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GlueX Experiment Document 4373-v4

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Measuring the Neutral Pion Polarizability

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Submitted by:
Elton Smith
Updated by:
Elton Smith
Document Created:
06 Mar 2020, 18:16
Contents Revised:
01 Jul 2020, 16:47
Metadata Revised:
01 Jul 2020, 16:47
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17 Jun 2020, 08:00
09 May 2020, 11:41
07 Mar 2020, 09:54
This proposal presents our plan to make a precision measurement of the
cross section for $\gamma \gamma \rightarrow \pi^0 \pi^0$ via the
Primakoff effect using the GlueX detector in Hall D. The aim is to
significantly improve the data in the low $\pi^0\pi^0$ invariant mass
domain, which is essential for understanding the low-energy regime of
Compton scattering on the $\pi^0$. In particular, the aim is to obtain
a first-ever experimental determination of the neutral pion
polarizability $\alpha_\pi - \beta_\pi$, which is one of the important
predictions of chiral perturbation theory and a key test of chiral
dynamics. Our goal is to measure
$\sigma(\gamma\gamma\rightarrow\pi^0\pi^0)$ to a precision of about
5.1\%, which will determine the combination of
$\alpha_{\pi^0}-\beta_{\pi^0}$ to a precision of 39\%. We expect this
experiment to run concurrently with the previously approved experiment
to measure the charged pion polarizability (CPP)~\cite{CPPexp} in Hall~D.
Files in Document:
Notes and Changes:
Update to final document submitted to PAC. Mostly typos and clarifications.
Also added the pdf document summarizing the collaboration review
Associated with Events:
held from 11 May 2020 to 15 May 2020 in Jefferson Lab
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