[G14_run] Corrections for deuteron structure when extracting the neutron structure functions

[Dr. A.M. Sandorfi]

Hi Reinhard,

Thanks for pointing out the connection to the CLAS electroproduction paper.
Since I was not involved in that experiment and don't consider myself an
author, I did not read the draft that is circulating.

I have previously talked with Harry Lee about the Ciofi degli Atti
correction. (There is an even older reference.) It gives a ball-park
estimate, but Harry was very skeptical about a full correction showing a
constant number - and his IA calculations certainly aren't.

I'm generally in favor of the spirit of presenting quasi-free asymmetries
from deuterium and with that giving what intelligent estimates we can, even
if they are incomplete.

Andy




On 4/27/15, 2:52 PM, "Reinhard Schumacher" <schumacher at cmu.edu> wrote:

> Hi All,
> 
> Our CLAS collaborators N. Guler et al. are publishing a paper on the
> neutron spin structure in electroproduction at CLAS.  We are all
> supposed to be reading and commenting on this paper by April 29th.  I
> finally got to doing it today.  You can find the  paper at
> 
> https://clasweb.jlab.org/membership/phonebook.php
> 
> In this paper they have to face the problem of how to extract the
> neutron structure from a polarized deuteron target.  That is the same
> issue we have been talking about for some time.  They are measuring
> g1(x,Q^2) via the double spin asymmetry A_para.   In the limit that Q^2
> goes to 0, this is about the same thing as our neutron structure
> function "E".
> 
> Their solution is the following:  they publish the CLAS results with no
> correction for the deuteron D state, and no correction for final state
> interactions.  They do discuss the corrections that could be made, but
> refrain from applying any.
> 
> In the former case, they cite an interesting paper written specifically
> to address the depolarization effect of the deuteron D state, namely
> 
> C. Ciofi degli Atti, et al, Phys. Lett. B 376 (1996) 309-314.
> 
> The paper cites a simple formula to account for nuclear depolarization
> in the deuteron, with a constant factor of (1-(3/2)P_D), where P_D is
> the D-state fraction given as ~0.4-~0.6.  This gives a slight
> suppression of the observable relative to the free neutron.  Using P_D =
> 0.05, this amounts to a factor of 7.5%.  Note that this is quite close
> to the factor that Dao and I worked out based on our extrapolation of
> the measured data  (though that is likely a numerical accident).
> 
> However, Ciofi delli Atti et al go on to show that this factor is quite
> unreliable in the resonance region (W<2 GeV) where the majority of our
> results for pi- p are located.  The reason is that resonances tend to
> get kinematically washed out in the deuteron, which in turn seems to
> have a significant x-dependent effect on the extracted structure
> functions.
> 
> My point in this message is to say, like was mentioned last week, that
> we might also want to publish the results with no binding or FSI effect
> corrections, but discuss our findings and beliefs about how big those
> corrections might be.
> 
> Reinhard