[d2n-analysis-talk] Comments on 1-pass 3He data

[Gregg B. Franklin]

I believe that Matt's 3He missing mass spectra (counts vs W) is 
dominated by quasi-free scattering.  Here's my reasoning (which may be 
wrong but...)

Diana's 1-pass hydrogen data show that the optics is properly calibrated 
and we have a peak in W corresponding to the proton mass and it has a 
width of about 40 MeV FWHM.  Thus I would expect the 3He data to have a 
peak at W=2.808 GeV, the mass of 3He, and a width of roughly 40 MeV 
also.  However, the peak of quasi-free scattering can be estimated by 
assuming the scattering takes place off a single neutron and calculating 
the energy of the outgoing electron.  One then calculates W using a 3He 
mass for the target and you get W=3.028 GeV.  Fermi-momentum will widen 
the peak and  binding effect will shift it slightly.

Matt's W spectrum for 3He has a peak about 3.05 GeV and a FWHM of maybe 
300 MeV.  To me, this seems consistent with quasi-free scattering.  We 
would like to see a bump at W=2.808 GeV, but I don't see it.

The 3-momentum transfer is about 800 MeV.  This is far above the Fermi 
momentum, so I would not expect the elastic cross section to dominate.





-- 
Prof. Gregg B Franklin
Head, Department of Physics
Carnegie Mellon University
phone: (412) 268-2743   fax: (412) 681-0648