[Halld-tagger] PS energy table in ccdb

[Richard Jones]

Hello Nathan and all,

I had understood that the values in this lookup table were provided by
Sascha. The formula listed in the quoted message below is not a good
starting point for a dipole spectrometer because the displacement from the
beam axis is approximately linear in 1/p, not in p. To get a zeroth order
lookup, I suggest that the formula be rewritten using the same inputs 1-3
listed in Nathan's message, but rewritten to scale the 1/E linearly in
distance along the fine array rather than E.

This should be quick to do, and will impact what Alex Barnes is doing, so
it would make sense to do this right away. If someone (Alex?) is planning
to implement this right away, please let me know, otherwise if I do not
hear before the end of the evening tonight, I will do it.

-Richard Jones

On Mon, Apr 11, 2016 at 2:19 PM, Nathan Sparks <nsparks at jlab.org> wrote:

> At today’s meeting, the question came up about what the current PS energy
> table is based on.
>
> There are 145 tiles in each arm of the PS.
>
> Here are the rough estimates used to calculate the table, taken from Sasha
> during Fall 2014 commissioning:
> 1. 13 MeV/(mm of PS tile)
>         - tiles 1 to 105 (2 mm tiles) are 26 MeV wide
>         - tiles 106 to 145 (1 mm tiles) are 13 MeV wide
> 2. energy at the center of tile 18 is 3.45 GeV
> 3. energy at the center of tile 106 is 5.73 GeV
>
> So, the energy boundaries are calculated by
> tiles 1 to 105:      Elow(i) = 2.995 GeV + (i-1)*0.026 GeV, where “i" is
> the tile number.
> tiles 106 to 145:  Elow(i) = Ehigh(105) + (i-106)*0.013 GeV
>
> Best regards,
> -Nathan
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