[b1_ana] Fwd: comments/questions to PR12-13-011

[Oscar Rondon-Aramayo]

Hi Karl,

On Sun, 9 Jun 2013 23:07:39 -0400
  Karl Slifer <karl.slifer at unh.edu> wrote:
> 
> In general, also the authors call the measurement "ratio method"  it is 
>the
> cross section difference method
> as the two data sets are taken at different time. Advantage of "ratio
> method" can be fully used when two
> target cels are exposed at the same time and next order is reversed. Such
> configuration allows several
> additional cross checks, but requires two cell target.
> 
> RESPONSE : We have examined a two cell configuration, and while it is
> attractive for the reason you point
>                      out, it was not clear at the time of the proposal
> submission that it significantly reduced the
>                      overall systematic uncertainty.  We will continue to
> examine this option and are open to using
>                      it if we are convinced the systematic improvement is
> significant.

The reader is pointing out that the method of sequential differences is not 
a ratio, and that taking differences between two cells exposed 
simultaneously to the beam has advantages over our method.

EMC, SMC and now COMPASS (the reader is on COMPASS), have used the two 
method for all their data, so they know how to form ratios and ratios of 
ratios to cancel systematics. Ratios do work with the double cell method, as 
the reader points out. The latest COMPASS target actually takes data in the 
quads fashion used by Qweak, that was mentioned by JP.

I don't think it is a good idea to claim that the sequential difference 
seemed to have better systematics. At worst, they may ask us to show the 
numbers, which we don't have investigated thoroughly. It think it's better 
to say that our initial aim is to use existing equipment, which does not 
allow the use of the double  cell configuration, but that we plan to explore 
it as an option.

Cheers,

Oscar