Klein Re: Coherent Brem, double goniometers, SOS (fwd)

[Elton Smith <elton@jlab.org>]

---------- Forwarded message ----------
Date: Tue, 16 Mar 2004 11:25:24 -0500 (EST)
From: Franz Klein <fklein@jlab.org>
To: Ken Livingston <k.livingston@physics.gla.ac.uk>,
     James Kellie <j.kellie@physics.gla.ac.uk>
Cc: Elton Smith <elton@jlab.org>, Richard Jones <jonesrt@UCONNVM.UCONN.EDU>,
     mecking@jlab.org, Dan Sober <sober@cua.edu>
Subject: Re: Coherent Brem, double goniometers, SOS


Hi Jim and Ken,

the Yerevan group has considerably improved their analyzer technique.
For sure, the procedure would have been more successful if the beam
were less divergent: the combination of 4 crystals in the NA59 setup 
caused lots of troubles.
Ken, I am not against using an analyzing goniometer (in case that
beam emmittance at that position is good). However, the idea to
focus on this analyzing process suffers from the lack of analyzing 
power of pair production (3 body system - at Hall-D energies 28%).
Besides, the result reported in hep-ex/0306028 is somewhat worse 
than ours using the micorstrip pair polarimeter.
Nonetheless, I am not very satisfied with the pair polarimeter 
sitting in the beam for 15-20 minutes before we get reasonable 
results.
 
The design of Hall-D includes a pair polarimeter to measure the 
polarization directly. Additionally, I requested to analyze 
diffractive VM production ONLINE - there will be lots of these events
in the data stream (it may be good to have a special L3-trigger for
these events). 
I think we should consider the option of an analyzing crystal as well.

Have a nice day

Franz

On Tue, 16 Mar 2004, Ken Livingston wrote:

> Hi Franz et el,
> SOS indeed at the prospect of 2 goniometers! Then I find at a glance 
> through ref: hep-ex/0306028, that not only was a second goniometer 
> needed, but, due to the infalated beam spot at the point where it was 
> placed,  4 separate diamond crystals had to be aligned rather well with 
> each other within the 2nd goniometer. This would really have to offer 
> huge advantages over other polarimetry solutions to make it worth the 
> effort.
> 
> I'm more interested in the prospect of channeling radiation as a source 
> of polarised photons. Glasgow is leading a newly funded project called 
> Eutorag, involving groups who use tagged photons. Our main contribution 
> is to build a 2d photon detector to put in the beam at Mainz to 
> investigate channeling radiation.
> 
> I've just heard about a relevant workshop in Frascati November:
> "November 2-6 at Frascati will be planned Workshop on Charged and 
> Neutral Particles Channeling Phenomena."
> 
> Cheers,
> Ken
> 
> >Hi Jim,
> >
> >I looked into that when we "designed" the Hall-B coherent beamline.
> >The 2nd goniometer/crystal must have considerably heigher quality 
> >than the 1st (production goni), otherwise the analyzing power is
> >too low. Yerevan used such a setup 10+ years ago (although at lower
> >energies).
> >The question should be: do we want/need high degrees of photon
> >polarization or only high flux?
> >When it comes to baryon resonances, we'll NEED as much information
> >on polarization in the initial state - for meson spectroscopy this
> >will also be necessary if there are many overlapping states 
> >(otherwise you depend too much on "perfect" calibration/understanding
> >of the detector).
> >
> >Greetings
> >
> >Franz
> >
> >  
> >
> -- 
> =======================================================
> Ken Livingston          
> 
> Dept. of Physics & Astronomy,        Tel: +44 141 330 6428
> University of Glasgow,               Fax: +44 141 330 5889
> Glasgow G12 8QQ.
> Scotland. UK.
> =======================================================
> 
> 

===============================================================
                  Franz J. Klein, Assistant Professor 
                  CUA, Department of Physics
                  Washington, DC 20064
  office: Hannan Hall 210          phone: 202-319-6190 
  or: Jefferson Lab,TR 92/CC 123   phone: 757-269-7578 (or 5271)
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