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

[Reinhard Schumacher]

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

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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
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