[d2n-analysis-talk] Pions from run 1530 where pre-shower sum was not included in trigger

[Diana Parno]

> ... the blue peak corresponds to pions that have a sharp red peak
> in pre-shower to give total energy around 0.6 GeV ...

> ... momentum cut abs(BB.tr.p-0.6)<0.1 takes only
> pions that deposit more than 0.1 GeV energy in pre-shower.

Do we know this is true? (That is, that the total energy is around 0.6  
GeV?) The momentum cut is on the track reconstruction in the wire  
chambers, not on the total energy deposit in the calorimeter. There  
are lots of events where the momentum is different from the total  
energy deposit, and that's a major piece of the pion rejection.

Also, any time that you want to look at tracking variables (momentum,  
angle, etc), it is really important to impose the basic optics  
validity cuts so that you can trust the numbers coming out of the  
tracks. Momentum reconstruction, front-track reconstruction, etc, are  
not calibrated for some regions of the magnet. I strongly suggest that  
you add the cuts mag && projx to your basic toolkit here. (Those are  
the names they have in my macro. The actual cuts are defined thus:
	TCut mag = "BB.optics.vzflag[]==1 && BB.tr.tg_th[]<0.2";
	TCut projx = "(BB.optics.bendx + 0.23*BB.tr.ph)>-0.097 &&  
(BB.optics.bendx + 0.23*BB.tr.ph)<0.13"; )
The mag cut excludes the uncalibrated regions of the magnet  
acceptance. The projx cut excludes a certain part of the acceptance  
where we think that rescattering has taken place.

There are also a lot of accidentals to consider, i.e. situations where  
the reconstructed track does not line up with the location of the  
preshower or shower hit. The trps and trsh cuts are supposed to impose  
alignment between the two systems. The basic_qual cut in my macro  
combines a number of these data-quality cuts. If you're looking at a  
replayed root file, you can modify it so that it doesn't include the  
skim.* variables, which are present only in the skimmed root files.

Best,
Diana

On Dec 2, 2011, at 6:44 AM, Vahe Mamyan wrote:

>  Hello,
>
> In  run 1530 pre-shower sum was not included in trigger and pions  
> are plenty.
> Attached is pre-shower and shower energy distribution with  Cerenkov  
> cut Diana had in her macro.
> TCut = cer_cut = basic_e&&cer_tot&&"abs(BB.tr.p-0.6)<0.1";
>
> Since I applied a cut on BB.tr.p to be around 0.6 GeV the blue peak  
> corresponds to pions that have a sharp red peak
> in pre-shower to give total energy around 0.6 GeV. As you can see if  
> one removes the pion peak from shower energy
> distribution the remaining spectrum in shower looks symmetric and in  
> pre-shower too.
> Also it can be seen that the blue pion peak is centred at around 0.5  
> GeV and looking at
> https://hallaweb.jlab.org/wiki/images/e/e0/Bbsimulation_new.pdf page  
> 2 left blue spectrum one can see that there is similar peak in  
> around 0.5 GeV.
> The peak in page 2 is not as visible as in run 1530 because pre- 
> shower sum was included in the trigger and momentum cut  
> abs(BB.tr.p-0.6)<0.1 takes only
> pions that deposit more than 0.1 GeV energy in pre-shower.
>
> I still think that Cerenkov adc cut was not enough to remove much  
> pions as Mattew showed in page 11 of his report.
> I estimated Cerenkov rejection power to be 1:5.5 from run 1530.
> According to Wiser parametrization there are about 24 pions for each  
> electron in BigBite acceptance, so roughly
> there are  4.3 pions for each electron and taking account that most  
> pions are at lower energy, this number is higher.
>
> Best regards,
> Vahe
> <pre- 
> shower_shower_energy 
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