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

[Reinhard Schumacher]

Hi Andy,
	Indeed, Ciofi degli Atti says in that paper that the simple correction 
is NOT suitable in the resonance region, and outlines a procedure for 
making a better correction.   However, the CLAS people did not make use 
of it.  Instead, they came up with their own way of combining the 
deuteron data with separate proton data using a "impulse approximation 
folding prescription" to get g1n and A1n.  For most of their paper, the 
CLAS people present quasi-free results on the deuteron.

Reinhard

______________________________________________________________________
Reinhard Schumacher         Department of Physics, 5000 Forbes Ave.
Carnegie Mellon University, Pittsburgh, PA 15213, U.S.A.
phone: 412-268-5177         web: http://www-meg.phys.cmu.edu/~schumach
______________________________________________________________________

On 04/27/2015 05:54 PM, Dr. A.M. Sandorfi wrote:
> 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
>
>