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
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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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