[Clascomment] OPT-IN: Near Threshold Neutral Pion Electroproduction at High Momentum Transfers and Generalized Form Factors

[Puneet Khetarpal]

Hi Stepan,

Please see my responses to your questions below:

On Nov 12, 2012, at 4:03 PM, Stepan Stepanyan <stepanya at jlab.org> wrote:

> Hello Punit et al.,
> 
> I have a question on figure 8 and cuts applied. 
> First simple questions just for understanding, what are these two vertical bands above the red line that are at the pre- and post-radiative \Delata\theta.  

-- The two vertical bands above the red line are the extensions of the pre and post-radiative tails.

> The second is more serious in my mind, your "pi0" band (horizontal) has a \Delta\theta dependence. How is the MM2 dependence on other kinematic parameters, like proton momentum, or electron angle etc. I could not find analysis note to see if there are any studies on MM@ dependence on kinematics.


The proton kinematics in the CM frame is complementary to the pion as they are produced back to back (Fig. 1). The electron information is encoded in Q^2 and W, the kinematics over which we have reported the results. We performed the necessary
corrections for the electron and proton angle and momentum. The results after the correction can be seen in the following plots:

http://clasweb.jlab.org/rungroups/piprod/wiki/index.php/Corrections

> What worries me is the after using elliptical and linear cuts, the projections of MM2 does not look truly Gaussian and you assumed that it is due to reaming BH events. It might be that there are still some BH events left there, but when you have kinematic dependence of MM2, it never can be treated as a Gaussian and fitted as is to get the number of events. This will boil down to what the systematic uncertainty will be due to this type of extraction. I want to know what the contribution of the second Gaussian is in the spectrum relative to your extracted pi0 number, and I think that should be quoted as a systematic uncertainty. 
> Another related question, if there are kinematic dependences of MM2, than some of parameters are not measured (corrected) well. So, what are the level of uncertainties in [absolute value of] measured parameters. Since measurements are close to threshold, small changes in kinematics may bring  big changes in cross section.
> 
> Stepan  

The MM^2 dependence plots for W and Q2 and cos theta of the pion in CM bins can be seen here: 

http://www.jlab.org/Hall-B/secure/e1-6/puneetk/semi-inclusive-epx-all/feb10/mm2_epx_fit_1.png

http://www.jlab.org/Hall-B/secure/e1-6/puneetk/semi-inclusive-epx-all/dec09/ct_wbin_3.png 
(please ignore the black curves in this plot)

Of course, the MM2 is not truly Gaussian and there may indeed be some BH events present after subtraction, which is why we have a systematic uncertainty of +-6% (on average) assigned to this
procedure. This procedure includes the difference in the cross section and structure functions after applying this Gaussian background subtraction and without applying this Gaussian background subtraction. As such, the possibility of contamination is appropriately accounted for.

Thank you,
Puneet

http://about.me/puneetk

"No word is true until it is eaten" - 36 Lessons of Vivec, Sermon 27