Q/A "Charged-pion polarisability and more measurements of chiral dynamics at COMPASS", Chiral Dynamics workshop 2015, Pisa

Q1 (Dean Lee) Did you consider to measure also with positive pion beam, in
order to understand better possible nuclear/Coulomb interference effects? (for
Primakoff Compton)

A1 It is very appealing to measure with negative and positive pions.
Technically the positive hadron beam contains predominantly protons, and the
identification of the proton, pion and kaon components can not be done as
accurately as for the negative beam.

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Q2 (Gerhard Ecker) What about the scale dependence of the loop contributions?

A2 We apply a (chrial) loop correction only at first order, which has no
contribution to the polarisability in the s->mpi2 limit. [from the discussion
in te coffee break: when possibly applying second (or higher) order chiral
corrections, their contribution to the polarisability has to be taken into
account consistently]