Measuring the charged pion polarizability in the gamma gamma -> pi+pi- reaction

Development has begun of a new experiment to measure the charged pion polarizability $$\alpha_{\pi}-\beta_{\pi}$$. The charged pion polarizability ranks among the most important tests of low-energy QCD presently unresolved by experiment. Analogous to precision measurements of $$\pi^{\circ}\rightarrow\gamma\gamma$$ that test the intrinsic odd-parity (anomalous) sector of QCD, the pion polarizability tests the intrinsic even-parity sector of QCD. The measurement will be performed using the $$\gamma\gamma\rightarrow\pi^{+{}}\pi^{-{}}$$ cross section accessed via the Primakoff mechanism on nuclear targets using the GlueX detector in Hall D at Jefferson Lab. The linearly polarized photon source in Hall-D will be utilized to separate the Primakoff cross-section from coherent $$\rho^{\circ}$$ production.