Future Circular Collider

Energy and luminosity upgrade in an integrated program

FCC-ee (Z, WW, H, ttbar):
Highest luminosities at Z, W, ZH among
proposed Higgs and EW factories with
indirect discovery potential up to ~ 70 TeV
FCC-hh (~100 TeV):
Direct exploration of next energy frontier (~ x10 LHC) and unparalleled measurements
Feasibility Status Report in 2025
More than 150 institutes from 30 countries already involved

source: FCC Layout — Aerial View

Ingredients of FCC Physics Software

Key4hep

Set of common software packages, tools, and standards for different Detector/Collider Concepts

Common effort from FCC, CLIC/ILC, EIC, CEPC, …
- Preserves and adapts existing functionanlity from iLCSoft, FCCSW, CEPCSW, …
Individual participants adjust their stack to their needs
Main ingredients:
- Event data model: EDM4hep
- Data processing framework: Gaudi
- Detector description: DD4hep
- Software distribution: Spack
Bi-weekly meetings
- Tuesday, 9:00 AM GVA; Indico category

EDM4hep I.

Describes event data with the set of standard objects

Specification in a single YAML file
Generated with the help of Podio

EDM4hep II.

Example object:

 #-------------  CalorimeterHit
edm4hep::CalorimeterHit:
  Description: "Calorimeter hit"
  Author: "EDM4hep authors"
  Members:
    - uint64_t cellID                 // detector specific (geometrical) cell id
    - float energy [GeV]              // energy of the hit
    - float energyError [GeV]         // error of the hit energy
    - float time [ns]                 // time of the hit
    - edm4hep::Vector3f position [mm] // position of the hit in world coordinates
    - int32_t type                    // type of hit

Current version: v0.99.0
- Approaching version 1.0
- Backward compatibility
Objects can be extended / new created
Bi-weekly discussion:
- Tuesday, 9:00 AM GVA; Indico

Podio

Generates Event Data Model and serves as I/O Layer

Generates EDM from YAML files
Employs plain-old-data (POD) data structures
I/O machinery consists of three layers
- POD Layer - actual data structures
- Object Layer - helps resolve the relations
- User Layer - full fledged EDM objects
Supports multiple backends:
- ROOT, SIO, ...
Current version: 1.0.1

Podio Reader

Constructs the EDM4hep objects for the user

Example usage of Podio Reader in Pyhton:

                  from podio.root_io import Reader
reader = Reader("one or many input files")
for event in reader.get("events"):
  hits = store.get("hits")
  for hit in hits:
    # ...

To inspect contents of the EDM4hep file use: podio-dump

Gaudi

Battle tested event processing framework

Job of an event processing framework
- Stitches and steers various algorithms together
- Controls event loop
- Manages transient storage and I/O
Used by current experiments: ATLAS, LHCb
New developments: Gaudi::Functional
Key4hep started life by attempting to reuse algorithms already developed
Need for converters/wrappers:
k4MarlinWrapper, k4CLUE, k4GaudiPandora, …
Selected over Marlin due to MT support

Hello World in Gaudi:

                from Gaudi.Configuration import *
from Configurables import HelloWorldEx
 
alg = HelloWorldEx()
 
ApplicationMgr(
    EvtMax = 10,
    EvtSel = 'NONE',
    HistogramPersistency = 'NONE',
    TopAlg = [alg],
)

Source: Gaudi

k4FWCore

Package with Key4hep Gaudi components

Provides input and output of files, but also among algorithms
- IOSvc, DataHandle, MetaDataHandle
Main program to run Gaudi steering: k4run

Gaudi Functional allows proper multithreading

            #include "Gaudi/Property.h"
#include "edm4hep/MCParticleCollection.h"
#include "k4FWCore/Consumer.h"
#include <stdexcept>
#include <string>
 
struct ExampleFunctionalConsumer final : k4FWCore::Consumer<void(const edm4hep::MCParticleCollection& input)> {
  // The pair in KeyValues can be changed from python and it corresponds
  // to the name of the input collection
  ExampleFunctionalConsumer(const std::string& name, ISvcLocator* svcLoc)
      : Consumer(name, svcLoc, KeyValues("InputCollection", {"MCParticles"})) {}
 
  // This is the function that will be called to transform the data
  // Note that the function has to be const, as well as the collections
  // we get from the input
  void operator()(const edm4hep::MCParticleCollection& input) const override {
    debug() << "Received MCParticle collection with " << input.size() << " elements" << endmsg;
    if (input.size() != 2) {
      fatal() << "Wrong size of MCParticle collection, expected 2 got " << input.size() << endmsg;
      throw std::runtime_error("Wrong size of MCParticle collection");
    }
    int i = 0;
    for (const auto& particle : input) {
      if ((particle.getPDG() != 1 + i + m_offset) || (particle.getGeneratorStatus() != 2 + i + m_offset) ||
          (particle.getSimulatorStatus() != 3 + i + m_offset) || (particle.getCharge() != 4 + i + m_offset) ||
          (particle.getTime() != 5 + i + m_offset) || (particle.getMass() != 6 + i + m_offset)) {
        std::stringstream error;
        error << "Wrong data in MCParticle collection, expected " << 1 + i + m_offset << ", " << 2 + i + m_offset
              << ", " << 3 + i + m_offset << ", " << 4 + i + m_offset << ", " << 5 + i + m_offset << ", "
              << 6 + i + m_offset << " got " << particle.getPDG() << ", " << particle.getGeneratorStatus() << ", "
              << particle.getSimulatorStatus() << ", " << particle.getCharge() << ", " << particle.getTime() << ", "
              << particle.getMass();
        throw std::runtime_error(error.str());
      }
      i++;
    }
  }
 
  Gaudi::Property<int> m_offset{this, "Offset", 10, "Integer to add to the dummy values written to the edm"};
};
 
DECLARE_COMPONENT(ExampleFunctionalConsumer)

LCIO ↔ EDM4hep Converters

Integration of tools developed by linear collider community

k4MarlinWrapper wraps Marlin processor in a Gaudi algorithm and allows to run them unchanged
LCIO ↔ EDM4hep converters do the conversion on the fly

Detector description

The detector is completely described with the help of DD4hep

The description itself done by C++ builder and XML compact file(s)
- Every sub-detector needs specialized C++ builder class
- The XML compact files are organized in tree structure, which allows Plug-and-Play
XML Schema defined by LCSim
Specialized data can be attached to each sub-detector at runtime
Simulation for FCC-ee done with ddsim — standalone simulation executable
All FCC-ee (sub)detectors collected in k4geo repository in /FCCee
FCC-hh baseline detector stayed in FCCDetectors repository

Phoenix@FCC

Spack in Key4hep

Package management for supercomputing centers

Distributes software in source form
Every package can have multiple versions and configuration options
Strives to not depend on the underlying OS as much as possible
Peace of software is packaged by creating a recipe script
The packages are stored in two repositories
- Main Spack repository
- Specialized Key4hep repository
Compiled packages are published on CVMFS
- source /cvmfs/sw.hsf.org/key4hep/setup.sh
- source /cvmfs/sw-nightlies.hsf.org/key4hep/setup.sh
- source /cvmfs/fcc.cern.ch/sw/latest/setup.sh

source: T. Madlener

Event Processing Workflow

source: G. Ganis

Generation

Theoretical efforts for ee generators is rumping up

Most of the generators already packaged in Key4hep
- MadGraph5_aMC@NLO, Pythia6/8, Herwig3, Whizard, BabaYaga, KKMCee, Guinea-Pig, Sherpa, EvtGen, …
Set of Gaudi algorithms and helpers packaged in k4Gen
- Particle gun, particle filters, vertex smearing, …
New effort for unified generator configuration packaged in k4GeneratorsConfig
- Integrated: BabaYaga, KKMC, MadGraph, Pythia, Sherpa, Whizard
Any generator outputting established format (HepMC2/3, hepevt, stdhep, …) can be input for Geant4 simulation with ddsim
Prefered formats: HepMC3 and EDM4hep
- Ongoing effort to make EDM4hep more suitable for generators
Open topics include: ISR treatment, accuracy, Beam Energy Spread, crossing angle (+ spread), effect of the beams on final state

Simulation

Propagation of particles or decay products through detector

Full simulation for FCC-ee detectors using ddsim (part of DD4hep)
Fast simulation handled by k4SimDelphes
Framework integration with k4SimGeant4 and Gaussino on back burner
Ongoing work on three FCCee detector concepts IDEA, CLD and ALLEGRO almost complete
- Effort now shifting from detector description towards Digitization and Reconstruction
- Bi-weekly meeting, Wed 11:00 AM GVA: Indico category

Reconstruction

Pandora and Key4hep wrapper
k4Clue Logo

Efforts are packaged per sub-detector type, for example
- kRecCalorimeter: Reconstruction of Noble Liquid based calorimeter
- k4RecTracker: vertex and tracker reconstruction as well as tracking
Or per reconstruction solution, e.g.
- k4GaudiPandora: Wrapping of the Particle flow framework
- k4Clue: Clustering algorithm from HGCAL
Some of the ongoing efforts also include
- Particle identification with Array of RICH Cells (ARC)
- Integration of ACTS tracking into Key4hep
- Machine learning based flavor tagging

Analysis with FCCAnalyses

Analysis framework build on top of ROOT RDataFrame
with input from EDM4hep

Dependent on Key4hep Stack
Manages input samples
Has standard library of functions/functors
Runs the dataframe
Helps with histograms/plots
Analyses Catalog:
- FCCeePhysicsPerformance
- FCChhPhysicsPerformance
Bi-weekly meeting: Wed 4:00 PM GVA
- Indico category

ROOT RDataFrame

Describes processing of data as actions on table columns
- Defines of new columns
- Filter rules
- Result definitions (histogram, graph)
The actions are lazily evaluated
Multi threading is available out of the box
Optimized for bulk processing
Allows integration of existing C++ libraries

Developing Key4hep / FCC Software

Access to CVMFS is crucial

Start by sourcing Key4hep stack from CVMFS

            source /cvmfs/sw.hsf.org/key4hep/setup.sh
# or
source /cvmfs/sw-nightlies.hsf.org/key4hep/setup.sh

Usually, the packages are build with CMake

            mkdir build install
cd build
cmake -DCMAKE_INSTALL_PREFIX=install ..
make -j4
make install
cd ..

To make your local version visible in your current shell, run

            k4_local_repo

Documentation

FCC Software: Main page with signpost
FCC Tutorials: Tutorials on how to get started with FCC Software
Key4hep Documentation: Growing documentation of the Key4hep and its components.
FCC-ee Detector Full Sim: FCC-ee detectors implementation, simulation and reconstruction documentation
FCC Software Glossary: A glossary of HEP and FCC-specific terms and concepts.
ALEPH Documentation: Resurrecting ALEPH data in EDM4hep format (CERN log-in required).

Conclusions

FCC is main stakeholder in the Key4hep stack project, which is
becoming established stack delivering physics results
Strive for integration and/or interoperability continues
EDM4hep reached version 1.0 — backwards compatibility from this release
Functional Gaudi on the way
Simulation, FullSim and Recontruction far from complete
Plenty of work ahead of us and You can join our meetings
- FCC Software Indico Category
- Key4hep Indico Category

	#------------- CalorimeterHit
	edm4hep::CalorimeterHit:
	Description: "Calorimeter hit"
	Author: "EDM4hep authors"
	Members:
	- uint64_t cellID // detector specific (geometrical) cell id
	- float energy [GeV] // energy of the hit
	- float energyError [GeV] // error of the hit energy
	- float time [ns] // time of the hit
	- edm4hep::Vector3f position [mm] // position of the hit in world coordinates
	- int32_t type // type of hit

	from podio.root_io import Reader
	reader = Reader("one or many input files")
	for event in reader.get("events"):
	hits = store.get("hits")
	for hit in hits:
	# ...

	from Gaudi.Configuration import *
	from Configurables import HelloWorldEx

	alg = HelloWorldEx()

	ApplicationMgr(
	EvtMax = 10,
	EvtSel = 'NONE',
	HistogramPersistency = 'NONE',
	TopAlg = [alg],
	)

	#include "Gaudi/Property.h"
	#include "edm4hep/MCParticleCollection.h"
	#include "k4FWCore/Consumer.h"
	#include <stdexcept>
	#include <string>

	struct ExampleFunctionalConsumer final : k4FWCore::Consumer<void(const edm4hep::MCParticleCollection& input)> {
	// The pair in KeyValues can be changed from python and it corresponds
	// to the name of the input collection
	ExampleFunctionalConsumer(const std::string& name, ISvcLocator* svcLoc)
	: Consumer(name, svcLoc, KeyValues("InputCollection", {"MCParticles"})) {}

	// This is the function that will be called to transform the data
	// Note that the function has to be const, as well as the collections
	// we get from the input
	void operator()(const edm4hep::MCParticleCollection& input) const override {
	debug() << "Received MCParticle collection with " << input.size() << " elements" << endmsg;
	if (input.size() != 2) {
	fatal() << "Wrong size of MCParticle collection, expected 2 got " << input.size() << endmsg;
	throw std::runtime_error("Wrong size of MCParticle collection");
	}
	int i = 0;
	for (const auto& particle : input) {
	if ((particle.getPDG() != 1 + i + m_offset) \|\| (particle.getGeneratorStatus() != 2 + i + m_offset) \|\|
	(particle.getSimulatorStatus() != 3 + i + m_offset) \|\| (particle.getCharge() != 4 + i + m_offset) \|\|
	(particle.getTime() != 5 + i + m_offset) \|\| (particle.getMass() != 6 + i + m_offset)) {
	std::stringstream error;
	error << "Wrong data in MCParticle collection, expected " << 1 + i + m_offset << ", " << 2 + i + m_offset
	<< ", " << 3 + i + m_offset << ", " << 4 + i + m_offset << ", " << 5 + i + m_offset << ", "
	<< 6 + i + m_offset << " got " << particle.getPDG() << ", " << particle.getGeneratorStatus() << ", "
	<< particle.getSimulatorStatus() << ", " << particle.getCharge() << ", " << particle.getTime() << ", "
	<< particle.getMass();
	throw std::runtime_error(error.str());
	}
	i++;
	}
	}

	Gaudi::Property<int> m_offset{this, "Offset", 10, "Integer to add to the dummy values written to the edm"};
	};

	DECLARE_COMPONENT(ExampleFunctionalConsumer)

	source /cvmfs/sw.hsf.org/key4hep/setup.sh
	# or
	source /cvmfs/sw-nightlies.hsf.org/key4hep/setup.sh

	mkdir build install
	cd build
	cmake -DCMAKE_INSTALL_PREFIX=install ..
	make -j4
	make install
	cd ..