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Is a muon collider feasible?

  1. Jul 7, 2012 #1
    New boson sparks call for 'Higgs factory' - physicsworld.com

    That article mentions a possible muon collider for making Higgs particles. Muons have the nice feature of having much less synchrotron-radiation loss, permitting a much smaller accelerator.

    However, muons have a problem. Their mean life is about 2.2 microseconds, and with time dilation at 100 Gev, it would become 2 milliseconds.

    That seems to offer very little margin of error. If a muon does not collide with another muon in a few microseconds of its proper time, it will decay.

    It may also be necessary to get both the negative and the positive muon from each muon pair production, unless it's feasible to make more than a million muons per second.

    That collider will produce Higgs particles by associated production:

    mu+ + mu- -> (Z) -> Z + H

    The energy threshold will be 216 GeV. Curiously, the LEP's maximum total energy was 209; the LEP barely missed discovering the Higgs particle.
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  3. Jul 8, 2012 #2


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    Unless the LHC finds new particles with higher mass, I doubt that a muon collider will be built within the next decades. 216 GeV cms-energy is well within the range of linear colliders, and they could be cheaper than the planned ILC (which is designed for 500 GeV+). You could even re-use the LHC tunnel for "LEP3" to reach this energy. Improvements in cavities should make reaching those additional GeVs easy.

    A muon collider would be very cool, but probably much worse in terms of luminosity. It is not just the production and limited time - synchrotron radiation is a very powerful cooling mechanism!
  4. Jul 8, 2012 #3


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    You might want to read this document from last year:


  5. Jul 8, 2012 #4

    Vanadium 50

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    The fact of the matter is, we don't know how to build a muon collider. In 10 or 15 or 20 years, maybe that will change, but right now, we couldn't build one if we wanted to.

    Also, the lower energy you want to go, the more challenging it becomes. This technology is best suited for multi-TeV colliders.

    Not really. Ignoring the problem that the tunnel is already filled with equipment and 6000 people who want to use it, you still have a problem. To get a reasonable Higgs rate, you need a substantially better final focus than LEP had. Remember, it doesn't do you any good to make Higgses at the same rate as the LHC: you need to go well beyond that to justify a new machine.

    With a final focus that tight, you get "beamstrahlung" - the two beams perturb each other as they pass, and lose energy to radiation, and are lost because they can no longer complete an orbit. The lifetime of a typical electron is about a second, and even with a dedicated new injector ring, that is far too short to keep the ring "topped off" - it needs to be about 100 seconds.

    You need a bigger tunnel.
  6. Jul 8, 2012 #5


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    You would have to wait for the end of the LHC, of course - just as LHC "waited" for LEP.

    Raising the Higgs production rate of the LHC is not necessary to improve the measurements. The lower overall cross-section and multiplicity of the events would allow for a better trigger selection (maybe even the storage of all data), which increases the rate of recorded Higgs events. And you can perform full event reconstructions, of course.

    Extrapolating the data given here to a higher cms energy (no drop in the cross-section as real HZ would be allowed) and Higgs mass, I would expect a cross-section of about ~0.1pb.
    According to the same source, the LEP experiments collected ~250/pb per year (each), which would correspond to ~2500 Higgs bosons per year, including machine availability. LEP3 would have ~30 years of innovations to improve that. The B-factories have luminosities up to 2E34/cm^2/s (KEKB), which would give ~10 Higgs per hour, if the same value can be reached by a "LEP3" (not including machine downtimes).
  7. Jul 8, 2012 #6

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    The problem is that if you start using B-factory type final foci, you run into the problem of beamstrahlung I mentioned earlier. You really are limited to the ~2000 per year mentioned. That's comparable to what you get at the LHC at design.

    It is true that you have access to different channels in the different machines, like Higgs to c cbar in the e+e- collider and ttbarH in the pp collider. But it's also true that placing them in the same tunnel puts this in competition with each other.

    Either a new linear machine or a circular machine in a larger tunnel makes sense. LEP-3 has too many problems - both physical and practical.
  8. Jul 9, 2012 #7
    > mu+ + mu- -> (Z) -> Z + H
    > The energy threshold will be 216 GeV.
    No. You could produce Higgs boson in so called s-chanel:
    μ+ + μ- -> H
    ... if sum of μ energies is very close to H rest mass (thanks to Heisenberg :smile: don't have to be exact ).
    Production in s-chanel is mass squared dependent, so:
    e+ + e- -> H
    ... is possible in ~125-GeV e+e- collider, but with 40000 times lower number of bosons produced than in similar muon collider, which is to low to be visible above background.

    >you would have to wait for the end of the LHC,
    End of 14 TeV LHC will be probably about year 2030, and there are firm plans to change NbTi magnets to Nb3Sn ones and move to ~28 TeV than.
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