Check sign of Pi5 term in polarimeter vector computation for a1 decay channel

[veelken]

I compared the C matrix for pi+_a1- vs pi-_a1+ and saw that the C matrix is the same for both charge combinations.

This means that the sign of the Pi5 term in the polarimeter vector computation for a1 decay channel indeed needs to be different for tau+ and tau-.

It could still be, however, that the currently used sign is wrong for both tau charges.

Action item: invert sign of Pi5 term in polarimeter vector computation for a1 decay channel and check if this makes the C matrix for the pi_a1 and a1_a1 decay channels more similar to the pi_pi channel or more different.

[veelken]

The inverted sign of the P5 term indeed seems to improve the agreement of the spin correlation matrix C in the a1_a1 channel with the Standard Model expectation, see here:
TTauSpin/PolarimetricVectorTau2a1#1