[Frost] Systematic uncertainty estimate

[Steffen Strauch]

Dear Michael,

Your study of the bound-nucleon contributions from He4, O16, and C12 reminded me that I looked at the quasi-free single-pion production off 4He (g3a data) when we prepared the proposal PR03-105.  Figure 15 in the proposal shows the missing-mass distributions.  The shape of these distributions are comparable to what I get for the pi+n channel using the C12-region data of g9a.  The one exception is a narrow
peak in the g9a distribution at the mass of the neutron.  The g3a data do not show any sign of such a peak.  Looking into this in more detail I am starting to believe that the FROST C12 data is contaminated with hydrogen on the downstream side of the C12 target.  You can find some plots to illustrate my points at:

http://clasweb.jlab.org/rungroups/g9/wiki/index.php/Steffen%27s_analysis_page#Carbon_Target

For my analysis this is a big issue as it directly affects the dilution.  In my analysis I use the scaled carbon distribution for background subtraction.  The problem likely affects other analyses of the FROST data also.  We can discuss this in more detail at tomorrow's meeting.

All the best,
Steffen



On Aug 17, 2012, at 6:17 PM, Michael Dugger wrote:

> 
> Hi,
> 
> We have an estimate for the systematic uncertainty due to He4 and O16 not 
> being the same as C12.
> 
> A presentation regarding the estimate can be found at
> http://www.jlab.org/Hall-B/secure/g9/ASU/recoil2b.pdf
> 
> Please feel free to give comments and suggestions. The most important 
> thing is to determine if there is a consensus as to the general method 
> used for obtaining the estimate. If the FROST group thinks the method is 
> OK, then we can figure out where the model needs to be made more 
> realistic. If the method is not OK, I need some suggestions on how to 
> proceed.
> 
> Thanks for your time.
> 
> Sincerely,
> Michael
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