Dear All,

          The other important parameter is the longitudinal polarization 
achievable as a function of
instantaneous luminosity particularly for A_LR etc. It seems clear that 
high polarization would come
at a price in luminosity for this kind of design.

      regards
              Graham

On 4/18/2013 12:09 AM, Peskin, Michael E. 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/
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-- 
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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