[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

[Michel Gar�on]

Hello,

I only have very detailed comments, avoiding repetition with Dan's.

- line 25: define r,v
- line 175: threshold in mV is meaningless for the reader. If you want to indicate a threshold, translate in energy. In EPJA 24, 445 (the first paper on e1-6 data), it was about (since it is not a sharp threshold in energy) 575 MeV.
- lines 300+: the same reasoning (which is right) would lead to (3n-4)-differential cross sections for n particles in the final state, hence 8-fold, and not 7 for eppipi. I would add in line 309: "... variables W, Q2 that, in the absence of any dependence on the scattered electron azimuthal angle, fully define...." or something to that effect (the 8th variable is the lab phi_e which does not enter in the absence of transverse polarization in the initial state)
- line 283: "with its direction given as shown in Fig. 8" is an ambiguous definition. One needs a definition which is independent of the figure. In general one uses "along the direction of k x k'" (or e x e', or Pe x Pe'), although your Fig. 8 seems opposite to that.
- lines 330+: the definitions of angles are cumbersome. I would a minima merge Eqs 4 and 5 in a single one, and Eqs 6 and 7 in a single one. Preferably, I would remove all eqs 3-9 and write: "In Fig. 8, we denote by theta_pi- the angle between the initial virtual photon and the final pi- in the CM frame. The phi_pi- angle is defined as the angle between the electron scattering plane (C) and the gammapi- plane (A), with the convention that it is 0 when e x e' and gamma x pi- point in the same direction (or reverse ??) and between O and pi when the pi- is emitted in the same hemisphere as e x e' ( or Pypi- >0) (or reverse ??). " I am not sure what your convention is since Fig. 8a shows 0 < phi_pi- < pi/2 whereas Pxpi- and Pypi- look negative. If I am not mistaken, to make consistent Fig. 8a with your eqs (provided you keep them), you would need to add a half circle to the phi_pi- angle.
- Likewise, the definition of alpha can be simplified in the same spirit. " We define  alpha as the angle between the pi+p' plane (B) and the gammapi- plane (A), with the convention that ...."
- lines 350 and 353: is not there a (language) contradiction between "impossible to evaluate 5-fold sigmas" and "integrating over these 5-fold..." (the second statement implies that you calculated these cross sections) ?
- line 384: "After applying the fiducial cuts,...
- Fig. 12 caption: "The horizontal lines represent +/- 10% deviations from unity."
- line 582: contributions
- line 663: by more than a factor 2
- line 706: more slowly

Best regards,
Michel Garçon.

PS: I agree with Reinhard's comment on the title.