[Clascomment] OPT-IN:Measurements of ep -> e'pi+pi-p' Cross Sections with CLAS at 1.40 GeV < W < 2.0 GeV and 2.0 GeV2 < Q2 < 5.0 GeV2

[Viktor Mokeev]

   Dear Mikhail,

 Thank you for your comments!

We will work on your and others comments and will provide the updated paper text and response on your particular comments.

 Right now I just have a quick response to your comment #3


 First, the paper is not the conclusion, but just the beginning of the physics analysis. In the paper we make projections of the resonance contributions based on already available information on N* electrocouplings. Electrocouplings were extracted from the data on Npi electroproduction at Q^2 from 2.0 GeV^2 to 5.0 GeV^2 for the N* states in the mass range M<1.6 GeV. At this low mass range (M<1.6 GeV) we indeed observed the impressive growth of the relative resonance contribution based on the experimental results from CLAS. Npi data also demonstrated relative growth of the resonance contributions in this low-W range (see discussion in  Gothe R. W. et al.: Nucleon Resonance Studies with CLAS12. Jlab Experiment E12-09-003). The situation at W>1.6 GeV is more complex. For the N(1680)5/2+, N(1675)5/2-, and N(1710)1/2+ the information on electrocouplings is available from the CLAS Npi data at Q^2 from 2.0 GeV^2 to 5.0 GeV^2 (see Park K. et al.,CLAS Collaboration.: Measurements of $ep \to e' \pi^+ n$ at W = 1.6 - 2.0 GeV and extraction of nucleon resonance electrocouplings at CLAS. Phys. Rev. C {\bf 91}, 045203 (2015)). However, several N* states in the third resonance region \Delta(1620)1/2-, \Delta(1700)3/2-, N(1720)3/2+ decay preferentially (>70% BF) to the Npipi final states. The information on this state electrocouplings is available from the published CLAS pi^+pi^-p electroproduction data only in the limited range of photon vrtualities Q^2<1.5 GeV^2 (see Nucleon Resonance Photo-/Electrocouplings Determined from Analyses of Experimental Data on Exclusive Meson Electroproduction off Protons. https://userweb.jlab.org/~mokeev/resonance\_electrocouplings and references therein). The paper statements on the resonance contributions at W>1.6 GeV and Q^2 from 2.0 to 5.0 GeV^2 for the states with preferential Npipi decays is based on extrapolation of the available from CLAS results on the aforementioned state electrocouplings at Q^2<1.5 GeV^2 to the Q^2-range from 2.0 GeV^2 to 5.0 GeV^2.  Therefore, for W>1.6 GeV we have expectation/projection of the resonance contributions. Future analyses of the data in the paper draft will provide the first information on electrocouplings of high mass states (1.6 GeV<M<2.0 GeV), in particular, for those with preferential Npipi decays at 2.0 <Q^2<5.0 GeV^2. Only after that we will be able to make a firm quantitative conclusion on the N* contributions in this kinematics range based on the experimental data. Right now, for high mass range we have just expectations which demonstrate a good prospects for extraction of the high mass N* (M>1.6 GeV) electrocouplings.

I would be very prudent with the statements on the N* contributions to DIS structure functions before:
a) experimental information on most prominent N* electrocouplings, including high mass region, will become available;
b) exprrimental results on gvpN* electrocouplings will be incorporated to the DIS analysis framework. 

In my view, this joint activity between N*/DIS physics is very important and beneficial for both areas of research.


  With Best Regards,
                             Victor





----- Original Message -----
From: "Mikhail Osipenko" <osipenko at ge.infn.it>
To: "clasmbr" <clasmbr at jlab.org>, "clascomment" <clascomment at jlab.org>, "burkert" <burkert at jlab.org>, "Kenneth Hicks" <hicks at ohio.edu>, "Viktor Mokeev" <mokeev at jlab.org>, ioana at jlab.org, "Ivan Bedlinskiy" <bedlinsk at jlab.org>, "bsi" <BSI at depni.sinp.msu.ru>, "Evgeny Isupov" <isupov at jlab.org>, mkunkel at jlab.org
Sent: Wednesday, March 8, 2017 5:17:56 AM
Subject: OPT-IN:Measurements of ep -> e'pi+pi-p' Cross Sections with CLAS at 1.40 GeV < W < 2.0 GeV and 2.0 GeV2 < Q2 < 5.0 GeV2

Dear Authors of 2pi paper,

Congratulations with conclusion of such a complex analysis.
Few observations:

1) in the text just before Eq.20 you probably need to specify that you set "eff=1" for these "blind" bins in Eq.13.

2) The explanation of Fig.10 is perhaps misleading: as it is written now one may conclude that CLAS acceptance for pi+p(pi-) hadronic system (in CM) is 100%. I may only guess that Fig.10 actually shows the effect of "blind" bins inside fiducial cuts (bins outside fiducial cuts are also "blind" according your current definition i.e. the number of reconstructed MC events =0). Please could you explain it better in the text/caption?

3) The increase of the ratio of model resonance contribution to the data is very impressive and, I believe, is opposite to what observed in the inclusive cross section. Given the low W-values only few channels are allowed/significant in the resonance region. If I am correct, your observation, indirectly, suggests that in single-pion electroproduction the ratio (resonance/total) has opposite Q2-behaviour with respect to two-pion electroproduction. Is it true? Why this difference?

Best Regards,
                Mikhail.