Hi Graham,
I think that if one wanted to get the most physics out of a precision electroweak, then there are some
interesting aspects to look in the mu collider program. I don't know enough about the challenges to know
what will be better or worse in the long run for EW physics. But it is important to avoid complete mistakes
in understanding about different machine capabilities - which are best understood by discussing them.
The point about the 10^32 inst. luminosity on the H pole, as you know, is that the inst. luminosity is a special
number for an s-channel machine (unlike an ILC). The beam energy spread is tightened to ~0.2MeV so that
the maximum rate can be achieved by running on a Breit-Wigner. If you don't run in a narrow energy mode
(maximizing the Higgs boson rate), the luminosity is 10^34 at the Z pole and into the 3 TeV region. As with LEP,
different operating energies have optimal inst. luminosity with different lattice structure, and there is a lattice
structure for Z running with 10^34 (just ask Mark) - this was discussed at the BNL meeting.
But related to this, I was also curious about the extremely narrow and well understood beam energy of the
mu collider for the top quark threshold energy scan. I suspect that the mu collider machine capabilities would far
exceed what e+e- can do in the way of energy spread. Also, (speaking as one who maintained a LEP lumi readout
system), I do find the issue of the lumi measurement to be interesting. One might be able to get a far
better measurement from pointing muon tracks in the forward region than a Si-W sampling calorimeter (such as the
OPAL lumi) for electrons. We are in fact working on diamond telescopes for the LHC for point luminosity measurements
as tracking systems have unique pointing capabiltiies.
What important is to see where the strongest capabilities are for different facilities - I worry that too many people
are quick to 2nd guess experimental and machine issues without pursing them to see where they hit a fundamental
obstacle. In fact, the general idea that one should stop or not pursue things because they may be challenging or
overkill is just going to kill the field.
Best,
Chris
On Apr 21, 2013, at 2:40 PM, "Graham W. Wilson" <[log in to unmask]>
wrote:
>
> Hi Chris,
>
> The other essential point re precision Z physics in the same breath
> as muon collider is integrated luminosity.
>
> To my knowledge muon collider designs have not been targeted at sqrt(s)=mZ as it is not credible to
> improve substantially in integrated luminosity over LEP/SLC (LEP was 1.6e31 per IP) - and also highly
> polarized beams are not feasible.
>
> MC Higgs factory designs claim L at 126 GeV of 1.7e31 - 1e32. (Mark Palmer's talk at MIT).
> This may or may not be technically realizable in a future era -
> but it is mostly of potential interest because of the (m_mu/m_e)**2 factor for s-channel Higgs
> - not as a machine to improve on LEP/SLC.
>
> regards
> Graham
>
> On 4/19/2013 9:49 AM, Peskin, Michael E. wrote:
>> Chris:
>>
>> > I was wondering if much thought went into the way an EW program would look at a muon collider.
>>
>> I think that your remarks miss two points:
>>
>> 1. It is true that, in the LEP and SLC experiments, the tree level peak height is 40 nb and it is shifted to 30 nb by initial state radiation. However, ISR does not go away at a muon collider. The strength of ISR is proportional to
>>
>> log ( mz^2/ml^2) = 24 for e , = 14 for mu
>>
>> So the smearing and shift of the Z peak is smaller for muons but still substantial.
>>
>> 2. On the other hand, another ingredient is the precision luminosity measurement, which is done in e+e- with very high statistics using small-angle Bhabhas. At a muon collider, the small angle region has very large machine backgrounds, and it is probably not possible to have a precision luminosity counter like the ones at LEP. A viable strategy has to be defined.
>>
>> Best wishes,
>>
>> Michael
>>
>> -------------------------------------------------------------------------------------------
>> Michael E. Peskin [log in to unmask]
>> HEP Theory Group, MS 81 -------
>> SLAC National Accelerator Lab. phone: 1-(650)-926-3250
>> 2575 Sand Hill Road fax: 1-(650)-926-2525
>> Menlo Park, CA 94025 USA www.slac.stanford.edu/~mpeskin/
>> ---------------------------------------------------------------------------------------------
>> ________________________________________
>> From: Christopher G. Tully [[log in to unmask]]
>> Sent: Friday, April 19, 2013 6:53 AM
>> To: Ayres Freitas
>> Cc: Ashutosh Kotwal; Peskin, Michael E.; Michael Schmitt; snowmass-electroweak; [log in to unmask]
>> Subject: Re: [SNOWMASS-ELECTROWEAK] question from the Capabilities group
>>
>> Hi Ashutosh,
>> I was wondering if much thought went into the way an EW program would look at a muon collider.
>> I recall the raw Born level peak cross section was ~40nb and then shifted to 30nb with radiation corrections.
>> Also, the precision of the forward Bhabha scattering for the lump measurement (and acceptance) from
>> Alibaba, BHlumi, and other calculations made it hard to go far below 0.1% on the lump measurement.
>> I assume for a muon collider, the radiative corrects would be very different and the way the luminosity is measured
>> would be very different (at least from a detector aspect). Here the beam energy would be known to 10keV
>> and the beam energy spread could be substantially smaller than e+e-.
>> Best,
>> Chris
>>
>>
>> On Apr 19, 2013, at 9:02 AM, Ayres Freitas <[log in to unmask]> wrote:
>>
>>> Hi Ashutosh,
>>>
>>> I totally agree with you as far as GigaZ is concerned. Something like GigaZ is an extremely worthwhile effort, and theorists will likely live up to that challenge during the next 1-2 decades. However, Michael was asking about a machine that will accumulate 100 times the luminosity of GigaZ (effectly a TeraZ), and I honestly believe that it is unclear whether we can even approximately match this level of precision with other experimental inputs and theory.
>>>
>>> Best,
>>> Ayres
>>>
>>>
>>> On Fri, 19 Apr 2013, Ashutosh Kotwal wrote:
>>>
>>>> Dear Michael, all,
>>>> Thanks for this information - I also read the responses. My opinion is different from those stated.
>>>>
>>>> One way to state my opinion is that for almost 2 decades, MZ and GF have been 10 times more precise than sin2theta. MW has now caught up with sin2theta, but for most of this time it was also lagging.
>>>>
>>>> 10 years ago, alphaEM(MZ) was 4 times worse that it is now, and was at the same level then as sin2theta and MW are now.
>>>>
>>>> My point is, despite all this, we never thought that MZ and GF was "wasted precision" for the last two decades while the other measurements slowly caught up, including Mtop.
>>>>
>>>> So I think there is nothing wrong with sin2theta leapfroging to become the pack leader in precision. EWPO have been global program. We will find ways for other EWPOs to catch up.
>>>>
>>>> GigaZ will produce sin2theta precision equal to current MZ and GF precision. I see no reason to stop there.
>>>>
>>>> Another example - when Tevatron MW was 100 MeV error, alphaEM was an equivalent 15 MeV error - this was in year 2000. One could have "given up" on MW ambitions by saying "alphaEM would limit us anyway". Yet here we are, with MW at 15 MeV and alphaEM at 4 MeV equivalent.
>>>>
>>>> I wonder if Lattice QCD can help on the non-perturbative QCD loops in alphaEM running.
>>>>
>>>> regards,
>>>> Ashutosh
>>>>
>>>>
>>>>
>>>>
>>>> On Apr 18, 2013, at 1:09 AM, "Peskin, Michael E." <[log in to unmask]> wrote:
>>>>
>>>>> Dear Colleagues,
>>>>>
>>>>> Last week, the accelerator physicists' group in Frontier Capabilities met to discuss
>>>>> lepton colliders. The following question was raised, and your group should answer it.
>>>>>
>>>>> For a long time, ILC has been contemplating a run at the Z pole with 10^34 luminosity
>>>>> ("Giga-Z"). This would be able to improve most precision electroweak observables by
>>>>> about 1 decimal place. This program is by now well documented.
>>>>>
>>>>> The TLEP proposal includes a program at the Z with luminosity 10^36 ("Tera-Z"). TLEP is
>>>>> limited by the total amount of synchrotron radiation power that has to be carried
>>>>> off. There is less synchrotron radiation per particle at lower energies, so higher
>>>>> beam currents are possible.
>>>>>
>>>>> However, really getting 10^36 luminosity at the Z puts other constraints on the design.
>>>>> The machine physicists remarked that TLEP is much easier to build for a program at
>>>>> 250 GeV with 10^35 if one would back off to 10^35 also at the Z.
>>>>>
>>>>> The question for you is, how much would the extra factor of 10 at the Z pole (or the
>>>>> extra factor of 100 beyond Giga-Z) buy you in terms of the physics? My quick impression
>>>>> is that it is not easy to convert the extra luminosity into physics. GF and MZ must be
>>>>> improved, and NNLO electroweak becomes relevant. The uncertainty in alpha(mZ) also
>>>>> needs improvement, and I do not see a way to do that.
>>>>>
>>>>> However, these are just off-the-cuff remarks. If someone is interested in doing a real
>>>>> analysis of this question for the Snowmass study, I encourage you.
>>>>>
>>>>> Here is a reference on TLEP at the Z:
>>>>>
>>>>> https://indico.cern.ch/conferenceDisplay.py?confId=222458
>>>>> talk of Alain Blondel at the bottom of the page
>>>>>
>>>>> Thank you!
>>>>>
>>>>> Michael
>>>>>
>>>>>
>>>>> -------------------------------------------------------------------------------------------
>>>>> Michael E. Peskin [log in to unmask]
>>>>> HEP Theory Group, MS 81 -------
>>>>> SLAC National Accelerator Lab. phone: 1-(650)-926-3250
>>>>> 2575 Sand Hill Road fax: 1-(650)-926-2525
>>>>> Menlo Park, CA 94025 USA www.slac.stanford.edu/~mpeskin/
>>>>> ---------------------------------------------------------------------------------------------
>>>>>
>>>>> ########################################################################
>>>>> Use REPLY-ALL to reply to list
>>>>>
>>>>> To unsubscribe from the SNOWMASS-ELECTROWEAK list, click the following link:
>>>>> https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=SNOWMASS-ELECTROWEAK&A=1
>>>> ########################################################################
>>>> Use REPLY-ALL to reply to list
>>>>
>>>> To unsubscribe from the SNOWMASS-ELECTROWEAK list, click the following link:
>>>> https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=SNOWMASS-ELECTROWEAK&A=1
>>>>
>>> ########################################################################
>>> Use REPLY-ALL to reply to list
>>>
>>> To unsubscribe from the SNOWMASS-ELECTROWEAK list, click the following link:
>>> https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=SNOWMASS-ELECTROWEAK&A=1
>> ########################################################################
>> Use REPLY-ALL to reply to list
>>
>> To unsubscribe from the SNOWMASS-ELECTROWEAK list, click the following link:
>> https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=SNOWMASS-ELECTROWEAK&A=1
>>
>
>
> --
> 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/
>
>
########################################################################
Use REPLY-ALL to reply to list
To unsubscribe from the SNOWMASS-ELECTROWEAK list, click the following link:
https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=SNOWMASS-ELECTROWEAK&A=1
|
