I How Can Neutral Currents Be Detected in Particle Physics Experiments?

[Wledig]

In decay processes where no mixing between quark families is present, the mediator of the weak force is the neutral $Z^0$ boson. If that is the case, how is it experimentally possible to detect neutral currents in processes such as: $$\bar{\nu}_\mu + e \rightarrow \bar{\nu}_\mu + e$$ What trace could the neutral boson possibly leave in the detector?

 

[Vanadium 50]

An electron shooting out from an atom.

 

[Orodruin]

In decay processes ... such as: $$\bar{\nu}_\mu + e \rightarrow \bar{\nu}_\mu + e$$

That is elastic scattering, not decay.

 

[Wledig]

An electron shooting out from an atom.

I had a vague idea of how things could work out, let me see if it's what you're suggesting. If we bombard an atom with muon antineutrinos we ought to observe electrons being scattered out of it, which would give an indirect confirmation for the existence of the $Z^0$ boson. Is that it? No hope for direct observation then, I believe? Or at least not in processes like this?

That is elastic scattering, not decay.

Sure. But the weak neutral boson is the mediator of the interaction, right? Or am I getting something wrong?

 

[mfb]

I had a vague idea of how things could work out, let me see if it's what you're suggesting. If we bombard an atom with muon antineutrinos we ought to observe electrons being scattered out of it, which would give an indirect confirmation for the existence of the $Z^0$ boson. Is that it? No hope for direct observation then, I believe? Or at least not in processes like this?

Indirect confirmation of the existence of something like the Z and for the existence of neutrinos.

Sure. But the weak neutral boson is the mediator of the interaction, right? Or am I getting something wrong?

Yes, interaction is the right term. A decay needs to start with a single particle.

 

[Orodruin]

I had a vague idea of how things could work out, let me see if it's what you're suggesting. If we bombard an atom with muon antineutrinos we ought to observe electrons being scattered out of it, which would give an indirect confirmation for the existence of the $Z^0$ boson. Is that it? No hope for direct observation then, I believe? Or at least not in processes like this?

Neutral currents were discovered in accelerator experiments, not through neutrino interactions. Being neutral, you will never really see Z interactions with a detector. It also has a very short lifetime. What you see in accelerators when you produce on-shell Zs is a peak in the invariant mass distribution of the decay products.

 

[mfb]

What you see in accelerators when you produce on-shell Zs is a peak in the invariant mass distribution of the decay products.

That's a really nice signature, luckily. Here is a graph, dots are measurements.

Tristan was just a bit too small to find the rise towards the peak.

 

[Vanadium 50]

Neutral currents were discovered in accelerator experiments, not through neutrino interactions.

Neutral currents were discovered in accelerator experiments, not through neutrino interactions.

They were discovered in 1973 by the Gargamelle experiment at CERN, via a process similar to described in post #2. The Z, on the other hand, was discovered by colliders. While in principle, one could use the sort of measurement as described in #2 to determine the mass of the Z, it requires impractically precise measurements and/or impractically high energy beams to measure the Z mass this way.

 

[Orodruin]

Neutral currents were discovered in accelerator experiments, not through neutrino interactions.

They were discovered in 1973 by the Gargamelle experiment at CERN, via a process similar to described in post #2. The Z, on the other hand, was discovered by colliders. While in principle, one could use the sort of measurement as described in #2 to determine the mass of the Z, it requires impractically precise measurements and/or impractically high energy beams to measure the Z mass this way.

Agreed, I should have formulated that more carefully.