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 

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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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________________________________________
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

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