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 title: "eAST proposal"
 layout: base
 name: proposal
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 <h1>Project eAST proposal</h1>
 
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 * TOC
 {:toc}
 
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 ## Motivation 
 
 
 Large-scale detector systems for the EIC are designed by larger
 communities. The simulation efforts typically start as standalone
 exercises for each detector component with various levels of maturity,
 analytical calculations, simplified Monte Carlo exercises (fast
 simulations), Geant4-based Monte Carlo approaches (full simulations),
 and are later being extended in several different frameworks.
 
 It is critical in the longer term to perform studies where the
 information from various detector elements and also the interaction
 region, support structures and other dead material is taken into
 account, which is only possible in a comprehensive simulation. This is
 essential to understand, e.g., the performance at the edges of the
 detector system or the effect of combining different technologies for
 the electro-magnetic calorimeter. For studies of the physics reach and
 detection capabilities, it is important to be able to switch detector
 options with varying levels of detail, combining full simulations for
 some detector components with fast simulations for the rest of the
 detector system. It is also critical to build a sustainable effort for
 the entire time scale of the experiments with common tunes and commonly
 validated results for both fast and full simulations.
 
 However, such detailed studies are time consuming, both from people and
 computing view. To ease leveraging new and rapidly evolving computing
 technologies, we plan to implement a common and integrated approach for
 fast and full simulations in Geant4 with a plug and play modular
 approach.
 
 ---
 
 ## Requirements 
 
 A comprehensive and centrally maintained simulation tool based on Geant4
 for both fast and full simulations with a library of potential detector
 options has to be developed. The initial focus on the development will
 be:
 
 -   ability to reuse existing simulation works,
 -   ease of switching detector options with comparable levels of detail,
 -   ease of switching between detailed and coarse detector descriptions,
 -   ease of leveraging new and rapidly evolving technologies
 (e.g., AI/ML) and computing hardware (e.g. heterogeneous architectures)
 
 After validation of the Geant4 simulations, they will be simplified
 (replacing some physics aspects) for fast simulations. This approach
 will allow us to use everywhere the same geometry (very important to
 reduce debugging and development time) and to combine full simulation
 for a subset of detectors with fast simulations for the rest of the
 integrated detector. Geant4 itself and various NP and HEP experiments
 already provide sub-systems for fast simulations. This will reduce the
 development time of the fast simulations substantially.
 
 The detector simulation tool will be modular, and its development will
 be targeted. It will provide an interface to the output of Monte Carlo
 event generators but no further work on generators. The simulation of
 detector effects and detector responses (digitization) will be clearly
 separated. There will be a common geometry interface between the
 detector simulation and reconstruction.
 
 The timely development of a comprehensive, unified and centrally
 maintained detector simulation tool for both fast and full simulations
 to serve the needs of the detector collaborations or groups is no small
 task. It must take place in the context of strong development teams in
 the labs together with important contributors in the universities, and
 go beyond legacy software to a new common effort to be successful. This
 effort builds on a sustainable common project based on Geant4 and
 tailored to needs of NP experiments as they exist today and will evolve
 to the 2030s.
 
 Geant4 has the capability to support both fast and full simulation,
 which we want to use for large-scale detector systems. Geant4 through
 its multi-threaded reengineering has already been able to support high
 concurrency heterogeneous architectures, with excellent results in the
 memory economizations achieved. Leveraging and evolving this capability
 as heterogeneous architectures become ever more prevalent is of great
 importance for data processing and analyses for large-scale detector
 systems at the EIC.
 
 ---
 ## Work program and deliverables
 
 ### Create CAD interface to the detector simulation tool
 
 Fast and detailed simulations need to be able to implement updates on
 detector layout fast, where these updates need to be based on detailed
 design drawings with parametric surfaces in 3D. This requires as crucial
 *first step* compatibility with the CAD applications being used at BNL
 and JLab, for easy exchange. The most flexible format for Geant4 to
 import CAD geometry is GDML. STEP is the file format commonly available
 to many CAD systems. Several tools exist that convert STEP files to GDML
 files. We will work with experts at BNL and JLab to conduct a survey if
 STEP is available for the variety of CAD applications used. These break
 down into two broad categories: mesh vs. nurbs. Mesh CAD applications
 represent a structure using a collection of flat polygons that emulate
 curved surfaces that can be used to represent volumes. The granularity
 of the polygon surfaces can be scaled up or down to create smoother or
 coarser surfaces, respectively. Examples are AutoCad and Sketchup which
 are excellent for expansive structural/architectural representations of
 components and buildings. Nurbs models use parameters that describe the
 shape and extent of a surface, the curvature of each element, and the
 thickness of the material. In effect they can produce very close
 approximations of real-life entities but are difficult to exchange or
 import by non-nurbs systems. Examples are CREO, SolidWorks, and Siemens
 NX which are used for mechanical design. GDML also supports various
 shapes and extruded solids, some of them may correspond to nurbs.
 Lastly, CAD files often only contain sparse information about the
 composed material, often just the name of the materials. On the other
 hand, detailed detector simulations require the full composition of each
 material, often down to the isotope composition level. We will develop a
 mechanism, e.g., through a macro file, to associate such additional
 information needed to the detector simulation.
 
 *Deliverables:
 1) Development of a CAD Interface for Detector
 Simulations.
 2) Macro file that allows material composition information to be easily ported to detector simulations.*
 
 ### Create an initial version of the fast and full detector simulation tool
 
 The detector simulation tool has to be capable of doing both fast and
 full simulations in one application, easily configurable for each
 detector component. Also, the detector simulation tool has to easily
 integrate (“plug-in”) already existing standalone simulation
 applications. These requirements will be fulfilled by utilizing the
 “region” mechanism of Geant4. Each detector component is represented as
 a region, where geometry description including different levels of
 detail, physics options including fast simulation and unique physics
 model configurations, and detector responses based on geometry and
 physics options are taken care of. We will develop an initial version of
 such a detector simulation tool.
 
 *Deliverable: First running version of detector simulation tool.*
 
 ### Communicate with detector study groups
 
 The existing standalone simulation applications that are to be adapted
 to the new detector simulation tool have to be examined and converted to
 be “plug-able” using the “region” mechanism. We will communicate with
 detector study groups and work with them to drive the efforts of
 integration. Through these interactions the requirements to the detector
 simulation tool will be refined as needed. The detector simulation tool
 may also integrate beam-test configurations if applicable. The
 deliverable will be a prototype integration of an existing simulation,
 the specific target to be chosen in the first month on the basis of
 importance and available developer effort during the initial funded
 period. Other detector components will be added by the detector
 community based on the experience from the prototype.
 
 *Deliverable: Documented prototype integration of an existing simulation.*
 
 ### Develop and deliver a common physics list 
 
 Geant4 offers several alternative physics models. To make comparisons
 over different detector configurations, one has to use a common set of
 physics models that is appropriate to NP detectors. We will develop and
 deliver such a physics list. We will consult with detector study groups
 and advise on validations of the physics models with beam-test results.
 
 *Deliverable: Documented common physics list.*
 
 ### Integrate with overall software efforts
 
 We will compile the requirements of detector simulation to the software
 infrastructure (e.g., common geometry and data formats) to be shared
 across the whole software chain including physics event generation,
 simulation, digitization, reconstruction and analysis programs.
 
 *Deliverable: Requirements document. *
 
 ### Deliver a detector simulation tool extensible to heterogeneous architectures
 
 <span id="_4d34og8" class="anchor"></span>In the future, simulation jobs
 may run on computers with heterogeneous hardware configurations, e.g.,
 with GPGPU and/or FPGA, and with cutting edge IT technologies such as
 AI/ML. Enabling the effective use of such technologies requires design
 and implementation choices in the detector simulation tool. We will
 ensure the extensibility of the detector simulation tool through the use
 of a tasking mechanism (either PTL or TBB). We will also support the
 developers of detector components of the thread-safety of their code.
 
 *Deliverable: Proven use of a tasking mechanism.*
 
 ---
 ## Project leader
 
 <span id="_2s8eyo1" class="anchor"></span>This project aims to take
 advantage of the proven value for detailed nuclear and particle physics
 experiment simulations by the HEP-developed Geant4 software and the
 growing prospects of use of advanced computing techniques. Any
 large-scale detector system will benefit from the project on “*Fast and
 full simulations in Geant4 for large-scale detector systems with a plug
 and play modular approach”*, with the foreseen EIC detectors prime
 examples. For example, EIC detector simulation development must be able
 to progress rapidly to provide the EIC user community proper flexible
 and forward-looking tools to meet the simulation needs of the detailed
 detector design and EIC science performance studies. This requires a
 common simulation framework and effort if the EIC community is to be
 properly served by a unified effort drawing on pooled expertise. This
 also requires simulation tools ready to take advantage of the growing
 use of heterogeneous computing environments and the prospects they
 offer. This work will seed a new common effort through the leadership of
 an expert of unique stature and technical expertise, who has the trust
 and confidence of the full community to establish a common effort, while
 also being a technical expert. The *“Fast and full simulations in Geant4
 for large-scale detector systems with a plug and play modular approach”*
 will ensure that any work on AI/ML and running on computers with
 heterogeneous hardware configurations can be directly applied.
 
 In Dr. Makoto Asai we identify the individual who can uniquely fill this
 role. Dr. Asai has been both a Geant4 project leader and deep technical
 expert for over 20 years. He is well known to and respected by the EIC
 community with which he has collaborated for many years on EIC Geant4
 simulation needs. He is the designer and principal developer of Geant4's
 capability to support both fast and full simulation, which we want to
 use for the EIC. He led Geant4 through its multi-threaded reengineering
 to support high concurrency heterogeneous architectures, with excellent
 results in the memory economizations achieved. Leveraging and evolving
 this capability as heterogeneous architectures become ever more
 prevalent is of great importance for the EIC, and together with the
 integrated fast simulation support opens the door to leveraging AI/ML in
 the unified simulation. Dr. Asai is also an expert in the geometry and
 modular detector description tools that will be the basis of unified
 geometry in detector simulations. He is also an expert in the Geant4
 physics models that have to be tuned for NP experiments, having presided
 over their development and integration for much of the past 20 years. No
 other individual has an array of attributes better tailored to the
 leader we are looking for. Finally and crucially, Dr. Asai is available
 for this work if we act promptly.
 
 ---
 ## Appendix
 ### Notes from the [*March 25 EIC software meeting*](https://indico.bnl.gov/event/11102/) discussion (Torre)
 
 -   CAD work is a distinct project, \~1mo duration, it goes first both
     because Elke and Rolf need it and because it gives us a month to
     plan the simu project specifics before it launches
 -   discussion about time ordering and priorities. Note that there is no
     time or priority ordering implicit in the ordering of deliverables
     in the proposal.
 -   comments from several that physics list should be highest/earliest
     priority
 -   test beams should be considered and included. Test beam data is
     essential to validating physics lists. The simulation software
     should support test beam configurations.
     -   comment asking whether factoring out digitization is compatible
         with physics list tuning, which can be dependent on digi
         tuning, e.g. Birk’s constant.
     -   tuning won’t happen without actual data, will rely on test beam
     -   noted that we do already have relevant test beam data already in
         hand
     -   comment that in talking about ‘tuning’ we should really be
         calling it ‘validation’
 -   discussion about the extent to which (very) fast 4vector based
     simulation like eic-smear should be integrated. Would Geant4
     integration slow it down? Why carry Geant4 dependencies for what
     would otherwise have lightweight dependencies?
     -   in writing the proposal we expected that eic-smear type
         simulations would not be integrated into Geant4 (because it
         would slow them down), but would be incorporated in as
         seamlessly as possible for ease of use, e.g. uniformity of
         user interfaces, of course uniformity of MCEG interfaces
     -   Makoto commented that it is possible to integrate such very fast
         simulations in Geant4 without a performance hit.
 -   comment that it should be possible for the user to “own the event
     loop”, treating the simulation software fully as an on-call
     toolkit rather than handing over control, especially for fast
     simulation
 -   comment on whether we should put such emphasis on Geant4; what if a
     new simu toolkit comes along or ‘GeantV’ emerges.
 
     -   ‘GeantV’ as a rewrite/reengineering of Geant4 has been laid to
         rest in recent years, as a useful learning exercise that was
         successful when it worked to augment Geant4 rather than
         replace it (e.g. VecGeom came out of it). There is not a
         prospective Geant4 replacement in sight, and there is a wide
         range of Geant4-directed R&D underway, including new projects
         in utilizing GPUs, particularly for EM/photon physics.
 -   comment that it is difficult to evaluate the intended scope of
     the proposal. How will it integrate with the simu activities of
     the proto-collaborations.
     -   one reason the scope is somewhat fuzzy is that the duration
         is fuzzy. The present commitment is 4 months. Clearly the
         complete program envisioned can’t be done in 4 months (the
         specific deliverables though are intended to be achievable in
         4 months). We’ll seek support for extending it if it looks
         successful after the first couple of months.
     -   the project isn’t intended to have (and can’t
         realistically have) deliverables targeting the
         proto-collaborations in 2021, ie pre detector proposals (such
         is our expectation in writing it at least). The 2021 work in
         both the project and the proto-collaborations can focus on
         2022 convergence.
         -   possible/probable exception is providing an EIC physics list
         asap, could be used this year.
 -   this simulation tool software should be in self-consistent repo(s)
     in the EIC GitHub
 -   should be containerized and easily distributable/usable
 
 ### Notes from the [*March 2 EIC software meeting*](https://indico.bnl.gov/event/11151/) discussion (Markus)
 
 -   Wouter asked about the steps after the community input. We clarified
     that there will be regular updates in the weekly EIC Software
     meetings as well as regular meetings by the developers.
 
 -   Jin asked to publish the validation setup as part of the deliverable
     (see his comment above). We will add this to the deliverable. We
     also summarized last week’s discussion on the topic, in particular
     the requirement for test-beam data and Elke’s suggestion to
     collect information from the EIC Generic Detector R&D consortia on
     tuning and validation of detector simulations in Geant4.
 
 -   Dmitry asked how the plug and play modular approach will
     be implemented. He also asked about the user interface, in
     particular using the Geant4 macros or Python bindings.

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