MU2E Computing

The information on this page describes a high level view of Mu2e computing; there is another page that describes Mu2e computing in detail.

The muon to electron conversion experiment (Mu2e) at Fermilab will search for the coherent, neutrino-less conversion of a muon to an electron, in the Coulomb field of a nucleus.  Should this process be observed it will provide dramatic evidence of a new physical process that is beyond our current understanding of elementary particle physics.  Such a discovery will blaze a trail towards a new understanding of the universe. 

This experiment is in the midst of its R&D and approval processes.To aid this process, a small team in the Fermilab Scientific Computing Division has developed an end‐to‐end Geant4-based simulation package and has developed reconstruction code that is now at the stage of an advanced prototype. Having these tools available at an early stage allows design options and tradeoffs to be studied using high level physics quantities. A key to the success of this effort has been, as much as possible, to acquire software and customize it, rather than to build it from scratch in‐house. 

The Software Tools 

G4beamline

• A layer on top of GEANT4; hides most G4 complexity from end users
• Easy-to-learn language for geometry and run-time configuration
• Output: ROOT ntuples and text files
• Vital for a fast turn around for early designs of the muon beamline.
• Not sufficiently powerful for design of the detector and the extinction monitor, or for advanced studies of the muon beamline. 

MARS

• Low energy neutrons critical for Mu2e: use MARS+MCNP
• Mu2e pioneered running MARS+MCNP on the grid
• Study heat and radiation load at the cryogenic solenoids, neutron sky-shine, and neutron fluxes throughout the detector.
• Critical calculations will be done with both MARS and GEANT4.

FastSim

• A surface based, fast, parameterized simulation and track fitting package.
• Pedigree: BaBar and SuperB.
• Mu2e improved treatment of very thin materials and improved navigation for curling tracks.
• Fast turn-around studies of: acceptance and resolution for variants of tracking system, optimal size and dimensions of the calorimeter, tolerance of tracker momentum resolution to B-field misalignment.

Mu2e Offline

• The workhorse for detector simulations and advanced beamline studies.  Taking over from G4beamline for routine beamline studies.
• Calibration, reconstruction and analysis will be done in his environment.
• Goal: use this software everywhere from the lowest level non-real-time layer in the trigger/DAQ, through calibration and reconstruction to final analyses.
• Acquired infrastructure software supported by Fermilab Scientific Computing Division:  the art framework, which drives the event loop; an event-data model, including persistency; run-time configuration; message logging; maintenance of random number engine state; management of singleton-like entities used for geometry and conditions data
• These tools are an evolution, starting from CMSSW.  
• Acquired the battle-tested BaBar track fit code (Kalman filter based) and ported it to run in in this environment.   All tracker results use this code.
• Authoritative geometry representation is optimized for reconstruction; the GEANT4 geometry is derived from this representation.  Planning to derive MARS and G4beamline geometries from this same source.
• G4 used as an engine that creates a complete parent-child history plus collections of track steps in sensitive volumes.  Conversion of G4 steps into DIGIs is done by Mu2e modules outside of G4.
• Merging in pileup events: in collaboration with the art team, Mu2e developed the technology to split the task into one part requiring detailed knowledge of persistency, but none of Mu2e, and a second part requiring detailed knowledge of Mu2e, but none of persistency.  This process preserves complete MC truth information.
• Pileup is accumulated before analog to DIGI conversion
• Event displays: G4 display plus a ROOT based display that runs within art.
• Under construction: interfaces to file catalogs and other databases.

 More Information: Mu2e experiment site