[Halld-npp] [EXTERNAL] Re: Small updates since this morning

[miskimen at physics.umass.edu]

Hi all, 

Here’s a short paragraph describing the what should be reasonable expectations for this measurement.   Rory


Measurements of hadron polarizabilities are among the most difficult experiments performed in photo-nuclear physics. For charged hadrons, because of the Born term,  the polarizability effect in the cross section can range from 10 to 20% depending on the kinematics.   For neutral hadrons, where the Born term is absent, the polarizability effect will be much less than this.    To set reasonable expectations for what can be accomplished in a measurement of this type, it is important to recognize that after 30 years of dedicated experiments using tagged photons at facilities across North America and Europe, the error on the proton electric polarizability is 4%, without doubt the paramount experimental achievement in this field. However, the error on the proton magnetic polarizability is 16% (reference PDG).  Absolute uncertainties provide a better gauge of a measurements sensitivity;  for proton electric and magnetic polarizabilities  the uncertainty in both is $\pm 0.4 \times 10^{-4} fm^3}.   Another level of precision to consider for setting expectations is the result Compass obtained for charged pion $\alpha - \beta$. Compass is also a Primakoff measurement. Compass achieved a relative error of 46% in $\alpha - \beta$ and an absolute error of $\pm 0.9 \times 10^{-4} fm^3$.  Compass cannot measure the neutral pion polarizability. 


Sent from my iPad

> On Mar 6, 2020, at 12:17 PM, Elton Smith <elton at jlab.org> wrote:
> 
> Dear collaborators,
> 
> I have updated the draft with some feedback from this morning:
> 1. Added Sergey and Lingyung to the theory list
> 2. Added title CPP/NPP to table of run conditions
> 3. Added comment that the cross section is model dependent
> 4. Corrected typo in sensitivity section
> 5. Modified precision goals in abstract to agree with sensitivity and summary
> 
> -- 
> Elton Smith
> Jefferson Lab MS 12H3
> 12000 Jefferson Ave STE 4
> Newport News, VA 23606
> (757)269-7625
> (757)269-6331 fax
> 
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