Geant4 in the FNAL g-2 Experiment Kevin Lynch Boston University August 2009 g-2 Collaboration Meeting

What are we trying to learn? How does the hardware in the Brookhaven ring control and limit the measurement, and what can we do to improve the situation? In particular: Injection and Beam Dynamics (Boston) Calorimeters (Illinois) In vacuum wire chambers (FNAL)

So Lee says.... “What happens if we add a fourth kicker?” “What about opening the inflector ends?” Answering these questions requires a fairly significant simulation to replace the aging g2geant3 model: g2MIGTRACE g-2 Muon Injection, Geometry, Tracking and Capture Efficiency

Current g2MIGTRACE features ● Accurate Physical Geometry: ● Vacuum Walls, including (finally) accurate scallops ● Inflector and (relevant parts of the) cryostat ● Quadrupole Plates and supports ● Kicker Plates ● Pickup Electrodes ● Collimators

Current g2MIGTRACE features ● Fields: ● Storage B field, including (average) radial and vertical gradients ● Quadrupole fields, including scraping ● Time dependent kicker fields (but no maps!) ● 3D Inflector field maps ● Highly flexible ● Internal or external muons (or pions, etc.) ● “Scriptable” control system ● Lots of settable features ● Ideal or LCR kicks ● Launch control ● etc.

The Ring

Inflector Detail

Quad Plate Detail

Kicker Plate Detail

Quad Field Details ● 24kV field ● n=0.134 ● fcbo=465kHz ● Field Map approach ● Interpolation on polar grid with 14-term multipole expansion ● E821 Scraping fully implemented

Injection and storage One plate support Two plate supports Beats me MeV

Things that are missing ● We don't propagate through the backleg hole ● Quadrupole fields outside storage region ● Full field distribution in kicker ● There's a picture in the NIM article... ● New kicker ideas (lower L by doubling plates) ● Spin tracking ● Hadrons (Geant bug?) ● Octupole CBO reduction scheme ● Calorimeter and chamber mockups ● We can't currently take input muons or generate output electrons

Calorimeter model ● Two tasks: ● Determine the optimal detector segmentation and position ● Determine the optimal light guide readout geometry Muon orbitDecay electron trajectory Calorimeter

Calorimeter Model  Muon orbit Vertical profile Radial profile

Light guide Model

Things that are missing ● Finish calorimeter simulation ● Determine geometry and segmentation ● Insert resulting distributions into existing light guide simulation ● Expand information from light guide simulation to tell us more about various light guide options

Wire Chambers The proposal has these in the vacuum scallops, upstream of the calorimeters Muon orbitDecay electron trajectory Calorimeter In vacuo chambers for y or x-y traceback

What we hope to learn ● Optical placement ● Effects of upstream materials ● Quad and kicker plates ● Effects on downstream detectors ● The allowed material budget

In summary... ● Geant4 is going to play a major role in this experiment, and significant work is ongoing ● Stay tuned for some actual results in the breakouts tomorrow