welcome to the science for the public lecture series the science for the public is an organization committed to bringing the science information issues to the general public this is our website for our program for science for the public and welcome to our lecture series tonight at the robins library in arlington and tonight we are very honored  professor of physics at boston university dr bows is the trigger coordinator for the compact move on sol annoyed the c m s project or experiment at the large hadron explain all that tonight if this present tahsin she brings the most recent news she's just here from there briefly and an explanation of what scientists are looking for this time around received her ph d an experimental high energy physics from columbia university in two thousand and six she did post doctoral work at brown university but her work has been in these kind of exotic particles so i hope she'll say something about that tonight she's been involved in a number of very interesting projects including the c m s project at cern she's worked extensively on trigger and data acquisition in all of these projects as well she's the author of numerous publications and is actively involved in searches for new physics using the data collected at the  two year shutdown at the large hadron collider to make the adjustments to double the practically double the collision energy the two fifteen run has begun and physicists are looking at new data at an unprecedented collision energy of thirteen terrible almost double the energy of the previous twenty ten twenty twelve run and that run produced all the but they found the discovery of the of the higgs bosun and this time they're anticipating entirely new discoveries and you can ask her all about that tonight we are very now firstly to begin with what is the large hadron collider as we call it the other c in short large in this case is really an understatement and you'll see more about this later how draw second would hear reference to what  the early twentieth century these were probably how you know you did experiments get ready with two things that you just throw at each other and see what comes out at the world today full collider physics is very different but  sort of motivate what it is and why do we want you know a large energies to get to what we want i have an analogy here for you this is an illustration supposed to show you know two helicopters and you should look at the bar at the bottom which is giving an idea of what the energy in this particular accelerator is where you going to try and collide these two so the the question is if these two come and collide what do you expect to see an explosion exactly so let's try to see make that happen and indeed that's what you see you have all of these particles that come out so what is saying is that these helicopters are what are called composition objects meaning they are composed of different things and you see the little bits that are thrown about so now let's go next step up you see the same picture but now if you look at the bottom the accelerator energy is larger so i've put in more energy into the accelerators they're going to come faster and then they're going to collide and then what do you expect to see after this collision a bigger explosion and as a result of the bigger explosion the particles that you see come out of it will they be bigger or will they be smaller smaller exactly so this is exactly your common into defense  correct and indeed what you see is smaller smaller pieces come out of this more energetic glycerin and doing experiments like this has allowed us to see sort of smaller and smaller particles over the course of the year not but the idea is the same so we've gone from you know when we knew about the molecule as being very you know an elementary sort of particle to understanding that no a molecule you know consists of atoms and then moreover an atom has you know an inner nucleus and surrounding it you have these electrons which you see in the extreme right there and they are elementary meaning we haven't been able to break an electron down into anything not elementary as well but rather they can be broken down into still smaller particles and in this particular case the particles composing the proton and neutron what are called forks and in particular two kinds of works up and down works the name doesn't mean anything it doesn't mean that one of them lives up in the other one means down these are just names that you know particle physics come up with and sometimes names are crazy but that's what they are what i call these up and down quarks are you know similar to what you think off as you know lego bricks i have a five year old who loves playing with lego and so this is you know like a little break of up a little break you know we're down and what we will have is that you have put in the lepton and that is the electron that i've talked about but now you can make different combinations of these corks to yield the hadron that we were talking about and this is the ans you know brick is your laptop so what do we do next well we can go with this we'll try to build an atom now so we have something that we are going to build with two protons that you see on the left nutrients that you see on the right and if you put these lego bricks together and anybody say what you create helium very good this is helium so now you can essentially take permutations and combinations and essentially that's what results in the universe that we know what we can observe it's composed of all of these various warks and leptons in different combinations but that is not the end of the story what we now get to is another case of the two helicopters in my analogy coming to collide now the acceleration energy is even higher ok we've reached the maximal point so again i will ask you they are going to collide and what you expect to see yes yes that's what you think that you would again you've created particles and these particles in turn will break into further smaller particles so you sort of moved ahead but what we're going to see is the same thing happening here now in this co mountains and it was here that they found some of these prehistoric dinosaur bones so the term jurassic as you know comes from the juror mountains surrounding serve about we don't do any of dinosaur production at sea but the main thing to highlight is what you saw was this collision yielded something completely surprising that you didn't expect a particle which is you know was there but  doesn't exist anymore so what you did was you took the energy and this energy of the collision was used to create these particles and of course what we will come to later is what is it that we actually detect do we detect these dinosaurs in our experiment and then we will answer the question that he already answered that no what we actually see is where the dinosaur decays into further meaning the dinosaur doesn't live as a dinosaur but instead splits up into still smaller particles and our detector we detect those smaller particles but i'll come to that so we've essentially taken the energy produced special particles and we try and look for these special particles that we have produced as a result of the energy and the more energy we can put in the more massive a particle we can hope to produce so that's the reason why we want to go in for more and more energetic hi i told you the names don't mean anything it's not like it's a charming words is a strange quirk but there are some historical reasons why the name the way they are but you just have to you know take them as they are and then the leptons the electron that we particle physicists like to work with but that's not the full picture because there is also what's called the anti version of these particles or anti matter or the fact that for every type of particle that we have there is essentially through charge it's has a similar properties but it is the opposite charge there is a special category and you will ask me because i showed you about the  associated with the muni train now and its anti particle is associated with the anti lepton so it is sort of linked to charge even spite of the fact that it doesn't have its own charge and so there is a connection and we so together with the particles and the anti particles that sort of constitutes our knowledge of essentially elementary particles and the neutrons and protons that we've mentioned those the not elementary because they are broken down into these constructs of course they are what we call composite particles because they are composed of other things ok now there is a very fundamental question associated with matter and i will get to that more later but it's the fact that you know we people and everything we see around us is matter at the very beginning the big bang we had our current understanding tells us that we had equal amounts of matter and anti matter and typically when they will come together they will and highlight somehow something happened which resulted in all the anti matter going away somewhere mostly leaving all  went happened to the anti matter and why is everything predominantly matter and come back to you know when i talk about what it is that we are actually looking at the ellipse so based on all of this that i've already told you that there is you know a lot of things that we now know however mostly i would say is we know actually very little and that is because there are many many fundamental questions that we still don't have an answer to what we have an  to are sort of the simple questions where you know you take all of the information that i've given you put it together in a model and we particle physicists call that the standard model it's nice and simple and and that sort of comprises our knowledge of the universe however they are as i have already been sort of hinting a number of mysteries and unknown cers unknown questions and i'll talk more about that but before we get to that i think it's useful to look at together with these particles the other big part of the standard model the what we call the fundamental forces or how is it that these particles interact with each now they're these are sort of broadly grouped into sort of four categories starting with the one on the extreme right the electromagnetic force this is the one that we sort of you know experience most commonly in our day to day lives was responsible for our you know magnets your t v working cet weak force which essentially is explaining radioactivity what powers the sun of the kind of you know interactions that powered the sun and it's and they are these three fundamental particles and they which sort of interact via the kind of force the weak force and then there is a force called the strong force which essentially is responsible for holding atoms together for holding the  while they're opposite they attract so if you have two protons within the nucleus you would expect them to repel each other and for the nucleus to break apart however there are various such nuclei existing and they exist because there is this force and that's why it's called the strong force because it's able to overcome this other force their beloved kinetic force which was trying to repel them and to break it apart to keep it together so they are there is this particle called the  on which literally is sort of gluing these quarks within it to sort of keep it together and that is therefore responsible for the strong force the standard model describes all of this beautifully so these are the photon w plus w  the force that the salmon model does not know how to deal with is a force that we experience as we walk as we go about in our everyday lives gravity which is responsible for keeping us you know we which are responsible in a way for particles interacting we have these forces there must be a particle and they call it the grab a ton which would be then responsible for gravity essentially of particles interacting be a gravity so a lot of fits in within our standard model so that's a fundamental open you know unknown question that we're trying to answer that is how can we get the standard model to include gravity then the other big question that we have made some headway in understanding but not completely is the mystery of math so what i think the question that i was aust as to you know what are the masses of these particles you know are they all massive this picture now has the same but now they're drawn on the basis of their mass meaning the stein is dots there are the least massive and the the bigger ones have more mass so to sort of give you an idea of the mass of the particle there is an empty and does anybody remember what that cork was yes very good that was a tough work and the reason i didn't have it here was if i tried to put it in here it's mass would make it sort of appear like this it's a whole lot massive than the other part and there was up until you know recently we did not really fully understand why it is so this was a big question that is why are some particles heavier than others and what the standard model did not ever predict the masses of these particles so you know we just went and did experiments to find them and they had the mass of the we discovered them out but there was no prediction because it really couldn't tell us together and and peter higgs who in that same year working independently came up with three seminal papers that tried to answer the same question and the the the the way they addressed it it was actually quite similar with you know different perhaps take on things but the the basic idea or principle was the same and you know they got published almost sequentially there's a lot of  debate about which came first the cetera but the bottom line is that all three of the papers came out in one hundred sixty four they all had the same mechanism for trying to explain how particles acquire mass so that's the question that we will now try to understand the way it's explained in these papers however i'm not going to read and i don't understand everything in the paper myself these are really you know very very mathematical explanations for for this process but i'll use a famous and knology to sort of try and explain to you this came about i think initially because margaret thatcher prime minister of england at that time wanted to understand this mechanism and issued a challenge to her science minister to try and get her to be able to understand this who then issued it to the physicists of the country and ultimately they had a competition and a professor from u c a london came up with a set of cartoons to sort of try and explain this which sort of since then became famous so i think in the original picture they have margaret thatcher they i have a later version that i you know got hold of so imagine there is a room of people  there you know i think they were supposed to be political party workers in the original cartoon we say you know they're having a party whatever now you have a famous person who shows his head through the door  happen if say we had you know barack obama walk in here now and say he's trying to head to the other end of the room there because there's food there now as he comes in what's going to happen what are you going to do are you just going to sit th yes what you want to do is you were like oh you know and then try to go near him to perhaps talk to him what are you doing here why are you here you know and you're going to just you know start talking to him with the result he's trying to get to the food there do you think you can get to the food very quickly no because you're going to stop him you're going to make him want to talk to him and he is unable to go to the other end of the room now imagine a completely random person from the road walked out of the picture now now get to the other end of the room so they'll move very quickly almost as if they are massless or very little mass they're moving very quickly on the other hand barack obama and his interaction with you means that he's slowed down heavy objects are slowed down and he by his interaction with you appears to acquire mass and get slowed down where somebody who doesn't interact with you with this through almost massless very fast so that's the basic idea here so you see it in pictures now coming in and he is surrounded by the people you can't get to the other end of the room and he is slowed down he's becoming more massive so that's the idea that there is this field we physicists call that a field this field exists and how much you interact with this field determines what kind of mass you have if you interact a and therefore is very light so that's the basic prince now field is a mathematical thing you can't really see a field so how in the experimental is ever going to prove that this correct this is what's happening because you can't really see the field and so part of the theory was that together with this field there would be a particle that would be associated with the field and and if you discovered this particle then you prove that the theory was correct and and this idea is what is sort of showing here that as we go back to our you know party of you know people somebody just puts his head through there and says oh rock a bomb ice coming down the corridor or you know he's going to be here soon so even though you know barack obama is not here the fact that he's going to be coming here will have all the few starting to talk wh here you know set right you start talking amongst yourself this field here this room sort of there isn't excitation in this in this room this and this sort of a cluster that ends up being formed associated with this field is what we call higgs the particle that you have heard about that we discover it so it's is higgs bows on which is sort of associated with this you know physical field which is responsible the field is the one that's responsible for the mass meaning the interaction with the field is what gives particles mass the higgs is just associated with this field so when you find the higgs bows on you prove that this field must therefore exist for this theory to work out because all of this was what was given in those three papers that i talked about where they predicted back in one thousand sixty four that there must be this esoteric expose on particle which is associated with this field and that is what's responsible for giving particles mass so as you can imagine that was the big search that went on in the last you know fifty years so this is another way you know imagine a field that permeates entire universe every particle feels field but is affected in different amounts the more a particle interacts with this invisible field as i said it's not really something you see the more mass it gets and i think i already told you that at this field is invisible how can we prove that it exists and we're  such that we can then see what happens and we prove that the higgs boson exists and therefore there must be a higgs field and therefore we have we understand how particles get mass so that's the the big  sort of you know the discovery that you might have heard about a couple of years ago however and this goes back to something we had alluded earlier that is if we go back to our analogy where we had our helicopters colliding and you remember the dinosaurs that came out and i told you so we'll try to do that as the absolute or energy you can think of is is again at the very very high end perhaps more we produce these dinosaurs but the dinosaurs actually challenge in our experiments is that we can create to expose on but it's not like we can actually just identify the higgs bosun because we're never going to be able to find the higgs bows on bites as such what we see is that the higgs bows on will be created and it will then in turn just like the dinosaur six goes on as a dinosaur in this case it will then decay to other particles what we find in our detectors are these other particles using information about these other particles we can figure out where they came from did they come from a higgs both gone did they come from somewhere else and that is how we discover particles by not incest really finding the particle itself but by seeing what  decays to and then finding the particles that it decays to but that makes it more challenging because it's not like there's a huge expose on lying there waiting for you to find it they expose on disintegrates almost instantaneously and you have to you know do a lot more work to figure out whether or not it was so it's like what i think of it is like being a detective you know you have say a murder that happens you have a lot of clues right and you use all of those clues to reconstruct who the murderer was and how the murder happened so what we see in our detector are all of these clues and we put the clues together to figure out where the witch particle that came from the certain ways meaning it will decay into for me ons it will decay into four electrons it will decay into two photons so in our detector we try and look for these states and event where they are for electrons or an event where they are for me once and then you go through lots and lots of this data because what you can do is this is energy and conservation laws of physics you can get the information about the energy and momentum of these me wants you can apply conservation of energy and momentum to figure out what was the mass of the particle that came from and then you look through billions and billions of events to categorize and break them down into groups of these events like for me on events and then in each case where these for me on events came from and if you get a large number of cases where these for me ons came from a single particle which had a single type of a mass of say hundred then you know that you produced in your detector this particle which had a mass of about one hundred i'm not using the units for a particular reason a mass of about one hundred and educated to for me once but you need to see enough of this because if you just saw two it could be from anything so you really need to see a very nice large number of such events to have confidence that you've actually got to write and talk more about this i'll show you how we actually solve the higgs but that's what we do so we analyze all of the state and there's tons of it to then figure out where they came from using a special arrangement of magnets which keeps about part most of the time and then brings them together at certain points and at that point we have detectors put in such that we could listen happens in the center of the detector and you see everything that comes out of that collision point now keep in mind that the proton as i said is not an elementary particle so you have a composite particle composed boundaries so part of the experiment is actually in france and part of it is in switzerland it's near geneva we had a first run which started in two thousand and ten went on to twenty eleven where we had  and some of it you know the sheer enormity of it is firstly it's what you would say almost the fastest you know racetrack on the planet and these are just aerial pictures i've already told you two different countries but you have essentially several thousand billion protons which are traveling at very much close to the speed of light and this is you know sixteen point eight mile range over you know and this is happening about you know eleven k times a second so each of these collisions that i'm talked to about having the detector is happening but forty million times per second inside the detector very very very very very quickly i can just even simulate that and this particular speed in case you're wondering what this is you know in our real world speeds it's that in miles per hour so this is literally protons moving you know close to the speed of light very much so the fastest racetrack of course in order to be able to do that this is particles it goes through what's called like a beam pipe and if there are lots of other particles in this being pipe these protons will interact with these particles and lose energy so you want to have this beam pipe kept in the nicest vacuum possible such that you can preserve the energy of the proton being such that you can have these high energetic collisions so essentially what we have is a vacuum the thumb of the literally to outer space and the pressure as well as such that it is about you know ten you do this with the use of magnets and what magnets allow you to do is if there is a particle of a certain charge then with the field of the magnetic field of the magnet you can make it go in a certain direction so if it's a positively charged particle it will bend in a certain direction so if you have another positively charged particle it will also bend in the same direction so but you can't have them both in the same because then they would interact with each other and then you would have collisions everywhere so you keep the beam pipes separate except at the collision point where you have an opening and then they come together and that's where the collision happens ok so the other thing is in order for all of this to happen to actually they use magnets and to be able to be pushing these protons of this kind of speed they again need to be using the latest technology which means that they work under extremely low temperature because under these low temperatures you know magnets become called superconductors meaning they don't have any resistance to the flow of current they can allow large amounts of current to go through large amounts of current means large magnetic field large magnetic field means you can do nice bending and therefore you want to be able to have things which make this happen and therefore you need to have these superconductors work at extremely low temperatures that's why these low temperatures are needed so when these two  temperatures like you know there's a billion times those at the heart of the sun so extremely extremely intense and then of course around this point as i mentioned what you have is the detector that is  situated so the indeed the beam pipe is going through this tiny center in the middle of the detector and that's where the interactions is opened up detector so this is my detector that i will talk about in a second but  it's sort of completely surrounds the b pipe because you don't want the particles that produce collision escaping you want all of them contained in your detector so the detector surrounds the pipe like that and happening so quickly so this is sort of a pictorial description of a typical particle physics detector and things haven't changed in this picture is probably you know the last you know forty years the  idea is the same we're just using the latest in technology to give us you know better resolution and better precision so the a particle detector typically we say is like an onion it has layers ok just like an onion has layers so we are now looking at sort of you know starting from the inside most of the in the most part what we do is we want to detect different kinds of particles and i've talked about electrons milan's photons various so we build not one detector but actually different detectors each of which is going for a particular kind of particle ok so we build a detector which is primarily aimed at measuring it interacts using the same kind of force we believe that its way of interacting is the same and therefore with the same kind of idea behind the detector we shall be able to figure it out so that breaks brings it particle physics experiments essentially because they wanted to build these extremely precise what we call tracking detectors to detect these particles and that advance led to where it is today so this is like a track is thinking off you know matching the person you know walking in the snow or skis on the snow you leave a track and essentially that's the kind of particle will leave a track as it goes through this select a detector it's you know it it processes call are there these detectors which are filled with gas a particle goes through it it does it it makes the market certain points and you have electronics which is attached to it to get these signals to figure out where in this detector this particle hit and using this only charged particles will leave a track through such a device that's how the belt neutral particle does not interact in the same way through this method that i talked about even these hits so already using the tracking detect we can differentiate between a neutral particle and a charged particle because a charged particle will be tracked a neutral particle the other wonderful thing about the tracking detector is this is you know anybody who's done or w to follow a circular path depending on the charge of the particle whether it's plus the electron charge or if it's negative it will bend meaning if the positively charged particle bends like this the negatively charged particle will bend like that so we will look in our detector to see how these tracks are in the tracks are like this or of the tracks are like that with that we can tell whether it is a plus or it's an us it's an electron or a  it's bent this way or it has been so you've identified that it is charged you've identified what is charges positive or negative the other thing you can identify is it's meant depending on the momentum of the large what we call the radius of curvature it typically means it's a high momentum particle if it has a small radius of curvature it's a low momentum particle and using our knowledge of magnetism and what this radius of curvature is the which we know because we put in the magnets we can actually figure out what the momentum of the particle is so we figured out the charge we figured out the momentum and whether or not you know it's neutral and all of this what you have is the next detector surrounding it because as you see i can go down further i see me wants me on sol to leave a track i have charged hadrons so you know protons for example they also leave a track neutral i can figure out that this has this momentum but it doesn't tell me whether it's you know a proton or whether it's an electron or it's a me on i need something else to be able to pinpoint it further down into whether it's an electron or a me on so i need another detect detector whereby the electrons and photons will stop there and then you can measure all of the energy that it deposits when it comes to a stop and so now you can using the top to detect top to you know the tracking detector and electromagnetic so this the lines that you see here would be you know it would be a collection ours because it sort of showers energy and comes to a stop using two detectors the tracking detector and the electromagnetic electron or it's positive particles or positrons so you can using these to detectors distinguish between the first sets now me wants are very special particles in the sense that they don't they leave a track through the tracking detector they don't interact with the the detectors that you see after that and what you have at the end is a special detector that's put in to measure the properties of the me one and in these does it doesn't and s and leave their energy there so now putting all of this together you can then starts to distinguish between all of these different particles so you need all of these sort of sub detectors to make up the full detector to be able to figure out what you had and what is meant and was and what this energy was and then there is a very special category of particles called the neutrinos which actually interact very little with our detector and essentially go unnoticed in it and the only way we detect their presence is you know for every physics process has to sort of follow conservation of energy and momentum and we find when we find that this is not coming out to be true produced and it went away with this missing moment so that's the complication so i should go a little quickly through the rest so i think the thing i want to point out is they're actually not one but there are four big detectors atlas compact in comparison to the other detector atlas which is larger and less dense whereas c m s is smaller and more dense you know it is huge it's about fifteen metres wide and twenty one point five meters long  but and it's taking you know these collisions are happening very very quickly and it's taking pictures as you can imagine you know seventy five megapixel three d camera with do and all of it was assembled all over the world and different components and then brought together it and they're now lowering it through a hole through the top and the detector is sort of you see this hole here it's being lowered this process took over  hours and it's getting down here now you see it arriving and this is just part and this is the whole thing coming together and in the final few minutes i think i'll just mention that you know if all of this was not challenging enough we talked about the the large rate of these collisions meaning they're happening you know forty million times a second that's what i call the bunch crossing rate there how much we are saving for analysis later is of the order of a few hundred events per second so we have forty million events happening per second and we're only saving about a few hundred per second so we need to have a mechanism to able to do that because the rates of the processes we are looking at like for example the higgs are extremely small and we want to make sure that in the in the  few events that we save we're actually saving the interesting once and we're not throwing them away because these decisions that you make on line are really for good meaning you keep it look for looking later or you throw it away so you really don't want to be discarding your higgs and your new physics advance in that fashion and that's what i call the trigger which is the work that yvonne you did to which is part of what i do and i'm happy to talk more about it later but also to give you an idea of have to go through all of this to actually get to your you know a few interesting events that you want to see so this is literally you know looking for a needle in a haystack the despite all of these difficulties we found the higgs and i think we see these are independent analyses that gives you a mass of about one hundred twenty five and this other analysis completely independent using different final objects gives you again a similar mass of hundred twenty five so this gives you confidence that you can do completely different analyses which make use of different parts of your sub detector and find the same particle which according to the theory was supposed to decay in these two different ways and not just that this was what my experiment found our competing experiment affluence also at cern exactly the same thing completely independent we don't share our results or discuss it until we get to the point of making a public announcement and then we find it was exactly the same point that gives everybody confidence which is you know why this ended up actually in the nobel prize for the sort of you know the main surviving people from the theorists are collaboration's half you know three thousand people you can't really do anything but they got it after the higgs was discovered and not before that and then finally i just want to say that you know this run discovered the higgs however the story is not complete because we need to look at it from every angle firstly is this is exactly the higgs that was predicted or is it very different or is it you know similar but not quite the same and you need to do that by looking at you know every angle of i like this picture because you know somebody is just looking in a very tiny space they think they're holding a rope this one things this holding a spear this one has a wall but then you look at that no they're all actually parts of something completely different ok and so you need to see the whole picture and that is part of what we're doing supposed to disappear but we live and therefore where has all the anti matter gone i don't know the answer and none of us know the answer and we're trying to find that and and then i think so that's i think a big question thing one of the big theories that helps to explain this which a lot of us are searching for is what's called super symmetry which says that for every standard model particle that you see on the left there  volts the first runs were at seven and eight so it is really a big and more energy means we can produce more massive dinosaurs more massive particles which will decay  more interesting ways that we will then try and one of my favorites because this is actually a real event that we got which has everybody very excited is an event which essentially shows two electrons and in the standard model there is this particle that i talked about the z bows on which decays into an electron and positron and what we have a new physics theories which predict that there is a partner to the zebras on and out of any particular c will allow us to therefore see it and so we had an amazing event which was that you know three trillion electron volts we've never seen any object that have a mass and this was indeed whatever it was was produced it decayed into an electron and positron and but it's just an event at this point you really can't say anything but if by the end of next year we see you know one hundred of these and all of them are at two point nine or three v then we've got your new particle so that's our hope that we have discoveries awaiting us next year and i think it's clear from all the various open questions i told you about you know matter anti matter we don't really understand a lot of the the standard model and perhaps you know there is a new standard model that's you know about to happen and maybe in a few years we'll have a new