[Clas12_verystrange] Cascade mass splitting

[Lei Guo]

Hi, Michael,

Actually I thought the tagger resolution IS in the simulation. Maybe  
Derek can confirm that? I believe that Derek's showed Omega-  
resolution from missing mass technique is similar to what you have  
here for the cascades. That is greatly improved once the Lambda is  
constrained to its nominal mass and the Omega- is calculated using the  
LambdaK- invariant mass. THis can be duplicated in the Xi- case. To do  
that in Xi0 channels, it would require detection of at least two more  
particles (proton pi-, or gamma gamma). That will decrease the  
statistics and increase the statistical uncertainty.

The uncertainty on the mass centroid SHOULD be this good, given the  
available statistics. I'm excited to see these plots.

As you said in your previous email, the tagger resolution will make  
the peak wider, but shouldn't affect much the uncertainty of the mass  
centroid.

Lei
On May 11, 2012, at 3:26 PM, Michael Dugger wrote:

>
> Hi,
>
> I have some plots of the Cascade mass splitting.
>
> For the Xi-, I plotted the missing mass distribution for gamma p -> K 
> + K+ X.
> For the Xi0, I plotted the missing mass distribution for gamma p -> K 
> + K0_short
> X.
>
> Each mass distribution was fit with a voigtian distribution. I could  
> not get a
> reasonable fit using just a Gaussian.
>
>> From the fit, the masses were found to be:
> mass(Xi-) = 1321.30 +/- 0.03 MeV
> mass(Xi0) = 1315.04 +/- 0.08 MeV
>
> This would give us a mass resolution better than 100 keV and that  
> sounds
> unreasonable to me.
>
> One of the reasons that the mass distribution is too good is that I  
> do not have
> the forward tagger in the fastmc code that I use. Neglecting the  
> tagger
> resolution issue, we can say that the uncertainty in the mass  
> measurement will
> most likely be dominated by systematics errors that I have not  
> estimated.
>
> Even if we did have the tagger resolution in the simulations, it  
> would probably
> just make the peak a bit wider and not shift the center too much  
> (just a
> guess).
>
> The plots can be found at
> eps format ->
> http://www.jlab.org/Hall-B/secure/clas12/omegaMinus/ASU/CascadeSplit.gif
>
> gif format ->
> http://www.jlab.org/Hall-B/secure/clas12/omegaMinus/ASU/CascadeSplit.gif
>
> Take care,
> Michael
> _______________________________________________
> Clas12_verystrange mailing list
> Clas12_verystrange at jlab.org
> https://mailman.jlab.org/mailman/listinfo/clas12_verystrange

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