Expected Performance of the ATLAS Inner Tracker at the High-Luminosity LHC Matthias Hamer on behalf of the ATLAS collaboration Introduction The ATLAS Phase II Inner Tracker Expected Tracking Performance
Introduction ATLAS experiment multipurpose detector at the LHC Large Hadron Collider p-p, p-hi, HI-HI collider up to 14 TeV p-p collisions discovery of the Higgs boson by the ATLAS and CMS experiments 2
Introduction 3
Physics Motivation & Challenges dense environments HL-LHC Physics Goals Higgs Precision Measurements VBS Precision Measurements BSM Searches high pt ts collimated jets boosted scenarios VBF/VBS forward jets tracker for large pseudo-rapidities: Pile-Up rejection by jet vertex association Requirements for the Tracker low occupancy low material budget radiation hardness fast/reliable readout high efficiency good track/vertex resolution... challenging to achieve in the high pile-up environment of the HL-LHC! 4
Introduction 2011: s = 7 TeV Lpeak = 2.1 1032 cm-2s-1 <m> = 10 15 5
Introduction 2011: s = 7 TeV Lpeak = 2.1 1032 cm-2s-1 <m> = 10 15 2012: s = 8 TeV Lpeak = 4 1033 cm-2s-1 <m> = 20 6
Introduction 2011: s = 7 TeV Lpeak = 2.1 1032 cm-2s-1 <m> = 10 15 2012: s = 8 TeV Lpeak = 4 1033 cm-2s-1 <m> = 20 2016: s = 13 TeV Lpeak = 1.4 1034 cm-2s-1 <m> = 24 7
Introduction 2011: s = 7 TeV Lpeak = 2.1 1032 cm-2s-1 <m> = 10 15 2012: s = 8 TeV Lpeak = 4 1033 cm-2s-1 <m> = 20 2026: s = 13-14 TeV Lpeak > 1035 cm-2s-1 2016: s = 13 TeV Lpeak = 1.4 1034 cm-2s-1 <m> = 24 <m> 200 8
The ATLAS Tracker in 2016 IBL as 4th pixel layer installed before Run 2 Pixel Detector: 92M pixels, 50x400 mm2 (50x250mm² in IBL) 4 barrel layers, 6 endcap discs 2 m² of active area Semiconductor Tracker: 4100 two sided strip modules 4 barrel layers, 18 endcap discs active area: 60m², 6M channels Transition Radiation Tracker 4mm diameter straw tubes 50k + 250k straws in total additional info on particle ID 9
The ATLAS ITk in 2026 Pixel Detector: >5G pixels 5 barrel layers + endcap structures 50x50 mm² or 25x100 mm² >13 m² active silicon coverage up to h < 4.0 two candidate layouts under consideration Strip Detector: 70M readout channels 4 barrel layers, 12 endcap discs barrel: 24mm/48mm strip-pairs endcaps: 19-60mm strip-pairs 75.5 mm pitch 200 m² active silicon 10
The ATLAS ITk in 2026 Inclined Layout Extended Layout 5 cylindrical pixel barrel layers flat wrt beam pipe long pixel clusters track finding / particle ID (de/dx) pixel modules inclined in barrel forward region less material in forward region multiple clusters per layer in forward region less silicon needed 11
ITk Simulation GEANT4 simulation Pixel Sensors: planar n-in-n with FE-I4 50x50 mm² 150 mm thick threshold 600e 1x1, 1x2, 2x1, 2x2 modules Strip Sensors: n-in-p sensors strip length 19-60 mm 320 mm thick 75.5 mm pitch 20/26 mrad stereo angle 12
ITk Material Budget 13
Disclaimer layouts simulated are still under development many details still under discussion general layout exact implementation of layout sensor type and size TFM = DT / (Power / Area ) required to be small to prevent thermal runaway crititcal leakage current new readout chips reconstruction algorithms not optimised for layouts some approximations used in the reconstruction 14
Monte Carlo Samples ITk performance estimated with dedicated MC single particle & physics samples tt sample for physics studies single muon for vertex and track parameter resolution single pion sample for reconstruction efficiency for converted photons single tau sample for tracking performance in dense environments 15
Track Reconstruction clusters from hits space points conservative estimate for performance of ITk: reco algorithm not optimised for layouts cluster position: geometric center merged clusters identified by NN emulator no detector defects track seeds track roads ambiguity resolving 16
Track Properties >13 clusters per track for both layouts <0.1 holes per track overlap between modules not perfect thresholds in thick sensors pattern recognition errors 17
Track Reconstruction Efficiency reconstruction efficiency > 90% in central region > 80% in forward region inefficiency from hadronic interactions with detector material comparable than Run 2 efficiency for loose tracks see Hide s talk tomorrow fake rate < 0.001 estimated using the tt sample with <m> = 200 for the inclined layout efficiency: P(track gen particle) considering primary, stable, charged particles with pt > 1 GeV and h < 4 18
Track Parameter Resolutions single muon samples outliers removed in estimation significant improvement wrt. current tracker ATLAS Run 2, 10 GeV tracks, 0 < h < 0.2 Impact Parameter Resolution ITk @ h = 3.5 performs equal or better than current tracker @ h = 2.5 Impact Parameter Resolution for low pt dominated by multiple scattering for high pt dominated by intrinsic detector resolution 19
Performance in Dense Environments ability to reconstruct tracks close to a jet axis from hadronically decaying taus in highly boosted scenarios evaluated with <m>=0 3-prong tau sample 3-prong tau reconstruction: probability to reconstruct all 3 tracks merged cluster identification performance estimated with NN emulator 60%-90% in central region 30%-75% in forward region Track Requirements 20
Photon Conversions p0 gg sample with logarithmic energy spectrum converted photons reconstructed from tracks 1 or 2 tracks required dedicated tracking algorithm runs after standard track finder not necessarily pointing to PV may begin at larger radius conversion probability slightly higher in central region for inclined layout slightly higher in forward region for extended layout in total 20% (40%) in full ITk in central (forward) region 21
Photon Conversions reconstruction efficiency ~35% in full ITk volume significantly higher for photons converting at smaller radii 22
Summary ATLAS will get a brand new inner tracker during LS3 TRT removed 5 pixel layers 4 strip layers ATL-PHYS-PUB-2016-025 expected performance much better than that of the current tracker coverage extended to h < 4 better impact parameter and curvature resolution reconstruction efficiency in different environments satisfactory but still many variables extended / inclined layout? how will the exact implementation look like? 3D sensors in the innermost pixel layers? monolithic sensors in the outermost pixel layer? 23
Thank you Location - Date 24