I don't understand  I thought this cut was intended as a theta_y cut (>10
mrad above or below the beam plane,so we only keep particles that might
hit a detector), and does v(np) not correctly describe theta_y?
So I buy that this explains the difference in the envelope of your MC
truth distribution from theory (the U shape) but not that this has
anything to do with the gap, or any dataMC discrepancy seen after
readout.
On Fri, 13 May 2016, Maurik Holtrop wrote:
> Hi Bradley,
>
> That is great investigative work. You should now indeed check the other EGS5 generators for similar issues. As we discussed yesterday, there may be an issue with the background events for tridents.
>
> Can you please mention (advertise) this new result at the analysis meeting today?
>
> Best,
> Maurik
>
>
>> On May 13, 2016, at 3:25 AM, Bradley T Yale <[log in to unmask]> 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  fullwave 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
>> <BadMollers.png><2pt3_mol_v3_moller_E.png>_______________________________________________
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>
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