Physics Processes Missing from our Current Simulation Tools

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

2. 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 toolboxand/or enhancing the tools we use. 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) 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 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). 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? 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? 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. Physics Processes Missing from our Current Simulation Tools

9. 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 Physics Processes Missing from our Current Simulation Tools

10. 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. Physics Processes Missing from our Current Simulation Tools

11. 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… Physics Processes Missing from our Current Simulation Tools

12. 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. Physics Processes Missing from our Current Simulation Tools