On the transformation of neutrino into electron

Neutrinos rarely interact with matter. When they do a neutrino can transform into an electron if the neutrino is very energetic (see details below). An electron, on the other hand, does not transform into a neutrino so easily.

Empirically speaking, electron is the most stable elementary particle in the universe. Electron decay has never been observed. Our theoretical understanding of the stability of the electron and its close relationship to neutrino is not satisfactory. The theoretical understanding of the weak nuclear force (mediated through W and Z virtual bosons) represents great progress but I predict that there is much more to be discovered about the neutrino-electron relationship in the future.

Speaking of stability, protons are very stable as well. Proton decay has never been observed. Protons do not decay but we can break them by colliding them against each other in colliders such as the Large Hadron Collider at CERN.

Can we break electrons? No. We cannot break electrons but we can annihilate them.

When we collide electron with antielectron (positron) they annihilate each other and turn into 2 photons at the interaction point. If the electron-positron collision is energetic the annihilation may produce a Z boson. If the annihilation is even more energetic a W(+)W(-) pair may be produced. This is how W and Z bosons were produced in great numbers and studied in detail at the LEP experiments at CERN. LEP operated in two phases. In phase 1 (1989-1995) it collided electrons with positrons to produce Z bosons. In phase 2 (1996-2000) it produced W(+)W(-) pairs. Note that Z and W were discovered earlier in proton-antiproton collision experiments at CERN in 1983. Later, LEP was built to generate more statistics about W and Z.

What about colliding electrons with electrons? Yes, it is possible (see this note by V. Shiltsev). Electrons scatter via the electromagnetic force (they repel each other). What happens when colliding electrons are very energetic? The same thing!  They scatter via the electromagnetic force. In principle it does not matter which particles are used to create  high energy density in a localized volume. If the energy density is high enough other particles will be created while obeying the conservation laws. Electron-electron collision may be used to create high energy density at the interaction point but the production of new particles will not be efficient because of the conservation laws.

Transformation of neutrinos into electron, muon, tau

“Neutrinos can interact via the neutral current (involving the exchange of a Z boson) or charged current (involving the exchange of a W boson) weak interactions.

In a neutral current interaction, the neutrino leaves the detector after having transferred some of its energy and momentum to a target particle. All three neutrino flavors can participate regardless of the neutrino energy. However, no neutrino flavor information is left behind.

In a charged current interaction, the neutrino transforms into its partner lepton (electron, muon, or tau). However, if the neutrino does not have sufficient energy to create its heavier partner’s mass, the charged current interaction is unavailable to it. Solar and reactor neutrinos have enough energy to create electrons. Most accelerator-based neutrino beams can also create muons, and a few can create taus. A detector which can distinguish among these leptons can reveal the flavor of the incident neutrino in a charged current interaction. Because the interaction involves the exchange of a charged boson, the target particle also changes character (e.g., neutron to proton).” [1]

n is neutron, p is proton, e^- is electron, e^+ is antielectron, \mu^- is muon, \mu^+ is antimuon, \tau^- is tau, \tau^+ is antitau, \nu_{e} is electron type neutrino, \nu_{\mu} is muon type neutrino, \nu_{\tau} is tau type neutrino, the \nu symbols with an overbar refer to the antineutrino.

Neutrino electron swap (Wolfenstein matter effect)

A neutrino passing through matter can interact with an electron bound to the matter atom and transform into an electron while the original electron becomes a neutrino. This is essentially a swap. This is a very rare process. It happens inside the stars.

The “neutrino electron swap” involves an intermediate step: creation of a virtual W(+) boson. See the first  figure above (left diagram). The incoming neutrino has to be energetic enough to create the W boson otherwise no interaction takes place.


[1] https://icecube.wisc.edu/outreach/neutrinos

I also recommend the Fermilab “All Things Neutrino” portal.

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