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

[Richard Jones]

Hello Sean,



> Great, thanks.  So that means that we expect a rate of 4.65 GHz of photons
> in the energy range E(gamma,beam) = 1.2 MeV - endpoint.
>


I don't understand what you are saying here. The number 4.65 x 10^9 tells
how many hdgeant beam events you need to simulate in order to cover one
second of commissioning beam. How that translates into the statement you
made, which makes no reference to MC simulations, is not clear to me.
Remember that most of these 4 billion photons (about 80%) hit the primary
collimator and never make it to the GlueX target.



>
> I'm a little concerned about the other email that you sent about the
> photon spectrum from bggen.  I've seen some residual peaks, but at nowhere
> near the level that you're reporting.  I've attached the photon spectrum
> that I am seeing from bggen.
>


Bggen has nothing to do with this discussion, right? We are talking about
hdgeant beam simulations. Beam simulations use the internal cobrems
generator inside HDGeant and do not read events from bggen or any other
external MC generator. The exact angles of the crystal that bggen uses to
put the coherent edge at 9.999GeV may be different than the one that I use
in HDGeant. There are a continuously infinite number of ways to put a
coherent edge at a given location in the spectrum, and the different
choices result in different locations for the secondary crystal reflections.



>
> In the end, you're right that it's better to turn off the coherent
> calculation completely.  I think that bggen has a check that prevents the
> solution that you suggest at the moment, but I'll make the necessary
> changes.
>


Yes. First you disable bggen entirely by commenting out the INFILE card in
control.in, then you change the BEAM card in control.in to put the coherent
edge above the endpoint to disable coherent generation, then you use the
normalization I provided to convert the number of simulated events into so
many seconds of beam under nominal commissioning conditions.

-Richard Jones
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.jlab.org/pipermail/halld-offline/attachments/20141017/00b410ca/attachment-0002.html>