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/ > --------------------------------------------------------------------------------------------- > > ######################################################################## > 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