Is it true that all neutrinos are left-handed?

Neutrinos, like people, can be either right-handed or left-handed. Southpaws will be relieved to learn that, unlike the world population, where left-handedness is uncommon, all neutrinos we’ve ever encountered are left-handed. Antineutrinos have always been right-handed in symmetry, according to scientists.

It might seem strange to think of particles as having “handedness.” The direction of a particle’s spin and how it relates to the direction the particle is going are referred to as handedness. Right-handed and left-handed particles can be seen by curling your hands into fists and extending your thumbs toward one another. They have the same spin, as indicated by the curling of your fingers, but travel in different directions, as indicated by the position of your thumb.

Another demonstration: Make fists with your hands and extend your thumbs towards the ceiling to see right-handed and left-handed particles. They have the same direction of travel but opposing spin (since your left fingers curl clockwise and your right fingers curl anticlockwise) (which way your thumb is pointing).

Neutrinos have proven to be an abnormality yet again. Other particles, such as quarks and the other three leptons (electron, muon, and tau), have left-handed and right-handed counterparts of their matter and antimatter partners.

This raises the question of where all the right-handed neutrinos and left-handed antineutrinos are hiding. It’s still a mystery, but scientists believe that if these right-handed neutrinos do exist, they’ll be substantially different from the left-handed neutrinos we’re familiar with. Perhaps they are significantly heavier, or they interact solely through gravity rather than the weak force (so-called “sterile neutrinos”). Right-handed neutrinos are a promising candidate for the sterile neutrinos that have been suggested but not yet discovered in numerous investigations. Many experiments are currently underway to determine whether sterile neutrinos do exist.

When physicists discuss handedness and neutrinos, they are referring to two distinct but related concepts: helicity and chirality. Despite the fact that helicity is a simpler notion to grasp, scientists are most likely referring to chirality when they say neutrinos are left-handed. Because there is a lot of overlap, the two names are frequently used interchangeably.

Helicity, like spin, energy, and momentum, is a conserved variable that varies depending on the reference frame. Helicity is essentially the same as it was in the first section: It’s the relationship between the spin and the direction of travel. Helicity is not a fixed feature; it varies depending on how the particle is viewed. Holding out your left fist, imagine a left-handed neutrino. It’s still a left-handed neutrino if your body stays motionless and your arm goes to the right. That is, the direction and spin (the curl of your fingers) are the same as they would be for a left-handed neutrino. Your fist looks to move to the left if you keep your left arm motionless and move your torso to the right. It now has the right-handed neutrino’s spin and orientation.

On the other hand, chirality is a particle’s inherent, fundamental feature. It is independent of the viewpoint or reference points. Left-chiral neutrinos and right-chiral neutrinos are both possible. Only left-chiral neutrinos and right-chiral antineutrinos have been observed by physicists.

So, while chirality is inherent, helicity is a matter of perception. The helicity of a neutrino would flip if something could overtake it, such as a fast photon. However, because people do not spend much time traveling at light speed, there is a lot of overlap between helicity and chirality. As a result, when it comes to handedness, there is confusion and free usage of the two terms.

The helicity and chirality of neutrinos would match if they were massless and traveled at the speed of light, as physicists first hypothesized and as the Standard Model predicts. However, when scientists discovered the particles possessed mass, they were startled to find no right-chiral neutrinos. Because right-chiral neutrinos have never been observed, scientists can assume that if they do exist, they are quite different from left-chiral neutrinos. They may be incredibly heavy, or they could not interact through the weak force, or they could be both.

If neutrinos are Majorana particles, particles that can behave as their own antiparticles, the subject of left-handedness or left chirality becomes even more intriguing. The only distinction between neutrinos and antineutrinos would be their chirality if neutrinos are Majorana particles. Left-chiral neutrinos are referred to as “neutrinos,” while right-chiral neutrinos are referred to as “antineutrinos.”

Many topics in neutrino physics could be answered by Majorana neutrinos. It would allow neutrinos to gain their mass in a different way than all other particles, in addition to helping us understand where the right-chiral neutrinos reside. Neutrinos are extremely light in comparison to all other mass particles, which get their mass through interactions with the Higgs field. Scientists are trying to figure out why neutrinos are so unaffected by the Higgs field, although it’s possible that neutrinos gain their minuscule masses through a different mechanism.