Dear Friends,
Several people have expressed the wish to gather
the material for the polarisation program at the linear collider
into a document containing the physics, experiment and accelerator
issues. At our last meeting in Oxford, the Ecfa/Desy OC agreed
that I have a go at getting a small group of us together to write
this up so that we have all of the information in one place.
Of course it should not be limited to the Ecfa/Desy study for
obvious reasons since there is probably activity in the American
and Asian studies. Herb Steiner/LBL has been saying for a while
we should do this (see his mail below), and independent of
that Eilam Gross/Weizmann and Peter Zerwas/Desy expressed interest
at the Ecfa/Desy Oxford meeting, so that would make 4 of us
in such a working group for the moment.
Polarisation is of course a powerful tool in e+e-,
as the SLC/SLD example is showing us, and at the LC it will
be even moreso. Each of the physics groups has polarisation on its
agenda, so a lot of information is out there but scattered for now.
But there is nitty gritty hardware which has to be understood
before any physics with polarisation gets done (Herb's note
below raises other points), and this has to be put in perspective
with other big jobs like building the accelerator or the detector.
Since manpower and money is involved, the hardware needed for
polarisation must be part of the proposal for the machine and for the
detector.
Because of SLC, e- polarisation is assured and essential
for many of the physics-with-polarisation experiments (in the end
there might be a scheduling problem, which would be a nice situation
to be in, but let's not worry about that now).
However e+ polarisation is less straightforward.
At Hawaii LCWS93 there was some discussion, and its usefulness was addressed
in our workshop series in 1995 and at Claudio Verzegnassi's workshop in
Lecce 1996 (and probably on several other occasions). Increasing statistics,
increasing the effective polarisation and measuring the degree of
polarisation (the Blondel scheme) were some of the arguments for e+
polarisation. Since a major hardware R&D program is needed
to make e+ polarisation possible, it was not clear if those reasons
were good enough. Recently at the Ecfa/Desy Oxford meeting, more potent
reasons appeared, and the physics groups should continue to think about this.
On the hardware side there are schemes on paper (JLC showed a source
at LC95 and TESLA has a design for a helical undulator DESY/TESLA 96-05),
but I don't know whether any real hardware prototypes are being built.
If you are interested in joining a LC polarisation wg,
please let me know.
Be seeing you at Sitges or elsewhere...
Ron
P.S. I've cludged the Slac LC mailing list and the European one
together for this mail, so apologies if you get this twice.
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From: SMTP%"[log in to unmask]" 29-OCT-1998 20:21:39.09
To: SMTP%"[log in to unmask]"
CC:
Subj: Re: LC Detector Sessions at Frascati Meeting 7-10 Nov.98
29-OCT-98
DEAR RON:
I WAS SORRY TO HAVE MISSED YOU DURING YOUR SHORT VISIT TO LBL RECENTLY.
I WANTED TO ASK YOU WHAT IS BEING DONE ABOUT POLARIZATION-RELATED ISSUES
IN YOUR STUDIES. IT SEEMS TO ME THAT EXPERIMENTS WITH POLARIZED BEAMS
WILL PLAY AN IMPORTANT ROLE IN ANY LINEAR-COLLIDER RESEARCH PROGRAM,
AND TO THAT END I THINK IT IS DESIRABLE TO INCLUDE THIS OPTION IN YOUR
PLANNING. I AM THINKING HERE OF PHYSICS-RELATED ISSUES, ACCELERATOR-RELATED
ISSUES, DETECTOR-RELATED ISSUES, AND ISSUES ASSOCIATED WITH TECHNOLOGICAL
IMPLIMENTATION. I AM SURE THAT YOU AND YOUR COLLEAGUES ARE WELL AWARE OF
THE ROLE OF POLARIZATION, BUT I HAVE NOT SEEN MUCH REFERENCE TO IT IN YOUR
VARIOUS STUDY DOCUMENTS. SOME OF THE TOPICS THAT COME TO MIND ARE POLARIZED
ELECTRON (POSITRON) SOURCES, POLARIZATION DILUTION AND DEPOLARIZATION EFFECTS,
POLARIMETRY (WHERE AND HOW), NEEDED ACCURACY (RELATIVE AND ABSOLUTE), ENERGY
CALIBRATION, COMPATIBILTY WITH ACCELERATOR/DETECTOR DESIGN AND OPERATION,
POLARIZATION ROTATORS, ETC.. IF YOU HAVE NOT ALREADY DONE SO, IT MIGHT MAKE
SENSE TO SET UP A WORKING GROUP OF INTERESTED PERSONS TO COME UP WITH A
DETAILED PLAN TO ADDRESS THESE ISSUES, TO MAKE SURE THAT THE ACCELERATOR AND
DETECTOR DESIGN TEAMS ARE WELL AWARE OF THE PERTINENT ISSUES, AND THEN TO
INTEGRATE THE RELEVANT PORTIONS IN YOUR DESIGN REPORTS. I THINK THERE ARE
HIGHLY QUALIFIED PHYSICISTS IN YOUR PART OF THE WORLD WHO COULD UNDERTAKE
THIS TASK VERY EFFECTIVELY.
BEST REGARDS,
HERB
