Tribute to Milla
The starting talk of this morning is a collection of memories of Milla Baldo Ceolin from selected participants. Rather than reporting these short speeches here, I will offer my own – so this becomes an addition to the conference rather than a report of it.
In 1988 I was a undergraduate in Physics and I followed a course of “Fisica Superiore”, a course mostly based on weak interactions which Milla held in Padova. Her lessons were extremely fun to follow, because she interspersed the physics with countless anecdotes from her own life of research. She had met monumental figures of Physics of the XXth century, such as Wolfgang Pauli (to name one) and she had fun episodes to report about all.
I remember one day -this was probably one of the first few days of lessons- when she was discussing the beta decay of the neutron, as an introduction to Fermi theory. She drew the process n -> p e on the blackboard (a neutron decays to a proton and an electron) and asked us: what’s wrong with this ? What is it that this reaction does not conserve ?
I was still a newbye in particle physics, but it occurred to me that the reaction violated the conservation of leptonic number (since you have an electron in the final state, NL=1 there, while there are none in the initial state), and I said so. To which Milla retorted “Ma come corre!!!!” (Don’t run that fast!). She was quick to explain that neutrinos had not been discovered yet, and that the conservation of leptonic number was not even on the table yet – leptonic number would come later as a quantum number.
Of course the reaction drawn on the blackboard violates several rules… So what was the answer to Milla’s question ?