[Hps-analysis] Moller gap solved

[Valery Kubarovsky]

Hi Brad,

I don't think that such a cut is statistically correct. Imagine that we have symmetric decay:
E1=E2=Ebeam/2. Due to the final resolution we will have after reconstruction:

1. 25% of the events E1<Ebeam/2 and E2<Ebeam/2 --- you will reject these events
2. 25% of the events E1>Ebeam/2 and E2>Ebeam/2 --- you will reject these events
3. 25% of the events E1<Ebeam/2 and E2>Ebeam/2 --- you will accept these  events
4. 25% of the events E1>Ebeam/2 and E2<Ebeam/2 --- you will accept these  events

Due to your cuts you will throw away events 1) and 2) and will accept 3) and 4). You will reject 50% ABSOLUTELY GOOD EVENTS. In such a way you can create dip in ANY distribution.

I would like to bring to your attention that you have dip in MC events without this cut.

I still have a question: are you going to present your MC analysis without trigger cuts?

Regards,
Valery


> 
> 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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