Measurement of the pion polarisability using the Primakoff reaction

The experimental determination of the pion polarizability has by now
30 years of history, and the spreading of the largely incompatible
results by more than a factor 3 reflects the big challenge
in measuring this quantity.

The talk puts the ongoing COMPASS program for measuring this important
natural constant through the Primakoff reaction in the context.
The theoretical background is highlighted, and the various
challenges of the measurement are discussed."