[Clas_lmd] lepton pion PID

Michael C. Kunkel mkunkel at jlab.org
Thu Jul 9 07:02:21 EDT 2015 

Greetings,

Can you overlay the MxP^2 with pion mass setting on this plot? Using the 
same kinematic cuts except with pion pid?


BR
MK
----------------------------------------
Michael C. Kunkel, PhD
Forschungszentrum Jülich
Nuclear Physics Institute and Juelich Center for Hadron Physics
Experimental Hadron Structure (IKP-1)
www.fz-juelich.de/ikp

On 7/9/15 1:11 AM, Amaryan, Moskov wrote:
> Dear all,
>
> I attach a plot with Mx(p)^2 and M(e+e-\gamma)^2 distributions 
> overlaid. Statistics of both histograms are the same,
> however, as one can see there is no peak of eta in the invariant mass 
> squared, data are from g11.
> Invariant mass has no eta in it similar  to what Michael showed for g12.
> One can think of two possibilities, either these are true eta’s 
> decaying to e+e-\gamma, or these are  remnants of eta->pi+pi-gamma events.
> The latter hypothesis was ruled out by plotting invariant mass of 
> pi+pi-\gamma or missing mass of proton for pion mass assignment
> for the same events that make Mx(p)^2 under lepton assignment.
>
> Best regards,
> Moskov.
>
> On Jul 8, 2015, at 11:02 PM, Amaryan, Moskov <MAmaryan at odu.edu 
> <mailto:MAmaryan at odu.edu>> wrote:
>
>> Hi Michael,
>>
>> Thanks for your message, looks interesting.
>>
>> However we have shown in the CAA and also Georgie has shown it in our 
>> meetings that invariant mass of pi+pi-\gamma
>> resolution is much worse than missing mass of  proton.  The reason is 
>> energy resolution of the final state photon and
>> vertex resolution as momentum of the photon is defined through both 
>> of these, energy and vertex.
>> Therefore we use missing mass of  proton with other cuts, which use 
>> pion mass assignment to \pi^+ and \pi^-.
>>
>> Now what I have shown on Tuesday, was missing mass of proton with 
>> electron (positron) mass assignments.
>> There we clearly see a peak of eta. The mass assignment is arbitrary, 
>> of course, but requirement of missing mass squared
>>  of pe+e- to be around zero (<0.01 GeV) and missing energy of pe+e- 
>> to be E_x>0.2 GeV makes this selection definite, not arbitrary.
>> And the fact that we see peak of eta is a proof that some of pi+pi- 
>> tracks are actually e+e- pairs
>>
>> The plot you sent around doesn’t show a peak of eta very clearly in 
>> the best topology with EC/CC, but one can imagine that with more 
>> statistics
>> the  eta peak will be visible. However without EC/CC there is no 
>> signature of eta whatsoever. Would it be visible in the missing mass 
>> of proton in g12?
>>
>> It wouldn’t make sense for me to argue that PID on leptons improves 
>> invariant mass e+e-\gamma, of course it does.
>>
>> The question was which fraction of events that make eta in the 
>> missing mass of proton with e+e-\gamma assignment is due to events 
>> that were
>> from pi+pi-\gamma final state.
>>  I think we have shown that this fraction is negligible.
>>
>> It will be interesting to compare missing mass of the proton squared 
>> from g11 and g12 (for pe+e-gamma final state)  to see if because of 
>> different
>> acceptances these two data sets have similar or very different 
>> numbers of eta’s.
>>
>> It appeared that ntuples we are using from g11 have been eloss 
>> applied. In this case eloss for pions and leptons will be the same, I 
>> am not sure how different they should be, but the fact that we see 
>> peaks of pi0 and eta in the missing mass of proton is indicative that 
>> in the first approximation we can neglect eloss uncertainties.
>>
>> Best regards,
>> Moskov.
>>
>> On Jul 8, 2015, at 1:33 PM, Michael C. Kunkel <mkunkel at jlab.org 
>> <mailto:mkunkel at jlab.org>> wrote:
>>
>>> Greetings,
>>>
>>> So I was curious to reproduce my study on pion contamination without 
>>> the use of CC or EC quantities.
>>> I am attaching a plot that shows G12 data that shows 3 lines.
>>> Red: G12 data with eloss on pions, pion mass setting, invariant mass 
>>> PipPimGam; conditions Ngamma > 0 && abs(mm2_PPipPimGam)<0.01 && 
>>> mE_PPipPim > 0.2
>>>
>>> Blue: G12 data with eloss on leptons,lepton mass setting , invariant 
>>> mass EpEmGam; conditions Ngamma > 0 && abs(mm2_PEpEmGam)<0.01 && 
>>> mE_PEpEm > 0.2
>>>
>>> Cyan: G12 data with eloss on leptons,lepton mass setting , invariant 
>>> mass EpEmGam; conditions Ngamma > 0 && abs(mm2_PEpEmGam)<0.01 && 
>>> mE_PEpEm > 0.2 && lepton PID through CC and EC. Histogram is scale 
>>> by x10
>>>
>>>
>>> As I concluded years ago, and is seen in the histogram, without CC 
>>> or EC, the eta peak cannot be reproduced in the proper place.
>>>
>>> Total data used:1/463 of g12 data set.
>>>
>>> Hope this helps.
>>>
>>>
>>> BR
>>> MK
>>> ----------------------------------------
>>> Michael C. Kunkel, PhD
>>> Forschungszentrum Jülich
>>> Nuclear Physics Institute and Juelich Center for Hadron Physics
>>> Experimental Hadron Structure (IKP-1)
>>> www.fz-juelich.de/ikp <http://www.fz-juelich.de/ikp>
>>>
>>>
>>>
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>>
>> Prof. Moskov Amaryan
>> Department of Physics
>> Old Dominion University
>> 4600 Elkhorn Avenue
>> Norfolk, VA 23529
>>
>> phone:757-683-4614
>>
>>
>>
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>
> Prof. Moskov Amaryan
> Department of Physics
> Old Dominion University
> 4600 Elkhorn Avenue
> Norfolk, VA 23529
>
> phone:757-683-4614
>
>
>
>
>
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