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