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neutrinos weren't supposed to be this way they should be massless ghost particles that never interact but we know they do interact although rarely and they do have mass now 60 years after they were first proposed neutrino masses are still a mystery to scientists why do neutrinos have mass and why don't they fit in with the pattern of other particles that's what we're talking about today on even bananas in the standard model of particle physics neutrinos are massless but we know they can't actually be massless because of neutrino oscillations if you need a refresher check out our neutrino oscillation video here it's important to remember two points first while neutrinos have both flavor States and
mass states only the mass states have one to one corresponding masses the masses of the flavor States are combinations of the mass States I know that can be a weird concept second we still don't know what the masses are for each Mass state but we know that they exist basically if you calculate the probability that a neutr will change from one flavor to another you find that the probability depends on the value Delta M squar the difference in squared masses between two neutrino Mass States Let's Pretend neutrinos didn't have mass then 0 minus 0 would give us zero and we'd never see neutrinos change flavor the fact that we do see neutrinos oscillate means that neutrinos must have mass measurements of
neutrino oscillations can tell us the size of Delta m^ s however that doesn't tell us which neutrino is heavier or lighter a problem called the mass ordering it also doesn't tell us what the masses of the neutrinos actually are if we measure a Delta m^2 of 10 are we talking 1 and 11 or 5 million and 5 10 other measurements can tell us a bit more cosmologists compare measurements of the cosmic microwave background to models of how the universe evolved including different amounts of total neutrino Mass those measurements tell us that if you add up the masses of all the different types of neutrinos the total mass should be less than 0.26 electron volts a more direct measurement comes
from an experiment called Katrin Katrine measures the energies of electrons produced from the beta decay of an isotope of hydrogen called tritium the maximum energy of the electrons can tell us how much energy went into making neutrinos and hence their Mass it's an incredibly complicated measurement with a highly sensitive detector But ultimately the experiment says that the mass of a neutrino is less than about 0.8 eight electron volts this brings us to our next problem both of these measurements are pointing towards neutrino masses that are at least 625,000 times smaller than the next lightest particle the electron any way you look at it neutrinos don't fit the pattern so why
are neutrino masses so different from all the other particles to answer this we first have to understand how particles get Mass to help us I've brought in my friend Pedro machard a theoretical physicist from fermilab hi Pedro one of the properties that particles can have along with charge and flavor is chirality or handedness particles can have components that are left-handed or right-handed you may have heard of this in chemistry class or on your own hands fans of particle physics May recognize this concept from the higs boson Discovery in 2012 the higs Bon gives particles mass by breaking the Symmetry that distinguishes left and right-handedness the weak symmetry interactions with the higs bow and combine left-handed and
right-handed parts of the particle which is what generates its mass this is very deep particle physics but the main thing to know is that it's very well defined and understood for most particles but if you apply this mechanism to neutrinos it gets a little bit tricky kind of by Chance the nutrino is special as far as We Know neutros are only left-handed they don't have a right-handed component that opens up a lot more possibilities theoretically it means that while other particles get their Mass through the higs the way neutrinos get their masses could be different some people hi even say it should be different well that is because the nutrino is different from the other particles there is another
possibility we've talked about how neutrinos could be a fundamentally different type particle called a myuran fermion the implications of that are super cool so definitely check out that video If you haven't myuran particles get their mass in a different way that's theoretically nice because it could explain why the nutrino masses are so much smaller than the other particles if you close your eyes and pick out the simplest theory for how neutrinos get their Mass you get myana particles with a seesaw mechanism this seesaw mechanism says that you have two particles a left-handed nutrino and a rightand nutrino the right-and nutrino never interacts and that's why we wouldn't have seen it yet mathematically if you raise the mass of the
right-handed guy the left-handed Mass goes down like a seesaw the reason the nutr masses we know about are so light could be because there is a really heavy right-handed nutrino that we just don't know about it yet we should give a caveat though we have no data to go guide the theory so it's kind of a Pandora's box once you start inventing new particles that you can't detect why is your new invisible particle better than mine why invent a right-handed neutrino rather than a special neutrino specific Hig particle in some sense neutrino masses should be a field as broad as dark matter we know it's there but there's 100 theories to explain nutrino masses and no way to test them with data yet
yep often when people say hundreds of theories they usually mean like five but in this case there are really over hundred theories that could actually work neutrinos are different because they all interact via the weak Force right-and neutrinos could exist and would have no interactions at all that's when all hell breaks loose theoretically speaking so there you have it nutrino masses are a mystery that have been going on since neutrinos were discovered and it doesn't seem like we'll solve anytime soon we still don't know the mass of each nutrino Mass state how the mass states are ordered or even how the neutrinos get their Mass that's what makes neutrino physics so much fun which theory for explaining how neutrinos get
their Mass do you like the best let us know in the comments and don't forget to like share and subscribe to hear more about these confusing particles fun fact the catchin experiment spectrometer is so big it couldn't do the 350 km trip from where it was built to the lab by land instead it was shipped 8,600 km by water down the danu river in Europe to the Black Sea through the Mediterranean Sea and the Atlantic Ocean and back up the rine to do a short 7 km by land when you see the photos of it kind of makes
