Hi Nezvat,
The statistical precision on these data is very impressive
and it's clear you've done a lot of nice work here for which
you should be commended, but I have to say I'm very skeptical
of the size of the systematics.
g2 is a major (often dominant) contribution to both gamma_0
and delta_LT, as shown in the attached plot. This estimate comes
from the MAID model, but I'd encourage you to doublecheck with
your own model and see for yourself. This can also be seen just
from the definitions of the polarizabilities: g2 enters with the
same weighting as g1 to delta_LT, and the factor 4M^2x^2/Q^2 in
gamma_0 is also of order 1 at these kinematics.
g2p is basically unknown in this region, and there's a wide
divergence of all models that I've seen (simula, hall B,
MAID etc), so I question how precise any of this can be.
I'm sorry, but as a relative outsider to this analysis,
I would expect the size of the systematics shown here
to be small even for the missing transverse contribution
to \int (x^2 g1) dx alone. The systematic from direct g2
contribution to the polarizabilities has to be much larger.
In short, I'd like to politely raise the question of whether
it's a good idea to even evaluate these quantities from purely
longitudinal data, when a major (often dominant) part of the
integral is unmeasured. If they are shown, I believe it
should be made clear how much of these quantities come
from data and how much comes from models.
best regards,
Karl
-------------------------------------------------------------
Karl Slifer, Assistant Professor, Department of Physics, UNH
DeMeritt Hall Room 335, 131 Main Street Durham, N.H. 03824
603-862-2827(office) 215-701-1122(voip) 757-871-6341(cell)
On Thu, 16 Oct 2008, nguler@jlab.org wrote:
> Hello,
> I genereted some preliminary plots for the forward spin polarizability gamma0
> and also for deltaLT.
> Gamma0 and deltaLT are calculated as described in:
> http://arxiv.org/pdf/nucl-ex/0406005v3
>
> For gamma0, I put two different plots, one is in normal scale, the other one
> is divided back to C kinematic factor.
>
> You will see plots for deuteron and proton and different plot types as you
> scroll down in:
> http://www.jlab.org/Hall-B/secure/eg1/EG2000/nevzat/RESULTS/FSP/
>
> I am thinking to show some of these plots, probably gamma0, in the DNP meeting
> if it is ok..? I will not show anything on the neutron extraction because we
> decided it should be done carefully and slowly. So, these gamma0 plots will be
> the only addition over Spin2008.
>
> Best regards,
>
> - Nevzat
>