1. Physics Processes Missing from our Current Simulation Tools
This is the current list −
Please help us to complete it.
Tom Roberts
Muons, Inc.
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

2. Physics Processes Missing from our Current Simulation Tools
Classes of Processes
Single-particle processes
Collective effects in vacuum
Collective effects in matter
Polarized muon processes
Normalization and Computation of Emittance
RF breakdown
Neutrino processes
Details
Some of these are implemented in other tools; we need to consider adding to our toolbox and/or enhancing the tools we use.
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

3. Single-Particle Processes
Accurate multiple-scattering model
Several are available in ICOOL
G4beamline has all Geant4 processes available
Geant4 9.4 changes this (again)
Energy-loss straggling model (incl. length dependence)
Vavilov model vs. Striganov model
Material dependence of energy loss and straggling
ICOOL and G4beamline disagree for LiH
Correlation of energy loss with multiple scattering angle
Effect of magnetic field on multiple scattering
Energy loss in matter for high-energy muons (> ~200GeV)
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

4. Collective Effects in Vacuum
Space charge
Basic computation in ICOOL
Two computations in G4beamline
Wake fields
Beam loading
Beam-beam interactions
G4beamline space charge implementations apply
Electron cloud effects
Decay of macro-particles
Interactions of macro-particles
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

5. Collective Effects in Matter (1)
Space charge screening by material
Bunch effect on the density term of the single-particle formula for energy loss (plasma density)
Bunch-induced polarization of material causing intensity-dependent increase in energy loss
Can induce an instability
Plasma effects from ionized electrons and ions
Dense beam boring a “hole” in the absorber, with the front of the bunch ionizing ~100%, so the back end of the bunch has reduced ionization loss
Absorber bubble formation, melting, or other thermal damage
Beam particles “ganging up” on atomic nuclei – a hydrogen nucleus is NOT heavy compared to 1,000 muons.
Energy loss and multiple scattering from ionized and excited atoms (prepared by earlier beam particles).
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

6. Collective Effects in Matter (2)
Beam particles screening each other, for both multiple scattering and energy loss.
Effect of plasma on atomic response, for both multiple scattering and energy loss.
Effect of matter on wake fields and beam loss, including EM radiation from bunches transiting windows (resonates in RF cavity…).
For all of the above:
Consider dependency on material properties
Consider time dependence
Head vs. tail of a single bunch
Effects involving successive bunches in a train
Are LH2 and RF-cavity windows important?
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

7. Polarized Muon Processes
Geant4 has no muon-polarized processes, we need ot implement them
Effect of ionization cooling on polarization.
For applications other than a muon collider or neutrino factory
Might it be interesting in a collider to trade a factor of ~100 reduction in luminosity for partially polarized beams? – Would it be possible?
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

8. Normalization and Computation of Emittance
Uncertainties remain about the accuracy of the pion production models used.
MARS, Fluka, MCNPX, Geant4, all differ in various ways
Direct experiments are scarce, but there are relevant ones
Cavitation and other distortions of the mercury jet production target
Proper calculation of the EM vector potential in the emittance computation.
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

9. Physics Processes Missing from our Current Simulation Tools
RF Breakdown
While not directly part of the particle simulations, modeling RF breakdown is an important aspect of the overall simulation of a muon collider.
Vacuum
High-pressure H2
Surface effects and processing
This is so important that experiments are required.
Will affect technology used, so must be done early
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

10. Physics Processes Missing from our Current Simulation Tools
Neutrino Processes
Surface radiation assessment will require accurate simulations of neutrino interactions
Need to significantly increase neutrino interaction cross-sections to make simulations feasible
Also needed for studying backgrounds in the MC detector.
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

11. Physics Processes Missing from our Current Simulation Tools
Details
Our current simulations are at best approximations to what would actually be built
Many details must be assessed and included if necessary, such as:
3-D effects in RF cavity field models
Realistic, non-pillbox cavities
Couplers
HOM absorbers
Engineering assessments
Thermal loads from the beam
Thermal loads from muon decay
Radiation levels
Surely others…
Ability to model a large and complex detector for background studies
Surely more…
March 2, TJR
Physics Processes Missing from our Current Simulation Tools

12. Physics Processes Missing from our Current Simulation Tools
Summary
There are a number of complicated and subtle physics processes not included in our current simulation tools.
We must expand the list to be as complete as possible.
Ultimately we will need a set of publications or MuCool notes, estimating the importance of each one.
We need to implement those that can significantly affect our modeling of facilities.
There are many other simulation tools available, and we need to assess whether to acquire and use additional tools, or to enhance the ones we already use.
There are of course myriads of engineering details, required for accurate simulations of a specific design.
March 2, TJR
Physics Processes Missing from our Current Simulation Tools