[Hps-analysis] Moller gap solved

[Maurik Holtrop]

Hello Bradley,

I am a little confused as well why this additional cut should make so much difference. If you already have E_1 + E_2 ≈ E_beam, wouldn’t that imply that if E_1 > E_beam/2 you must have E_2 < E_beam/2 to satisfy the sum?  If that is not the case, then the events you are cutting with your new condition must all be of a very particular type, where both are close to E_beam/2?

As you can tell, whenever you make progress, you generate new questions.

Best,
	Maurik

> On May 20, 2016, at 8:56 AM, Nathan Baltzell <baltzell at jlab.org> wrote:
> 
> Hi Brad,
> 
> So just applying this cut to the real data is sufficient to make mc
> and data look very similar regarding the hole at Eb/2?
> 
> Is there anything unique about the quality of these Moller tracks/clusters
> in the real data with E1>Eb/2 && E2>Eb/2 compared to the others?
> 
> Is there evidence of more background in your Moller selection for these
> events?  e.g. in a plot of E1 vs E2, M vs E1-E2 and E1+E2, or just M or E
> for (E1>Eb/2 && E2>Eb/2) and (E1<Eb/2 || E2<Eb/2)?
> 
> -Nathan
> 
> 
> On May 19, 2016, at 23:29, Bradley T Yale <btu29 at wildcats.unh.edu> wrote:
> 
>> I think the mystery of the Moller gap has finally been solved.
>> 
>> Looking at the reconstructed Moller events generated with the fixed cross section, not much was changed,
>> so I explicitly forced the condition such that if one Moller had track E > Ebeam/2, then the other had to have E < Ebeam/2, and vice versa.
>> 
>> Applying this to both MC and Data, along with modest ESum and phi cuts, gives the attached momentum plots. 
>> The other distributions match much better too, particularly track position at the ECal, which now shows the gap in data as well. The higher-energy bias for hits in the bottom half of the ECal can be seen from the asymmetry in where the electrons hit. Loosening the MC cuts a little (only cutting ESum) starts to close the gap and make it look even more like the data plots.
>> 
>> So in summary, the gap is likely due to electrons always being cleanly paired on opposite halves of Ebeam/2 in MC, but not necessarily in data. The gap is also apparent in background MC without forcing this condition, suggesting that the MC is too "clean".
>> -Brad
>> 
>> 
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>> <MC_TRACK_Energy.png><MC_tracksAtEcal.png><DATA_TRACK_Energy.png><DATA_tracksAtEcal.png><LOOSERMC_TRACK_Energy.png><LOOSERMC_tracksAtEcal.png>
> 
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