Neutrino, Measuring the unexpected

it's sunlight that makes life on Earth possible the Sun our star just a giant ball of burning gas how long could have been there you it must be making heat for millions of years what process could possibly make so much energy for so long understanding the mechanism on how the Sun produces photons explains how all is the Sun and this question is related to neutrinos Albert Einstein's famous equation e equals MC squared showed that a tiny amount of mass could in principle be converted into a tremendous amount of energy physicists believed that the core of the Sun acts like a nuclear fusion reactor the main process is the proton-proton chain reaction where hydrogen nuclei are fused to form helium producing vast amounts of energy which balances the gravitational collapse of the star however the chain also contains other secondary processes some very rare which produce other particles and energy these nuclear reactions are the only feasible way to continuously produce the amount of energy observed for billions of years we can easily see and understand the light coming from the Sun by observing the full spectrum of photons arriving at earth but they come from the surface and atmosphere of the star how can we see inside the Sun how can we confirm the existence of fusion surprisingly the answer comes in the form of a practically undetectable particle when a nucleus decays it emits energetic particles and becomes a more stable isotope in the early 20th century accurate measurements of the energy of beta decay products found that if only the nuclei and electron were involved energy and momentum were lost in the decay to reconcile this observation with the universal conservation of energy Wolfgang Pauli writing in 1930 felt obliged to invent a particle without mass or electric charge that could participate along with the nuclei and electron in the decay postulating a particle with little evidence for existence caused Polly some worry he said I've done a terrible thing I've postulated a particle that cannot be detected this particle was later dubbed neutrino or little neutral one by Enrico Fermi and his theory of beta decay ten years later one GaN Chung proposed that the neutrino can be detected in a rare process known as baited capture in the same nuclear reaction at the core of the Sun neutrinos are emitted at a rate of one neutrino for every million photons 90% of the neutrinos are released in the first proton proton reaction the most energetic neutrinos are produced in the so called proton proton three chain reactions but are much less abundant as this reaction is far less probable accounting for only 0.1 1% energy produced in the Sun photons take up to 500,000 years to get out of the Sun as they are constantly intercepted absorbed and re-emitted but neutrinos having no electric charge travel in a straight line from the core of the Sun they come out at the speed of light as soon as they are created hypothetically about three percent of the total energy radiated by the Sun is in the form of neutrino the flux of solar neutrinos at the Earth's surface is on the order of 60 billion per square centimetre per second unlike light neutrinos travels through us so about a trillion solar neutrinos pass through your thumb every second neutrinos are the most abundant particle in the universe after photons but how can we see them how can we detect something that is not affected by the electromagnetic force and has no mass how can we see a particle that supposedly interacts with nothing in 1962 John Bacall a theoretical physicist from the California Institute of Technology was introduced to Ray Davis jr. by Willy Fowler who was looking for a system to detect solar neutrinos ray Davis asked the call to calculate what amount of neutrinos the Sun could produce and be captured by his detector so bacall calculated the neutrino capture rate in the current solar model by hand in the early 1960s John McCole and Ray Davis started to consider how to verify how the Sun shines 1964 is the birth of neutrino astrophysics with a back-to-back paper by Trey Davis and John McCole the idea was to design a solar neutrino trap Earth's surface is constantly being bombarded by many forms of radiation like cosmic rays solar particles the detector had to be underground to prevent interference from these and other atmospheric particles with this in mind it was built inside the home state gold mine in lead South Dakota at the depth of 1478 meters the detector was a huge 380 cubic metre tank filled with a common dry cleaning fluid tetrachloroethylene which was chosen because of the amount of chlorine in the compound upon collision with the neutrino a chlorine atom transforms into a radioactive isotope of argon which can be extracted and counted it was necessary to use so much target material because there is a very small probability of a successful neutrino capture rate Davis designed a way to collect the argon that formed every few weeks he bubbled helium through the tank to collect the radioactive argon counting the amount of atoms allowed him to determine how many nuclei had undergone the reaction induced by a neutrino so it was able to determine how many neutrinos had been captured the Homestake experiment started to work in 1968 and it was an extraordinary success for the first time neutrinos from the Sun were detected but the first results observed the sun's output of neutrinos was less than expected in fact only one-third of those expected from Bacall's calculation this discrepancy between the number of predicted neutrinos and the number measured soon became known as the solar neutrino problem the theoretical calculations were refined and checked many times over the next two decades by many scientists but no significant errors were found in the model by John Bacall the Homestake experiment continued to operate for decades refining its measurements without any significant change in its observations it was more than 20 years before the new detectors were designed to measure solar neutrinos including lower energies making them more sensitive galux was built inside the gran sasso Mountains in Italy using liquid gallium sage also with gallium and the Caucasus Mountains in Russia even earlier kamiokande followed by super-kamiokande both using ultra pure water were built neared Kamioka in Japan and unlike other detectors were able to make real-time momentum measurements of the neutrino flux confirming the Sun as the dominant source in all cases observed flux was between 50 and 60 percent of that predicted by the standard solar model so their results still showed less neutrinos than original calculations the consistency of measurements could only mean one of two things the standard solar model was wrong and its success in describing other aspects of the solar evolution was an accident or there were other effects causing the flux of nutrients from the Sun to diminish before reaching earth this meant that a better theory of fundamental physics was required to solve the mystery of the missing neutrinos in the early 2000 there is no experiment that was able to measure electron neutrinos and also all the flavors of neutrinos all the families of neutrinos confirm the dissolution to the solar neutrino problem was the neutrinos changed flavor neutrinos change type when they come from the Sun to the earth we also say that they changed flavor we don't know why but neutrinos and all particles come in three families on the way from the Sun to the earth neutrinos that were produced in one family electron neutrinos changed to the other families knew or tau neutrinos this is called neutrino oscillations or neutrino flavor conversion raided this experiment was only sensitive to electron neutrinos and that's the reason why radius experiment was measuring less neutrinos than predicted by John McCole calculations the discovery derived by solving the solar neutrino problem is that neutrinos are massive we don't know why neutrinos have different masses it is taken more than 40 years to find the right amount of neutrinos coming from the Sun it has changed our description of the universe science is that unexpected full of big surprises like can give us a picture of the universe at night we see photons coming from the stars galaxies are objects photons are the most abundant particles in the universe but can we see what's going on inside stars how can we get a glimpse of the unknown good news and uncommon eye is opening up new frontiers why doing a strong away with neutrinos when they are so hard to detect well the reason is simple first of all the neutrino has no electric charge so it just is basically the same as a photon the particle of light so you are doing the same astronomy the critical difference between neutrinos and light this neutrinos go through walls light doesn't and so the inferences that they may reach us from places in the universe that we have never seen before so we build IceCube to do astronomy with neutrinos now the simplest way of thinking about astronomy is that you go out at night you look at the sky and you see beams of light coming from stars this is the perfect analogy IceCube is basically a big eye that looks at the sky and instead of seeing beams of light it's these beams of neutrinos now why were we interested in a tree nose why not use slightly cheaper and easier well we are very likely to see very different things and in fact at a moment we have detected our first beams and we are trying to figure out what we are actually seeing but educated guesses are that we are seeing very powerful cosmic accelerators maybe supernova remnants gamma-ray bursts active galactic nuclei all the things that are part of the high-energy universe what is so special about the South Pole the South Pole ice itself is the detector between one and a half and two and a half kilometers below the surface groups of light sensors are in position to see the light produced by particles passing through the ice over 5160 of these light sensors have been deployed instrumenting a volume of one square kilometer under the ice high-energy neutrinos produces ooh of charged particles when they interact with the ice these particles produce an explosion of light and Ice Cube captures it in its sensors what's critical in the design is how far light travels through the ice the light sensors have to be spaced according to the absorption length the average distance light travels in the ice in tap water light will travel two meters and distilled water eight meters and ice beneath the South Pole light travels more than 100 meters in some places even more than 200 meters the ice in the South Pole is one of the clearest solids that exists it may not be possible to build a solid in a laboratory as transparent as this ultra pure ice which in the end is just snow that condensed and fell on Antarctica about 100 thousand years ago at the depth of Ice Cube about two years ago we were doing an analysis where we are looking for extremely high-energy neutrinos we actually knew exactly what we are looking for we were looking for something that's called cosmogenic neutrinos it doesn't matter what are this we didn't find any but when we looked at the data we found something that we had never seen before I remember when I was shown these events the first time and you know over the years we have looked at thousands and thousands of events on the online display and I knew I'd never seen events like those - in fact they were so special we call them birthed an earthly after seeing them it was clear what was special about these events and we designed designed a new analysis that go could go and look for more of that of these so by now birthed an army has 26 more friends which we recently published claiming that we have evidence for neutrinos that come from space where do they come from that's our next frontier and of course everybody has already ideas we know that some of them are not emitted in the direction of the center of the center or the plane of our own galaxy so they come from outside the galaxy there are hints in the data that some of them actually may come from our own galaxy the problem is there is not enough statistics there are not enough events to come to a conclusion so then we started see approach in a different direction we started to look for more events and so I think I'm afraid you will have to stay tuned but eventually we'll figure it out what's next well clearly finding more of these very special events by the way what's special about these events is that they have enormous energies that's why they look different from anything I had seen before we detect a neutrino every six minutes but they are rather uninteresting and produced in our Earth's atmosphere these events have 10 times bigger energy so clearly we want to get more of these and so what you do is you build a bigger detector and we are now figuring out how to do that anytime's out it's not that difficult because we found out while building Ice Cube that the South Pole ice is much more clear than we had guessed and so this allows us to make build a much bigger detector by basically doubling the number of sensors that we have to deploy in the ice so we are busily designing our next step matter is what makes our world it's all around us matter is our universe but why matter what makes it more special than any other forms of energy trillions of particles pass through us every second one of them is so faint that it is extremely hard to detect could it be the answer to this question how could we find out how can you find a grain of salt on a beach there are three types of beta decay standard beta decay involves the nucleus decaying by emitting an electron and a neutrino the second is double beta decay where two electrons and two neutrinos are emitted simultaneously very few nuclei can undergo this decay since it requires that the isotope 1 beta decay from the original be more unstable making this simpler decay even more unlikely the nuclei for which this decay has been observed are extremely stable with life times greater than the age of the universe 1/3 as yet unobserved channel is neutrinoless double beta decay for this decay to exist the neutrinos must annihilate each other a process which requires the neutrino to be its own antiparticle and hence a distant type of matter to all other particles double beta decay is a very rare decay process so in some sense it's very strange but it has nothing special it happens in a number of nuclei what is very relevant is when this decay is produced without the emission of neutrinos why is that so because it marks the existence of a very peculiar property of the neutrino the fact that neutrinos its own anti particle the neutrinos antineutrinos in the standard model are supposed to be two different particles if this process happens neutrinos and that the neutrinos are the same particle because the nucleus the decayed duty no exist inside the nuclear is it an exchange between two parts of the nucleus to make possible this decay this decay was foreseen by by or a 1938 already neutrino would be in this case also also anti neutrino that is like matter to be also an tomato key to antimatter and that in the universe you have only practically matter so that might be an explanation why matter is so dominating in the universe we wanted to be able to make an experiment that could display a large mass and with very cleansing and there were a number of ideas round but eventually it came out of a discussion with Dave nygren professor from Berkeley who had the idea since a long time of using sidon so we started to discuss we came up with the idea we could build this chamber for the confront experiment and so next idea what next is a simple idea is a pressure chamber basically it's a pot at high pressure in which you feel a lot of sinan xenon is a gas that has the capability of scintillating producing ultraviolet light we are able to use this ultraviolet light to give us the signals that we will use to detect the event of disintegration of a particle so one next great idea is is the fact that the same gas that we use as a target because you can decay as a double beta is the very same detector the width the last 30 de que ésta next is contained within a pressure vessel made of a low radioactivity titanium steel alloy xenon gas is continuously purified and flowed through the vessel the central part of the vessel contains a system to produce a directed electric field the field cage the field causes electrons liberated from their atoms by passing charged particles to move towards the amplification region a plane of sensors at the opposite end of the vessel measures the deposited energy while another more finely instrumented and directly behind the amplification region records the event topology an array of large high sensitivity photomultipliers accurately records the amount of light produced allowing for a reconstruction of the energy deposited in the gas in the other plane an array of small closely packed silicon of photo multipliers are tasked with recording information about where the light was produced in a neutrino let's double beta decay of C 936 two electrons of a fixed energy at a medium so what we would expect to detect in next if double beta decay happens is to measure an event with the right energy 2.5 ma B and that it looks like two electrons coming from a common point this with the detector we would take a picture of this event it would look like like a long track with two blocks at the end the next team designed a matrix of thousands of silicon photomultipliers that allows the scientists to make a picture of the electron trajectory the sensors are at a strip of flexible captain that avoids the introduction of radioactivity inside the detector it is very difficult to design and build radio pure electronics that have no interference with a detection signal the electronics of the photomultipliers widened the signal so it can be reconstructed later point by point the electronics of the silicon photomultipliers integrates the signal every microsecond so it can make a million images per second the electrons that are produced in the ionization of the xenon gas by charged particles excited as seen on atoms which decay emitting v UV light near 172 nanometer the silicon photomultipliers are not sensitive at this short wavelength we have therefore to use an organic wavelength shifter core TPB to shift the VV light into blue light to which the silicon pm's are more sensitive we do this process by vacuum evaporation in a clean room at ich mall the instituto de ciencia molecular the vacuum evaporation of TPB allows us to obtain very clean and uniform coatings on the silicon pm's which makes them able to record the casino scintillation light and perform the tracking function in the tpc we're being bombarded constantly by particles how can we get a clean signal when we're surrounded by such din how can we see a glint through the glare the confront lavatory was first conceived by anta Morales and other researchers at the university of zaragoza in 1985 this first proposal to build experimental areas inside the old train tunnel under the Pyrenees was dismissed but later a larger facility was built placing detectors for rare events underground shields them from much of the radiation coming from the Sun an atmosphere stopping the interesting signals from being overwhelmed much like the light from distant stars can be overwhelmed by the light from the Sun or moon next we'll search for neutrino this double beta decay in the can Frank lavatory why are we here we know that the universe is made of matter and not of antimatter we also know that the early universe should have been made of equal parts matter and antimatter but where did all the antimatter go could this ghost of a particle hold the key could Amaya Anna neutrino caused the universe to favor matter the implication of neutrino that is its own antiparticle could be the reason why we are here to ask the question the reason why next is important and we think that it may have a great future for science in the discovery that the neutrino is on anti particle may take a great effort it may require to have masses of up to one ton of sin no other experiment is capable we think of the exploit at the same time the great energy solution the good appa logical signal in the large mass that we can deploy next therefore we do think that as the problem of discovering the neutrino as its own antiparticle becomes more and more difficult let's get more and more chances of being the discovery experiment an interesting question is why do we do this kind of science why do we search for these rare events and how do we know that we're going to succeed the answer as a matter of fact is that we don't know but we are willing to take the risks it's very interesting to compare what we are trying to do in next searching for neutrinoless double beta decay experiments with a recent success of the ice cube experiment run by Francis calcine what Carson has told us is that when they propose the experiments they gave a number of arguments none of those arguments were exactly true none of those arguments were perfectly convincing and as a matter of fact all the original ideas about the detector were good but not exactly as good as you could imagine but at the end things work at the end you put the faith the passion the years of work and you end up discovering something that you didn't even expect I think that what science is all about is not finding what you expect to find is to finding something you didn't have any idea you were going to find is to find the unexpected

Channel: SOMIFIC - Flavor and Origin of Matter

Views: 59,942

Keywords: som, ific, neutrino, astronomy, space, solar, physics, nuclear, south pole, icecube, next, double beta decay, atomic, neutrinos, outreach, science, unpredictable, bahcall, solar neutrinos, sno, neutrino oscillations, astroparticles, double beta, neutrinoles

Id: vPfWHVaQUAY

Length: 30min 36sec (1836 seconds)

Published: Fri Dec 12 2014