Missing neutrino

[XFool]

Neutrino result heralds new chapter in physics

BBC News

A new chapter in physics has opened, according to scientists who have been searching for a vital building block of the Universe.

"They were named sterile neutrinos because they are predicted not to interact with matter at all, whereas other neutrinos can - though very rarely. Detecting a sterile neutrino would have been a bigger discovery in sub-atomic physics than the Higgs boson because, unlike other forms of neutrino and the Higgs particle, it is not part of the current Standard Model of physics."

Though how do they know they are missing, if they don't interact with matter at all?

[Mike4]

Though how do they know they are missing, if they don't interact with matter at all?

Maybe the maths predicts them.

More pertinently, how would we detect them if they don't interact?

[ursaminortaur]

Though how do they know they are missing, if they don't interact with matter at all?

Maybe the maths predicts them.

More pertinently, how would we detect them if they don't interact?

They aren't part of the standard model but adding them as a theoretical extension to the standard model would help solve the mystery as to why neutrinos have mass (which according to the standard model they shouldn't have) and why neutrinos spontaneously switch between the three known types of neutrino (and if it exists also switch between them and sterile neutrinos). The switching behaviour is why we know that neutrinos must have a small mass since it could not occur with massless particles since they would travel at the speed of light and thus not experience time as they travel.

They would interact gravitationally (which makes them one candidate for dark matter). They would also be detectable indirectly by their theoretical effects on other interactions.

https://www.newscientist.com/article/2294958-physicists-fail-to-find-mysterious-sterile-neutrino-particles/

Sterile neutrinos get their name because, unlike the other three types, they would only interact via gravity and not the other fundamental forces. Many theoretical physicists found the idea of a sterile neutrino promising because it had the potential to explain several anomalies found in particle physics experiments, as well as being relevant to the mystery of dark matter. But because neutrinos are so small and interact so weakly with other matter, we can only observe them indirectly, via the products of collisions with other particles.

In the 1990s and early 2000s, two neutrino experiments found more of these products than expected. However, neither of them was able to tell the difference between electrons and photons in its results – and sterile neutrinos would only produce extra electrons, not photons. A newer experiment called MicroBooNE at the Fermi National Accelerator Laboratory in Illinois can tell the difference, but its first three years of data show no extra neutrino products at all.

“I would have really expected to see an excess in either the photons or the electrons and we haven’t seen one in either, which opens up more questions,” says MicroBooNE spokesperson Justin Evans at the University of Manchester in the UK. We still have no way to explain the earlier results, so they might point to more exotic physical processes that haven’t yet been considered, he says.

So is the hunt for the sterile neutrino over? “We definitely are not seeing any evidence for a sterile neutrino,” says Evans. “As to whether it is completely dead, I think that depends who you ask, but you’ve certainly got to get a lot more inventive to get a sterile neutrino into your particle physics models now.”