Z-Boson reasonance and the number of neutrino varieties

In summary, the experimental results of Z-Boson resonance confirm the theoretical expectations of 3 types of neutrinos, as determined through the LEP experiment. The total width of the Z boson is made up of two parts - a visible part consisting of decays to charged leptons and hadrons, and an invisible part consisting of decays to neutrinos. By subtracting the visible part from the total width, the number of active neutrinos can be determined, which is found to be very close to 3. Further understanding of the Z resonance and its relation to the number of active neutrinos can be gained through reading and solving problems in chapter 20 of Peskin & Schroeder.
  • #1
Ngineer
64
1
I've read that the experimental results of Z-Boson resonance confirm the theoretical expectations that there are 3-types of Neutrinos, not 2 or 4.

How are these theoretical expectations calculated? I.e. how does the number of neutrino varieties affect Z-boson resonance?

Thank you
 
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  • #3
At the LEP experiment Z bosons were produced through colliding electrons and positrons. This was a very clean experiment, unlike the LHC, allowing the properties of the Z boson to be studied to high precision. The presence of the Z boson shows up as a peak in the total cross-section as a function of center of mass energy with the peak located at ~91 GeV corresponding to the mass of the Z boson (there is a nice plot of this on p711 fig.20.5 of Peskin & Schroeder). By measuring the Z peak very carefully they can determine the total width (##\Gamma_{tot}##) and the cross-section at the peak (##\sigma_{peak}##).

The total Z width ##\Gamma_{tot}## is actually made up of two parts. The first is the visible part ##\Gamma_{vis}## made up of decays to charged leptons and hadrons and this is related to the observed peak cross-section ##\sigma_{peak}##. The second is the invisible part ##\Gamma_{inv}## made up of decays to neutrinos which are not observed in the experiment. This second part can be determined by taking ##\Gamma_{tot}-\Gamma_{vis}=\Gamma_{inv}=N_\nu\Gamma(Z\to \nu\overline{\nu})## where ##N_\nu## is the number of active neutrinos. Notice it is "active" neutrinos that matter not the number of neutrinos as there might be "sterile" neutrinos which the Z doesn't decay to. Putting it all together we can get ##N_\nu## from
$$N_\nu = (\Gamma_{tot}-\Gamma_{vis})/\Gamma(Z\to \nu\overline{\nu})$$
and the result is very close to ##N_\nu=3##.

You can try to look at chapter 20 of Peskin & schroeder and in particular do the problems 20.2 and 20.3 on p 728 which will give you a good understanding of the Z resonance and how it relates to the number of active neutrinos.
 
  • #4
This does help a lot. Thanks Vanadium and jkp.
 

Related to Z-Boson reasonance and the number of neutrino varieties

1. What is the Z-Boson resonance?

The Z-Boson resonance refers to a phenomenon in particle physics where the Z-Boson, a subatomic particle, is produced through the collision of other particles. It is a key process in understanding the fundamental interactions of particles and is studied extensively at particle accelerators.

2. How many types of neutrinos exist?

Currently, there are three confirmed types of neutrinos: electron neutrino, muon neutrino, and tau neutrino. These three types are collectively known as "flavors" of neutrinos. However, some experiments have shown evidence for a fourth type, known as the sterile neutrino, but this has yet to be confirmed.

3. How does the Z-Boson resonance relate to neutrinos?

The Z-Boson particle is responsible for the weak nuclear force, one of the four fundamental forces of nature. This force is responsible for interactions between particles, including the transformation of one type of neutrino into another. The Z-Boson resonance is a crucial process in understanding the behavior of neutrinos and their interactions with other particles.

4. Can the number of neutrino varieties change?

The number of confirmed neutrino varieties is currently three, but this may change as new experiments and technologies are developed. Scientists are constantly looking for evidence of new particles and interactions, which may lead to the discovery of additional types of neutrinos.

5. Why is the study of Z-Boson resonance and neutrinos important?

The study of Z-Boson resonance and neutrinos is essential in understanding the fundamental building blocks of our universe and how they interact. These particles play a crucial role in processes such as nuclear fusion in stars and the creation of matter in the early universe. Additionally, studying these particles can also lead to advancements in technology, such as more efficient energy production and medical imaging techniques.

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