[esa-t474] spectrometer uncertainty

[Yury Kolomensky]

	Hi Bino,

this is a good start, and good to see the formalism being put  
together in full detail. A full simulation is clearly needed: in the  
end, one needs to produce effectively a set of matrix elements to  
convert BPM measurements (1+2, 3+5, 4+7, or possibly adding 9-11)  
into energy (e.g. you can do this in simulation varying x, x', and E  
and then invert the matrix). The questions of strategy (3 BPM  
stations vs 4 (or 2 magnets vs 4), the use of SVD, the systematic  
effects and mitigation) need to be studied as well.

I actually think it is possible to use the SVD -- as long as the  
coefficients are fixed over the course of the energy measurement  
(e.g. computed for zero field and then applied to both +B and -B, or  
computed at +B and applied to both +B and -B). In some sense this is  
similar to the mover scan calibration. However, the details need to  
be worked out, in particular whether the matrix elements you compute  
in the simulation change with the SVD.

Anyway, good start.

Yury


On Dec 5, 2007, at 8:10 AM, Bino Maiheu wrote:

> 	Dear All,
>
> I've started some studies concerning the uncertainty and the overall
> layout of the chicane. I wanted to make some plots first of all in the
> style of Karl-Heinz Hiller ( see LC-DET-2004-031 ), but for a 4 magnet
> chicane. I think it's important that we have a think about how to
> calculate the energy in a 4 magnet chicane and that we fix the  
> formalism
> for later studies. So I've started a small writeup, which you can  
> see in
> attachment.
>
> I also included a plots which shows the \Delta E/E versus \Delta B/B,
> distance between the first 2 magnets, distance between the central BPM
> and the second magnet ( as these are the 2 independent  
> variables ! ) and
> the uncertainty on these quantities, for BPM resolutions of 1um, 500,
> 100 and 50 nm. There is more explanation in what I have written so  
> far,
> which are nothing more than some initial thoughts, but I wanted to
> distribute this already now for early feedback.
>
> My plan next is to extrapolate these plots for ILC chicane and
> subsequently use a full Geant 4 simulation with real fieldmaps to
> reproduce and study these curves more in detail as a function of
> magnetic field uniformity and misalignments of BPMs and Magnets.
>
> Questions and sort of drafting of a TODO list are welcome.
>
> Bino
>
>
> -- 
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