Answer to Question #161547 in Atomic and Nuclear Physics for Usama

Question

What is neutrino hypothesis? What is the need and significance of this hypothesis?

Answer 1

Pauli postulated the existence of new particle, “neutrino” as early as in 1930. According to Pauli, an additional particle called a neutrino denoted by “v” is emitted in process of β-decay.

This particle according to Pauli, carries away an amount of energy equal to difference between the observed energy for a β-particle and maximum energy of continuous beta spectrum. The principle of conservation of energy is thus satisfied.

To satisfy Principle of Conservation of Angular Momentum, neutrino must be assigned the following properties:

1. It must have zero charge; because in a β-decay process the charge is conserved without neutrino. Also if neutrino is charged, it would produce ionization which certainly could have been detected. Zero charge in turn implies negligible magnetic momentum.

2. It must have zero or almost zero mass: the mass-energy balance of β-decay processes shows that neutrino rest mass is negligible.

3. It must have a spin of ½: This will satisfy Law of Conservation of Angular Momentum in β-decay process. Further neutrino must be a fermion, so that nuclear statistical requirements are fulfilled.

4. A neutrino has an antiparticle called anti-neutrino which has zero rest mass, zero charge and spin-1/2.

The majority of neutrinos which are detected about the Earth are from nuclear reactions inside the Sun. At the surface of the Earth, the flux is about 65 billion solar neutrinos, per second per square centimeter. Neutrinos can be used for tomography of the interior of the earth.

Research is intense in the hunt to elucidate the essential nature of neutrinos, with aspirations of finding:

- the three neutrino mass values;

- the degree of CP violation in the leptonic sector (which may lead to leptogenesis);

- evidence of physics which might break the Standard Model of particle physics, such as neutrinoless double beta decay, which would be evidence for violation of lepton number conservation.