¥What can
cause this asymmetry?
¥It is
not the calculated time delay (this effect the position of the vertex
distribution for a specific counter combination, not the width).
¥Bug in
software when T0 event is created? Not likely, since asymmetry is clearly
visible in the raw FB data.
¥Effect
of magnetic field? No; runs with
no magnetic field show the same effect.
¥Secondaries? Most likely, but the asymmetry does not
show up in the Monte-Carlo simulations.
¥Conclusion: this is a
real effect but not understood yet.