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Folks, I am confused by this thread. The main barrier to improvement of alphas is the fact that it is difficult to disentangle perturbative and nonperturbative contributions to event shapes in e+e-. The nonperturbative contributions fall off as 1/Q, so a substantial moment arm in Q is needed. Currently what is done is to compare Z data with PEP/PETRA data, although the latter is taken with detectors that are now two generations old. If TLEP is built, it will be possible to get high-statistics samples of e+e- event shapes in the same, modern detector at 91 GeV, 250 GeV, and 350 GeV. Then it should be possible to fit out the 1/Q terms and reach per mil precision in alphas. Probably it is worth bringing in an alphas expert (e.g. Iain Stewart at MIT) to quantify this. Need I add that, if ILC is built in Japan, we can carry out this program even sooner and extend it to even higher energies? Thanks, 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: Ashutosh Kotwal [[log in to unmask]] Sent: Friday, April 19, 2013 12:48 AM To: Michael Schmitt Cc: Sven Heinemeyer; Peskin, Michael E.; snowmass-electroweak; [log in to unmask] Subject: Re: [SNOWMASS-ELECTROWEAK] question from the Capabilities group On Apr 18, 2013, at 8:08 AM, Michael Schmitt <[log in to unmask]> wrote: > Hi, > > I believe Sven is right. As you say, it is hard to see how to improve alpha_S > without a dedicated facility/program and no such thing is planned as far as > I know. it would be interesting to think about alpha_S measurement at GigaZ and TeraZ using event shapes etc. and how statistics and systematics play into that. Ashutosh ######################################################################## 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