J. Apostolakis PH/SFT 1

 The Geant4 toolkit and SFT ◦ Areas of SFT involvement ◦ Status for LHC production  open issues and ongoing actions ◦ Future perspectives  The LCG simulation project ◦ GENSER - Event Generator ◦ Physics Validation  Manpower 2

The Geant4 Toolkit Areas of SFT involvement Geant4 Reviews 3

 Designed for HEP ◦ Especially LHC and future experiments ◦ nuclear physics, heavy ion experiments, ◦ also medical physics, space application.  Open Architecture and full capabilities ◦ Flexible kernel, enabling ‘any type’ of application ◦ Powerful geometry modeler ◦ Physics models for EM, hadronic, weak interactions  Choices with different accuracy, CPU performance needs,.. ◦ OO used to decouple implementations of physics models, geometry shapes & navigation methods,..  Developed by the Geant4 collaboration ◦ About 90 physicists & computer scientists from HEP institutions & agencies, ESA and universities around the world. 4

 Team in IT ( ), moved to PH/SFT (2003)  Constant focus of Simulation/G4 team on LHC and HEP ◦ Driven by LHC use/issues, physics and capability needs  From RD44( ) – with all LHC experiments as alpha users,  through the G4 production ramp-up phase ( ) to today. ◦ Initiative on Test Beam Comparisons (2000)  Later part of Physics Validation in LCG Simulation Project ◦ New models for physics accuracy - at best CPU cost possible  Introduce new Physics models, then push for optimisation of CPU ◦ Developing functionality for additional use cases  E.g. biasing, scoring & parallel geometry for (cavern) background ◦ Liaison and support on all issues encountered by LHC experiments  Geant4 in production use by ATLAS, CMS, LHCb since 2004 ◦ The engine of the detector simulation ◦ Enabled use of Geant4 in R OOT Virtual Monte Carlo (VMC)  for use by ALICE, others 5

 Coordination, release preparation (staff) ◦ G4 Spokesperson/SB Chair, Release manager/QA  Physics Validation (mix of staff/associates/fellow) ◦ Thin-target benchmark data  Physics Model improvement (mainly by associates) ◦ Hadronic: String models, cascade, CHIPS ◦ EM Physics: Standard (HEP)  Geometry (mix) ◦ Navigation; solids; tracking in field; persistency. In the above areas support and maintenance are included - and are an increasing fraction – as well as validation, testing and development.  Testing: nightly integration tests, regression & release validation  Hosting web site and development tools  Contribute also to other areas, e.g. ◦ Performance improvement – collaborating with FNAL experts, LHC teams ◦ Training courses; multithreading prototype studies,.. 6

 Organized by the Geant4 Oversight Board  Followed Geant4 Review 2007Geant4 Review 2007 ◦ Previous reviews: 2001 full, 2002 delta  Addressed issues relevant to HEP users, medical & space communities ◦ Reviewers from Atlas, CMS, Alice, medical, space, hadronic MC code. [ 6 from HEP / 9 total ]  Topics covered included: ◦ EM & Hadronic physics, validation, computing performance, documentation.  Report made 22 recommendations ◦ 2009 actions underway ◦ Next actions to be formulated at Collaboration meeting (Oct 2009) 7

Overall Status Open Issues & Ongoing Actions 8

 Geant4 latest releases in production in ATLAS, CMS and LHCb ◦ All ongoing/starting productions with Geant4 9.2 (Dec 08) + patches ◦ Agreement to support 9.2 until Dec 2010 for LHC experiment use.  Enables complex geometrical descriptions ◦ From 10 microns to 100 meters (detector) and more  Robustness in production ◦ Most productions see event failure rates below  Occasional issues tracked down and addressed promptly  Combining ever better physics and low CPU is hard ◦ Experiments choose ever-better models for physics reasons ◦ So performance (CPU & memory use) was/is/will be a key challenge  EM processes targeted for LHC/HEP are ready ◦ Extensively validated at percent level  Benchmark data and experiment test beams ◦ Some models are being improved, refined ◦ Large suite of benchmark (including simplified versions of LHC calorimeter) 9

 Physics accuracy goals: ◦ Describe known thin target data and test beam data ◦ Predictive power for unmeasured regions.  Hadronic Models have limitations and applicable energy range ◦ Our physics lists mix different models Today’s physics list QGSP_BERT has transitions between: ◦ High-energy : string models (QGS) ◦ Intermediate: parameterised (LEP) ◦ low energy: cascade (BERTini) All feed into de-excitation models (Preco) 10 QGSP_BERT(_EMV) physics list is used in production By LHC (and other HEP) experiments Also tried/used in other applications Studies with other physics lists ongoing.

 Accurate Modeling is important tool ◦ For calibration, energy scale, jets, missing E T,   Many or most observables are modeled well (or adequately) ◦ Energy response (E>20 GeV) and  /e, ◦ Shower profile for pion projectiles. ◦ Resolution (typically smaller than data),  Some quantities have deficiencies ◦ Shower profile for protons ◦ Energy response (8-20 GeV).  Following slides illustrate some results & issues ◦ Concentrating on open issues and investigations ◦ Comparisons with data are taken from presentations by experiments at LCG Physics Validation meetings (recent, preliminary results)  Result of test beam comparisons of ATLAS, CMS – in close contact 11

12 Pion longitudinal shower profile in stand-alone ATLAS TileCal test-beam at 90 o Data For Protons : -(20%-40%) at 10 λ. MC within ~ ±10% up to 10 λ. Thanks to Atlas Tilecal

Problem of matching models :  CMS & ATLAS reported energy response shows unphysical features ◦ Kink (9 GeV) ◦ Change of slope (25 GeV)  These are the transition points between models  Reproduced in simple setups ◦ No detector effects 13 ATLAS Tile

Study single interaction:  on Fe  Study fraction of energy going into different particle types ◦ for each hadronic model  Identified microscopic reasons for transition issues ◦ Which differences of models  Identify potential anomalies ◦ Confirmed known model limitations & find new ones 14  Fe  0

 Search for thin-target data ◦ To distinguish between models ◦ To enable tuning / improvement  Find models that need replacing ◦ LEP disagrees with benchmark data  Assess potential alternatives ◦ QGS/Chips smoother than QGS/P ◦ FTF spans from 3 – 20+ GeV  Prepare Revised physics lists ◦ Seek feedback from LHC experiments  Improve physics models 15  Fe: p

Future perspectives 16

 LHC experiments needs during first years ◦ Expanded Support in most areas – especially physics  Identify source (& fix) discrepancies with data ◦ Improvement of hadronic and EM modeling ◦ High Stability & Robustness for large MC productions ◦ Performance improvement (CPU, memory)  LHC upgrade, ILC detectors, other ◦ Refined hadron shower modeling  Better lateral profile (ILC),.. ◦ Part of EUDET project since start (2006); CALICE contacts  Comparison with CALICE data probe different aspects of hadronic showering – resulting future improvements in models can benefit LHC ◦ We are following these key (physics) issues  And will continue to do so – to the degree that manpower will permit. 17

 Support/Maintenance ◦ In our main areas (Geometry, Physics) and beyond; ◦ Performance improvement  Physics Validation & Improvement ◦ Hadronic Physics: Models & Combinations (lists)  Identifying limitations and their causes (major role)  Contributing to improving models  Geant4 Architecture Review (start: 2010) ◦ Participate in planned major overhaul  Address design issues, drive to improve implementation  Integration & interaction with other SFT tools/projects ◦ Latest: migration to SPI nightly testing system (2008/9); ◦ Multi-threading and multi-core: Geant4 as proto-project. 18

 Depth of expertise in high-energy nuclear physics ◦ Experts with 10s years of experience few  Several working for other projects (e.g. MCNP),  Limitations of associates contracts. ◦ Simulation codes / models  Several projects focused on model improvement on ion-ion (UrQMD) or cosmic rays (QGSJET)  Data for validation of diffraction,  0 production,.. ◦ Difficulty to access data of some old experiments  Measurements of HELIOS (diffraction on nuclei),  Published data apparently corrected with faulty MC;  Search for data of  0 production (ANL?).  Increased load of maintenance ◦ Author/developer departures ◦ Reduced manpower 19

 Developed relations with model authors, experts ◦ Liege cascade (INCL) team  A. Boudard (Saclay) joined Geant4  INCL ported to Geant4; developments ongoing ◦ D. Cano (CIEMAT): low energy neutrons  New databases for neutrons E < 20 MeV  Recruited to Geant4, amongst others ◦ J.M. Quesada Molina (Univ. Sevilla)  Made full revision of pre-compound (the P in QGSP) & evaporation  Interfaces to other models ◦ DMPJET II.5: first for ion-ion (space funding)  Plan to extend it to hadron-ion 20

 Regular contacts with LHC experiments using G4 in production (ATLAS, CMS, LHCb) ◦ Many questions answered and issues addressed; ◦ Liaisons in Atlas (JA), CMS (GC): attend experiment simulation meetings,..  Dialog with FLUKA team in context of Simulation project ◦ Focus on validation of models; physics issues.  Collaboration with IT ◦ Extensive & fast testing of each Geant4 Release using WLCG (+OSG); ◦ Work with Openlab on Performance (sequential & multithreaded).  Physics Validation Meeting ◦ Forum for Physics issues, validation including test beams  Increasing channels with CALICE/ILC ◦ EUDET(2005), CALICE meetings (Mar & Sep 2009), CERN group.  Geant4 Open User ‘Technical Forum’ since 2003 ◦ Spreading information of experience by HEP experiments, other users ◦ Agrees priority on ‘big’ requirements, feeds into Geant4 workplan. 21

 In close contact with many Geant4 contributing teams/people, e.g. ◦ SLAC: hadronics (including neutrons), kernel, Vis ◦ KEK/Japan: kernel, particle properties, GUI ◦ FNAL: hadronics, performance improvement ◦ IN2P3 & INFN: EM Standard(HEP+), EM Low- Energy ◦ Northeastern Univ.: multi-core and multi-threading  These are in addition to formal channels: ◦ Steering Board ◦ Working group meetings 22

Brief Overview Event Generator Service 23

 Part of LCG Application Area that spans simulation  Encompasses ◦ SFT involvement in Geant4 and its support for experiments ◦ GENSER Event Generator Project  Hosted T. Sjöstrand- Pythia 8 development. ◦ Physics Validation (Geant4, Fluka)  cross-comparisons on thin-target data  Joint effort on test beam comparisons  Regular meeting including LHC (& other) experiments ◦ Garfield ◦ FLUKA – liaison with CERN Fluka team.  Led by Gabriele Cosmo 24

 LCG Simulation Project Provide: a repository of validated MC event generators, and related tools, useful for the experimental and theoretical LHC communities.

 GENSER ◦ Structure stable and used by experiments (ATLAS, CMS, LHCb) ◦ 25 generators installed (most of them with several versions)  Platforms supported: SLC4 and SLC5, 32- and 64-bits  For some generators, also Windows and Mac OS X ◦ New versions are installed as they are announced and tested  regression testing with respect to a reference version) ◦ Status of the generators and testing available on the Web ◦ Project planning meetings twice per year  Regular monthly technical meetings  HepMC ◦ Standard interface used heavily by the LHC community ◦ Meetings every 6 months to decide new releases (latest: 2.05, June 09)  MCDB ◦ Used in CMS productions LCG Simulation Project

 Staff ◦ JA: Geant4 spokesperson (Steering Board chair), geometry, hadronic physics. ◦ Gabriele Cosmo: release manager, geometry coordinator, quality assurance. ◦ Gunter Folger: hadronics, integration testing, software tool manager. ◦ Alberto Ribon (LD - Dec 09): SIM physics validation project, GENSER Event Generator service, G4 hadronic physics, Grid release validation.  Associates ◦ Vladimir Ivantchenko: EM coord. (HEP focus) + Hadronics; CMS 2 nd contact. ◦ Mikhail Kossov: Hadronic physics, validation & CHIPS model. ◦ Vladimir Uzhinskiy: Hadronic string modeling & validation  Fellow(s) ◦ Andrea Dotti (July 09-): Hadronic validation & physics (diffraction.)  Students ◦ Gabriele Camellini: Geometry & FLUGG (Fluka with G4 geometry) ◦ Victor Diaz: System Integration Testing (incl. move to SPI nightly system) ◦ Mary Tsagri (doctoral/MC-PAD): Modeling of neutrons in Gas detectors 27

 Profile ◦ Staff departures (not replaced)  Retirement of Geant4 testing coordinator (Mar 2008)  LD: Simulation/GENSER coordinator (Jan 2008) ◦ Sparser fellows ◦ Decline in number of associates  Upcoming changes (end-2009) ◦ Departure of A. Ribon (LD) - post was opened. ◦ End of several associates contracts. 28

 Geant4 new releases in production in ATLAS, CMS and LHCb ◦ Robustness, improved performance  Comparisons with benchmark data & LHC exper. test beams ◦ Good agreement in many quantities, discrepancies in others ◦ Key issues are being investigated, in particular model transitions  Ongoing improvement and preparation for support of LHC experiments’ data-taking  Challenges anticipated ◦ Enabling existing model authors to contribute closely ◦ Enabling collaboration with additional physics experts ◦ Finding key data for comparison ◦ Address new needs of future experiments 29

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 Coordination, release preparation ◦ G4 Spokesperson/SB Chair (JA), Release manager (GC)  Hadronic Physics: ◦ String models: V. Uzhinskyi (PJAS: 2009-), GF ◦ Cascade: GF; CHIPS: M. Kossov (PDAS) ◦ Validation: AR/new staff; A. Dotti (fellow)  EM Physics: ◦ Coordinator: V. Ivantchenko (PJAS: )  Geometry ◦ Coordinator (GC), deputy (JA), G.Cam.(student) - had fellow  Testing: integration tests, release validation 31

 Between LHC and other HEP experiments ◦ Hadronic physics is the same and experiment needs for good modeling is invariant ◦ Also high precision in EM physics is a challenge  Also with many other users ◦ Physics below 10 or 1 GeV is very relevant for energy deposition, fluctuations, missing energy,.. ◦ Low-energy (<1 GeV) hadronic physics is common  model improvement helps most/all users ◦ Need for CPU-performant models in common energy domain is widespread (HEP, medical phys.,..) 32

 Issue of early short hadronic showers (2004): QGSP  Addressed: added physics model, improvements ◦ Introduced cascade (BERTini) – and improved it ◦ Added Quasi-Elastic channel - to QGS model (2007)  Agreement is better with QGSP_BERT ◦ Pion shower profile within 10% at 10 lambda ◦ Proton profile 20-40% low at 10 lambda  Looking to improvements in diffraction to address this  Develop(ing) Fritiof (FTF) model as alternative ◦ Better results for protons than QGSP_BERT 33

34 Proton longitudinal shower profile in stand-alone ATLAS TileCal test-beam at 90 o MC: -20% to -40% at 10 λ.

35 Pion energy response in ATLAS barrel combined test-beam 2% above 10 GeV 4% below 10 GeV G4.9 Bertini cascade model increases the response. QGSP_BERT shows the best overall performance for the linearity (within 4%).

 Reports from CMS and ATLAS ◦ Non-monotonic energy response 8-12 GeV ◦ Kinks in response in transitions of physics models  Actions ◦ Confirmed in simple setups ◦ Investigations of properties of physics models ◦ Identified issues with particular models ◦ Feedback to improve modeling  comparing with thin-target data 36

37 Bertini cascade increases response for Tile and HEC by 4-5%. In Tile and HEC response ~2% too high with QGSP_BERT. Pion energy response in ATLAS stand-alone test-beams G4.9 HEC Tile

38 Pions and protons energy response in CMS combined test-beam Agreement between data and simulation on energy response is within systematic uncertainty b01 ECAL+HCAL ECAL(mip)+HCAL

Pi- beam on Fe (one interaction)  Study fraction of energy produced in reaction ◦ for individual model level ◦ Plot the sum of the energies of the secondaries of one particle type (e.g.  0 or protons)  / E beam   0 production responsible for most early energy deposition  Transitions in QGSP_BERT ◦ BERT to LEP between GeV ◦ LEP to QGS/Preco btwn GeV 39  Fe  Leading Particle

Some key observations / issue(s)  G4 Bertini cascade (BERT) ◦ Has large excess of energy in protons and neutrons for E>3 GeV  Revision is underway SLAC)  QGS/Chips smoother than QGS/P ◦ Appears plausable for E>10 GeV  LEP disagrees with other models ◦ Looking to replace it (with FTF)  Revised physics lists prepared ◦ First feedback from LHC experiments  Need data to compare (spectra) ◦ Especially those relevant to  0 production (e.g.  + +  - 40  Fe  

41 Pion resolution in ATLAS stand-alone test-beams Bertini cascade makes resolution better: in Tile: better agreement with data ( ± 10 % ‏ ). in HEC: MC resolution too good by -10%. HEC Tile

42 Pion resolution in ATLAS barrel combined test-beam Bertini cascade makes resolution better MC predicts too good resolution -5 ÷ -10%

43 Resolution is too good in Monte Carlo Pions and protons energy resolution in CMS combined test-beam ECAL+HCAL ECAL(mip)+HCAL

44 Bertini cascade makes shower wider, which is in better agreement with data, but data are still a bit wider. Pion lateral spread in stand-alone ATLAS TileCal o

45 Test Beam Comparisons: Short Summary and Outlook  The LHC experiments have carried out extensive tests of the Geant4 physics models and validated them with test beam data.  ATLAS and CMS have chosen QGSP_BERT(_EMV) as the default Physics List. Fritiof-based Physics Lists, FTF_BIC and FTFP_BERT show interesting features.  There are some remaining issues in hadronic physics 1) Discontinuity in energy response at the model boundaries 2)Proton longitudinal shower profiles are shorter than data in QGS-based Physics Lists (diffraction) 3)Lateral shower profiles are a bit narrower than data (not an issue for LHC experiments, but for ILC it could be important….)

Key Issues: ongoingRecent aspects (for each) 1. Identifying source of physics deviations ◦ Typically many sources could contribute 2. Deficiencies of hadronic models ◦ Responsive to tuning, or ◦ Intrinsic model limitations? 3. Transitions between hadronic models ◦ Trying to match mean, RMS, of diverse observables 4. Extending Validation ◦ More benchmarks, observables ◦ New data 1. Shower shape (  good, proton fair) ◦ Investigating diffraction 2. Simplification in older modeling ◦ LEP Energy non-conservation ◦ Cascade nucleon production. 3. Steps or ‘Discontinuities’ ◦ Energy Response (Atlas, CMS)  In region 8-12 GeV 4. Comparisons ◦ With FNAL & ITEP data 3-10 GeV ◦ With fine grained CALICE data. 46

 Made 22 recommendations ◦ Covered 8 different areas:  EM physics  Hadronic physics  Computing Performance  Physics Validation  Release Validation  Documentation  User Support  Resources.

1. Removal of less accurate EM models/options (overall simplification of choices where possible) 2. Provide guidance to users for available EM models and options 3. Study assumptions and parameterisations of physics models in FLUKA and improve corresponding hadronic models available in Geant4, where needed 4. Continue in monitoring CPU performance, perform code reviews for improvement 5. Development of multi-threading capability in Geant4 6. Conduct a code design assessment in view to also integrate thread- safety in code 7. Consolidation of the hadronic WG and low-energy WG web pages

1. Provide pointers to physics benchmark results and tests and related documentation 2. Adopt a range of metrics to characterize as broad a range of validation results as possible 3. Acquire/redirect resources to improve documentation and keep up with updates 4. Adopt periodic review of the documentation and improve documentation design 5. Identify new tools to adopt for the software installation 6. Involvement of the user community in the log-term support of physics models 7. Seek for additional support from all available sources; extend the Collaboration to new Institutions

 Focus areas of Internal G EANT 4 Review: ◦ Key interfaces ◦ Design of Geant4 kernel  Goals (proposed) ◦ Streamline design for features added ◦ Further improve performance, robustness ◦ Enhance maintainability, test-ability ◦ Adapt for multi-core / multi-threading ◦ Evaluate other recent / new technologies.  Effort to be in parallel with ◦ Support for existing Geant4 version(s) in production. 50