Neutrinos: Messengers from a Violent Universe

alright thanks thanks for coming welcome to Fermilab as he said I'm going to be talking about neutrinos which tell us rather a lot about the universe sort of a surprising amount I would say and the first question you probably won't have is why are you talking to a particle physicist instead of an astronomer I'm willing to bet a lot of people in this room probably know more about astronomy than I do but what I do know about is neutrinos and those neutrinos can tell us a lot about what's happening sort of in astronomical bodies as close as our Sun or as far away as distant extremely powerful galaxies so we start with a little bit of history on the neutrino itself and we'll come back around to what it has to do with astronomy in a little bit so the neutrino itself was introduced to solve a problem and that problem was that in the early 20th century they were making people were making measurements specifically this guy named James Chadwick was making measurements of nuclear decay and when he was finding was that when he looked at the energy coming out of those decays he wasn't getting all the energy out he expected right and the worry was at the time that maybe you know conservation of energy isn't just not true on a subatomic level but this is a really controversial statement at the time this is one of the fundamental laws of physics and the solution that was proposed was to introduce a new particle that was neutral and interacted so weakly you could never see it right so this is a very controversial thing at the time right they've introduced a particle that they thought no one would ever be able to measure and that was introduced by Wolfgang Pauli to solve this problem actually at the time it was called the neutron because the neutron had not yet been discovered also by this guy James James Chadwick and was first really put into the into theory and someone made a you know sense of what the neutrino could be was Enrico Fermi's of course the person is this laboratory is named after right of course it didn't go on being undetected though it did take something like 30 years from after after Fermi's theory to be able to really measure it in an experiment and that was these two guys James rynason Cohen who measured neutrinos coming from a nuclear reactor and detected them in this experimental setup you see over here you know the neutrino would come and interact in this water segment over here and then these sections around it were made up of scintillator material that emits light when charged particles pass through it it's one of the common techniques used to try and observe particles and it'll it'll come back later so these guys in 1956 first observed the neutrino right and the the neutrino then becomes just a member of the family of subatomic particles right that make up the standard model of particle physics they come in three flavors the new e the new mu and the Tao and in the original theory they didn't have any mass right they were believed to be totally massless weakly interacting particles so what do I mean when they say they only interact weakly right so when I say they only have weak interactions so in particle physics when we talk about the strength of an interaction what we're really talking about is what we would call a cross-section which basically just means how often the particle interacts when it passes through matter right and it turns out that neutrinos interact very very weakly which means they interact very infrequently right so you may have heard of you know alpha beta and gamma radiation right that the you know which alpha is stopped by something as thin as a sheet of paper but gamma radiation will even pass through a thin amount of lead right so that's a high-energy photon the kind of thing you see coming from you know in telescopes and you know a high-energy photon will get through about 20 centimeters of carbons and not so dense material by comparison and in order to stop a neutrino it on average has to go through a Lightyear of lead right there's an enormous amount of dis right so these these are very weakly interacting which means they interact very very rarely fact there's billions of them passing through us coming from the Sun having passed through the earth already and they just keep on going you know off into the universe so this is in some sense a blessing right so this means that the neutrinos can can escape from really dense areas and tell us about what's happening inside of astronomical bodies right so there are neutrinos that are coming from the center of the Sun and pass right out of it right compared to light which sometimes can take many thousands of years I maybe it's tens of thousands of years it's a surprise in a long time for light to get out of the center of the Sun and be able to reach us but the neutrinos just pass right out almost instantly the downside of course is that once those nutrients get to earth most of pass right through the earth and just completely avoid our detectors so that means that they have a lot of great information but they're really hard to spot and to try and do something with right so how do we see the neutrinos right so the first point is that you can never really see a neutrino what do you what do I you mean when you say you see something right you see something by having a photon bounce off of it and come into your and come into your eye or into your detector but photons only interact with material that has an electric charge so they just don't interact with neutrinos you literally can't see them what you can do however is take that neutrino and let it interact with an atom in this case an argon atom and when that neutrino interacts it will break up that atom or nucleus or nucleon right and emit charged particles which you can't which you can see in our detectors so this is what we're usually doing we talk about seeing neutrinos or measuring neutrinos what we're doing is letting the neutrinos interact in our detector and then seeing what comes out of those interactions so where do we get neutrinos from we'll come back to how we detect them in a little bit so there's a bunch of man-made sources of neutrinos right so as I said rynason cowan use neutrinos that came from a nuclear reactor which is a very copious producer of neutrinos we also can make them in accelerators like here at Fermilab mentioning in our introduction and you also get tons and tons of neutrinos from nuclear weapons you know there was a early idea to try and detect neutrinos before the nutrient before the neutrino had been observed try and put a detector deep underground near a nuclear test explosion which you know would have been really rough on that poor graduate student you know this actually comes from xkcd article about neutrinos which we haven't read it is quite good highly recommended but there are also Astrophysical analogues of these man-made sources right so the Sun in many ways is a nuclear reactor not so dissimilar to what we have it's fusion instead of fission but we're getting neutrinos from nuclear reactors you get neutrinos from explosions in space like supernovae and you can also get them from cosmic accelerators so we'll I'm going to talk about these three sources of neutrinos and what the neutrinos that come from them can tell us about universe we're going to start with the Sun because it's the closest the neutrinos are the lowest energy so this is the Sun as it looks in photons and this is the Sun as it looks in neutrinos as measured by the super-kamiokande detector so that seems really impressive until I tell you of course that the actual size of the Sun and this image is the size of one pixel in the middle you know the neutrinos are not a very high-resolution detecting you know detecting material but they out but they do tell us can tell us a lot about was coming from the inside right so the neutrinos that come from the Sun as I said come from nuclear fusion reactions so this is an example right if one of one of those reactions you can see that in this chain of getting from hydrogen and helium you emit a couple of neutrinos from these early interactions and so what that means is that the rate of neutrinos that come from the Sun tells us about the rate that these fusion interactions these fusion processes are happening at right and the rate that those usual processes are happening at those define the temperature of the Sun right so this is you can imagine a very interesting question to try and answer how hot is it in the center of the Sun and neutrinos can tell us that and it turns out that the when I say the flux of neutrinos that's how many neutrinos are coming per second into a into an area on the earth right so how many neutrinos we're getting from the Sun is a very sensitive measure of the temperature inside the Sun you know for some of the processes it goes as a factor of 10 to the 25 that's a really big exponent so what that means is that getting 10% less neutrinos means that the sun's temperature is 93 percent lower right so this is the very precise measure Jib question know of what's happening in the Sun so not that long after neutrinos were discovered a guy named ray Davis said you know what we should try and measure this flux of neutrinos because it's going to tell us all this interesting stuff about astrophysics so I set up this detector in the Homestake mine in South Dakota it's actually the mine from the show Deadwood if you've ever seen that right it's quite it's it's very near very near that town sets up this this detector underground basically full of dry-cleaning fluid and looks for a neutrino to come in and transform a chlorine atom into a different atom and try detective I think is barium something like that huh argh ah there we go so he sets up his detector waits around sees what happens and when he finds when he turns this detector on he gets significantly fewer neutrinos than he was expecting right so the standard solar models guy named brave a call Reba call something we call comes up with this model of what the how many neutrinos you expect to see given the tech even the sun's temperature and expects a number of eight in this extremely extremely precise unit called the solar neutrino unit right specs eight and what you actually observe in the detector is two to three right this this measurement goes on for 20 years here you see these data points bouncing around you see you're getting a number observing a flux of neutrinos about a third of what was being expected right so this sets off a decades-long search or they said this plots going up until the 90s where there's a bunch of other experiments that come along that try and measure the neutrino flux from the Sun in various ways and they keep coming out really low and how low it comes out depends a little bit on what technique you're using what atom you interact with but they all agree the flux and neutrinos is just not nearly high enough right and so this leads a lot of people to doubt this standard solar model causes a lot of controversy but it turns out that this what's happening here is not that we have the Sun wrong that we had neutrinos wrong right what this with the low flux of neutrinos was telling us was actually that the neutrinos were oscillating which is that they were changing from one flavor of neutrino to a different flavor of neutrino as they traveled from the Sun to the earth right so these types of these detectors were mostly just sensitive to electron neutrinos right so just that one particular flavor and so a bunch of those were missing the reason they were missing as they were changing flavors along the way so this problem was sorted out in 1998 by this experiment called super-kamiokande one of these experiments I worked on when I was in Japan were they and they figured it out by seeing that you know the flux of muon neutrinos coming from the bottom of the earth coming from a long way was much smaller than the ones coming from the top of the earth so it tells us that as the neutrinos travel with a longer distance some fraction of them oscillated away so this used actually not solar neutrinos used atmospheric neutrinos which come when cosmic rays collide with the atmosphere but it's you know the the physics of what's happening here is the same so this this is actually a scan of a transparency given by taka taka Aki cajeta in 1998 who just last year was given the Nobel Prize along with art McDonald for discovering this process for solving the solar neutrino problem discovering neutrino oscillations right so these neutrinos that were that came from the Sun that it turns out and it turns out we had the solar model walked right all along right that we had the temperature of the Sun right from neutrinos launched this whole field of study that these guys were awarded a Nobel Prize for and started a whole series of experiments to try and study you know neutrino oscillations in greater detail and these are three that happen to be here at Fermilab that studied this right so this is the Minos detector this is at least two are actually the far detectors which are in northern Minnesota and then the Dune experiment which is not yet built but we're trying to build this which is also going to go into the Homestake mine in South Dakota that same place that Ray Davis did his solar neutrino experiment you know I picked these three because these are the ones I worked on I've especially soft spot in my heart for this guys that was what I did my my PhD thesis on but so it's launched this whole field of trying to study what's happening with the neutrino right it became the first evidence of nutrient of physics beyond the standard model right you know became very interesting for us particle physicists right but that's you know but from your perspective what it's what the neutrinos are telling you is that we know the temperature of the inside of the Sun so problem solved move on to supernovas so supernovas I'm sure you all know but from as I put just in case right it means an energetic outburst resulting in the disruption of a star so I say this very technical definition to make clear the point that you know what we observe right is a big burst of energy and then the star is no longer there is different after that burst is done right and while that bursts with that supernova is going on the supernova itself can be as bright as the whole galaxy it's containing all right there's a really remarkable outburst of energy lasting a very very short period of time so this is a really interesting thing that we want to try and understand better the trouble is is that the information we have is pretty limited right if all we're doing is looking over here and seeing a bright light so I'll tell you a little bit right the supernova we're going to talk about here specifically called type 2 supernova which are you know these we think come from gravitational collapse I say we think because what we actually know is that type 2 supernova have h lines in the spectrum and they create compact remnants that means a neutron star or a black hole some very dense collection of matter and they produce lots and lots of neutrinos that's what we observe right those are the things we know the thing we think right about what's described what creates this effect is a model and that model is that you have some star which has a relatively old star it's got many layers of density of different material what happens is the innermost layer that's under an enormous amount of pressure starts to collapse in on itself right that's what these little and we're going arrows are it shrinks and shrinks and shrinks until the matter starts to collapse into each other so it's no longer even atoms anymore right and as that as that energy sort of collapses inward it creates a burst that explodes outwards and blows away some large fraction of the star leaving behind a neutron star in the middle so that's our model of what we think is happening and the neutrinos might be able to help tell us if that's really what's happening right so the idea here is that the energy is sort of the same in many senses as the energy that you get from dropping a piano say right the piano Falls there's some amount of gravitational potential energy there right and when it hits the ground it goes into kinetic energy and explodes outwards right so that's our idea of what we think is happening with us with a star going supernova right the star called the the gravitational energy potential energy is collapsing inwards right sort of going downwards and then that energy has to go someplace right it K has to end up somewhere the trouble is that it's got nowhere to go right you're at the center of this really dense object and the only thing that can escape are the neutrinos as we were just talking about they interact really really weakly and this is why when a supernova when a star goes supernova right you get 99% of the total energy comes out as neutrinos so remember when I was showing you this picture and this star is as bright as the whole galaxy its containing that brightness is less than 1% of the total energy released the rest of it is going into the neutrinos right and those neutrinos are coming from right at the very center from right where the gravitational info is happening so that we think they can tell us a lot about what's going on you know and it turns out we don't actually know that much about what's going on right like this is this is a nice simple picture but of course we want to understand it better than that simple picture right of arrows coming in we want to try and model what's really happening in the center of the star what are the dynamics and it turns out when you try and do that it gets really complicated right so these are some pretty pictures that come from some research at Caltech and they've been working to try and model these supernovae collapses for many years it's only been in the last few years that they can even get the models to explode right and you know it turns out it's really hard to try and make this happen and so we want to know right so they can play around with the models and try and see oh is this this makes it explode or I can make some other choices and this makes the star explode but we really want to know if we want to try and answer the question of what's really happening so we need to know what's happening in the center of the star and the only thing that can tell us that is the neutrinos so we have an example of this working in practice which is supernova 1987a which is really exciting to us I'm not sure it's exciting the most people this happened in the Large Magellanic Clouds about 55 kiloparsecs away it's one of these satellite galaxies surrounding the Milky Way right there's a picture of it of the supernova and then that little dot is the star that it originally came from it's really bright bright supernova and in this supernova we saw the neutrinos in in existing detectors we saw about 24 of them in two detectors kamiokande which is the predecessor to super-kamiokande and another one called imb which is in a salt mine in Indiana I think like that saw these 24 neutrinos right and you know I'll tell you that a you know uh this many papers at least a year gets published on these 24 neutrinos right it's it's since this time right it's a it's a remarkable thing but it's because this little peak right you see all this little peak of neutrino showed up of relatively high energy than the new energies got lower is we got we we expanded over ten seconds this is the best information we have about what's happening in on the inside of a supernova right and think about that too right this all happens in ten seconds you know this is on astronomical scales this is literally instantaneous that this explosion happens in oh oh we come how could you be sure that all of those neutrinos came from this very tiny point in the sky and are identified with that no that's a really good question the reason is that neutrino interactions in the detector are relatively rare right so we know that you know in in the course of a day you know these two you know modern detectors are seeing tannish 20-ish neutrinos a day these detectors are seeing maybe one or two and so to get twenty-four within 10 seconds was a really remarkable thing so I don't know maybe one of them isn't a supernova neutrino but there's more to it too right which that the energies tell us something so these if you look in the y-axis here right these energies range from about 8 MeV up to about 40 MeV right and we know from many years of studying the Sun that those that those neutrinos the highest energy solar neutrinos are 5 6 8 maybe 10 MeV these are sort of two energetic to be coming from the Sun but they're not but they're at the same time not energetic enough to be coming from the atmosphere exactly right the cosmic ray neutrinos tend to be you know another order of magnitude more energetic than these all right so it sits in this very narrow sweet spot where we could be sure that they were coming from this this supernova and I'll say that most of these were observed by a process called inverse beta decay right where you reverse the beta decay of a proton right and in that process you lose the directional information but a few of them can be observed via scattering right where you do get a little bit of directional information in your slide there it says it was detected two hours before the light exactly so we're talking about the violation of nothing travels faster than light excellent question so it so the reason that the niche we saw the neutrinos two hours earlier is because in this process the neutrinos escape faster than the light does right that the neutrino starts streaming out explode and start streaming outwards and the light is still trapped inside this incredibly dense medium for two hours or more right I mean the way the thing about it right is that this when this process happens if the star is a little bit bigger it turns into a black hole and the light doesn't escape at all right so you know as I said it takes many thousands of years for like to get out of the Sun because the material is so dense that the light can't escape it keeps bouncing into stuff right and it's an excellent point right it's not get to in a few slides that we can use this the neutrinos as an early warning system for a supernova happening somewhere in our vicinity right so this one so this discovery of the supernote supernova neutrinos also get led to a Nobel Prize back in 2002 for ray Davis and ma satoshi kojima who is the spokesperson of kamiokande at the time right so the next time a supernova occurs oh so you can tell I unfortunately both this talk a little fast I left up the slide saying that supernovas are really rare right supernovas in our galaxy happened somewhere between once every 30 years or once every hundred years they happen so infrequently that we don't even have a good measure of their rate right so you know this is a rare opportunity and we want to be ready when the neutrinos when the next supernova happens because there's a lot we can learn from it right we can learn about the physics of the star right the interest of this group right we can learn about the physics of the neutrinos right there's some stuff that happens in a supernova that doesn't happen anywhere else in the universe right the density of neutrinos is so high that the neutrinos interact with each other we might remember a neutrino will pass through a Lightyear of lead so you can imagine how many neutrinos you have to get in one place where the neutrinos start interacting with one another right and that the thing that makes all this possible is you need to measure sort of the the structure of the outgoing neutrinos right so what what neutrino flavors and what neutrino energies happen over time as that burst occurs right so what we saw here right as you see this axis is the energy this axis is the time so we want to fill this in in much finer detail the next time around great so the way we end so this is sort of an idea of what that would look like right you know that if you look at this this one right if we had a really close supernova we can see it in very fine detail this is telling us about the flux of these neutrino flavors the electron the anti electron and the new mew in the new tau in a liquid argon type detector right and so what you're seeing is that you can see from this structure right you see this rise up as the neutrino flux starts to increase as the matter starts to fall in right it gets a little denser then some I actually don't know what causes neutrino trapping but it creates this little kink in the spectrum and then all of a sudden the center of this of the star goes through what's called neutralization right what that means is that that process where you essentially take a bunch of individual atoms and turn them into one enormous atom that's what a neutron star is right it's essentially nuclear material the size of the earth and the mass of many times the Sun right it's a really crazy object but when that happens you get this huge burst of neutrinos coming out and you'll see that this burst only happens in the electron flavor so it's interesting so it's very important to try and observe all these different flavors of neutrinos over time during the bursts right and so the way you do that is you have lots of different kinds of detectors around that are sensitive to different parts of that spectrum right you have detectors using water like like super-kamiokande and then scintillator like I was talking about earlier in that first discovery the neutrino they use the detector with scintillator to try and detect it what I'm going to talk about here is you is using detectors made of liquid argon to try to detect them because it's something we're working on here at Fermilab right so I mentioned this doing experiment early on right this is an experiment that essentially exists because of measurements made of solar neutrinos basically people tried to do astrophysics and inadvertently discovered something about particle physics right so we've built this detector primarily to do particle physics but at the same time it can also then contribute back to astrophysics Rex you've built this detector to detect the neutrinos that we make but it can also detect the neutrinos that come from supernovas right now that said this detector will sit deep underground it's almost a mile underground in the Homestake homestead goldmine in South Dakota so this detector is a liquid argon is called a liquid argon time projection chamber you probably don't care about the details of what that means but the thing to know is that it can take very detailed and precise images of the of the neutrino interactions as they occur and specifically this type of detector is very sensitive to electron neutrinos right which is different from most of the other detectors that are out there the you know the water base detectors and the scintillator base detective which are most of the detectors that are around use this inverse beta decay reaction and that inverse beta decay reaction happens when you have a free proton and it interacts with an anti-electron neutrino that comes into the detector right that's how you reverse the beta decay process well if your detector is made of just liquid argon you don't have any free protons there right it's you know this is this is a argon is a noble gas right so the material is just argon atoms and so instead of seeing this inverse beta decay reaction we see an interaction of the electron neutrino with the argon atom itself so this can tell us about that Nui flux which can tell us about the neutralization burst and that little kink in the beginning and all those other interesting dynamics right so it's very important to try and make this detector sensitive sensitive to supernova neutrinos right and it's important because the neutrinos are on their way to us now right remember the galaxy is 650 light centuries across right which means that if we have the rates right there's about 2,000 core collapses that have already happened and if you tree know is already coming our way to get my facts wrong you could go back one slide there and take a look at that detector I see a cathode and an anode can you describe how that detects a neutral particle absolutely it's a great question so the detector itself the cathode and the anode aren't involved in teching the neutrino right as I said we never detect the neutrino directly what happens is the neutrino comes in hits an argon atom breaks up that argon atom and produces charged particles that come out of that that come out of that interaction right so you'll get an electron neutrino will give you an electron a muon neutrino will give you a muon it's what we call them the electron Trino in the muon neutrino and additionally you'll get some particles that come out of the nucleus itself so at the energies of supernova neutrinos typically what you'll see is analyze a single electron and then what are called D excitation photons because then because the supernova neutrino doesn't have enough energy to break up an argon nucleus but it does have enough energy to excite that nucleus and the way a nucleus D excites is it emits photons rights as it comes back down to the ground state so that's what you would see right it's a little a little electron my old adviser who you know helped me with this talk used to call them crummy little stubs because they're relatively small on the scale of what you normally see in these detectors but they're very sensitive so we can still see them right and the role that the anode and the cathode plane play in this right is that you know when a charged particle passes through through liquid argon what it does is it ionizes the argon as it goes right so the particle comes in you know neutrino breaks up a nucleus get an electron get some creates a little track of ionized argon where that electron passed through all right and normally what would happen is that argon acts as a scintillator the electrons fall back down light comes out of the argon but if you put a really strong electric field and so 500 volts per centimeter you know is not a meaningful unit probably but the this this creates a very scary amount of voltage right many many thousands of volts in some designs as much as a million volts to try and put this field across across a many meter long drift so with this strong electric field does is it takes that track right so this little bit of black is you can imagine representing that bit of the material that got ionized by the particle right so this strong electric field then pulls those electrons towards the anode right so it just pulls them pulls the electrons away from the now argon ions and they get collected on these wires that sit where the anode sits and so by looking for signals on those wires so what you see represented here you can reconstruct what that event looked like in space all right other questions here that will sort of a lot without a lot of slide to support it right so they said the neutrinos are on their way to us right so it's important that we try and that that if we see them and if we see them you know sometimes hours or a day before that supernova happens that we tell people about them right so we have the system set up what we call snooze right which is the supernova early warning network early warning system right where neutrinos and actually now gravitational waves now that we've discovered gravitational waves if they see a signal and more specifically if multiple experiments see a signal at the same time right then it sends out an automatic alert to all the other detectors and to the telescopes on earth saying now is not the time to be cleaning the lenses turn the telescope's towards towards the sky and start looking around a supernova just happened and we're going to see it soon right there so there is we don't we get you know in a in a lot of these detectors you lose you know the inverse beta decay reactions in water shrank off and in scintillated detectors lose the direction information but the charge counter actions like you have in are in argon and the electron scattering which you subject if you get a little bit of in water tranquol detectors do have a little bit of pointing information now it's not perfect because the neutrino comes in it's the nucleus and then the electrons coming out is correlated with the direction of the incoming neutrino but it doesn't have enough momentum for it to be perfectly lined up right so it comes out with some amount of angular scatter so you know if the if the supernova is close enough then some of these detectors may even be able to give some little corner of the sky and say we expect the supernova to be over here now if we're only collecting you know a small handful of events because the supernova is on the far side of the galaxy then we probably don't have that pointing information but if it's say Betelgeuse which is nearby and growing right that that were to go to have a supernova then we could definitely point right at it well right at the area around it as you saw from the hey well we'll find out we'll know about it in the neutrinos first yeah okay in the recent gravity wave detection that we had the gravity wave went through the Louisiana Livingston Louisiana detector first in about seven and a half milliseconds later went through the one at Hanford Washington with timing differences in these various detectors scattered around the planet just using geometry give us some sense of where they came from where we might look to see the Nova interesting question I don't I don't know that anyone's tried to try to make that work it's possible they could I don't know other questions all right so let's take one step further along two even crazier stuff out there in the universe this is of course an artist rendering we can't see that but there is stuff we can see right there is some really high-energy Astrophysical phenomena out there right in the belief is that these things might be acting as cosmic accelerators right taking individual particles and speeding them up to energies well beyond the stuff that we can create on earth right and it's tricky to try and figure out exactly what's happening so one of the ideas is this idea called the active galactic nuclei right this is one example of the thing that creates these very high-energy particles there are others and the idea here is that you've got some galaxies with a really strong black hole in the middle of it and depending on where you're pointed at with relative to the galaxies you see less or more of the energy that's coming out of that black hole because it accretes stuff in words and then ejects it outwards and these two things called jets right so you can see you get this really high energy stuff if you're looking right at the top of it but you get relatively low energy stuff if you're looking right at the side of it and so the thought is maybe maybe these things are also creating really high energy neutrinos right and as always the great advantage of neutrinos is that they're neutral so this stuff can escape from right out of the middle and the other thing of course is that as the neutrinos travel between the galaxy and us they don't get scattered by dust they don't get bent around by magnetic fields in prints well they could point right back at their source if we had enough of them to overcome the fact that our direction resolution was neutrinos is pretty poor so a question you might ask is how do you know a neutrino it comes from an Astrophysical source right that's opposed to one from much closer by right and the because of course the neutrino can't tell you where it's from the way you know is that it has really really high energy right there's this constant background of neutrinos that are coming from cosmic rays so protons flying around the galaxies interacting with the atmosphere that's creating those neutrinos that we used in super-kamiokande to discover neutrino oscillations but we also know that these energies these nutrients can only get so high in energy so what we're looking for is neutrinos in the pev energy scale right so these are a hundred billion times more energetic than the neutrinos that come out of a supernova right this is a whole other scale of energies we're talking about here we aren't even close to making pev neutrinos on earth right we're making maybe GeV neutrinos which are you know even a hundred million times you know less energetic than this right it's it's a it's a whole new scale of it right and so the thing you're looking for right is it you know we know we can predict sort of the spectrum of how of how many atmospheric Katrina's we expect to create very high energies and look and we look for an excess out above that so that's what you see here in these three points right is neutrinos that are so energetic they're just super unlikely to have come from our atmosphere right the challenge of course is out here in this long tail right even the soup the the extra galactic ones or Astrophysical neutrinos are happening very rarely so you need a really really big detector to try and detect them right and it's basically impossibly expensive if we have to build that detector out of materials so you try and look for opportunities to turn the something naturally-occurring into a neutrino detector and the two examples of experiments doing this are to turn the ice the southern polar ice cap at the South Pole into a neutrino detector that's an experiment called ice cube and this km3 net experiment is working to try and turn the Mediterranean into a neutrino detector right and and this gives you this huge amount of math to try and detect the neutrino in right so this is sort of the this is looking now at Ice Cube right the thing you're looking at here this little sis station sits right is that little square right in the middle and the detector itself is deep in the ice well below that and it creates the space of almost a cubic kilometer right so you can see compared to the other four power how big of a detector this is right it's really incredibly huge right it's sort of hard to comprehend in some ways but the advantage of having this much mass is that it was able to see these neutrinos that were so high in energy that can't possibly have come from right around us right in fact and they're rare enough that they've given them names which is called them the Muppets right just Bert Ernie and Big Bird right which are these are the most energetic neutrinos that we've ever seen anywhere right to give you a sense of scale like this is just you know a pretty picture right of what the inner what that neutrino looks like in that detector right you can see that each of these little strings here has a bunch of has a light collectors along the way right and so each of these little dots corresponds to one of those detectors that we've placed in the ice right and give you a sense of the scale here here's one of those detectors those those those neutrino events sitting on top of a football stadium right so this this event is really enormous right if you know comms interacts and just sends energy out in all directions right inside the detector right and so this is really exciting right so we can take these neutrinos and look at where they came from we have some pointing information and say where do these things come from in the sky and so that's that's the idea of what's happening here we've now detected 20-ish of these so far now you place them out on the sky and what do we find is mostly nothing right so even this little purple box is suggestive but it's not statistically significant yet but we're going to continue to look right to try and see if we can pinpoint a source that's giving us these incredibly high-energy neutrinos and see if the what we find there is there an active galactic nuclei they're something else what where where are these cosmic accelerators accelerators coming from right so like I said we haven't found anything yet but we keep looking so that's basically the story right the neutrinos are these really these neutral particles that interact very weekly and that's a curse because it makes them hard to detect but it's also a blessing right because they can tell us about breach of the universe that you just don't have access to with any other any other observable right and because they can escape these really dense regions they can tell us about the fusion happening in the middle of stars they can tell us about the the bursts and supernovas and maybe they can tell us about these cosmic cosmic accelerators but of course only if we're looking for them what we keep building new detectors to try and detect them better and better all right thank you if there's more questions I have a microphone here for anybody so what's the chance of those last ones the cosmic accelerators just mean you're saying it's on a whole entire different scale yeah being just a whole different particle or element of some sort not a neutrino but something else I think we're fairly confident that these are these are neutrinos right because they come and they interact so these three look you know they only sort of look like blobs here right but the we can associate these particular shapes with the with electron or neutral current interactions there are other ones that where you can see what look like really long muon tracks that sort of cross that whole detector right so very similar to what you would see in another kind of particle detector but at a very you know at a much larger scale and so it's some sense right if it behaves like a neutrino it is a neutrino or it's the only way we have to have to tell all right so question was how long did it take to build Ice Cube and who was responsible for building it effectively for running it yeah absolutely so it took I want to say six or so okay actually wait we can count it up here so one two three four five six seasons too you know in a season is sort of the the south polar summer right I you know I my information and Ice Cube is somewhat limited so I was never an ice cube collaborator I just think it's super cool the you know it's a very cool experiment the it was of course it was built by a consortium of a big international collaboration a collaboration actually that is both particle physicists and detector experts and astronomers and astrophysicists both it's a very sort of cross-cutting group and it was built sort of funded by the NSF polar programs actually is the one who paid for a large fraction of it basically basically the whole cost of this experiment was shipping diesel fuel to the South Pole because the way you you create these long you know these kilometer and a half holes right and put the in put the wall to put the light collectors in it right as you just melt a column downwards and lower a string of photon detectors in and then let it refreeze into ice right so was melting out these columns of ice was most of the cost of the detector all right and I don't know how big the collaboration is my guess is hundreds yeah yeah exactly it's very you know it was a real undertaking what's the schedule and the probability that dooms going to be completed here what's the splits the schedule and the probability so the you know I am very confident that we're going to have going to build a detector in South Dakota underground the schedule is to have the first the first detectors underground in the early 2020s and to have a beam pointed at them around 2026 it's Kranti I think it's 2023 is the is the timescale for the first detector underground racial right there's a you know I showed you a picture of these these modules right there's going to be four of these right and the idea is to build them sort of in series right so the first one will turn on and then the second one will turn on and then the beam will be pointed at them and then we'll build the other two and that's going to that process will take from you know 20 24 until 2028 or something Alex and if you go back to the galactic map a second the galactic map wait where we a this guy no the other one where you showed the purplish oh yes this is yes this guy question is in the center they're larger now is that one event or is it recurring events we're seeing from that area so these little crosses as I as I understand right bearing in mind that I didn't make this plot I'm not a member of the experiment that made this plot right these little these crosses correspond to candidate neutrinos is my understanding right so you know we can't they can't you know those three pev neutrinos definitely definitely you know cosmological and origin or Astrophysical and origin these right if you if you come to slightly lower energies on this plot right you can pick up some that are likely to be Astrophysical but not guaranteed right then but you can then look at them on the sky and say is there a concentration of high-energy neutrinos somewhere right so this little purple spot is essentially telling you that you know these four happen to be nearby one another so maybe that's a sign that there's something there but the significance is is not yet high enough to be statistically significant yet it could just be chance still the way to find it is to detect more of them right yeah is there any evidence that mass affects neutrinos either extra-extra galactic Allah lensing or just in the field of a very massive star yes there's actually we actually know that being in a dense medium does affect how how the neutrinos behave the place we know so we don't really see lensing with neutrinos but what you do see a very interesting point it's a little subtle so I skipped over it at the time right so if you've got neutrinos that are coming out of the Sun right which I said that the what the flux and neutrinos is lower than we expect because some of them are oscillating way to different flavors what's interesting is that all of that oscillation happens between the center of the Sun and the outside of the Sun all right by the time we get to the outside of the Sun the neutrinos aren't oscillating anymore they've reached a stable mix of neutrinos and they just transit rate you know come to the earth in that in that state and that's because that being around loss of electrons changes the oscillation probability among the electron neutrino among the different neutrinos right and so what's happening is you have this you know if you've studied thermodynamics it's something called an adiabatic transition as you go from the center of the summer you've got this very high mass high density you fall down this exponential curve of densities you go from the center out to the outside and by coming out having that adiabatic transition you put the neutrinos into this they go from starting out it's sort of all electron neutrinos in the middle to this very stable mix of electron muon and tau neutrinos on the outside edge and that mix as they travel of course the individual neutrino will continue to oscillate but the mix of new e nu mu and nu tau all stays the same right and the reason that happens is because of what we call the matter effects of the MSW matter effects named after three guys you know as the SN T Trina's passed through so we know that matter makes a big difference and in fact one of the things we're trying to study at the Dune detector here right is we want to look for those matter effects happening in in neutrinos traveling through the earth now of course the earth isn't nearly as dense as the Sun so those matter effects are a lot more subtle why we need we haven't found them yet yeah you showed some some some neutrino detectors that are there are taking accelerator produced neutrinos yeah right and he's like Minos or yeah well I mean it's not anymore it shut down this year but you know it's but Nova is this the question will apply to mino-san Nova sure Minnie boon and whatever um these are what you're what you're mainly studying is accelerator produce neutrinos that are protected by these things but I presume they have some capacity to look at neutrinos from Astrophysical sources when the beam is off sure and and I wondered if you can say something about about what experimenters do they they leave it on they're keeping an eye on the on the uneventful for looking at supernovas or well this is a very good question so Minos is particularly troublesome for supernova neutrinos because them there's lots of dead material on the detector right most of the mass and the meanest detectors or is or was made out of steel right so you can't see any of the interactions happening in the steel you can only see them in the scintillator planes to sit between the steel now nova is all active now all by all active I mean about 85% active but still a much better fraction so if a supernova were to go off right we will be able to see those events inside nova the challenge of course is that the Nova detector unlike do nor me knows a lot of the other ones I was talking about or super-k is actually on the surface in northern Minnesota right so it's being constantly constantly bombarded by cosmic rays in fact we see 8 billion cosmic rays a day in this detector right so that's a lot to try and sift through but Nova is in the snooze Network right and we are in fact literally today we were having a meeting talking about getting our trigger going so that we could detect a supernova ourselves right if we saw a lot of low energy events happening at the same time right we would say ah we've detected a supernova we record those events and we send a trigger out to the snoo to this news network and then do and of course is being built with supernova neutrinos in mind right and so beam on or beam off it will always be looking for a supernova burst or some you know a collection of neutrinos happening sort of in sequence in time that we can detect and say a supernovas happening in fact a lot of works going into the the data acquisition system so that in the triggering system so that if a supernova occurs we definitely detect it and we definitely trigger on and record the because they're so rare we don't want to miss one right other questions yeah I I assume from the discussion that the you observe a track in and the track itself tell me if I'm right or wrong the track itself is is not the neutrino the track is the decay from the collision of the neutrinos exactly right okay exactly right this is a very very important point right which is that you never detect a new tree new itself because they're neutral right that all of our detection technologies don't rely on either light or charge so you know you need to have some charge to be able to see it yeah my question was you produced the neutrinos using accelerated particles uh-huh what are those particles how are they produced and how are they accelerated excellent question so you know this is this is this is more in my my wheelhouse right about how we so the way the way you make neutrinos in an accelerator right is the thing you accelerate is protons right so here at Fermilab right you take hydrogen you ionize it you get the individual protons out you accelerate them in a linear linear accelerator which is happening down here right goes into what goes into a small ring gets accelerated some more goes into a large ring gets accelerated even more Oh going the wrong way gets accelerated even more so you now get these protons up to 120 GeV and energy which is 99.9999 something that I'm actually don't know the number of nines very close to the speed of light then you take those particles you pull them out of the ring and you collide them with the target so in our case we use graphite you can also use beryllium right there's various other materials take those part those protons they collide with the target and then when they collide with that target they produce a whole spray of other particles coming out right of all sorts of also various kinds but the car ones we care the most about are called maisons so Amazon is a bound state of a quark and an antiquark and so and they're unstable and the lowest energy ones are called PI ons pi plus PI minuses and those PI ons decay after a certain amount of time basically always into a muon neutrino and and a muon 99.9% of the time something like that and so what you do is the the proton hits the target produces a bunch of Pi ons then those pints have an electric charge so you use these things called focusing horns right which essentially act like big lenses to point all of those pie ons towards your experiment and then you let the PI ons just travel in decay Piper's the big volume that well it used to be vacuum because you didn't want the pines interacting with stuff now it's full of helium so you don't have to worry about keeping it a pressure vessel right you let those PI ons decay and because you've pointed the plans at your detector when the pine is decaying most of the neutrinos are pointed at your detector - right so that's that's how you create a beam of neutrinos and and the fact that pi ons mostly the k2 muon neutrinos is why long baseline neutrino experiments look for muon neutrino oscillations muon neutrinos disappearing or muon neutrinos becoming electron neutrinos right because muon neutrinos are the convenient thing to make with a particle accelerator mm-hmm so on give one second for the mic in that chart where you had 220 events in the show - super know yeah so actually how many neutrinos probably passed through that same detector but we're not detected Oh probably trillions trillions right so I'm still but didn't confuse it when you say you see the trail or whatever you want to call it yeah as the as the neutrino ionizes liquid argon yeah yeah so and look at all right so so a neutrino then passes through many electrons you just said it does not hit yeah yes exactly right which that you only ever see only neutrino you ever see is the neutrino that stops hits a nucleus and produces charged particles mostly neutrinos that's right through well that's why I'm confused now the difference between ionizing the atoms of argon versus impacting the nucleus so yeah so if it if it hits lots of why aren't you detecting all of them so the neutrino isn't actually ionizing stuff any of the atoms right because the you know the you need to have an electromagnetic charge to be able to do that ionizing right so the neutrinos mostly just pass through and do nothing very occasionally in a neutrino hits an argon atom produces a charged particle in the charged particle does the ionizing okay now it's clear uh-huh more questions is that it from everybody I guess we got one more UPS oh I'll bring in my mic do other types do other types of supernovae like type 1 a's produce neutrinos - and are they different from the kind you see from type 2 a great question so type 1 supernovas tend not to produce nearly so many neutrinos right I can't tell you they don't produce they don't produce any but the mechanism is pretty different right it happens in the type 1 right so the you know as I'm trying to remember the details of it I there's this very interesting idea with type 1 supernovas because they act as these sort of standard candles because you have some my memories that you have a star next to a black hole when it's pulling material away right and that that process just doesn't produce this large burst of neutrinos all at once right because this is the key is that you know you think about I say that 99% of the energy in the supernova goes into neutrinos this is an unfathomable quantity of neutrinos and then though and then we detect 24 of them right so you need this enormous burst all at once to be able to detect those neutrinos now it's probable that our detectors have detected neutrinos that come from supernovas there's this thing called the relic supernova neutrino background there's this constant flux of neutrinos coming from supernovas of various kinds going around the universe all the time but the rate is pretty low because Funes don't interact that often right so it's there are detectors being built to try and detect this specific rate trying to tech the supernova neutrino spectrum but not from any particular supernova but we have we haven't done that yet right you need this big burst all at once because you need that time coincidence right you need that these you need to know that these 24 neutrinos happened in these 10 seconds to know that it they came from a supernova at this stage right so this sort of slow accretion process doesn't just doesn't create that big burst huh you said earlier that in the Sun the neutrinos start out in the center as electron neutrinos exactly and as they're going through the Sun they change yeah and do the other flavors yeah so I assume a larger star mm-hmm would have a different ratio because the neutrinos are going through more mass because it's larger so probably they it probably wouldn't actually so and the reason is because the mix of flavors when you get to the outside core tell is is not beta is not a feature of the density of the star it's a feature of the inter of the physics of the neutrino mixing right which is that you get so a sort of technical level right what's happening with neutrinos is you've got two different ways of looking at those nutrient those three types of neutrinos right you can think of them as the electron the muon and the Tau neutrino but you can also do what's effectively a coordinate transformation into what we call nu 1 nu 2 and nu 3 which are the three different which are neutrinos that have very definite mass this very weird quantum mechanical thing right which is that the neutrino of a particular flavor doesn't have a well-defined mass and the neutrino of a particular mass doesn't have a well-defined flavor what you have is that a neutrino of a particular flavor has a mix of masses in some some ratio right a neutrino of a particular mass has a mix of flavors in some ratio so what's happening in the Sun or in any star right is in the middle you start in a pure electron neutrino state and as you do that adiabatic transition from the center to the outside you Trant you rotate from an electron neutrino state into a new one state right so that's why it doesn't oscillate anymore because it's all new one but a when a new one reaches your detector you've got say a 60% chance of seeing a new e a 20% chance of seeing a new mu and a 20% chance of seeing a new towel but it's not oscillating anymore because it's already a new one can't change to anything else so if your star is bigger and denser as long as you have that adiabatic transition down that exponential curve I think you'll end up with the same state at the outside edge no matter how big the star was your yep maybe I just don't understand the standard model well enough but all right it this is a particle right yeah is it does it have a carrier that I don't even know if I'm phrasing that Clark so okay so the I think the I can I can and I think I I think I know what you get in that all that and how does it deal with like Higgs boson and a kind of fun stuff sure so the the these are leptons the part of the standard model if one too so what lepton means is it doesn't interact but so the the leptons don't interact via the strong nuclear force right so the gravity so the the gluon here is the force carrier for the strong nuclear force doesn't interact with the neutrinos the photon is the force carrier of the electromagnetic force right and we know it doesn't interact with that because they're in neutral right that's what having a charge means that you have a charge for the electromagnetic force the only force carriers that these interact with are the W and the Z which are the force carriers of the weak nuclear force and the reason that it's weak is that this is massless and this is massless and these have relatively high masses right so they're very short range and very weak because of that right and then we know that they have mass so that we know they must interact with the Higgs boson at some level but they are so much less massive than the other particles in the standard model that those couplings are very very small in fact the idea is that the read that the the mechanism in the model that gives the neutrinos mass is believed to be different from the one that gives the other particles mass because it's so small that we have that you have to invent this new mechanism otherwise you have this very unnaturally tiny coupling between the Higgs and the neutrino uh so it doesn't well yes but what it suggests is that there are three more neutrinos that are very very heavy that are the partners to the three light neutrinos you have this thing that gets called the seesaw mechanism which is the heavy ones are so heavy they make the light ones really light I you know it sounds crazy but that's actually the model yeah sure yeah so if a neutrino if a neutrino interacts with the nucleus there's often no neutrino anymore right you know the interaction is that you know a neutrino comes in you get a neutrino and and you know nucleus right and what comes out the other end is a different nucleus and the charged partner of the neutrino right basically neutrino comes in exchanges the W with the put with that with that particle and the neutrino is gone and you have an electron on the other side because you have to conserve lepton number in that interaction so the new e becomes an E or a new mu becomes mu well if that's it on the questions then thank you very much Alex we appreciate it you

Channel: Fermilab

Views: 126,180

Rating: 4.8240867 out of 5

Keywords: Fermilab, Physics, neutrinos, astronomy, Naperville Astronomical Association

Id: UgG4V-GuCrA

Length: 61min 8sec (3668 seconds)

Published: Thu Jan 19 2017