Neutrinos Could Be Their Own Antiparticle and Rewrite Physics

antimatter it sounds like something made up just for sci-fi books and movies but it's very much real we create and send huge quantities of antimatter particles through our accelerators at fermilab to test the known laws of physics but what if a particle could also be its own anti-particle that's what we're talking about today on even bananas could a particle be its own anti-particle what does that even have to do with neutrinos first we have to talk about what antimatter is it something at the heart of some evil plan to destroy the world yes sorry no that's Professor Steve biller and I

guess he's my guest for this episode Steve is a professor of physics at the University of Oxford and works on the snow plus experiment in 1920 28 Paul direct came up with an equation that brought together the two pillars of physics quantum mechanics and special relativity uh there just one problem it gave two solutions for energy so this happens with a quadratic equation like for example x^2 = 4 uh X can be two or minus 2 both work well direct equation was quadratic in energy so you could have a positive energy solution and a negative energy solution so when this sort of thing happens in physics we tend to just throw away the non-physical solution and keep going but direct

wondered whether the negative energy solution could have a physical interpretation and that led him to postulate the existence of anti particles so nowadays we don't think of anti particles as having negative energy we think of them as particles that have their fundamental properties reversed and amazingly a few years later 1932 the anti particle to the electron was discovered the positron which looks identically like an electron but with a positive charge if we know anything about neutrinos we know that there is weird as possible at every opportunity it's kind of their thing true to form they might not fit into the particle antiparticle pattern either in fact there's a possibility that neutrinos could be turned into their own

antiparticles which isn't unheard of photons are their own anti particles but this would be a first for massive particle and one more reason that neutrinos are unique three important properties that distinguish one particle from another are mass charge and spin one of the easiest ways to tell a particle from its anti particle is by looking at its mass and charge got a particle with the same mass as the electron but positive charge that's a positron of course neutrinos don't have charge so we can't use that to tell them apart from anti neutrinos what about spin we often refer to particle helicities to refer to whether a particle spins clockwise or anticlockwise relative to its direction of motion neutrinos are particularly

weird and they all spin anticlockwise whereas anti neutrinos spin clockwise as far as we can tell this may be the only difference between them if so then maybe it's possible to flip an anti neutrino into nutrino or vice versa the ability to formform such a flip is directly dependent on the particle Mass the more massive it is the easier it is to flip around trinos are incredibly small in their Mass uh at least a million times smaller than that of the electron but against all expectations of the standard model the mass is not zero so maybe it is possible to perform this flip if this flipping were possible it would mean neutrinos were a different type of particle called a myana particle

named after the Italian physicist Ator myana who proposed them no massive myana particle has ever been discovered and neutrinos are the only particles we know that could be one so why is this a big deal there's a problem with the universe when it was created you must have had equal amounts of matter and antimatter because you started from nothing so it should all still add up to nothing but if that's the case it should have all annihilated with itself and there should be nothing left so fortunately for us something must have happened to prevent this from occurring somehow a small amount of antimatter must have flipped over into matter so maybe neutrinos hold the key to understanding how this

happened but how do you test for this flipping the only practical way we know is to look for an extremely rare process called neutralis double beta Decay to understand that let's take two steps back to normal beta Decay it's a radioactive decay that happens a lot in nature where a neutron in an atomic nucleus decays into a proton an electron and an electron anti-neutrino longtime fans of this show will remember that this is why bananas produce neutrinos in double beta Decay two neutrons do this simultaneously so you get two protons two electrons and two anti neutrinos this is a process predicted by Maria goer Meyer and it's incredibly rare but it does happen in certain Isotopes it's been measured if

one of those anti neutrinos was to flip around and become a neutrino it could then effectively cancel out the other anti nutrino as matter and antimatter tends to do that would give us neutrinoless double beta Decay where we get two electrons and no neutrinos if we see this happening then we'll know with confidence that we observe myON particles what we're looking for in our experiments are decays where all of the energy goes into the two electrons with none of it disappearing into the anti neutrinos the experiments use radioactive isotopes that are known to undergo double beta Decay like torium 130 or Xenon 136 or geranium 76 but it's a really tough game because if this happens at all it's ridiculously rare and we're trying to distinguish it

from all the other decays that are happening all the time some experiments like snow plus use large detector volumes uh to try to maximize the number of decays that they see whereas others like legend or nexo or Cupid will have smaller detector volumes but better energy resolution to try to distinguish them clearly uh from normal decays Legend combines the expertise from two previous experiments gerder and Mayana the Mayana demonstrator was located at Sanford underground research facility right down the tunnel from the new home of the firy laab hosted experiment June so why are we so excited about this well you've heard me say before that neutrinos could explain the matter anti matter imbalance in our universe the bit

you might not have heard is that it only works if neutrinos and myana particles measuring neutralist double beta Decay could also give us information about the neutrino mass and particle physicist would be really excited because it's a whole new kind of particle and that's the kind of thing we love complicating this is the fact that we don't in fact know what the actual value of nutrino mass is which plays a crucial part of the flipping probability depending on what this value is a discovery might be right around the corner or it could be several years before we know the answer but neutrinos have revolutionized our ideas of physics many times so maybe they could do this again couldn't have said it better

myself thanks Steve bye Kirsty there are a lot of mysteries in the neutrino world and we're just getting into them like share and subscribe to come along and let me know in the comments what do you think is the most interesting nutrino conundrum fun in fact Italian physicist Ator Mayana who worked on neutrino masses famously disappeared in 1938 enrio fery once said there are several categories of scientists in the world those of second or third rank do their best but never get very far then there is the first rank those who make important discoveries fundamental to Scientific progress but then there are the Geniuses like galile and Newton Mayana was one of these