[Clas_lmd] lepton pion PID

[Amaryan, Moskov]

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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<Lepton_Pion_mass_comparision.pdf>_______________________________________________
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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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