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Bill Marciano (BNL) "High Energy Muon Colliders: Physics Goals And Pathways"

  1. In this question, we are trying to understand the rationale for a muon collider in several possible scenarios related to Higgs/Susy physics. The general question is, after the LEP/Tevatron/LHC results are in, how we might frame the justification for a muon collider? This general question is relevant separately for both low energy (TeV scale) and high energy (greater than 3 TeV) colliders:
    1. Is there a physics case for a muon collider in the TeV scale replacing or co-existing with an electron collider of the same approximate energy?
    2. For the high energy muon collider, are there general arguments (similar to the WW scattering unitarity that focuses our attention on the 1 TeV scale) that point to new physics at the multi-TeV scale? How would discoveries, or the lack thereof, at the TeV scale affect the argument for a multi-TeV collider? How would a multi-TeV muon collider and a 100 TeV hadron collider compare in exploration of this higher mass regime?
    A specific way of asking the question:
    Suppose that at the LEP+Tevatron+LHC the only discovery turns out to be one of the following:
    1. a light mass (between 100 and 200 GeV) Standard Model Higgs boson;
    2. a light Higgs boson with unusual decay modes (e.g. a large dijet branching ratio);
    3. no Higgs, no Susy;
    4. a light Higgs boson, a heavy CP-odd scalar, and a charged Higgs;
    5. a light Higgs boson + some superpartners (e.g. a few neutralinos, charginos and squarks);
    6. a 400 GeV Standard-Model-Higgs-boson.
    What are the chances for discovering some new physics in experiments at a multi-TeV muon collider in each of these six cases?

  2. What is the rationale for running the muon collider at the Higgs pole(s) in view of what we may expect to have learned from the LHC, or compared with what we may learn from a linear ee collider? What are the necessary parameters of the machine (luminosity, polarization and fractional energy spread) needed to make this program successful?
    What is the best way of measuring the Higgs trilinear coupling?

  3. A low energy muon collider, as well as its Front End and a muon storage ring offer many opportunities, including m-e conversion, ne - nt neutrino oscillation measurements, deep-inelastic neutrino scattering, physics with stopped/slow muons and low-energy hadrons. Can these topics be incorporated as part of the early stages of muon collider development in a natural way, consistent with going ultimately to a high energy machine?
    A low energy muon collider offers potential advantages over an e+e- collider in the precision to which the top mass can be measured (at ttbar threshold). Are there any practical reasons why measuring the top quark mass, say, to better than 200 MeV is useful?

  4. Muons are different from electrons as representatives of second generation fermions. In what ways can a muon collider exploit these differences to help illuminate the way in which flavor arises and flavor symmetry is broken?

  5. What bounds could a 3 - 4 TeV muon collider put on extra dimensions, for example on the first Kaluza-Klein excitations of the Z, gluon, or top quark? What might be the reach in probing the scale of quantum gravity in the scenario with large extra dimensions accessible only to gravity?