[Clas12_verystrange] Cascade mass splitting

[Michael Dugger]

Lei,

I think that you are correct about Derek having the forward tagger in his 
version of fastmc.

I'm glad that the mass resolution does not seem too good to you. I am not 
used to working on determining mass with high resolution. My biggest worry 
would be that the energy loss corrections would have systematics 
much larger than 100 keV. However, having a vertex resolution of 1mm or 
better will probably go a long way to making the target energy loss 
corrections fairly accurate.

Take care,
Michael

On Fri, 11 May 2012, Lei Guo wrote:

> 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
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>
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