Measuring the Charged Pion Polarizability in the $\gamma\gamma\rightarrow\pi^{+{}}\pi^{-{}}$ Reaction

A new measurement of the charged pion polarizability $\alpha_{\pi}-\beta_{\pi}$ is approved to run at Jefferson Lab using the GlueX detector in experimental Hall D. The charged pion polarizability ranks among the most important tests of low-energy QCD presently unresolved by experiment. Analogous to precision measurements of $\pi^{0}\rightarrow\gamma\gamma$ that test the intrinsic odd-parity (anomalous) sector of QCD, the pion polarizability tests the intrinsic even-parity sector of QCD. The $\gamma\gamma\rightarrow\pi^{+{}}\pi^{-{}}$ cross section will be accessed via the Primakoff mechanism on a nuclear target. The linearly polarized photon source in Hall D will allow the separation of the Primakoff cross section from coherent $\rho^{0}(770)$ production. An additional detector will also need to be constructed to help distinguish $\pi^{+{}}\pi^{-{}}$ and $\mu^{+{}}\mu^{-{}}$ events. An update on the status of the experiment will be given.