[b1_ana] b1 higher twist

[Simonetta Liuti]

Hi All,

even if higher twists are negligible, I am skeptical of the Jaffe et al. formulae for extracting  b_1 (Chapter 6).

In fact, I checked that the observable is OK in the sense that they are referring to the electron beam (and not the virtual photon).

However, I expect systematic errors to be very big. The "polarized cross sections" observables can be obtained with two separate measurements. A polarized spin 1 target one, and an unpolarized one. The two measurements have to be carried out separately, just to be clear. And this is going to impact the systematics. 
This is exactly why Hermes came up with A_zz which only involves target polarization. 
I do not see the advantage of going back to Section 6 of Jaffe et al., while one could do something new and exciting  measuring deuteron DVCS asymmetries.

However...please let me know what you think.
Simonetta 
 
On Thu, 18 Apr 2013 16:06:07 -0400
 "O. A. Rondon" <or at virginia.edu> wrote:
>Hi,
>
>There is a paper by Hoodbhoy, Jaffe and Sather, which says that higher
>twist (twist-4) effects on b1 at Q^2 = 1 GeV^2 are only 5%. So they
>would seem negligible at the kinematics of our proposal or HERMES. See
>
>http://dx.doi.org/10.1103/PhysRevD.43.3071
>
>Cheers,
>
>Oscar
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