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

Fri May 13 13:11:45 EDT 2016

Hi Brad,

It is very nice that you found the bug in the Moller MC.
As I see the generated Moller electrons energy distribution is very close now to the theoretical cross section (that red line that I plotted over the old distribution, top right panel). That's very good.

But I would like to say that the discrepancy between data and MC reconstructed energy will be even worse then before. Old MC had almost flat energy distribution (top right panel in the attached file). New one has dip for the symmetric decay when E=0.5Ebeam. It means that the dip in the reconstructed MC events will be even more pronounced (see bottom left panel).

The data in opposite have maximum for the symmetric decays (top left panel).

We have to find the reason for that. We discussed many times that the first test is to remove the trigger requirements for the MC analysis and see what will come out from this analysis.

best regards,
Valery

----- Original Message -----
> From: "Sho Uemura" <meeg at slac.stanford.edu>
> To: "Bradley T Yale" <btu29 at wildcats.unh.edu>
> Cc: "Maurik Holtrop" <maurik at physics.unh.edu>, hps-analysis at jlab.org, "HPS Software" <hps-software at slac.stanford.edu>,
> "Valery Kubarovsky" <vpk at jlab.org>, "Norman A. Graf" <ngraf at slac.stanford.edu>
> Sent: Friday, May 13, 2016 12:00:05 PM
> Subject: Re: [Hps-analysis] Moller Generator Fixed! (again)

> By the usual definition of theta_y (angle of elevation from the xz plane),
> the direction cosine cos(b) (where b is the angle of inclination from the
> y-axis) exactly equals sin(theta_y).
> 
> What I meant to say is that in small angle, sin(theta_y)~=theta_y. The
> relation sin(theta)sin(phi)=sin(theta_y) is exact.
> 
> On Fri, 13 May 2016, Bradley T Yale wrote:
> 
>> Even if theta is a small angle, it is multiplied by sin(phi), where phi is not.
>> ________________________________________
>> From: hps-software at SLAC.STANFORD.EDU <hps-software at SLAC.STANFORD.EDU> on behalf
>> of Sho Uemura <meeg at slac.stanford.edu>
>> Sent: Friday, May 13, 2016 11:00:46 AM
>> To: Maurik Holtrop
>> Cc: Bradley T Yale; hps-analysis at jlab.org; HPS Software; Valeri Koubarovski;
>> Norman A. Graf
>> Subject: Re: [Hps-analysis] Moller Generator Fixed! (again)
>>
>> 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 data-MC 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 <btu29 at wildcats.unh.edu> 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
>>>> <BadMollers.png><2pt3_mol_v3_moller_E.png>_______________________________________________
>>>> Hps-analysis mailing list
>>>> Hps-analysis at jlab.org <mailto:Hps-analysis at jlab.org>
>>>> https://mailman.jlab.org/mailman/listinfo/hps-analysis
>>>> <https://mailman.jlab.org/mailman/listinfo/hps-analysis>
>>>
>>
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