MARKUS KLUTE: Welcome back to 8.701.
In this short section, you're going
to look at the weak interaction a little bit more,
and specifically discuss neutral currents.
We looked in some detail at charged currents--
specifically, the interaction with quarks.
So here, I'm going to look at the Z boson specifically,
and the weak interaction via the neutral current.
So studying those two processes here,
where there is an electron and a positron
through some process including a Z boson and a photon
and resulting in a muon and an anti-muon--
those processes have been studied in great detail
at SLAC and at CERN, at the SLC, and the Large Electron-Positron
Collider.
So if we want to calculate the cross-section
and study the cross-section of the center of mass energy,
we see a number of interesting effects.
At low energies, and at very large energies,
the cross-section runs with 1 over the energy squared.
But at the mass of the Z boson, we see this enormous resonance
here.
The cross-section at the resonance from the Z boson
is about 200 times that of just a photon exchange.
So this allows you to study the Z boson with great precision
at those colliders.
You have sizable cross-section when you are
in electron-positron colliders.
And then you can, with precision,
look at, what is the rate into a muon/anti-muon?
What is the rate into a quark/anti-quark?
And so on.
And you can study the mass, the width of the Z boson
with an enormous level of precision.
Again, so I will not go into too much detail here.
And please have a look at chapter 9.6 in Griffiths,
for example.
But there's many other resources where you can learn more
about [? neutral ?] currents.
Neutral currents, electroweak neutral currents
are specifically important in the study of neutrinos,
as we will discuss more in the lectures as well.