Public Lecture—ANTIMATTER: What is it and where did it go?

I'd like to welcome you to the Stanford Linear Accelerator Center actually please excuse me - the SLAC National Accelerator Laboratory and and to our public lecture series many of you I know come very often and we're very grateful and we hope that we can provide you with a lot of interesting ideas and insights today the talk is on antimatter I guess that's why the crowd is so large so thank you very much the speaker is Aaron roodman who is a faculty member a professor at the laboratory he's also a member of the Bob our collaboration the big experiment that's been going on here for 10 years to measure the properties of antimatter he's the discoverer of one of the very elusive and tricky decay channels of the beam as on the decay to to neutral pie massan's very hard thing to find and very rare he's a contributor to the experimental techniques of the collaboration in very profound ways and he's also well loves to talk about this stuff so today he will tell you about matter and antimatter and what it is and where did it go thank you very much thanks Michael thank you in 1933 antimatter was discovered with this single picture this is a picture from a cloud chamber taken by Carl Anderson and Caltech in it he saw the track of what appeared to be an electron however an electron would have bent to the right and what he observed was a particle that bent to the left this mysterious object was the first sign of antimatter and this track is this is the remnant of the antimatter version of the electron a particle we call the positron more remarkable perhaps is that the existence of this particle was predicted to solve certain inconsistencies in quantum mechanics by Paul Dirac only three years earlier for their work both won the Nobel Prize if we fast-forward 20-some years the antiproton was discovered at Berkeley by Chamberlain and sue grey at a large accelerator at the Berkeley Lab and this is the first measured view of the antimatter version of the proton what's happening in this in this picture is that up here is an accelerator that in some complicated way produces the antimatter version of the proton and antiproton and we see in this picture that particle coming in and ultimately comes to rest and then what must have happened is that antimatter proton annihilated with a regular matter proton that annihilation releases a huge amount of energy that's equals MC squared in fact and produces nine and I think you can see them one two three four five six seven just one here eight and there's a little one here nine nine new particles and this is the first the first view of the antiproton and in fact this picture was not alone enough to establish the existence of this particle in fact they had to do a number of other studies but with those studies they concluded that they had discovered the antimatter version of the proton what we call the antiproton that's very good so let's let me give you the answers or the first question in my title what is antimatter the best way I can answer that is to tell you that all fundamental particles all elementary particles such as the ones I hope you've learned about in school the electron the electron the proton and the neutron they all have an antimatter version our names for them are the positron that's the antimatter version of the electron then antiproton and antineutron these antimatter particles are exactly the same as their matter versions except they have the opposite electric charge and you can think about the difference between matter and antimatter is a mirror that's a common analogy we make that there the matter particles and then if we look in a special kind of mirror an abstract mirror not the normal mirror that you look at your reflection in but a mirror that changes matter and antimatter if you look in that kind of abstract mirror you see the electron turns into the positron the proton turns into the antiproton it I'll stop for one little note or we'd like to write things since compact ways and physics in our compact way of writing an antiparticle is to put a little bar on top so when you see when you see this in the slides remember the little bar means it's antimatter there's also the antimatter version of the neutron now you may be asking well how does a neutron have an antimatter version the neutron is neutral so what does it mean to have the opposite electric charge so it doesn't make sense in fact the neutron is not a single particle it's made up of three quarks it has an internal structure it has an a cork we call the up cork and has two corks that we call the down quark and those particles do have a charge the up cork has a charge of 2/3 and the down quark has a charge of minus 1/3 and so they balance and make a neutral particle but then when we look in our antimatter mirror we see that the charges of those constituents the charges of the quarks have flipped it's still neutral but inside the charges are actually different it's really a different particle so that's my answer to the first question that's what it is but now let's talk about where it is what happened to it if we look at the world around us we see only matter the earth is made of only matter only protons neutrons and electrons not their antimatter versions except for a tiny residual of antimatter in certain radioactive processes a little bit of antimatter is produced in cosmic rays those are particles mainly protons that come from outer space and are hitting the earth at all times some antimatter is produced then and we can make antimatter in our accelerators like we do here at SLAC but except for those sources the whole earth is matter how about the moon well if the moon had a lot of antimatter if it was made of antimatter the Apollo astronauts would come to a bad end I'm afraid because when I mentioned before that an antiproton annihilates with a proton that would happen both for an individual particle and for big masses of particles and in fact if you've if you've heard of antimatter before in the show Star Trek the antimatter drive that's there's actually a kernel of truth in that if you had a big lump of antimatter that is a very potent energy source the problem of course is containing it because if it touched its walls a big explosion so we know the moon is made of matter we've touched it what about the Sun well we see particles coming to us from the Sun all of those particles are matter particles no antimatter but about galaxies there it's a little more complicated but if there was a lot of antimatter in our galaxy you would see the signs of the annihilation between the antimatter and the matter and we don't see that we don't see that anywhere in our galaxy and if we look further afield this is a picture from the Hubble Space Telescope we don't see signs of antimatter in the spaces between galaxies either we would see again signs of annihilation between matter and antimatter releasing a huge amount of energy and very distinctive phenomenon and we don't see that now of course we can only see so far away and past these very large distances we just don't know but as far as we can see we do not see any signs of antimatter in the universe and so we're left with the question where did the antimatter go if antimatter is just as good as matter why is the whole universe made of just matter let me see if I'll show you a little cartoon movie with a picture of some of the features of the early universe to try to explain what might have happened so if we imagine and this is just a cartoon you imagine very early in the universe a minute after the Big Bang there's a soup of matter and antimatter the blue and the red with pure energy with light particles which are the little arrows but then the universe expands I hope people know that the universe is expanding and cooling down and so the matter and antimatter is spreading apart and slowing down and gradually what happens is that the matter and antimatter annihilate each other and that's the blue and the red dots disappearing until eventually you're left with just a tiny amount of matter and lots of energy and that tiny amount of matter is everything we see in the universe so to review it so just after the Big Bang the ER verse had to have we have very good reasons for thinking groups had to have equal parts of matter and antimatter then somehow a tiny excess of matter of the size one part in ten billion was created and then as the universe expanded cooled down all the particles move more slowly all of the antimatter annihilated with almost all the matter and the tiny bit left that's us that's everything we see in the universe is that tiny remnant but the question is how was that tiny excess created so that's the topic of the talk and in broadest brush and we'll see what we've learned about this question what must have been true is that early in the universe a minute after the Big Bang sometime in the first minute after the Big Bang some interaction between particles I'm going to call it in this lecture a force a force between these elementary particles must have been a little bit different between matter and antimatter and that produced the excess of matter and so what we want to do is discover the force that caused that and understand how it how it operates so with that let me just say a little bit about the fundamental forces the forces that exist between elementary particles therefore the first one we call the strong force that's the force that holds the three quarks together in a proton it also holds protons and neutrons together in atomic nuclei we looked and as far as we can see this force is the same between matter and antimatter you don't see any differences the next force in actually I'm going in order of strength the strong force is the strongest force the next force is electromagnetism and we've looked there as well and as far as we know there's no difference between matter and antimatter for electromagnetism what's the next force the next force is something called the weak force and the weak force is responsible for certain radioactive decays now I'm going to use this word decay a lot in the lecture and so I want to define it precisely because the way we use it in particle physics is different a little bit different than the common usage it's not so far but somewhat different what we mean by decay is when one particle disintegrates into two or more other they have to be less massive particles that's what we mean by a decay and I'll use that I'll use that word repeatedly in this talk so the weak force is responsible for particles decaying and we'll see that actually the weak force does have a way to affect matter and antimatter differently and so that that too will be the topic of much that we talked about today there's one more force of course it's the weakest force by far and that is gravity it may surprise you to know that gravity is actually very weak compared to any of these other forces but it is now the typical theories of our typical understanding gravity implies that there should not be a difference between matter and antimatter for gravity but it's an interesting fact that that has not been experimentally tested it's actually very difficult because gravity is so very weak to isolate just the force of gravity and see if it's the same for matter and antimatter it doesn't help that antimatter is hard to make hard to hold on to so this has not been tested although recently people have proposed doing experiments to test exactly that okay so let's let's talk about the difference between matter and antimatter as seen in this weak force in 1964 Jim Cronin Val fetch discovered that in the decay of a particle called the neutral the neutral K Mezen there was a difference between matter and antimatter I'm going to tell you a little about that the neutral pion is an interesting particle and I've drawn it in this way half blue and half red and I think you'll see that my convention is that blue is antimatter red is matter and this particle it's the K on its neutral that's the zero and it's the special one that's long lived long lived means it lives for let's see it's a hundred millionth of a second that's a long time so this particle is neither matter antimatter it's some mixture of the two it's both at the same time okay and that has that has some interesting properties and we'll see that several times in this talk the particles that are neither matter antimatter are important for us now it decays in a number of different ways one of the ways it decays is this and I'll warn you though I'll mention a lot of different elementary particles in this talk there are lots of them I'll only mention a fraction of the ones that exist and I'll mention them as as I need them so don't be intimidated by all the Greek letters and the different particles there are just different beasts in the particles oh and I'll try to describe the properties that are relevant as we go so this neutral K on decays to a particle called the PI on so this is the antimatter version of the PI on it's a case to the positron we've already seen that and another particle called a neutrino and it instigated a matter version it also decays the mirror way so if you look in our antimatter mirror again you see that all the particles have flipped this neutral antimatter Payan has turned into a matter positive ion the positron is turned into an electron and this neutrino has changed as well so that's the we've got the regular version or we've got one version and the antimatter version of it and we can ask how often does our friend the K on decay this way and how often does it decay that way and I should say that this decay happens by the weak force well it turns out that the top the top one happens one point zero six six times more often than this one so by a tiny tiny amount one of these versions of the case favored that is an example of what we call an asymmetry it's something that's different for the antimatter version compared to the matter version they're a little bit different and that that's a sign that the weak force responsible for this decay is actually different between matter and antimatter and again it's this tiny amount so the asymmetry so this is the one equation in the talk I'll but I'll show this with this equation three or four times right this is the only equation it's an asymmetry is this way - that way divided by the sum and it's not zero it's 0.003 three if it were zero we would say that matter and antimatter are the same and if it's different than zero well there's an asymmetry so with with this measurement and actually some other measurements we saw for the first time that matter and antimatter were different in some important way and when this was discovered there were a whole wealth of ideas presented to explain why that occurs many different ideas some involved new forces besides the four we talked about some involved a partner called the Higgs which if you read the New York Times science section you may have read about because we hope to find it at an accelerator in Europe haven't found it yet okay so people at the time proposed maybe the Higgs has something to do with this asymmetry there were a lot of ideas but none of them were very convincing so let's look now in the story to see how the weak interaction the weak force makes a difference between matter and antimatter and that will be very important because understanding how that happens will guide the experiment that we've built here at SLAC the B Factory whose results I want to tell you about today all right so the first step though we're going to again we're going to talk about how quarks decay by the weak force the first step happened in 1963 by an Italian physicist Nicola could be Bell who noticed that there was certain regularity in the way oops I didn't want to do that too soon let's try again certain regularity in the way down quarks decayed to up quarks and the way strange quark decayed to up quarks what he saw is that there was a connection a relationship between these two apparently disparate decays and that all of the cases of decays of these particles obey that relationship but that wasn't enough what happened next is to Japanese physicists kobayashi and maskawa in 1973 said ok we can take that idea of a relationship in the way particles decay one big step further if we hypothesize that there are three more quarks the charm quark this is what we call them today the charm quark the bottom quark and the top quark so there are a total of six quarks we assume that a lot to assume and that the way that they decay into each other obeys certain regular relationships a matrix of relationships if we assume those two things not and there was no evidence in 1973 of either of them whatsoever so this is a very bold prediction we assume those two things then we can explain how the weak force makes a difference between matter and antimatter there's a very bold thing to predict you know there are only so many particles and predicting new ones is difficult difficult thing to do especially predicting three but in the intervening years we have discovered the charm quark that was discovered here at SLAC and then the laboratory on Long Island in 1974 and both the bottom and top quarks were discovered at the lab outside Chicago Fermilab the bottom in the late 70s and the top in the mid 90s so that was a good it was actually a good prediction they were right about that and moreover they predicted I said certain relationships between the way the particles decay they didn't predict exactly how often the case would happen they didn't say well we know exactly how often a top cork will decay to a strange quark what they said instead is that how often a top decays to a strange is related to how often a bottom cork decays into a charm quark and those relationships have allowed us to make a number of important predictions so now I'll use one piece of jargon in the talk and that is I'll show you that jargon is that this whole picture this theory about how the weak force works I'm going to call the C care model for the three guys could be the v-belt kobayashi and maskawa so i'll say that a lot c km c km so that's what it means it means this theory so this model or theory predicts relationships between the ways different quarks decay and it predicts that there'll be a big matter/antimatter difference in asymmetry in decays of the beam as on what's the B meson so here's another definition the B meson that's another yet another particle we ran out of Greek letters so at some point we had to start using regular letters it's a particle that has a bottom quark the B quark and another quark and it's it's an up or down quark it turns out so they predicted you'd see a large effect remember in the K on the size of the asymmetry was point zero three three tiny in this case they predict that the asymmetry will be large 0.7 or 0.8 so that sounds great because it's a lot easier to measure a big effect in a small effect and so what we have done over the last 15 years is to build an accelerator and a detector to make lots and lots of B mesons and to try to prove that the ckm model is correct we wanted to discover matter/antimatter asymmetries in this particle the beam as on one and perhaps to share that the size the value that asymmetry agrees with our prediction okay so that's that's what we're going to talk about today too but there's a problem I just have to mention a problem the problem is that this theory this model the ckm model of differences between matter and antimatter cannot unfortunately explain why there's matter left in the universe if the ckm model were the only way that forces were different between matter and antimatter we would have 110 billion of the amount of matter in the universe that we actually have so it's not that the size of the asymmetry is small it's really in the structure of the theory the structure of the particle interactions people have tried to devise clever models to get around this they have not worked and so to understand why there's matter left so infect in that way the title is a misnomer so it's not really what happens the antimatter title could have been why is there any matter left at all so what we'd like to do if we can is to find a matter antimatter asymmetry using the bead the B particles the B meson particles that is different than our model okay so maybe we'll find so in fact what are we going to find the slack beef at you was built to discover matter antimatter asymmetries and maybe two things could happen either we'd find a symmetries that agree with the ckm model but then we'd have the problem why is there matter left in the universe or maybe we'd find these symmetries don't agree with the model and maybe what we really find will point the way to understanding why there's matter in the universe or of course there's a third possibility maybe somewhere in between you'll see at the end of the talk what we've learned which of these three possibilities it is okay this is a nice animation since I can't take this big group to see the accelerator this is a little animation showing you schematically what is what goes under 280 this is the Loon act this is the long two-mile accelerator under 280 we use it to accelerate electrons and we use it to make positrons we make antimatter for use in the bee factory and then those particles are fed into that ring that you just saw there are two rings going in opposite directions and eventually the electrons and the positrons collide the two beams collide we don't smash any atoms we smash smaller particles they collide and applied in the middle of the babar detector and you can see different drawings showing you pictures of the bar detector and then you make actually you don't make one B meson you make two we make two at the same time and this is an artist's conception of what happens afterwards those B mesons decay after around a trillionth of a second and we see the particles they decay into with our detector called the bar and here at the end you see a little view of the of the B factory it's gone the B factory ring with the long Lin AK the long accelerator in the distance so the slack B factory took thinking about this accelerator started in the late 80s it was approved and I have to thank everyone here it's your tax dollars at work that went into this project it was approved in 1994 took four years to build and it started operation in 1999 and we took data as much as we could until April 2008 and in April we shut off and to observe the decays of the B mesons we built the babar detector we have the best mascot in particle physics by a long shot and of course Babar is a good name because we make a B meson and the antimatter version the B bar so the name makes perfect sense B and B bar Babar actually we got permission from the bar people to use the elephant and so we like we like the elephant this is a picture of the Babar detector this is a one person so you can get the scale of it it's big there are there bigger ones out there but it's pretty big and it has lots of apparatus designed to detect the decay of the bee particles and actually someone point out you can see on the walls there some more I think that's that's exactly the same picture right there there's another picture there of some of the innards being worked on now I've mentioned a few people and so I want since this is the it's the home crowd I want to mention a few others one of the key ideas behind the bee factory what I'm not going to tell you about I'm afraid but one of the key ideas was a was from PR donae that's PR they're sitting this is the bee factory itself and then Jonathan Dorfman there's Jonathan it's really the person who got the be factory built if you had to say one single person it would be him he led the bee factory project for many years the team of people who built and operated the bee factory is this group led by John seaman and then the group that built and analyzed the data from the Babar detector is this fantastic collection here and this isn't even everybody okay it's a big group and at its peak had almost 600 physicists from around the world and I think I have a few colleagues in the audience today and you should always wear a red shirt on picture day because then you can find yourself okay so so it takes a huge team to uh to build to operate to study the data in one of these experiments now I want to tell you a little bit about how we measure a matter/antimatter asymmetry there there are a couple different ways we do it one way is the way I already showed you for the K on but that's not the main way so I want to tell you about the main way we do it and there are three facts you have to know I'm going to tell you the three fat fact 1 a particle like the beam s on has an exponential decay what does that mean if you had a thousand B mesons in the first tenth of a picosecond so a trillionth of a second you might have around 60 of those B mesons decaying but then if you looked one half-life later at one picosecond you'd have half as many decay and a picosecond later you'd have half as many of that and a case when things go down by halves is we call an exponential decay you may have you may remember that from high school math if you don't I just hope you'll accept it so if we look at the decays as a function of time in this great unit picosecond again that's a trillionth of a second trillionth of a second is actually not so hard to measure it turns out you get this curve so that's fact number one back number two cool fact number two is that a matter b meson here's the way I'll draw it so it's it's neutral so I've got the zero and it's red so it's matter a matter B meson can just change instantly into an antimatter beam s on it just happens okay it's it's due to the weak force but it just happens likewise the antimatter beam s on and all of a sudden just change into a matter version they can go back and forth now it's not completely random there's some regularity to how it occurs but they can do that's cool fact to now important fact three is that sometimes you can get the following occurrence you could have a matter be messin decay into a combination of particles that's neither matter antimatter so I said I was going to introduce lots of Greek letters here's another one the sy this is actually its nickname some people call it the j sy it was discovered here at SLAC it once discovers the Nobel Prize about a year and a half later so it was a big deal so the B can decay into this side and a neutral K on and instead of the long-lived one this is the short-lived one don't worry too much about that the key is again it's the whole combination is neither matter/antimatter it's some of each that's one thing that can happen but another thing could happen and the other thing that can happen is that matter B meson could first change into the antimatter version and then that guy could decay into the same set of particles if that happens there are two paths and when you have two paths that something can occur you can get a phenomenon called interference you might have encountered interference uh not on partners maybe with sound if you listen to two tuning forks with a sound that's very close you might hear a beat frequency so those are you that are musicians may be familiar with that and there are a number of other phenomenon of interference all that happened when there are two ways to get from the beginning to the end and so I want to show you a little demonstration let's see let's look at here I want to show you a little demonstration it doesn't have anything to do with antimatter but has everything to do with the interference when you have two paths so the demonstration I'm going to show you is something called the mickelson interferometer it was actually very important in discovering that the speed of light was a constant and it has it we have a little one right here and we're going to take a laser and shine it on this slab of glass which is sort of half a mirror half of the toe half of the light will go this way on path one and half will just go straight through on path two in each of these paths we'll put a mirror to bounce the light back bounce the light back and then some of this light will go straight and some of this light will bounce and so the light will get out here by two paths here's path one here's path two and we'll get an interference pattern and I think this is really so this doesn't have anything to with antimatter per se but it's an analogy to show you what happens when you have two paths the way things can interfere so let's let's turn on so some luck it'll just work right off the bat and on the laser turn off that oh yeah we're good okay turn off the lights okay so there are a lot of people so things are bouncing but in this little gizmo down here I've got those those two mirrors and they're the two paths and you can see on the wall a pattern everyone stay really still as you can see it's bouncing around okay let's see so what you see is they're alternating light and dark regions and that's the interference can people see that okay so when it's when you're on a light region and you can see what a bounce is then the the interference is ruined on a light region that's when the two paths coincide and add and it's light and when they coincide and cancel that's dark that's the dark we call these fringes and this is a nice example it's a nice analog of interference okay so if people watch a movie afterwards we can we can look at that a little more people are interested after the question-and-answer period but let me let me turn on the projector and I'm going to turn on a little bit of the light I will turn the laser off okay so that's that's our analog of this process of interference there are other examples of interference and I should say that if people have read a little bit about quantum mechanics may have heard people talk about going from a wave description to a particle description the quantum mechanics mixes the two our example with light with the laser you can think of as the wave version but what we see with the two paths these two paths so remember this path and that path is the particle version and so here we get to the crux of the matter if matter and antimatter are the same then it doesn't we don't care whether it's this process this path or that path since if any matter and matter the same there's no way they can interfere with each other because they're the same and when you look at the decay of your beam essence that decay will have the same exponential shape I told you about in fact 1 but if matter and antimatter are different then the two paths will interfere and they can interfere to have fewer decays that would be the red curve so instead of the exponential decay you get a non exponential decay with fewer decays the analog here is the dark fringes this is the case where the two paths cancelled and instead of a dark fringe a dark a dark pattern instead of that we get fewer decays I don't know if you can see it but here right you get the same number of decays and as you go along in time now not in the space not in distance that we saw on the screen but in time you get fewer you get a bigger difference here fewer decays gets darker and eventually out here you can barely see it but it actually the red curve goes above the black curve and you start to get more decays and that would be like the the light the light region the light fringe also if you flip this whole process in the mirror in our antimatter mirror and you start with antimatter and the paths differ then you get more decays than in the exponential case that's like the lights the bright the bright region so we have the bright region and the dark region and the size of the difference is our asymmetry it's the size of the difference between matter and antimatter so that's what we're looking for that's what we've built all this stuff to do to look for exactly this effect what did we find so remind you the prediction of the ckm model for this asymmetry was between 0.7 0.8 these are more exact numbers this is what we saw after 9 years of taking data collecting almost a billion B mesons some small fraction about 6,000 decay in the way that we want here so even though we're looking for a big asymmetry it's hard to do because the beam as on doesn't always decay the way you want it after all that this is what we see here's the case where we start with antimatter and we have this number of decays as a function of time but only start with matter when it's when we start with a matter B meson we have this pattern and you can see very clearly the difference and the exponential case would be exactly in between the two of them now often to look at this effect better will form the asymmetry we'll subtract the blue - the red and divide by their sum so again that's the one equation and this is the curve you get so here's our equation same equation the number of times when you start as a B bar the antimatter version versus the number of times when you start as the matter version here's that difference over the sum and you can see very clearly that asymmetry what do we find numerically we find that asymmetry is 0.69 with an uncertainty of only 0.03 it took us 10 years almost to measure it this well let's really well measured and you can see it does agree quite well with the predictions from the ckm model we should celebrate we have celebrated and in fact earlier this month K&M kobayashi and maskawa of the ckm model were awarded at 2008 Nobel Prize in Physics and although there's actually some controversy about khabib oh why didn't kabhi bow get a share Kobayashi maskawa 1/2 the prize the other half of the prize went to a physicist at the University of Chicago for sort of related work but not really the same and so plenty of people that have wondered why didn't Kobe bow get the prize so us visitors can argue a lot about such things and if you look at the Nobel Committee citation for the prize they said the prizes for the discovery of the origin of the broken symmetry broken means it's an asymmetry that's not symmetric it's asymmetric which predicts the existence of at least three families a family is a pair of quarks so three families two quarks in each family is six quarks in nature and of course that's what we see we see six quarks in nature they also went on to say the two particle detectors Babar at Stanford and Bell in scuba Japan we have competitors there's actually a bee factory in Japan very similar the factory that's gotten results in this case that agree perfectly both detected broken symmetries independently of each other the results were exactly as kobayashi and maskawa had predicted almost three decades earlier so I feel I think as many of my collaborators on Babar feel that this Nobel Prize is one that we had something to deal with so how we feel good about it till now that's not the end of the story we have so many we have almost a billion B mesons and there's not just this one way that we can look for differences between matter and antimatter there are many ways I'm going to tell you about two more of them so let me remind you one thing we think that we now believe the ckm model is is demonstrated we think it's true it's a the right description of the weak force but remember there's a problem we still don't understand why there's any matter left in the universe I said before the ckm model can't explain that so we've understood the how the weak force produces a difference between matter and antimatter but we don't understand why the universe has so much matter in it so it's worth looking for something else maybe we can find maybe it's that middle case we've shown the ckm models right maybe we can find something else that's new one way that we do that is to look instead of before it was the sigh and this case short we could also look for a different particle called the Phi and a case short again it's just another particle but in this case so when it's the sigh the ckm model has a big effect and this is a very popular decay mode it happens a lot this decay mode with a Phi is much rarer it's about 20 times rarer it's harder for the B to decay that way I draw it with a little or box so we we think now the CK model is right so certainly the ckm model is going to affect any matter antimatter asymmetry as we see in this other decay but maybe there's something new and if there's something new it's probably small and if there's something new that slowly be swamped by the effect in this decay but if we look at a rarer smaller decay maybe there's something new will have a bigger fractional effect and it turns out looking with this decay the Phi and the K on is a good way to search for something new it's not the only way there are actually several different decays of this sort but this is the one I want to tell you about and if the CK model will right then we would see the same song is a fact with the thigh as we do as the sign so again the prediction would be between point six nine and point eight four what do we see we see an asymmetry of 0.26 with an uncertainty unfortunately of 0.26 it just it's happenstance that those are the same but what's important is that this this number is is too big and you can't tell whether this point to six is the same as that are different it's a little bit different but does it mean anything we don't know we don't know it's not accurate enough and the conclusion unfortunately even after ten years of work the conclusion is that um you need more data so we don't know whether there's something different here now there are other decays of this sort where there's a little bit more data there it's a more popular decay and so far we don't see any evidence of something new in those but you couldn't argue that there isn't something and and we think that maybe there is something new to be found and the fact that we don't understand why there's so much matter is one of the clues one of the reasons to keep searching I want to tell you about one more one more decay one more case of looking for a symmetries and that's with this decay it's a if we start with the antimatter be it could decay to this is the same K on but now it's a neutral version so the antimatter version plus a PI on that's the matter version but the decay could happen in the mirror version so again we're going to have our we have our antimatter mirror it can happen in the mirror where we switched all the Reds and the blues matter and antimatter you happen either way and we look for this decay we see quite a few of them this is a this is a plot that shows you the energy of these bees and the real bees should be right here with some distribution we shouldn't have anything out here and we don't and you see the red is the number of B decays we have when it's this way and the blue is the number when it's that way and you can see by eye that there's a big difference between the two so if you take the number of those minus the number of those divided by the sum so again our asymmetry equation you get minus point 107 with an uncertainty of 0.01 seven so that uncertainty is small enough that it's very clear there's yet another matter/antimatter difference this one is actually completely different than the one I told you about with the sigh and the K on and the case short this is a different effect so we could ask what does the ckm model predict for this case and my personal feeling is that the CK model does not make a reliable prediction in this case now this is actually an area of active research some of my colleagues completely disagree with this and they argue that this measurement coupled with some with other measurements of similar decays actually indicates that there is something new that is outside of the ckm model but other of my colleagues thinks that the the first group don't know what they're talking about and that in reality you can't make any reliable predictions so in some sense I have to say and it's interesting in particle physics there are two groups there are experimentalists who build experiments take data make measurements and there's another group theorists who calculate the implications of certain theories or in the case of kobayashi and maskawa make up new theories this is one case where I think the experimenters have done their job but the theorists have not held up their end of the bargain now in their defense this is a very difficult thing to calculate so but unfortunately we just don't know we just don't know right now but it could be an indication of something new with that I think I'm going to conclude so we've seen matter/antimatter asymmetries in the B weave this is really a huge accomplishment and we've shown that the ckm model is correct it describes that the effects the asymmetries we've seen and it describes how the weak force operates we've seen many additional asymmetries but unfortunately the reason why there's so much matter in the universe and we do not have extra insight into we still don't know what are we going to do what what next well there's a new accelerator in Geneva Switzerland at the lab called CERN and one of those experiments is going to make a lot of B mesons and they hope to continue this work using somewhat different techniques but searching again for a new asymmetry and also other of my colleagues working both in Japan and in Italy are working towards building what has been dubbed a super B Factory a B factory that would produce a hundred times more B mesons than the current ones do and with and so it's very possible in either this experiment which is starting now or one of these future projects we'll be able to get some insight into why there's so much matter in the universe and with that I thank so I'm sure your folks have some questions we're happy to take some questions sir okay so the question if people couldn't hear is how do you know whether it starts out as a matter beam as on or an antimatter beam s on so I I left out a few things in this talk and one of the things I left out is that I maybe I mentioned attention so we make two B mesons we make a matter B meson and an antimatter beam s on and one of the B mesons will decay this way to a sigh and a K on or a fine and the K on the other one will do something else we look at the other one and see whether it was a matter or an antimatter version and that we know that at at any given point in time you have one of each and that that's how we do it that's how we do well you can't compare at the large head on fire you can't compare exactly because the way the particles are created is different and they'll make more B mesons but some things they'll do will not be as good in fact the thing I just mentioned the using the other beam as on to tell you something about the one you're interested in that doesn't work nearly that works a factor of 10 worse in their case but they might be able to make fifty or a hundred times more Part B mesons so they they have a there'll be a lot of capabilities there I let's see well it's so we made it we made almost a billion in nine years and they will make let's let's call it 50 times more than that in a given amount of time but they won't be as useful that's the best way I can answer this let's see especially no it doesn't matter whether they're near each other what manner so for an individual particle it's random but if you have lots of them they obey certain certain trends and the trend they obey is in fact you can see it let's see the trend they obey is sinusoidal and I click a couple more times there so the trend that they obey when they oscillate is is similar to this one and this is actually a sine curve right the same sine curve you learned about in trigonometry so on average they obey a sine or cosine within time but for any individual one it's random just like many processes are random in quantum mechanics no no afraid not so oh I'm sorry let's fill in the white chart has been very ok yes okay so the question is what's difference between a neutrino and an anti-neutrino the difference is I think the best way to say it is the neutrinos when a tree noes appear they appear with an electron or with another product called a muon they always appear in concert with those so the neutrino that appears with an electron is a different particle than the neutrino that appears with a positron the difference isn't the charge and this is one of the things that I think I you know I generalized perhaps too much there are other charges besides electric charge and there are more abstract charges and those change that's probably the best way to explain it um those guys over the herring well so the question is is the second model too simplistic now or could there be more quarks well those are two different questions people do hypothesize that there are extra quarks and look at the implications that would have there is one one of my colleagues who is very fond of pictures where there are more quarks and he claims that you can explain the small differences we saw with the Phi and can explain why the universe has matter in it just by hypothesizing one extra quark okay no one else believes that's right but he thinks so okay and you know it's an interesting it's an interest those papers are very interesting so that's something people work on now the other thing that is interesting is that you'll notice that this value is on the lower end of this range and some other of my colleagues are making a great deal of a fuss about that difference and it's possible that that indicates that there is a small problem or a small opportunity that is the first sign that something is a little bit different but I have to say the problem the problem with that in turn is that this uncertainty is very well determined okay we know what what this means is that we think we are 68 percent sure that the real answer lies between point six six and point seven two right that's a statistical statement we can make this range involves many different measurements and a number of different calculations again the kind of difficult calculations that I alluded to before it involves many of those put together with some complicated statistical model and how much you trust the size of that range other people argue a huge amount about so these two kids are yeah oh okay I'll answer the second question first I like that one so the question is if a particles matter antimatter why doesn't it explode the reason well sometimes it does actually sometimes it does the there are certain decays that are not by the weak force you can decay also by the strong force or by the electromagnetic force and that's exactly what happens when a proton and antiproton annihilate okay so I think the answer is yes it can annihilate itself and it decays right the first question what is a neutrino the neutrino is a very very light particle that's sort of the partner of the electron or another product called the muon or a third one called the Tau and you know when people ask what is a certain particle it's actually kind of a hard question to answer you know if you say what is a chair well you can say well it's something you sit on but for an electron the only way to describe it is by its properties how heavy is it what's its mass what's its electric charge how does it interact by the four forces that's as that's as much as we can do so I could list all those things for neutrino and that's that's as much as you can say about what it is okay I think this young fellow right here okay good question you know you may be familiar with in Stein's equation e equals MC squared and what that equation tells us is that matter and turn into energy okay so the M is the matter and the E is the energy C is the speed of light so when the particles annihilate quite a lot of their matter or their mass M gets turned into energy and so you know it's not quite true that energy can't be created or destroyed it's really that the combination of energy and matter energy and mass can't be created or destroyed that's a good question well in the back yes yes so the question is with anteye anji proton and a positron make antihydrogen the answer is yes and in fact anti hydrogen has been observed at both the lab in Switzerland and I think also at Fermilab they managed to do it it's very difficult Angi protons are hard to make but you can make them and it's hard to slow them down without them annihilating but you can do it and some tiny fraction of the time it can latch on to a positron and make antihydrogen and so that if you wanted to see how does the force of gravity affect antimatter that's the next step if you can make antihydrogen and hold on to it and watch it either fall or maybe it goes up probably not but it probably falls but you want to see that's how you do it so that's actually that's that's the case where people are searching for for how matter and HT met are different with gravity this young fellow here yes so the question is is there another kind of mirror that can do the same thing with energy maybe not energy but there is another kind of mirror that people are very interested in it's not between matter and antimatter it's between all the particles we know about and there and different versions of them that have a property called spin may not know what spin is but it's like something spinning around so people think there may be a different matter that changes the spin of particles in fact Michael is one of the leading proponents of that theory and many people hope that at the new accelerator in Switzerland people will observe those this different kind of mirror particles that are a result of this different kind of mirror that would revolutionize our understanding of the world if those particles exist yeah I'm not sure what anti-gravity is so we you know there's just gravity as far as we can see now gravity on antimatter I don't personally but there are people both at the lab outside of Chicago Fermilab and at the lab in Switzerland who are interested in that who's just been holding a hand okay all right so the question is about the Higgs so that the Higgs is a big deal now the Higgs doesn't we think doesn't have anything to do with the matter/antimatter differences I've talked about today but the Higgs is a particle that has an important role to play in the mass of all other particles and so it's it's in some sense it's the one thing that we're almost sure exists that we haven't seen yet we've seen all the other particles we expect so it'll be a big deal if it's there and we find it it'll be an even bigger deal if we don't find about Ernie so the question is what you're asking about this one so the question is what where does this uncertainty come from so I think I said when I described the ckm model that the that model didn't predict the strength of the force between a top and a bottom or a top and a strange it just told you about the relationships between them who we use those relationships and we take many different measurements of other weak force observations we use the ckm model and putting it all together we see that it's consistent and that we infer that this asymmetry will have this value the problem is that some of the measurements are very hard and some of the calculations are even harder and they just cannot be done perfectly well and there's some range of uncertainty in all of those things and when we put it together we get this kind of uncertainty this is taken to get to this level has also taken you know the last 30 years if you if you asked what was this range 15 years ago it was much much broader so oh well you can yes you can even go backwards yes good Bernie so the question is do the particles have different energies um I mean some cases yes in some cases no we're nice thing about making the beam as on and the antimatter version of the beam as on is that when they're created they have very little energy and they roughly have the same amount of energy and that fact is very useful when we search for those decays but in other cases they have different issue the energy itself doesn't affect the matter/antimatter asymmetry so okay so um it's the hour is getting late there are some goodies outside let's take one more question and then Aaron and I and other members of the bar collaboration will be around here if you want to ask us questions privately so one more please take a kid there's uh this one I'm sorry sorry okay young fella over here so the question is could you make an antimatter did you make a big thing out of antimatter so the answer is yes there's nothing that prevents it but a problem is when we make a little bit of antimatter in our accelerator we are making a tiny tiny amount of stuff unbelievably small amount of stuff you could never see it with your own eyes it's so difficult to make in fact in some ways anti protons are the most expensive thing on earth if you calculate how much money and electrical energy it takes to make them they are so much more expensive than anything else so there's nothing to prevent it but it would be very expensive

Channel: SLAC National Accelerator Laboratory

Views: 43,025

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Keywords: physics, Department of Energy, DOE, Stanford University, science, laboratory, lecture, SLAC, accelerator, positrons, electrons, atoms, subatomic particles, neutrinos, quarks, matter, anti-matter, cosmology, dark matter, dark energy, black holes, galaxy, cosmos, big bang, Kavli Institute, astrophysics, KIPAC, space, universe, space-time, BaBar, HEP, science video, physics video

Id: dqsBa-zwBm0

Length: 88min 10sec (5290 seconds)

Published: Wed Jan 26 2011