[Halld-offline] MC beam sim rates normalization for commissioning

[Sean Dobbs]

Richard,  thanks very much for making these calculations.

I was planning on putting these results on the commissioning simulation
wiki page, but maybe the rate calculations deserve their own page, if
they'll be used for reference while running?

---Sean

On Fri, Oct 17, 2014 at 7:49 AM, David Lawrence <davidl at jlab.org> wrote:

>
>  Hi,
>
>    This looks important enough that it should be put into an easily
> accessible wiki page so we can get
> to it quickly while on shift.
>
>  -Dave
>
>  On Oct 16, 2014, at 10:59 PM, Richard Jones <richard.t.jones at uconn.edu>
> wrote:
>
>  <commissioning-normfact.gif>Sean,
>
>  I have matched the beam simulation spectrum to the calculated
> bremsstrahlung spectral rate to compute the beam sim normalization factor
> as shown above, assuming:
>
>    - 100nA beam
>    - 10 micron Aluminum radiator (1.12e-4 rad.len.)
>    - 5mm collimator 75m from radiator
>
> You can rescale this with radiator thickness * beam current for other
> settings.
>
>  See the attached plot. The red curve is the computed rate incident on
> the face of the primary collimator in units of /GeV/s under these
> conditions. The histogram is a simulation of 1 million beam events with a
> special ntuple configured to measure the spectrum at the primary collimator
> face, converted from counts/bin to counts/GeV and scaled up by a factor 975
> so that it matches the theoretical rate curve.
>
>  The normalization factor is that each beam sim event subtends 1.025 ns.
>
>  Please be careful in how you use this, because in beam sim mode not
> every event is written out to hddm. Only events with hits in the detector
> actually get written to hddm, and many of the beam photons get stopped in
> the primary collimator. So when you normalize you need to use the number of
> triggers you actually simulated in the simulation (or the eventNo of the
> last event) and not the number of event records that happen to appear in
> the hddm output stream.
>
>  -Richard Jones
>  <commissioning-normfact.eps>
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>


-- 
Sean Dobbs
Department of Physics & Astronomy
Northwestern University
phone: 847-467-2826
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