[Clas12_first_exp] My comments on some of notes

[Stepan Stepanyan]

Andrey,

Tanks for the reply and additional plots.

Regards, Stepan

On Oct 8, 2019, at 2:32 AM, Andrey Kim <kenjo at jlab.org<mailto:kenjo at jlab.org>> wrote:

Dear Stepan,
- The shape difference comes from the threshold on photon energy in Stefan's note (600 MeV). I have attached the distributions of pi0 masses for final sample (all, one photon<600MeV, both photons>600MeV) with fits as you suggested. the final sample has width similar to Stefan's.
- E_{energy} means missing energy, correct.
- see attached
- will add momentum distributions, I have used Event Builder pid for photons and electrons, positive tracks for protons (see exclusive variable distributions for positive tracks passing exclusivity cuts but not identified as protons)
- I have attached additional pdf file with better binning and comparison with available CLAS6 data, some bins are consistent but some are not.



On Sun, Oct 6, 2019 at 11:41 AM Stepan Stepanyan <stepanya at jlab.org<mailto:stepanya at jlab.org>> wrote:
Dear all,

Below are my comments on the posted notes.

Stepan

Timothy:
- show A_LU vs \phi distributions, at least the ones that will be shown in the talk
- since events with more than 2 charged particles are used, W>1.05 GeV cut may not be a good cut to avoid exclusive channels
- what was the fraction of more than 2 pion events
- is there a reason to have the highest x bin from 0.398 to 1?
- “matching fraction”, is this matching of truth and reconstructed kinematical variable (momenta)?
- in order for Fig.5 to be meaningful, will be good to see some A_LU vs \phi distributions with a fit, for example, how these distributions and fits look like for very small \chi2~0.4 and ver large \chi2~1. Or \chi2~1, are these all for fits to \phi dependence for a specific kinematic variable, e.g. x_B dependence?
- we are still working out systematic uncertainties of the Moller measurements, in the past we (CLAS) used 3% value

Stefan:
- beta cut for photons, while 3-sigma cut in lower edge of beta is fine, the statement about improving the neutron rejection especially at high energies is misleading. High energy for photons (large energy deposition in the calorimeter) does not translate to “high energy” for neutrons.
The choice of 5 sigma is also strange, most of accidentals are probably at low energies, where the tail of the beta goes above 1.2. The beta~1.2 is where one expects peak of the accidental photons from the late beam bucket by 4 ns. It seems if the upper cut is mainly to reject uncorrelated neutral hit, it should be tied to beam bucket not to the sigma.
- charged pion identification, since the probability is calculated with equal weights for all particle spices, it is no different from what is given by event builder. The only difference is that the event builder uses \sigma (resolution) in measured time, while in the probability selection method uses sigma (resolution ) in beta. Simple adjustment of the cut on “chi2pid” in REC::Particle should have given similar results.
- Fig.10, will be good in both plots to show the same thing, either invM^2 or invM.
- Fig.10 what is the background fit function
- what was the average multiplicity of photons with E>600 MeV
- typo in the 2nd line of the paragraph above Fig.12 (no page numbers to point), instead of "\pi^+ and \pi-“ it should be “\pi+ and \pi^0” (or figure description is wrong)
- please give the kinematics of asymmetries in Fig.12 and Fig.13 (x, Q2, z, p_T)
- can you provide a number for PID systematics? As stated it is small, but what is the average value
- we are still working out systematic uncertainties of the Moller measurements, in the past we (CLAS) used 3% value
- so what went into final systematic uncertainties of the charged pion asymmetry?
- the same for pi0, what is the value of systematic uncertainty

Guillaume
- electrons are selected with p>1 GeV/c, the trigger was set >2 GeV/c
- page 1, last line of Section 1, should be ep-> e\gamma (not ep->ep)
- page 1, 3rd bullet of Section 2, should be ep->e\gamma
- selection of best photon, since missing mass of the proton (see below) is not in right place, was this taken into account in the selection of the best photon
- is it understood why missing proton mass peak is >1 GeV, Fig.1c
- what is the band in proton momentum vs. angle distribution, Fig.2c
- page 4, why missing mass of ep->e\pi0X was not included in the exclusivity cuts?
- page 4, the last sentence, do you need to know also helicity dependence of the exclusive pi0s in order to subtract contamination?

Christopher:
- Looks like the final results are only for \pi+\pi-, is this the only channel will be shown at DNP
- page 5, what it means “95% of the inclusive h_!h_2 sample is the leading energy h_1h_2 in the event”, why only 95% why not take all leading hadron pairs?
- it seems most of the analysis use z-vertex cut only for electron, considering a poor vertex reconstruction, pion z-vertex cut may not be a good thing to do
- results section: what is the average P_perp/M
- will be more informative to show A_1 and A_2 on the same plot for different fits, otherwise it is hard gauge the differences. For example statement is that A_2 is “somewhat different” in fits 3 and 4, I think it is very different in 4 as it changes the sign. The same goes for A_1.

Andrey:
- Fit to the 2\gamma invariant mass, Fig.1, why sigma is larger, 14 MeV, than in Sefan’s fit, 11 MeV. Is there any motivation for such background shape (different from Stefan)
- in the cuts, E_{energy} means missing energy?
- will be good to see fit of M_{\gamma\gamma} in Fig.5, this I assume is the final event sample orate
- will be interesting to see angular-momentum distributions of final state particles, no mention of particle selection criteria
- can you elaborate what that means “not compatible with CLAS6 data"



<pi0m.pdf><eppi0_bsa.pdf>

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