Elastic Scattering from 3He for absolute normalizations, July 24, 1999, K. Aniol
Below is a table comparing Amroun et al. cross sections from their appendix 10 to a Plane Wave Born Approximation calculation using the charge form factor from Akio Hotta and Otterman's magnetic form factor.
 
E (MeV)data/pwb th_e(degree) Q2(/fm2) Amroun - sigma 
fm2, e-5
dsigma,% PWBA*
sigma
fm2,e-5
data/PWBA* PWBA **
sigma
fm2,e-5
data/PWBA**
640 35 1.92 1.29 3.7 1.29 1.00 1.56 0.83
413.3 30 1.16 65.47 3.2 64.4 1.017 69.8 0.94
  35 1.55 23.14 3.3 22.7 1.019 24.9 0.93
  40 1.99 8.69 3.2 8.43 1.031 9.40 0.92
  45 2.47 3.33 3.5 3.27 1.018 3.70 0.9
  50 2.98 1.32 3.2 1.31 1.008 1.52 0.87
394.5 50 2.73 1.83 3.4 1.82 1.005 2.09 0.88
  53 3.02 1.06 3.1 1.09 0.972 1.26 0.84
  55 3.22 0.787 3.1 0.775 1.015 0.909 0.87
*PWBA uses the charge FF and magnetic FF given in Otterman et al. paper
** PWBA uses the charge FF from U.Mass (1999) and the magnetic form factor from Otterman , et al. for Q2 < 3.7 /fm2.
 

Determining accurate cross sections from form factors derived from global fits
In Amroun's paper the form factors they determine come from a large body of data. We should be able to use those form factors to calculate cross sections to a better accuracy than the cross sections Amroun et al. measured. From their global fit we can deduce the following uncertainties in the charge form factor and thus the uncertainty in sigma elastic. These values are read from the graphs. The first column shows the beam energies and the minimum Q2 we can reach. Actually for the 995 and 1245 MeV runs we can get to 1.2 and 1.87 /fm2.
 
 
E(MeV)     Q2  /fm2 Fchg dFchg  dsigma/sigma (%)
995,1245       2. 3.5 e-1 1.5e-3 0.9
2045               5.  9.e-2 1.e-3 2.2
2895.             10 5.0e-3 1.8e-4 3.6
4045.             20 3.5e-3 1.3e-4 7.4
4795               27 2.0e-3 1.e-4 10.

Issues and questions

1) It would be useful to see how accurately the U. Mass. people judge their form factor to be.  Otterman's form factors give much closer agreement with the data of Amroun.
Perhaps Akio could find out for us?

2) From the comparison of the data and PWBA in the first table it is clear we need to take Coulomb distortions into account to calculate cross sections from the form factors. Does any one have access to such a program?

3) Is it plausible that we could use the 2045 MeV elastic scattering run to normalize the 4045 MeV quasi-elastic data? We would need to take current scans for the beam heating effect at both energies.
If the current monitoring is accurate we could deduce the product of (target density)*(solid angle) to within 2.2% from the elastic scattering. As long as the target is leak tight we will not have lost any 3He switching between  4045 and 2045 MeV.

a)   at 4045 MeV,    Nqe(4045,13.51)/Q(4045) = (rho*length @ 4045)*sig_qe(4045,13.51)*domega

b) at 2045 MeV, Nelastic(2045,12.5))/Q(2045)/sig_el(2045,12.5) = (rho*length@2045)*domega

c) so sig_qe(4045,13.51) = Nqe(4045,13.51)/Q4045)/Nelastic(2045,12.5)*Q(2045)*sig_el(2045,12.5)

Q is the total number of incident electrons in each run.

We could then use the quasi elastic electron scattering to normalize the 4045 MeV data.