Particle physics made easy - with Pauline Gagnon

foreign [Music] will be to give you an idea about what is particle physics well try to make that as simple as possible to give you a sense of what we do as particle physicists looking at what we have achieved so far and then looking at in the future what is left to do and you know London is the capital city of uh musicals and I had the the occasion to see my first musical on Saturday night that Tina show it was absolutely mesmerizing and I don't know if we'll be able to do something as entertaining here tonight but I'll certainly do my best so um the outline for the talk tonight first will be particle physics in a nutshell how it works then what is the Higgs boson I know you've all heard something about it but if you have to describe it it might be something else so I say a few words to help you better understand what it does oh sorry and uh why do we bother to look for those particles that's a good question and what is left to do because there are lots of students here and it's not much fun when you you realize that we have already done all the jobs but you'll see we are far from there so the aim of particle physics is quite simple is to find out what are the smallest constituent of matter we want to know what are the building bricks of better and if we were in Copenhagen that's where Lego bricks were invented in Denmark and there is a museum in the called Legoland and there everything is made of Lego bricks so if someone there was to ask me what what are the smallest constituent of matter it'd be easy you know when nobody watches I will take one of the exhibits I would break it apart and I will see all the fundamental particles coming out of it all the building buildings but Lego bricks is not so simple because they have more more than 3700 different fundamental bricks but when we when we look at um so at Legolands these are the smallest constituent of matter but when we look at real matter like a piece of wood our body this room everything in the stars and galaxies it's not so simple because you know it's made of atoms but the atoms are so small we don't see them so it's not so easy and at home is in fact a million times smaller than a human hair so it's really not big it's 10 to the minus 10 meter so a meter is a yard roughly and 10 to the minus 10 is the scientific notation so you take the decimal point and you move it by 10 position so instead of being one it's 0.1 0.000 you insert nine zeros in there and so that's the size so it's 10 billionth of a meter and at home as you know is made sorry I backtrack Anatomy is made of uh a nucleus and some electrons that gravitate around it if I was a nucleus my electrons would be 12 miles apart so most of an atom is in fact emptiness vacuum the nucleus itself is quite small it's 10 10 to the minus 14 it means 10 000 times smaller than an atom and inside the nucleus you find protons and neutrons I think up to here you have probably all heard this so the protons and the neutrons themselves they are much smaller they're about 10 to the minus 15 I believe and inside the protons and the neutron you will find quarks and the quarks are smaller than 10 to the minus 19 meters so if I ask Yuna what are the smallest constituent of matters that you see there that we cannot break any further which ones do you see across quarks yeah and electron that's it so those are the only fundamental particles there electrons and quarks I'll show you that with just two types of quarks two different types of Quark the up quarks and the don't quarks I can build an electrons I can build all the material that we see here on Earth stars and galaxies see if you take an up Quark an up Quark as an electric charge equivalent to two-thirds of the charge of an electron but it's positive and you don't Quark as a negatively charged and it corresponds to one third of the charge of an electron so if I want to make a positively charged particle then I can take two up quarks add two-thirds of a the charge of an electron twice so it's four thirds and I add to that a down quark and then I get to plus one so that's the charge of a proton and so with up and down quarks could you make up a particle that is neutral yeah who said yes okay so what do you do voila two down quarks and one up Quark so that's what a neutron is made of okay very simple and you know that the whole periodic table the only difference from one element to the next like the lightest one is up here the hydrogen it has only one proton in its nucleus and one electron around the next one is helium all you do to change electric element you just add one proton to the nucleus so helium has two protons two neutrons for stability and two electrons around then the third one is lithium and there you have three protons and so on and so forth so you see you can build all the 119 of those elements just by putting more protons in the in the nucleus and that's the difference between the different elements that we find in the periodic table so that's it with up quarks down quarks I've just built all type of chemical elements and you know that everything that we have on earth is made of those elements it was my dream when I was a about 14 and in 1969 when they went on the the it was which one Apollo 9 mission that went on the on the moon foreign of by two specifically Apollo 11 and they went on on the moon and I was hoping they would find new elements Mano they found the same area chemical elements that were here and so um so in the in the 60s it was really difficult because we had hundreds of different particles today there are two more than 230 different particles that are listed in this little booklet with all their properties and now we know that it's not so complex at first you can have a look at that you can pass it around at first people didn't understand why there were so many and it's far from being like the Lego bricks with more than 3 700 different pieces today we know that it's very simple and it's so simple that we we can make it even simpler than the periodic table and that's what we call the standard model the standard model is just a theoretical model to help us classify the particles and it tells us it has two principles the first principle is that all matter is made of particles all matter can be broken down into the elementary particles and it tells us that they are in fact 12 different particles these particles come in two families the family of leptons and the family of had runs the ones that are built out of quarks like protons and neutrons All in the Family of Advent just a family name so I already introduced the up and down quarks for the quarks those are the lightest one and then there is the charm and the strange Quark strange Quark got its name because all the particles that contain that Quark were having a very strange lifetime which was much longer than all the other particles that we knew before so it was called The Strange quack the next one came that was a discover next Quark then people saw why not the charm Quark this one had Sean and then they went for truth and Beauty but then now we said okay enough of that and we called it we get we kept the true tea for top and Beauty B for the bottom Quark so now we have the top and bottom quarks so the top Quark is the heaviest of all the particles and it's it's quite heavy so that's the family of uh quarks and headphones and the family of leptons you know the electron the results the electron also come with a mu one uh sorry with the neutrino when we create electrons in the laboratory they're often it's always produce either with an anti-electron or a neutrino all these particles that you see here are also have their antimatter so particles that are identical except that all their Quantum charges are inverted like they have their spin will be inverted they will spin in the other direction their electric charge will be positive for a positron instead of the electron which is negative okay so in the family of leptons we have the electron then the MU one which is 200 times heavier but similar to an electron and it also comes with its neutrino and finally the top particle which is four thousand times heavier than the electron and it also comes with a neutrino and I brought one here and those are the so now you know that it's real and so this uh this uh the series of a little uh characters come from the particle zoom and it's a young woman Julie Beasley from California who attended the lecture like this one day and then she thought it was cute and she was a seamstress so she started producing the particle zoom and you can you can order them on the web so I can pass the tell neutrino and what is really weird it's like you know we have a construction set but the only particles that we need to build everything that we see on Earth and in the universe is the first generation of particles up quarks down quarks electrons it's like I'm giving you a very nice construction set at the Christmas sign and it has all sorts of models that you can build but in all those things you never use the the second and third generation it's like you have the basic particles up and down quarks and then the other ones they don't fit there the blues they're not Lego and that that it doesn't fit together so it's a funny construction set because the TA mu one at the lepton is four thousand times bigger than the electron so it's a very weird construction set and you never use it so it's strange that's one thing that we don't understand but we know now that there are these 12 basic particles and their antimatter their antibarticle the second principle of the standard model says that matter is made of fundamental particles and the interact with each other by exchanging other particles that we call bosons and those particles mediate the forces between those particles and the first one that is there is the glue one that's what you find that will glue hence the name that will glue the quarks together to form protons and neutrons for example so those are blue ones then you have the Photon which is associated with the electromagnetic force so here is a photon and you have which is massless then you have the w and z bosons which are the mediators of the weak nuclear force which is way stronger than a bit a bit weaker than the strong interaction between quarks and the blue ones and that's the process that takes place on the sun in the sun uh and how the sun burns its energy graviton we haven't found it yet but we have found about 10 years ago we found the first uh gravitational waves so we think that they will probably come with a graviton and finally the Higgs boson the Higgs boson which recently got discovered 10 years ago at CERN and I will talk more about that here's the explosion and you notice the difference this one has mass what is this business of exchanging particles those bosons it works like this like imagine two particles like two skaters that are evolving you know skating on the ice and they ignore each other they don't know that the other one is there they do their own business and they would go on a straight line but the first one nasty tosses a heavy bowl at the second one and makes him deviate and she himself will recoil so both of them are recoiling so instead of continuing like this they will recoil and then they change their trajectory so see if I was to look at that from far away I would say oh look at that there is a strange interaction at a distance that took place no no that's not they simply Exchange a heavy boson and it made them recoil so that's how particles interact with each other it's by exchanging the various bosons associated with forces so that's all there is to the standard model in terms of principles everything is made of particles all matter is made of particle and those particles Exchange interact with each other by exchanging bosons Okay so the situation was much clearer than having those 230 different particles that we didn't know what they were made of and all that but in the 60s there was a major problem is that all the equations that come with the standard model predicted particles that were massive but all of them in the equations were coming out with massless particles all the particles were massless so the models was describing things properly but all those particles in these equations were massless and we knew we had measured that in the laboratory we knew that they had a mass so it was difficult to understand so a bunch of theories were all working independently these two were together Francois angler a Robert Brown to a Belgian physicists and they they were the first ones to propose a new field they said that our universe was permeated by this field that was and through this field particles could acquire a mass okay strangely enough those names were until recently not very well known but everybody has heard now the name of Peter Hicks why is he well known because he was the second one to publish similar ideas and he sent his paper to a news to a journal as a physics journal and the editor rejected this paper saying useless Theory you don't make any practical uh prediction with your theory so useless Higgs was bummed out so they said we may it comes with a new boson and so he he modified this paper a little bit and submitted it to another journal and then it got published and he was the first one to mention that this new field would come associated with a new version like the little Higgs boson that he's going around right now so with this so that's why the the name stuck being the boson Higgs boson and what is the proposing their theory was a mechanism to explain how particles would acquire Mass and uh but this required that we would introduce a new field and that particles would acquire a mass by interacting with this field okay now let's try to look at those Concepts one after the other and get somewhere what is a field in physics has nothing to do with that kind of weed feel it's more like a magnetic field you know if you put a magnet somewhere it will simply change the properties of the space around it such that any any uh anything that is easily that is reacting to the magnetic force will behave differently for example if I have a magnet here and I put a a piece of plastic and then I with a salt shaker I put some iron filing on it all the little pieces of a iron filing will align themselves around in the direction of the magnetic field line around the the magnet so those iron filings grains will all behave differently in the present presence of a magnetic field when there is a gravitational field we stick to the ground you know we don't float around okay so keep that in mind now I I will go and introduce three concepts that we use in the physics math what is mass mass is the resistance to the change of your state of motion so say that you're a huge cruise ship like this and it's a it's in motion if you want to stop it it will take a lot of energy because it has a lot of mass so to it will offer resistance to the change of its state of motion likewise when you want to put it in the motion and energy and mass are equivalent the equivalence between energy and mass is well known with this equation is represented by this equation E equals m c Square you've all heard that equation at some point e represents the energy and M the mass C square is simply the square of the speed of light and that's the conversion factor between energy and mass this equation tells me that I can take energy and produce matter Mass out of it that's what we do at CERN when we concentrate a lot of energy with the accelerator in one tiny point and we make new particles appear there and you can take a mass material and you can break it apart in a nuclear reactor and produce energy so the two are equivalent you can see you can look at the mass like being congealed energy okay and mass and energy are just two different uh manifestation of the same Essence like here you know I live in Germany so I have Euros in my pocket normally I'm here today so I have pounds but I don't know why because everybody only uses credit cards so absolutely useless but anyway so I have pounds and euros and there is a conversion factor so it's not the same thing but they represent the same Essence which is money and there is a agreed upon exchange rate between the two and that's the same between energy and matter and Mass third concept energy conservation energy can take different form but must always be conserved you cannot just lose energy like this so if if I represent energy with a fluid that I have in a bottle I can then take my quantity of energy here and Pull It in two different containers but the total amount of fluid that I have at the beginning will always be the same just don't have to spill it's okay you're not allowed to spill that's the thing for a fundamental particle that is moving there is only two ways that it has energy it has energy due to its motion kinetic energy and it has energy congealed energy in its mass okay okay ready here is how the drought and glut Hicks field gives Mass two fundamental particle let's go back a little bit back in time at the time just after the big bang but we don't have much time it lasted less than 10 to the minus 25 30 seconds where there was absolutely no Broad and alert Hicks field then there was no time there was nothing before the Big Bang I'm told I wasn't there but so imagine that a particle wants to go from point A to point B there is no brout and glut Hicks field and then uh the space is empty and the particle can go from A to B on a straight line at the speed of light because it's massless huh so only massless particles can travel at the speed of light okay I'll do it slower so you can see it's going on a straight line so for this particle which is massless all its energy is in the form of motion kinetic energy it has no Mass so the mass container is empty but something like I said I forgot was 10 to the minus 32 seconds shortly after the Big Bang someone or something turned on the broad and blurred Hicks field and now the space the the properties of the space were modified and it made it like it's like uh in the previous case it's like a kid wants to go across the schoolyard and when the schoolyard is empty the kid can easily run at full speed in this on a straight line but if that kid is trying to cross the schoolyard when all the kids are out at recess then it will start interacting you know saying hello to the friends and bumping into each other and it no longer goes on a straight line it interacts with the space around it it stopped getting his feet cut in the carpet in the flowers of the carpet like my grandmother would say so you've noticed this particle is not going as fast as it was before so it has less kinetic energy and you all agree with me where did the missing energy go yes that's it so this particle acquired mass by interacting with the broad angular Hicksville ta-da that's how it works and it's suddenly this way that the particle would transform some of its energy into mass then you will have congealed energy in the form of mass it's sometimes an image that is given is that it's like the the space becomes viscous and the particle cannot move so easily it's good for another analogy but then viscosity is something that is dispersive and you would lose energy by friction and that's not the case here did you notice that having said a word yet about the Higgs boson in that whole story so bright and gluten Higgs independently all came up with the same idea and the three other guys who were on the picture that I forgot to mention that there was this uh this field that permeated the whole universe soon after the big bang and we could say that the bratengler Hicks field is we could make an analogy with the surface of the ocean and you know that uh we can excite the surface of the ocean either with the wind or an earthquake a tsunami and then you can produce waves so the Higgs boson is like that it's just a wave at the surface of the Broad and blurred eggs feel now you will all ask me where did I get my drugs and it's pretty good to come up with those things no it's pretty far off but that's the way it is wave our waves are excitations of the ocean surface and the Higgs bosons are excitations of the brown and glut Hicks field we can create Higgs bosons by exciting the proud and Lord Hicksville of course you can all say come on now she's full of it what is this and so to prove it to you it's like imagine that I have an aquarium here and I tell you the aquarium is full of water can you see the water no okay so to convince him and all of you what I can do is easy I can tap on the side of the aquarium what happens you see little ripples huh did you see it [Music] okay no good drugs for example so okay so all that we had to do us particle physicists experimentalists at CERN was to go and excite the canvas of the universe to make Higgs boson and that's what that's what we did but how did we excite the fabric of the universe you know that's the job we are given okay go and excite the fabric of the universe sure what time would you like that and so what we did was to do it with the Large Hadron Collider and this is a very energetic machine that can put a lot of energy in one tiny point in space and this energy can resonate with the fabric of the universe and then when you just give it the right energy like a string of guitar will will start to vibrate that's exactly what happened so the Large Hadron Collider is built at CERN CERN is the largest particle physics letter laboratory window in the world it's near Geneva uh in Switzerland and it's very large it's 17 Mars in circumference 27 kilometers around and you don't see anything but the four experiments are built along this tunnel but 100 meters on the ground so 100 yards on the ground and there we have huge Caverns that have been excavated and a tunnel that looks pretty much like a Subway tunnel in which we have a vacuum pipe and we have protons that are accelerated at this near the speed of light it's at 99.99997 of the speed of light and we have the particles the protons that circulate in the the accelerator like that 27 kilometer and then they come and they collide we bring them into collisions and then of this Collision the energy materialize and produces new particles so we have two types of tools to work at CERN we have accelerators that accelerate particles and we have detectors and guess what they do they detect the particles that come out of it so we produce those collisions new particles form right there but they're very unstable they break apart and they create like mini fireworks and all the fragments fly apart and they go through the different layers of our detector which are huge cylinders with end caps and it goes through all the layers and leaving signals everywhere and then we can tell that yes we saw something it looks like a mini Firework and we're trying to catch all the fragments that come out and then we we can reconstruct what was created at the first to start with and then analyze what kind of particles can be produced and how do they Decay and all that and from from that we infer the various laws of that these particles follow so here is how it works with this accelerator so protons are put in a tiny accelerator at the beginning they gain enough energy they go to the next stage which is about 630 yards around and then they go in the larger one that is about five miles around and they gain more energy at each step until they get in the LHC 27 kilometers or 17 miles and they go and circulate they go through this vacuum pipe accelerated by Electric fields and we have huge magnets that will bend them around to keep them on the circular orbit you see the three little quarks are a bit excited before action and then they come from both ends we send them in two direction and then they come smack in the middle of where we put the detectors and then they collide energy materializes in the form of various particles will and we try to catch all fragments to tell what happened and so we we do that happily and our detector is built it's like a giant camera except that it's a pretty good one it takes it we have collisions every 20 nanoseconds 20 billionth of a second we have collisions and it's not only one proton coming here and one there but it's a huge bundle of uh protons in one side same with billions of protons like a b swarms and they come and they Collide and sometimes they are more than one collision at the same time and so it gets really difficult to disentangle all that it's a huge machine with 4 000 kilometers of cables here we're looking at the care of emitter from a atlas a calorimeter is a a layer that is there to measure the energy that each fragment had so we have four thousand kilometers of cables and four thousand kilometers of tubing with cooling fluids and various gases the whole detector is uh weighs 7 000 tons that's the weight of the Eiffel Tower but Eiffel Tower is just rusty Steel whereas here like my my friend Monica Dunford said in the movie A Particle Fever it's like a Swiss watch on steroids you know it's everything is done of ultra precise little detectors all built by hand assembled by hand and for the atlas detector we built it under in the cavern like we build a ship in a bottle then cannot come out of the lair and it's six stories high so it's a here is what we call the muon wheel so it's a detector just to detect new ones and show their role later and it's a hell of a time to make a good selfie there the big question uh is how we turned on the detectors and all that and it all worked it was so amazing the accelerator the four Detectors of course we had done some testing all that but the one day when we turned everything and it worked it was amazing it took about 20 years to build all that concept and all that so how did we manage make it all work it's a mystery but let's go back to our Higgs boson how did we find the heat exposure so we excited the canvas of the universe produced that very unstable particle which broke apart but I was telling you earlier that those particles were fundamental particles the the leptons and the the quarks and the bosons at the bottom those are fundamental particles so then they don't contain other particles inside it's not a composite object like this it's like when I make when a particles Decay it's like when I make change for coins if I put the two euro coins in a change machine and then I will receive two one Euro cons coins or they can also break into 450 something 50 cents it's not that the 4 50 50 cents were hidden inside the two Euro coin it's just that we exchanged the value of two-year-old for two Euros in the form of four 50 cents and so that's what happened with the Higgs boson the Higgs boson will disappear but it's equivalent in mass and energy will reappear in the form of 2z boson which bosons which are lighter so the bosons will go fast and then these two in turn will also break apart and sometimes they can produce form new ones so in the end we find four muons but it could happen too that we had produced those four muons simply because we had produced two Zed boson which is often much more often than the uh Higgs boson producing a Higgs boson took a lot of energy but two Zed boson was relatively easy so when I find an uh an event like this that I took with my detector which is like a camera and when I have done all the analysis I can tell I have four new ones coming out real fast the four lines that you see in red that went through our Giant muon Wheel if I ask you is that does that contain an event with uh Higgs boson or two Zed boson that were created in the first place Nobody Knows the only way to tell the difference is by looking at um statistics if they were only if the Higgs boson didn't exist and we were finding events with four muons we can count on the vertical axis and putting the number of events that I'm finding and on the horizontal axis it's the combined mass and energy of the four muons and you can see the theorist would tell us are you should get a distribution that looks about like this okay so this number but if in addition to those Z to Z boson if in addition to that there is a Higgs boson then we will see extra events appearing at a at the value that the he exposure Mass has we didn't know the mass of the Higgs boson to start with okay fine so we were shooting a lot of protons and exciting ourselves and the fabric of the universe and then you know we started collecting events so each black that is an event that we collect in our detector and you see the number are growing with time and at the beginning it's it pretty much reproduces just the red curve but we see now that here in the uh sorry in this area we start seeing an excess of events and these correspond to what theories we're predicting would happen if Higgs boson had a mass of 125 gev so that's how we could tell on the 4th of July 2012 that we had found the Higgs boson we started collecting data in 2011 then 2012 we were at a higher energy and for ATV so just to see it again and so it takes time and you see a little excess that shows up here and that's how we could tell we had found one because they were more events than what was just predicted by random ZZ events but still when we look at an event like this I cannot tell you this is a Higgs boson decaying into four muons I don't know it's just in the statistics that can tell the difference so the lifetime of the Higgs boson is 10 to the minus 25 seconds so you have to get up pretty early to find something to do with that so we will probably never find any practical application for the Higgs bosons but in around 18 25 whatever when Michael Faraday was working here on electromagnetic waves the equivalent of the Minister of Finance came to visit him and he was asking him what are you going to do with that Faraday said no clue but I'm sure you'll find a way to tax us on this and Michael Faraday was done right and we we pay for that now so why do we bother to find those particles we bother because when we do that we develop new technologies new techniques for example the largest benefit to humanity from CERN is not the hex boson ex boson is as useless as can be but is the World Wide Web we were 13 000 physicists from 118 countries working at CERN so of course we needed ways to communicate with each other and that's how this need brought into play that we put efforts to communicate with each other and that was the world wide web and for telecommunications that's the same thing all the work that Michael Faraday did on electromagnetic waves that we put that to use uh the work that physicists did on electrons now we have all these electronic devices that end up in the garbage and so yeah so computers and electronic devices thanks to the creativity of countless engineers and technicians we have that put into use Medical Imaging is probably the most direct byproduct of the research that we do at CERN because that's the kind of techniques we use to detect particles and so X-rays and computer tomography with uh with uh MRI magnetic resonance imaging all those techniques come from particle physics there is a new one that just got invented and it was published at CERN a month ago and it's called spectroscopic x-ray Imaging so instead of operating X-rays at just one frequency now they use many frequencies so a large spectrum of X-ray values and they can do things in color as if before it was just black and white so they can now it's cheaper than computed tomography and magnetic resonance imaging it goes it gives better resolution lower doses of radiation to patient and it could make a city and a MRI superfluous these are two pictures with conventional x-ray or computer tomography done on a small Mouse and to the right with the spectroscopic City and you see you can see the biochemical content and a better contrast so the images are much better than we have before so we'll have better diet Medical Diagnostic with that another technique that was developed here at the at the Royal Institution by Bragg was this technique we called this um particles like made of headphones like protons neutrons no mostly protons carbon with an electric charge as well will deposit most of them and all their energy or most of their energy at a specific depth so if you have a tumerous cancer something in your liver which is uh I don't know three four inches inside your body that this tumor is if you were to use a x-rays if we look at that here x-rays are here the black curve you see that the x-rays will deposit energy all along the way see that our tumor is here and so it will damage healthy tissues at the same time as zapping the tumerous cancer cells but with protons they will deposit all their energy exactly at where we tell them to go we can just tune where we want that so it's a very powerful technique to fight cancer and it's called hadron therapy and this is a center that a certain contributed to building in Italy That's What patients see when they go in for treatment and this is what is behind the door the wall that nobody sees and you can see the touch of uh CERN there with this particle accelerator just about all the best things we have today come from fundamental research okay and I'm going to close this discussion the next 10 minutes or so on have we already found everything so especially for the young people here that's a big question because you know if we've already done all the job why would you bother to study in science well please hang on in the con the content of the universe we now have a good idea what is inside the universe everything that we know as matter visible matter made of quarks and emitting light when it's heated up like a stars and galaxies we can see them all that is made and we call it visible matter because it emits light when it's heated up and we see it so this visible matter only accounts for five percent of the content of the universe so 100 200 years of work by particle physicists and we have only understood five percent of what is there in the universe we now know that there is dark matter a type of matter which is five times more prevalent than a regular matter visible matter it's matter that reacts to gravitational waves it has mass so we can see it with the gravitational lenses we can fill the effects the presence of this mass that this matter but we don't see it it doesn't emit light so we call it dark matter and not only that and that's 27 of the content of the universe we have no clue what it is no clue we just know it's there and we have lots of uh ways to know that it's there I can talk about that later if some people is are interested and finally 68 it's embarrassing 68 of the content of the universe is in the form of uh energy that we know nothing about and it's called Dark Energy but we know it's there because about 20 years ago some uh astrophysicists realized that you know that since the Big Bang the universe is in expansion but in fact they realize that not only is that in expansion but this expansion grows is always accelerating so the expansion of the universe is going accelerating you know that if you want to accelerate in your curve or on your bicycle you need to give energy where does this energy come from no clue but you you can imagine that we need a lot of energy to accelerate the expansion of the universe and that's why the dark energy accounts for so much so all the particles that I described before are only describing the tip of the the visible part of the iceberg and the rest is completely unknown so we know five percent of the content of the universe and you all the young people who came tonight it will be your job to find what is this 95 percent that is missing so there are some good job opportunities ahead flowers in the standard model there are no particles that we know of that is suitable for the dark matter it doesn't predict anything that we could use appearance of antimatter every time we produce matter in the Laboratories we always produce as much antimatter at the same time but and so we know that right at the Big Bang just as much matter as antimatter was produced but it has completely disappeared from here many of you are saying yes they knew that maybe you have seen the talk that Tara Shears gave here a few years ago it's available on the website from a the ri and so it's a big mystery we don't know what happened there is a disparity in the the masses of the fundamental particles what I was telling you before three generations of particles would completely uh different masses makes no sense the worst construction set you find on the market and it does not include gravitation so the best theories are hard at work like here John Ellis very famous physicist from certain theorists who works also here at King's College and his assistant and then they're just now trying to figure out what what could it be what what theory would be better or could be what could we build on top of the standard model to go a bit further and answer those unanswered questions and so he has these Paths of papers in his office so when I was there taking the picture and I said but Joan have you read those papers said I read your paper I was impressed okay and then I said do you know where it is you said don't push your luck anyway so theories are really stuck they come up with all sorts of theories but we don't know if any of those theories are good it's only when we will find new particles that we will be able to tell which one of those uh theories was valid now we have no clue that theories are producing tons of new ideas but no one knows which one is true every time we have a small anomaly everybody gets excited for example a few years ago in the 2000 at December 2016 just before the end of the year Atlas showed some preliminary results and we were seeing already a little excess of events now a bit like what I was showing for how we found the Higgs Bose and you see here there's a little more events in the number of events we found and the distribution in energy for when we were looking at two photons coming out of the detector and so nobody would have been too excited especially at the end of the year when everybody wants to go on vacation but then CMS also found the same thing then it was the end of the year and we always stopped the excavator for three or four months to for the maintenance so we had to wait a few months before we accumulated enough data and to check if this was real or not but unfortunately uh it it all disappeared it turned out to be a pile of Ash so there was nothing there but in the meantime the theories got so excited 554 papers were written to explain what could produce such things and in fact they came up with the weirdest things you know like a composite Higgs Motel Grand unification therapy D3 brain liked stringy states there are wimzillas they are hubertron there are all sorts of weird things that are being proposed but until we find an experimental evidence we don't know what is there the theories are really really creative trying to imagine what could work because there are tons of constraints that they have to respect so it's unbelievable that they still manage to do 554 I'm sure that at least a few hundred were really good right now we have a few a handful of events again that are intriguing for example the CMS experiment found events where there are jets of particle Jets when when you have quarks coming out quarks never come alone they always produce more quarks and we end up with the uh a jet uh a bunch of headphones coming out all finely culminated together and we call that a jet so they found some events with the two Jets coming in One Direction and two other Jets and those each each pair of two Jets weighs about 1.9 tev we measure everything the mass of a particle measure to always in energy because mass and energy are equivalent so those are Terra electron volts it's just a measure a unit of energy and so both uh digits have about the same mass and the other one would be ATV so it's huge and they have two events like that they have found and it would be possible that a new type of boson a white boson would Decay into two x bosons and each of them would decay in turn in two Jets so that would be something new and extremely exciting but it could also happen that it comes from two Zed bosons producing two Jets each and we've seen billions of those you know things that were winning Nobel prizes 10 15 20 years ago are now just background noise that we we're irritated with that so we don't know what will happen in in physics everything in particle physics everything relies on uh statistics and so uh we always measure when we measure something we also measure also the error margin and we set our error margin we call that one standard deviation when we know that there are 68 chances that the real value will be plus or minus one standard deviation standard deviation we represent by Sigma and if we take two standard deviations twice the error margin on each side then we know that the real value of what we have measured there are 95 percent chance that it's within that range so this is the value that I have measured the mean value view we see here and within two standard deviation there are 95 percent chance that the real value is there so in physics we don't get excited until we have a five Sigma discrepancy five Sigma corresponds to 99.9999994 confidence level we don't want to be looking like fools you know saying that we found something and it turned out to be nothing so the two events that are from CMS that I was showing earlier if we were just to look at the distribution of uh two uh two uh four Jets coming from two Zeds they would roughly be distributed like this so here is the average mass of each double pair of jets and here for the four jet mass in total and that would be the kind of distribution and the extra events that are found correspond to what we will find within a one Sigma value so 68 chance that it could come from a white boson going to X to I exposes so the chances are weak but we don't have much to go on these days so when there are little things like that we get happy the biggest anomaly that we have at this point is with when we measure the W boson Mass very recently about a year ago uh the CDF experiment which was an experiment experiment going on at fermilab near Chicago they measured this Mass with the highest ever precision and it was about the measured the mass they measured was 80 433 Mev plus or minus nine so it's really really precise but the value that theories can predict from the standard model equation they're all sort of constraints with all the mass of the Higgs and the other particles and they say that it should be 80 357 plus or minus six it doesn't match there are about seven standard deviation apart exciting but it will take years before another experiment CDF is finished so they've done it it took 10 years to do their calculation precisely so they're done and Atlas at the Large Hadron the collider could have only used three percent of their data and they have an error margin of 19 which is too big to be compared to a CDF but to do the uh the measurement again will take a huge amount of efforts because there are neutrinos involved and neutrinos are very sneaky that's why the little character is with the mask like this because they can go through the air there are billions of neutrinos good that went through this room during the time that I spoke and it didn't even stop to say hello so you know we they go through our detectors and we don't see them so it's it makes the measurements difficult for the mass of the W and plus there is this pile of phenomenon that many collisions happen at the same time so it's it's difficult to disentangle all this and it has to be so precise that it will take several years before we have new measurements on that the so the CMS collaboration at CERN plans to use 12 of their data where there is a little less pile up we say not so many events on top of each other but it's an extremely difficult measurement so it will take a while before we get there the good news is that the LHC is now running and it's running at a slightly higher energy than before and with higher Luminosity which means that it will have more data so what are the benefits of that is that if you're working at higher energy it's like I'm telling you uh there is a beautiful book hidden somewhere in a library ancient book with all sort of wonderful things and I'm giving you finally a taller ladder so you can reach the last rows of books at the last shelves so when we were using 13 tev the energy of the accelerator now we have a bit more so we can reach new particles that we were not uh that were not accessible before and higher Luminosity means that they will have more data so we're not limited to a small section of the library but to a large one so maybe we have a chance to find something new but now it's really painstaking work of accumulating billions and billions and billions of events and in the next 10 years or so we should manage that and maybe we'll come up with something so here are my take-home messages for you before uh to slowly ending this lecture so if you can't remember that all matter is made of a handful of Elementary particles and those particles are the up down quarks and the electron the but this visible matter only accounts for five percent of the content of the universe so what we have studied only explains five percent of what is out there they will probably never be any application for the Higgs boson but fundamental research drives Economic Development and has completely changed how we live with the World Wide Web it's a sure statement to say it has changed our lives electricity as well you know it's thank you Michael Faraday and any new particle or new phenomenon that we find from now on will revolutionize and our understanding of the universe because then it will finally tell us ah what is this new theory that we need to add on to the standard model so before you go I just want to tell you that I have this book who cares about particle physics and I swear this is the best popular science book on uh particle physics that I have ever written and so I highly recommend to you all and of course tonight you know I had an hour to explain to you all this and with a bad accent on top of it this is all written in absolutely proper Oxford English so it would be much easier and so you will learn everything about the standard model how the detectors and accelerator Works how we work at CERN because nobody gives orders we all go freely and do what we want and it works and because you you you ask people to give their best and then and then uh also about uh diversity and science or the lack thereof and also the story of milieva marichenstein I've mentioned a few times the equation E equals m c Square who wrote this equation everything that Albert did in the in the beginning of his career was done in collaboration with his wife milega marichenstein but this part of the story is unfortunately not known but there is a chapter in my book on this so I'll be offering the book at a reduced price from Oxford University press tonight and a special prize as well for the students so if you're interested I'll be there and before I go I tell you this musical about Tina Tina Turner and all that Alicia Paul Moses did such a performance and such a finale and all that and then she just you have to see it it's amazing you know but I need you to help me no we should Rock The Royal Institution tonight so please join me stand up all of you please and let's try to give a bit of spice in that lecture you know and that's one way to get a standing ovation but what I was going to tell you from Tina was hello what's Higgs what's Higgs got to do got to do with it but now I hope you can answer that question thanks a lot and then I will take your questions [Applause]

Channel: The Royal Institution

Views: 79,071

Keywords: Ri, Royal Institution, royal institute, large hadron collider, particle physics, pauline gagnon, particle physics explained, large hadron collider explained, large hadron collider turned on, pauline gagnon physicist

Id: Gg35wa82pLQ

Length: 66min 2sec (3962 seconds)

Published: Fri Dec 23 2022