[Hps-analysis] Moller Generator Fixed! (again)

[Stepan Stepanyan]

Bradley,

Great work. Is this cut unique for Mollers or similar thing may be in 
the trident generator.

Stepan

On 5/13/16 3:25 AM, Bradley T Yale wrote:
>
> I think I found the real problem with how the Moller generator was 
> initially set up.
>
> This one affects the generated distribution a LOT more than the RNG 
> precision probably did, and explains the remaining strangeness in the 
> generated distribution.
>
>
> Looking at the egs5 Moller procedure, the angular cut was defined as:
>
>
> abs(v(np)) > 0.010 radians
>
>
> where v(np) is supposed to be theta.
>
> However, the variables u, v, and w in egs are actually *directional 
> cosines*, p_x = p*u,   p_y = p*v,   and   p_z = p*w.
>
>
> So this means that in reality, the generator was saving Moller events 
> such that
>
> abs [ sin(theta)*sin(phi) ] > 0.010
>
>
> which has a periodic nature to it. Plot this equation for some value 
> of phi (or just think about it) and you'll see what was likely making 
> these strange hills and gaps in the energy distribution - full-wave 
> rectified Mollers!
>
>
> The scattered beam simulation does correctly define theta though:
> sqrt[ u^2 + v^2 ]
>
> I made a moller_v3 procedure with this correction (still with a >10 
> mrad cut), and the comparison between before and after is shown.
> The generated events now agree with the calculated cross section (XS 
> curve is shown on the 'bad' plot), and no apparent missing events.
>
> These will be run through recon to see if we can finally get good 
> Moller agreement with data.
> I'm also going to try changing the scattered beam energy cut shown in 
> the software meeting to see if it fixes Tim's phi vs. energy discrepancy.
> -Brad
>
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