Date: Sun, 31 Aug 2003 15:00:22 +0200 (MEST)
From: Achim Stahl <astahl@ifh.de>
To: Gudrid Moortgat <g.a.moortgat-pick@durham.ac.uk>,
     Uriel Nauenberg <uriel@pizero.colorado.edu>
Subject: Polarisation Write-up

I have spend a little bit of time thinking about our write-up.
Here are my thoughts about a more detail contents.
(I'm starting from the outline on Gudi's webpage
  http://www.ippp.dur.ac.uk/~gudrid/power/draft.html )

                                          Achim

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I would subdivide section II into three sections.

 II. Physics with Polarization

  II.1 The Physics Case for Polarized Electrons

        There is general agreement that we need polarized electrons
        therefore we can call it 'Physics Case'. It is also well
        documented, therefore we can keep it short.

  II.2 Physics with Longitudinally Polarized Electrons and Positrons
        This would include the sections of Uriel and myself as well
        as the section of Gudi and Herb.
        It has the same topic and I think it should go into one
        chapter, even if it is written by different people.

        More details below.

  II.3 Physics with Transverse Polarization

------------------------------------------------------------------------

For longitudinal positron polarization I see 5 general arguments how it
can improve the physics output of a linear collider. I would subdivide
section II.2 along these 5 points and sort them decreasing importance.
We'll have to figure out the ranking. This is just a first guess:

II.2.1 Observations that require both beams polarized

  Here I would put things that cannot be done with electron polarization
  only, even not with an ideal detector.

  The assignment of the left- and right-handed selectrons to e_L and e_R
  goes here. Is there anyting else?

II.2.2 Selfcalibrating Polarization Measurement: Giga-Z

  It is really quite different from all the other stuff. I would put it
  in a seperate chapter.
  There is a new note form Gideon and his student explaining in detail the
  gain from the positron polarization ind two different schemes and for
  various assumptions on the achievable polariztion. They confirmed the
  conclusion that it is only worth doing with positron polarization.


II.2.3 Improved Precision on the Measurement of Effective Polarization

  - Introduce the concept of effective polarization.
    Specify the assumptions under which a cross section can be specified
      from the effective polarization only. Here we need some input
      from theory!
    Error propagation: How much smaller is the error on the effective
      polarization compared to the input from the polarimeters.

  - Physics examples:
      Which processes need a precision knowledge of the polarization?
      Explain a few examples.

II.2.4 Supression of Background Channels

  - Is it actually possible to do this in a systematic way?
    Can we plot the cross section for the two different helicity 
configurations
    of the beams as a function of paticle mass for a fixed center-of-mass
    energy for the important types of processe:
      - s-channel production of a spin-1 particle
      - s-channel production of a spin-0 particle
      - t-channel production of a spin-0/-1/-2 particle
      - anything else?

  - Examples
    - Higgs production in the Bjorken process and in WW-fusion
    - Supression of the t-channel in TGC studies in e+e- --> W+W-
    - Separation of left- and right-handed SUSY particles.
    - CP study in top quark production
    I know there is more here. But I wouldn't give to many examples.
    Are these the most important examples?

II.2.5 Improved Statistics

  - Explain why we improve in statistics


  - Examples on how much we gain.
      For example for e+/e- --> gamma/Z --> ff for a given luminosity
      the number of events relative to unpolarized beams for various
      degrees of polarization.

  - Can we combine our results from II.2.4 and II.2.5 into a figure of
    merrit?

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