[d2n-analysis-talk] LHRS Cross Section Systematic Errors (Update)

[Brad Sawatzky]

Hi Dave,

I'm glad that the interpolation uncertainty is down to the couple percent
level now.

I worry a little that we're underestimating the uncertainty associated
with the F1F209 model, but I think the approach you followed to
establish your errors is valid -- perhaps it really is only a couple
percent uncertainty in the end.

For now, I would declare the radiative correction procedure "finished",
but make a note that we should think about other ways to bound the
model-dependent uncertainties.  We'll want to run through this during
one of our upcoming analysis meetings -- I'm a little worried attendance
at on the 21st might be poor due to the JLab PAC this week, so maybe the
following week would be better for a general discussion.  (I think the
uncertainties you have are probably pretty close though, so I'm not
*too* worried about it.)

-- Brad

On Fri, 15 Jun 2012, David Flay wrote:

> Hi all,
> 
> Yesterday (6/14/12) I presented the systematic errors incurred by
> using a fit of:
> 
> f(x) = (1/x^2)*exp(p0+p1*x)
> 
> to model the background signals (positrons or diluted nitrogen) when
> subtracting them off from the raw cross section.  I found that the
> error is ~1--2% at 4-pass, and 1--8% at 5-pass.  The talk can be found
> here:
> 
> https://hallaweb.jlab.org/wiki/images/3/37/DF_LHRS_6_12_12.pdf
> 
> Following up with Brad's comment to see how it adds to the overall
> systematic errors, I have computed the in-quadrature sum including
> these new errors, and also <excluding> the error estimated for the
> interpolation in RADCOR (which was as large as 15% at high Ep) since I
> now use 44 spectra (in steps of 100 MeV) to unfold our data, which
> effectively minimizes the error incurred by the interpolation
> procedure.
> 
> The errors are as follows:
> 
> Es = 4730.00 MeV
> 600	  3.66	2.50	        3.67
> 800	  3.95	2.50  	3.95
> 1120	  3.50	2.50  	3.51
> 1190	  3.40	2.50         3.40
> 1260	  3.59	2.50  	3.59
> 1340	  3.59	2.50  	3.59
> 1420	  3.66	2.50  	3.66
> 1510	  3.66	2.50  	3.66
> 1600	  3.72	2.50  	3.79
> 
> Es = 5890.00 MeV
> 600	  3.55	2.12  	3.57
> 700	  8.69	2.12  	8.70
> 900	  3.30	2.12  	3.32
> 1130	  3.68	2.12  	3.68
> 1200	  3.88	2.12  	3.89
> 1270	  3.67	2.12  	3.67
> 1340	  4.25	2.12  	4.25
> 1420	  4.00	2.12  	4.00
> 1510	  4.40	2.12  	4.40
> 1600	  4.00	2.12  	4.00
> 1700	  6.13	2.12  	6.17
> 
> where the first column is Ep (MeV) and the second column is the
> 'experimental' systematic error (that is, contributions from PID and
> acceptance cuts, target density and now the fits);
> the third column is that due from radiative corrections (in-quadrature
> sum of errors from varying the radiation lengths and the variation of
> the F1F209 model).  In contributes a very small amount due to the way
> it is added to the experimental error, as shown in my talk at the d2n
> analysis workshop.
> 
> The errors due to the fit are typically 1% bin-to-bin with the
> exception of a few bins, where it escalated to 8% (700 MeV at 5-pass)
> and a few other bins where it jumped to 2--5% (which can be seen in my
> talk above).
> 
> Are we satisfied with this estimation, or is another method needed to
> asess the fit errors (or do we need a new method entirely to subtract
> the background?)
> 
> Thanks,
> 
> Dave
> 
> -------------------------------------------------
> David Flay
> Physics Department
> Temple University
> Philadelphia, PA 19122
> 
> office: Barton Hall, BA319
> phone: (215) 204-1331
> 
> e-mail: flay at jlab.org
>             flay at temple.edu
> 
> website: http://www.jlab.org/~flay
>               http://quarks.temple.edu
> -------------------------------------------------
> 
-- 
Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
Ph: 757-269-5947  -<>-  Fax: 757-269-5235  -<>- Pager: brads-page at jlab.org
The most exciting phrase to hear in science, the one that heralds new
  discoveries, is not "Eureka!" but "That's funny..."   -- Isaac Asimov