Implemention of ACTS Into Sphenix Track Reconstruction

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Implemention of ACTS into sPHENIX Track Reconstruction

Joe Osborn May 17, 2021 Next Generation of QCD at RHIC

sPHENIX

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory

Joe Osborn 2 Collaboration Timeline

DOE “Mission need” PD-2/3, CD-0 construction begins You are here Start physics

Collaboration DOE CD-1/3A: cost, Installation and formed schedule, advance commissioning purchase approval

Joe Osborn 3 sPHENIX

• Study QCD matter at varying temperatures for direct comparisons to LHC • Study partonic structure of protons and nuclei

Joe Osborn 4 • Primary tracking detectors: • Micro vertexing (MVTX) - 3 layers of MAPS staves • Intermediate silicon tracker (INTT) - 2 layers of silicon strips (fast integration time) • Compact GEM-based TPC - continuous readout

sPHENIX Detector

Joe Osborn 5 sPHENIX Detector

• sPHENIX detector designed for high precision tracking and jet measurements at RHIC • Large, hermetic acceptance • Hadronic calorimetery (ﬁrst at RHIC) • Large ofﬂine data rate of ∼100 Gbit/s for collecting large minimum bias sample • Primary tracking detectors: • Micro vertexing (MVTX) - 3 layers of MAPS staves • Intermediate silicon tracker (INTT) - 2 layers of silicon strips (fast integration time) • Compact GEM-based TPC - continuous readout

Joe Osborn 5 • Additionally, TPC will contain charge from 2-3 Au+Au collisions at a given time • Hit occupancies of O(100,000) expected • Track reconstruction must be robust to high occupancies from pile up charge

sPHENIX Computing Challenges

Joe Osborn 6 • Track reconstruction must be robust to high occupancies from pile up charge

sPHENIX Computing Challenges

• RHIC will deliver Au+Au collisions at 50 kHz, while sPHENIX will record at 15 kHz • In a 3 year, ∼24 cryo-week per year data taking campaign, sPHENIX will collect ∼ 250 PB of data • Data will be processed on a ﬁxed size computational farm at BNL • Necessitates fast, efﬁcient track reconstruction • Goal is a CPU budget of 5 seconds-per-event on a single tracking pass • Additionally, TPC will contain charge from 2-3 Au+Au collisions at a given time • Hit occupancies of O(100,000) expected

Joe Osborn 6 • Track reconstruction must be robust to high occupancies from pile up charge

sPHENIX Computing Challenges

Joe Osborn 6 sPHENIX Computing Challenges

Joe Osborn 6 sPHENIX-ACTS Track Reconstruction

• To work towards meeting these goals, sPHENIX has implemented the A Common Tracking Software (ACTS) toolkit into our software stack • ACTS is intended to be a modern, performant, ﬂexible track reconstruction toolkit that is experiment independent • Largely developed by ATLAS tracking experts; however, user/developer base has grown • ACTS has modern development practices, e.g. • Semantic versioning/releases • Full CI/CD implemented in Github Actions ACTS Github link • Issue tracking • Documentation • Unit testing • ... Joe Osborn 7 • Eventually plan to move to a paradigm where sPHENIX objects == ACTS objects, for saving memory and time • Fun4All-sPHENIX code available on Github - code is open source and containerized with Singularity. Feel free to ask for more details!

ACTS Implementation Strategy

ACTS info Call tool

sPHENIX Object sPHENIX-ACTS Module ACTS Tool

Update ACTS result

Joe Osborn 8 • Fun4All-sPHENIX code available on Github - code is open source and containerized with Singularity. Feel free to ask for more details!

ACTS Implementation Strategy

ACTS info Call tool

sPHENIX Object sPHENIX-ACTS Module ACTS Tool

Update ACTS result

Joe Osborn 8 ACTS Implementation Strategy

ACTS info Call tool

sPHENIX Object sPHENIX-ACTS Module ACTS Tool

Update ACTS result

• ACTS requires geometry and measurement objects (that’s all) • sPHENIX objects store necessary information for ACTS objects • Modules act as wrappers for calling ACTS tools and updating sPHENIX objects • Eventually plan to move to a paradigm where sPHENIX objects == ACTS objects, for saving memory and time • Fun4All-sPHENIX code available on Github - code is open source and containerized with Singularity. Feel free to ask for more details!

Joe Osborn 8 ACTS Geometry - Silicon

INTT • ACTS is able to perform material calculations quickly due to a simpliﬁed geometry model • ACTS contains an available MVTX TGeometry plugin which takes TGeoNodes and builds Acts::Surfaces

• Any changes to sPHENIX GEANT 4 silicon surfaces are then reﬂected in ACTS transparently

Joe Osborn 9 ACTS Geometry - TPC

• ACTS geometry model not immediately suited to TPC geometries, since surfaces are required • With TPC, charge can exist anywhere in 3D volume • Side note: ongoing development within ACTS to allow for 3D ﬁtting • In place, create planar surfaces that mock cylindrical surfaces 48 TPC layers • Surfaces are set at readout layers, so there is a direct mapping from a TPC readout module to n planar surfaces

Joe Osborn 1010 Track Reconstruction Strategy

Joe Osborn 11 Track Reconstruction Strategy

Joe Osborn 11 Silicon Seeding

1 • ACTS track seeding tool takes a list 0.98 of space points and creates 0.96 three-measurement seeds 0.94 sPHENIX simulation • Ideally suited for MVTX, which has 0.92 100 pions 3 layers 0.9 |φ-φ |<0.02 truth • ACTS seeding efﬁciency shown in Acts Seeding Efficiency 0.88 |η-η |<0.004 truth 100 pion events 0.86 nMVTX>2 • MVTX triplets are propagated to 0.84 INTT to ﬁnd additional 0.82 measurements 0.8 0 5 10 15 20 25 30 • Final output is a set of 3-5 p [GeV] T measurement silicon seeds

Joe Osborn 12 ACTS Vertex Finding

m] 20 µ

) [ 18 sPHENIX simulation vtx

• Silicon track seeds have excellent (z σ 16 Initial vertex finding spatial resolution, and almost 14 entirely deﬁne the event vertex 12 • Acts::IterativeVertexFinder is used to assign silicon seeds a 10 vertex position 8 • Seeds are clustered to identify 6 outliers and remaining seeds are 4 provided to the ACTS tool 2 0 20 40 60 80 100

Ntracks

Joe Osborn 13 CA Seeding in TPC

1 • Independently (from ACTS) developed Cellular Automaton 0.9 Efficiency seeder is deployed in TPC 0.8 sPHENIX simulation 100 pions • Measurement gathering algorithm 0.7 |φ-φ |<0.02 is a reimplementation of concept truth 0.6 |η-η |<0.006 underpinning ALICE TPC tracking truth software 0.5

• Seeder is efﬁcient - continuing 0.4 development on producing high 0.3 quality seeds encompassing entire 0 2 4 6 8 10 12 14 16 18 20 22 p [GeV] TPC T

Joe Osborn 14 Track Matching

• Track seeds in silicon and TPC are

matched to one another with φ/η 9

windows match si 8 N 103 • Windows tuned to limit duplicate 7 matches while ensuring real tracks 6 5 are matched 102 4 • Predominantly have 1 silicon 3 tracklet per TPC tracklet. 2 10 Continuing development to reduce 1 number of multiple matches 0 1 • ACTS ﬁtter (next page) is very good 0 2 4 6 8 10 12 14 16 18 20 sPHENIX simulation p [GeV] at identifying bad seeds in T sPHENIX geometry

Joe Osborn 15 • Single upsilon mass spectrum from ﬁrst mock data challenge meets sPHENIX physics goals • Continued improvement on TPC seeds expected

Track Fitting

T 0.03 )/p T sPHENIX simulation (p 0.025 • Use tool to σ Acts::KalmanFitter 100 pions ﬁt fully assembled track seeds 0.02 nMVTX>2, nTPC>20 • Tool performs a full ﬁt outwards, then smooths result inwards to 0.015 vertex 0.01

0.005

0 0 2 4 6 8 10 12 14 16 18 20 p [GeV] T

Joe Osborn 16 Track Fitting

1000 • Use Acts::KalmanFitter tool to sPHENIX simulation fit fully assembled track seeds Υ Arb. Units 800 Single (1S) • Tool performs a full fit outwards, nMVTX>2, nTPC>30 then smooths result inwards to 600 σ = 86 ± 1 MeV vertex • Single upsilon mass spectrum from 400 first mock data challenge meets 200 sPHENIX physics goals

• Continued improvement on TPC 0 7 7.5 8 8.5 9 9.5 10 10.5 11 seeds expected Me+e- [GeV]

Joe Osborn 16 Track Fit Timing

2 120 1.8 sPHENIX simulation 100 • One of the primary motivations for 1.6 switching to ACTS was for speed 1.4 80 1.2 • Acts::KalmanFitter 1 60 time-per-track is shown here with 0.8 sPHENIX silicon+TPC geometry 40 0.6 • After ACTS + CA seeding 0.4 ACTS Single Track Fit Time [ms] 20 implementation, sPHENIX track 0.2 reconstruction is O(10)x faster than 0 0 0 5 10 15 20 25 30 previous implementations p [GeV] T

Joe Osborn 17 High Occupancy Performance

T 0.05 80 )/p

T 0.045

(p sPHENIX simulation sPHENIX simulation σ 0.04 70 50 kHz 0-20 fm Au+Au 50 kHz 0-20 fm HIJING 0.035 60 nMVTX>2, nTPC>20 0.03 50

0.025 40 0.02 30 0.015 20 0.01 10 0.005 0 −0 − − − 0 2 4 6 8 10 12 14 16 18 20 0.02 0.015 0.01 0.005 0 0.005 0.01 0.015 0.02 reco truth p [GeV] zvtx -zvtx [cm] T • High occupancy performance continues to be tuned and improved

• So far sPHENIX pT , DCA resolution goals can be met with current implementation • Continued work on : • Improving quality of track seeds • Reducing number of ghost/duplicate track seeds

Joe Osborn 18 TPC Space Charge Distortions

• Space charge buildup from ion back ﬂow in the TPC distorts measurements from true position • Presents a challenge within ACTS due to 2D surface description • Ongoing development: • Within sPHENIX - shift measurements along surfaces that account for full 3D distortions • Within ACTS - Full 3D track ﬁtting to accomodate TPC/DC geometries

Joe Osborn 19 ACTS Tools

• ACTS tools described so far are “pre-packaged” 140 • Versatility of ACTS - [rad] 0.04 sPHENIX simulation

CEMC 120 φ

Acts::Propagator, used in - 0.02 100 Acts::KalmanFitter, can be track φ

used freely as a tool 0 80 • Use propagator to identify track 60 −0.02 states for TPC space charge 40

distortions and track-to-calorimeter 20 −0.04 projections 0 −0.04 −0.02 0 0.02 0.04 • Tools are available for experiments η -η track CEMC to explore new and/or unforeseen use cases

Joe Osborn 20 Conclusions

• sPHENIX is the next generation QCD experiment being constructed at RHIC • RHIC will deliver highest luminosities ever to sPHENIX, resulting in large hit occupancies • To reconstruct data in a timely manner, sPHENIX has recently implemented the ACTS toolkit into our software stack • First implementation of TPC in ACTS - more development ongoing both within ACTS and sPHENIX • We have the ACTS seeding, vertexing, and ﬁtting tools deployed in our default track reconstruction. Have explored other ACTS tools as well • Development is active and ongoing as we prepare for commissioning and data taking in 2022/2023! • Much more work to be done than what was shown today!

Joe Osborn 21