# Why ratio atmospheric ##\nu_\mu : \nu_e = 2:1##

• ChrisVer
In summary, the ratio of atmospheric neutrino fluxes is expected to be R= \frac{\nu_\mu + \bar{\nu}_\mu}{\nu_e +\bar{\nu}_e} =2 for no Neutrino Oscillations. However, this is only an approximation and can vary based on factors such as the Zenith angle and particle energies. There are also other particles that contribute to the production of muon pairs, leading to a more complex spectrum dominated by low-energy particles.
ChrisVer
Gold Member
Why is the ratio of atmospheric neutrino fluxes expected to be:
$R= \frac{\nu_\mu + \bar{\nu}_\mu}{\nu_e +\bar{\nu}_e} =2$
for no Neutrino Oscillations?
An answer that I found gives:
$\pi \rightarrow \mu \nu_{\mu} \rightarrow e \nu_e \nu_\mu \nu_\mu$
But I think this is "wrong" in general, because the muons can reach the Earth before interacting... at least it should be a function of the Zenith angle $\theta$ and their energies (boost).

In general, the spectrum is dominated by low-energetic particles, and low-energetic muons decay in flight.
You also have some other particles producing muon pairs. That ratio of 2 is only an approximation.

## What is the significance of the atmospheric neutrino ratio?

The atmospheric neutrino ratio, also known as the muon-to-electron neutrino ratio, is an important measure in particle physics. It helps us understand the properties and behavior of neutrinos, which are fundamental particles that play a key role in the Standard Model of particle physics.

## Why is the ratio of atmospheric neutrinos specifically 2:1?

This ratio is a result of the decay of pions and kaons, which are produced when cosmic rays interact with the Earth's atmosphere. These particles decay into muons and muon neutrinos at a higher rate compared to electrons and electron neutrinos. As a result, there are more muon neutrinos in the atmosphere, leading to a ratio of 2:1.

## How is the atmospheric neutrino ratio measured?

The ratio is measured using large detectors, such as Super-Kamiokande and IceCube, which are designed to detect and differentiate between different types of neutrinos. These detectors observe the interactions of neutrinos with matter, allowing scientists to determine the ratio of muon to electron neutrinos.

## Does the atmospheric neutrino ratio vary at different locations on Earth?

Yes, the ratio can vary depending on the location and the energy of the cosmic rays that are interacting with the Earth's atmosphere. For example, the ratio may be slightly different at higher altitudes compared to sea level.

## What implications does the atmospheric neutrino ratio have for our understanding of the universe?

The atmospheric neutrino ratio is an important piece of evidence for the Standard Model of particle physics, which helps us understand the fundamental building blocks of the universe. Studying this ratio can also provide insights into the behavior of neutrinos and their role in the formation and evolution of our universe.

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