / 12
Momentum resolution of the TPC with delta removal and coverage For low momentum tracks performance of pads and pixels is similar, because the resolution is limited by multiple scattering For high momentum tracks pixels are ∼ 20% better -1 ] [GeV − Pads Pixels (without deltas) 2 10 Pixels 1/PT − 3 10 σ − 4 10 − 5 10 Ratio 1.5 1 0.5 10 20 30 40 50 Momentum [GeV] Simulated muons at φ = 0 . 01 and θ = 85 ° with coverage mask Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 9 / 12
Tracking with silicon Full ILD tracking with the TPC and silicon detectors is functional Pixel and pad performance is similar Momentum Resolution o θ = 10 Pixels o θ = 20 Pixels ) -1 θ o (GeV = 40 Pixels − 1 o 10 θ = 85 Pixels θ o = 10 Pads T 1/p θ o = 20 Pads σ θ o = 40 Pads θ o = 85 Pads − 2 10 − 3 10 − 4 10 − 5 10 2 1 10 10 P (GeV) Momentum resolution of muons without delta electrons Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 10 / 12
Tracking efficiency in a t ¯ t event Pads Pixels High momentum tracking is efficient for pixels The efficiency of low momentum tracks is under investigation Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 11 / 12
Conclusions A full pixel simulation for the ILD TPC is implemented Work on the pixel TPC simulation has progressed A coverage mask was implemented A simple delta electron removal algorithm was added Tracking in combination with the silicon detectors is being developed Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 12 / 12
Backup Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 13 / 12
Seed finding for pixel TPC Pad seed finding is not suitable for a pixel TPC because the nearest neighbour clustering algorithm scales as O ( N 2 ) Instead, perform clustering by φ (Hough-transform like) Fill histogram of hits by φ in pad row range of 750 pixel rows Maximum bin is cluster with track candidate if more than 200 hits construct a straight line from the detector center to the average position Cut hits on distance from this line (10mm in r φ and 3mm rz ) initialise track fit with this line Tracks are found and fitted by extending seeds inwards using a Kalman filter, which has been adapted for pixels (see last year’s presentation) Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 14 / 12
Tracking at a uniform angle ] -1 [GeV − 2 Pads Pixels (without deltas) 10 φ Pixels (Uniform ) 1/PT − 3 10 σ − 4 10 − 5 10 Ratio 1.5 1 0.5 10 20 30 40 50 Momentum [GeV] Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 15 / 12
Simulation of pad TPC Detector is described by DD4HEP geometry Pads have have inter-module gaps in the radial direction Geant4 processes interactions of particle(s) from gun or event 6 mm Single hit in TPC is deposited if energy is above threshold (32eV) in a single pad. Position of pad centre crossing is recorded Diffusion and hit resolution is simulated by smearing the hits by the expected resolution in r φ and z directions Tracks are found and fitted by extending seeds inwards using a Kalman filter Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 16 / 12
Simulation of pixel TPC Pixels are described by the same cylindrical volumes in DD4HEP Pixels have ideal 100% coverage (to be 55 µ m 18 rows scaled) 990 µ m Multiple hits per row can be deposited In order to simulate diffusion, hits are smeared transverse to track in r , φ and z directions x 2 ∆ s φ 2 Optional: interpolate the track with a parabola over a volume of 0 . 99 mm x 1 (18 pixel rows) φ 1 Tracks are found and fitted by extending seeds inwards using a Kalman filter Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 17 / 12
Pad simulation of a 700 MeV muon Simulated pad hits are only at layer centre crossing Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 18 / 12
Pixel simulation of a 700 MeV muon Interpolated pixel hits are placed everywhere along the track Kees Ligtenberg (Nikhef) Pixel TPC simulation January 14, 2020 19 / 12
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