[Clas_hadron] QNP Slides

[Viktor Mokeev]

  Dear Mark,

 I have few comments:

1. Are you sure that you have enough time to show ~30 slides? May be you need to present the density matrix formalism in more focused way, reducing amount of expressions down to relevant for your analysis.

2. From  pi^+pi^- mass distribution in the slide #30 it is clear that you have no access to rho-meson density matrix. Instead, you do have access to the density matrix for pi^-pi^+ system inside the rho peak. My point is: even within rho-peak pi^+pi^-p density matrix is determined by superposition of the processes:
                     a) gp-----> rho p----->pi^+pi^-P
                            as well as
                     b) gp---> pi^- Delta^++ --->pi^+pi^-p
                     c) gp----> pi^+ Delta^0--->pi^+pi^-p
                     d) gp----->pi^+N(1520)3/2- ---> pi^+pi^-p
                     e) gp--->pi^+ N(1685)5/2+ ---> pi^+pi^-p
                     f) gp--->pi^+pi^-p direct, without formation of unstable hadron in the intermediate states.

It is impossible to get rid of b)-f) process employing kinematic cuts. You always have the tails from them beneath rho peak. They may have pronounced influence on the matrix elements of density matrix, in particular on those that are sensitive to interference between different contributions.  

This conclusion comes from the results of physics analyses of the CLAS data on pi^+pi^-p photo (preliminary data) and electroproduction (published data).

 From the other hand, the information on density matrix of pi^+pi^- system available from your experiment offer valuable constraints, making it possible to extract cross sections of all aforementioned processes from the experimental data. For this purpose your results should be analysed combined with unpolarized cross sections and other polarization asymmetries.   

3 slide #2
``QCD and its shortcomings. " in your slide sounds unbelievable! 

I am not aware of any contradiction with QCD from any data in the range of energies from Mev to 10 TeV. It should be rephrased. I am not sure what do you mean by your statement.


``Spin of final state particles affected by resonances"------------->
Spin density matrix of the final state particles affected by resonances

Spin of any particle remains unchanged in any process as consequence of Poincare invariance.

``and 1.7GeV two pion channel becomes dominant"----->

and 1.7GeV two pion channel becomes the biggest


4. slide #12 needs references
  How these curves were obtained? Note, that density matrix should be affected by both resonant and non-resonant contributions. Even if you demonstrate the sensitivity to resonance parameters, it is not the unambiguous evidence for the possibility to access N* parameters, since density matrix is sensitive to the non-resonant parameter variation too. We need to demonstrate reliable separation between resonant/non-resonant contributions.

 Have a nice talk!

   Brest Regards,
                      Victor

----- Original Message -----
From: "MARK ANDERSON" <m.anderson.1 at research.gla.ac.uk>
To: "clas hadron" <clas_hadron at jlab.org>
Sent: Wednesday, February 25, 2015 12:40:30 PM
Subject: [Clas_hadron] QNP Slides

Hi everyone,

I am due to give a talk at this year's Quark and Nuclear Physics conference in Valparaiso next week on the work I have done analysing the rho channel.  I apologies for the short notice but I wanted to present my work at a working group session before checking the slides were ok.  Here is a link to the talk:

http://nuclear.gla.ac.uk/~marka/QNP_v2.pdf

Any comments would be greatly appreciated.

Thanks,
Mark Anderson

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