Dear Eric, Graham, et al.
I think we have to be very clear about the technical readiness levels of these different machines.
o ILC has a detailed TDR and, importantly, the accelerating structures will be tested in anger in the coming years at XFEL.
o CLIC has a detailed conceptual design report based on a long programme of R&D. The CDR provided validation of the elements of the accelerator and no show stoppers were identified. This strong R&D programme is continuing at CERN with a development phase 2012-2016. The aim of this phase is to be in a position where CLIC could be proposed as a realistic option for a TeV lepton collider on the timescale of the results from the LHC Run 2.
o The muon collider is an extremely challenging project and there are a number of key areas that need to be demonstrated. I agree with Eric that the MAP has the potential to support a rich programme of physics. However, in the context of the EF, the muon collider is at a significantly lower TRL than CLIC. For example, we are likely to have to wait until the end of the decade before 4D muon cooling is demonstrated.
o At this stage TLEP is a concept; there is no CDR.
In my opinion there is a clear hierarchy here.
cheers,
Mark
On 31 Jul 2013, at 15:54, Eric J Prebys <[log in to unmask]> wrote:
> Graham,
>
> While it might indeed be a mistake to lump electron and muon
> colliders into the same category, it is equally a mistake to lump
> CLIC together with the ILC or TLEP.
>
> No one would argue that the ILC is a well studied
> and feasible machine. However, if the LHC results or
> indirect measurements point to a mass scale out
> of the range of the ILC, then it might well be
> that the muon collider is the better option to reach
> those scales in a "lepton collider".
>
> I've said many times that accelerators have historically
> been evolutionary rather than revolutionary and that
> "No accelerator has ever done two new things at
> once". The Tevatron did one new thing (superconducting
> magnets in a synchrotron). The LHC did nothing new,
> and that turned out to not be without risks.
>
> In contrast, both CLIC and the muon collider require
> *lots* of new things and are both "impossible"
> to first order. Which one is declared more feasible is
> largely a function of one's on experience and prejudice.
> Certainly, no one can axiomatically declare one
> more reasonable than the other.
>
> As with the ILC, the Higgs factory would be a step
> along the way, rather than a "niche application".
>
> The Muon Acceleration Program has something of an advantage
> (IMHO) in that it supports a lot of interesting physics
> along the way, even if a collider is never built, whereas
> CLIC is totally uninteresting until it succeeds (if
> it succeeds).
>
> How things are categorized is largely book keeping, but
> it's important that they be represented and compared
> correctly.
>
> -Eric
>
>
> On Jul 31, 2013, at 3:23 PM, Graham W. Wilson wrote:
>
>>
>> Dear Physics Group Conveners,
>>
>> I appreciate very much all your hard work that is helping to produce compelling reports
>> on the high energy colliding beam approach to exploring high energy physics.
>>
>> I do want to re-state more clearly my remark from yesterday at the
>> end of Mark Palmer's capabilities talk on lepton colliders.
>>
>> I think it is a mistake and very misleading to lump all "lepton colliders" together in the
>> physics reports - and more generally in discussion of our field.
>> I urge you to say e+e- when you mean e+e- and say mu+mu- when you mean mu+mu-.
>>
>> This is essentially the same remark as I made at the Seattle workshop in response
>> to elements of the Higgs group report. It was also heavily triggered by the repeated use
>> of the word "lepton colliders" in the new physics summary talk when in fact the relevant
>> conclusions and inputs to the working group were only applicable to the proposed
>> high energy e+e- colliders ILC and CLIC.
>>
>> The e+e- and mu+mu- approaches are fundamentally different.
>> Much of the rationale for a future high energy lepton collider is to explore
>> the Higgs and explore new physics possibilities in a way that is complementary to LHC.
>> The e+e- approach has shown that it is very well suited to measuring final states with
>> missing energy and such states are at the heart of the envisaged ILC and CLIC Higgs programs.
>>
>> e+e- is a well established "stable lepton collider" accelerator technology
>> with well understood and comprehensive detector capabilities with high longitudinal
>> polarization capabilities for linear colliders. It is a real option that has been
>> under development for decades and is on the table now for ILC with realistic detector
>> designs and an understanding of the machine backgrounds. The detector hermeticity
>> capability is impeccable. Precision absolute normalization is possible using Bhabhas at the 0.1% level.
>>
>> The mu+mu- collider is a highly speculative "decaying lepton collider" with
>> much R&D to do to establish the accelerator technology and luminosity performance
>> with a potential niche application to things like a Higgs resonance scan, heavy Higgs
>> and direct production of Z'. It can in principle do very well on beam energy determination.
>> It features a "novel" (according to Mark), insane according to others, background regime
>> from muon decays in the detector. This makes instrumentation of close to 4pi steradians
>> extremely difficult at a muon collider and will severely limit the ability to detect final states with
>> missing transverse momentum.
>>
>> Instrumentation below something like 150 mrad is not known to
>> be feasible at a muon collider. Assuming no instrumentation below 150 mrad, it has been shown
>> for an e+e- collider from simple kinematic considerations that this would limit the clean region
>> of detection of missing energy to transverse momenta of about 30% of the beam energy.
>> Given the actual minimum detection angle for e+e- (15 mrad), the reach is extended by a
>> factor of 10 to about 3% of the beam energy.
>>
>> As an example, the direct production of WIMP pairs in association
>> with a soft initial state photon and missing energy is something that can be
>> done very well in e+e-. Exploration of "compressed" SUSY spectra is also one of the main issues
>> of complementarity to LHC - a potentially natural explanation of current LHC results
>> (SUSY particles are being produced - but with not enough missing ET to be detectable).
>> This will be a much greater strength of e+e- compared to mu+mu- at the same center-of-mass energy
>> for the same reasons.
>>
>> In conclusion, please be careful to avoid implicitly assuming that what is feasible and
>> documented in e+e- is also obviously feasible in mu+mu-.
>> It has been demonstrated that an e+e- machine is very well suited to measurements with missing energy
>> such as nu-nu-H and supersymmetry.
>>
>>
>> regards
>>
>> Graham Wilson
>> --
>> Graham W. Wilson
>> Associate Professor
>> Dept. of Physics and Astronomy
>> University of Kansas
>> Lawrence, KS 66045
>> Office Tel. 785-864-5231
>> Web:
>> http://heplx3.phsx.ku.edu/~graham/
>>
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>>
>
> -------------------------------------------------------------------
> Eric Prebys, Fermi National Accelerator Laboratory
> Office: 630-840-8369, Email: [log in to unmask]
> WWW: http://home.fnal.gov/~prebys
> -------------------------------------------------------------------
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Prof. Mark Thomson
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