Demystifying the Higgs Boson with Leonard Susskind

[Music] Stanford University the goal tonight is not to tell you why the higs B arm is the best

thing since flush toilets you've read all of that anybody who here has probably read all of the um the hype the

uh excited breathless uh superlatives that uh that have the newspapers and so forth things B arm is going to explain

the origin of the universe and this and that I'm not going to do that first of all before I say it the the excitement and the enthusiasm is

Justified it's not that it's not justified it is Justified uh the history is fantastic it's an unbelievable event and so forth

but that's not what my thing is it's not what I do well what I do well is explain how things work my goal tonight is going

to show it be to show you as so far as I can in one hour which is tough which is hard and it may not work but as well as

I can to explain to you the nuts and bolts of what higs physics is about one of my closest friends

incidentally is is named franois laare and Fran glair would be appalled if you knew that I was standing here talking about the kids effect since Fran onir

was the discoverer of it so from time to time they may call it the brout onir higs effect but I also May slip and slide and just call it the effect

because I tend to get like everybody else uh all right so how it works first of all

there's a lot of moving Parts a lot of pieces that I would have to that I would have to explain to you first uh to really do it right and I'm

going to try to explain those pieces in little in little modules should we say it's a highly quantum mechanical effect it cannot really be understood

without quantum mechanics and so I would begin with a course in quantum mechanics and let's say the course in quantum mechanics

consists of just one thing things are quantized quantized means that they come in discrete integer

quantities the most famous example of this is angular momentum angular momentum the rotational Properties or

the rotational momentum of an object are quantized which means they come come in discrete steps and the discrete steps

are one plunk unit one unit of plants constant we'll take that as all we really need to know about for the most part about quantum mechanics

tonight the next concept which is an easier one at least I think it's an easier one it's a classical concept is the idea of a field a field is just a condition in space it could be the

electric field it could be the magnetic field it could be a gravitational field whatever you think of is being present in space which

characterizes the conf the behavior of space at that instant and in that place in uh in space in time so field space

can be filled with Fields now ordinarily you imagine in empty space empty space is the thing we

call a vacuum from a quantum mechanics point of view the vacuum is just a state of lowest energy nothing there no

energy other than what quantum mechanics requires there to be there and so you ordinarily think that

the fields that could inhabit space are zero in empty space the electric field the magnetic field and so forth but

there's no important requirement of physics that says that that should be the case let's imagine a world filled with electric

field how could that electric field get there well it might be there because there are capacitor plates infinitely far away so far away we can't tell they're there there we would have a world in

which there was an electric field it would just be there empty space would have an electric field now when you think about Fields oh we're beginning a little bit too early

okay you're going to wait all right so what I was saying to the audience two things the first was that quantum mechanics were going to

summarize by one simple statement that things are quantized in quantum mechanics quantized means they come in discrete bits the most important example

is angular momentum not the most important necessarily the most important example but the most important um example for me tonight will be angular

momentum and angular momentum is has to do with rotating objects and so forth angular momentum in quantum mechanics unlike classical mechanics comes in

discrete units the unit is Plank's constant you can't have a tenth of a unit of angular momentum you can only

have angular momentum 0 1 2 3 -1 -2 -3 you can also have half integers but we're not going to worry about that tonight but no you can't have angular

momentum Pi only discrete integers that's the first uh fact that I want you to remember the other fact from quantum mechanics that we'll have to remember

also is the uncertainty principle that we come to it now the other thing we spoke about was Fields fields are things that can fill space electric field

magnetic field gravitational field other kinds of fields that exist in physics they are functions of space they can vary from place to

place and they affect for example the way things move an example would be an electric field affecting the way a Charged particle moves now the other thing I said was you

can imagine a world in which for all practical purposes empty space is filled with a

field an example would be if I went out to Alpha centuri at that end and excuse me I don't know what's out

there excuse me yeah whatever's out there and place some capacitor plates big capacitor plate out there big

one out there make an electric field in between they're so far apart that we can't see them we would say that the world is a world that exists with a magnetic

field and we would say that charged particles move in Peculiar ways but that was just a fact of nature

um generally speaking Fields cost energy space without an electric field has zero energy with an electric field

it has energy and if we were to PL not the energy of a field a typical field could be electric could be a magnetic could be something

else generally we imagine that the field energy as a function of the field horizontally imagine the value of a

field vertically its energy zero field right here and we imagine exciting the field causing it to

vibrate causing it to vibrate by giving it a push some region of space and nearby the field will vibrate those

vibrations are quanta of the field they are particles they are particles the quanta of vibration of a field of

particles now you might have a situation where there is more than one field relevant let's call it fi and F prime or whatever you want to call it doesn't

matter then instead of plotting the field as one dimension we might plot it as two-dimensional now this is not space this is the value of

some collection of fields and then the energy would depend on both Fields here's an example an energy function which looks like that which simply says that no

matter how you displace the field it costs energy now imagine that

this upside down paraboloid or whatever it is was nice and symmetric nice and rotationally symmetric in the field

space exactly like the top of my hat here which as you can see is symmetric and so the field as a oh yes

where's my little that's that's it right the field as a function of position would most likely if the energy is as

low as possible just sit at the bottom of the potential energy of the field just to lower the energy as much as possible so we might think of the field

at every point in space a little ball which can be made to oscillate Back in Forth and do things and those are just oscillations of the behavior of physics in a local region of space as I said

they often correspond the quantum particles those oscillations but for the moment they're just oscillations now one of the things we could do if we had a field whose values

were like the position in the Hat here would be to start it out displaced from the origin let's say up to here and then start it

moving in a circle just in the same way you could take this ball and if it was if the Hat was really nice and smooth and symmetric give it a push and it would go around in

a in a circle that circular motion of the field is very very similar in a way to angular momentum it's not angular momentum in

space but it's a kind of angular momentum that exists in the field space that angular momentum like all angular momenta are quantized come in

integer multiples of Plank's constant what do they correspond to they correspond to something else that is also quantized in nature the value for

example of el charge so in modern physics the way one thinks about the electric charge in a region is that in some region of space a

particle a Charged particle a Charged particle is viewed as an excitation of the field in which the field is made to spin

around in the internal space of the field not in real space but in the internal space of the field that's one way in fact it's the main way that we think about without

charge as a kind of rotation in an internal space okay now what I want you to do is

Imagine taking the hat and turning it over imagine that the potential energy was not turn it over this way excuse me

this way is the way that the potential energy is minimum at the crown of the hat but if the potential energy really looked like that so that it was Max imum at the top of the Hat then the top of

the hat would not be a position of equilibrium it would be a position of unstable equilibrium it would look like this turning over the Hat the crown of the Hat

now this is the way you know the real hat looks like this and it doesn't uh okay let's just let's make the um

how's that that look like a hat yeah looks like a hat what kind of hat does it look like to you looks like a Soma right looks like a Mexican hat physicists call this kind of

potential energy function a Mexican hat believe it or not it's called a Mexican hat it turns back up the top is

unstable if a PO a ball was put at the top it would roll down and where would it go it would go to the brim of the

hat if for some reason the potential energy of a field was like this then the state of lowest energy would not be at

zero field it would be out here now that's kind of interesting it would be a vacuum a world which had a field just like having an electric field

except it's not an electric field in which the value of the field at every point in space was not zero you might notice it how would you notice it well you might notice it because it might

affect other things and indeed it does affect other things as we will see but there's now something interesting you can do that you couldn't

do here over here if you wanted to set this thing into rotation you would have to displace the field a little bit because it doesn't mean anything to rotate right at the center if you wanted

to set up a rotation you displace the field and then give it a flip so making a Charged particle costs some energy

here you can imagine setting this thing into rotation with just a little flick that costs no energy it costs no energy because you don't have to ride up the

side of the Hat other words you could have a motion in which I'm not got it you got it you got it you understand right you got to have a

motion in which that field slowly wound around the top of the potential in fact it could do it everywhere simultaneously not in real space but in this field

space that would correspond again to a charge if rotation in this internal space corresponds to some kind of charge but now the whole world if the whole

field was moving like that would have a little bit of charge in it a charge density charge filling space and essentially no cost of

energy that phenomenon is called a condensate it's called spontaneous symmetry braking but it's also called a

condensate a condensate in space of charge now you might say okay look I want to find the lowest energy that the vacuum can have that empty space can

have my best bet is to make the field not move with time just like a ball at the bottom of the sombrero hat here there's also kinetic energy of motion

causing the field to move around in a circle like that would cost some energy so you would say the true lowest energy state of the world should be with a

field either here or here or here it could be anywhere along the the rim of the hat but it should be standing still

right the problem with no angular momentum or no charge empty space should not have charge the problem with that is the uncertainty principle let me remind you what the

uncertainty principle says it says that if you have a object and you're interested in its

position X in ordinary space now and its momentum P velocity if you like the uncertainty principle says that the

uncertainty in its position times the uncertainty in the momentum is greater than or equal to what plunks

constant you can't have something both standing still and having zero momentum if it's stand sorry you can't have

something standing still namely no momentum and also localize at a point Delta P * Delta X is greater than H bar

same thing here if you know where the field is on this Mexican hat if you know with great Precision then it follows from the uncertainty principle that it

must have a very large uncertainty in how fast it's moving around here Ah that's interesting now that would say that you can't have empty space with no

charge in it can't have empty space with no charge in it because if you lay the field down at this point you know where it is on the rim of the hat and if you

know where it is there's a necessary uncertainty in the charge the charge being like the angular momentum all right so where are we then if this were

the case for electric charge for ordinary electric charge we would say that the vacuum empty space Not only is filled with charges in a certain sense

but a totally uncertain amount of charge totally uncertain and this is a Quantum effect a totally un certain amount of charge there would be equal probability

let's take a little volume of space there would be equal probability that the charge was

zero or that the charge was one or minus one or two or minus two 3 minus three now this is truly odd this is not

something you should try to visualize because you can't visualize an uncertain amount of charge but nevertheless that is what a region of space would look like if you measured its charge it could

be anything from minus infinity to plus infinity okay now I want you to imagine that you have an extra charged

particle an extra charged particle and you throw it in you don't know initially what the charge is but what does that do it displaces the charge by one unit

let's suppose it was a positive charge you've displac the charge by one unit and so if it was zero to begin with it's now one if it was one to begin with it's

now two if it was two to begin with it's three if it was minus one it's 0o 1 - one min-2 and so forth but that's exactly the same as what we started with

we started with something which had an uncertain amount of charge equally likely for any value of charge and what did we end up with after

we threw the charge in exactly the same thing what if we pluck the charge out of this thing same thing so a condensate is a

funny configuration of space where with respect to whatever kind of charge we're talking about it's so uncertain that you wouldn't even realize it if you put an extra one in or

pulled one out now the real world is not like that with respect to electric charge we know if we have a charge in space so it's not

like that with respect to electric charge however there are materials that behave like this superconductors superconductors are exactly like

this so it's not unheard of it's not a totally new thing to have a condensate of charge where in a region the charge is completely uncertain

okay that was module number one if you like condensates or what is sometimes called the spontaneous breaking of symmetry module number two the standard

model now we come to particle physics and I'll give you a short course in particle physics first of all particles have mass and the mass can be

anywhere from zero we're talking about small particles now we're not talking about railroad engines or uh or Stars we're talking about small

particles we call them Elementary particles but there's also a maximum Mass they can have if they were bigger than that they would form a black hole if they were more massive than that if a

point particle was more massive than something it would form a black hole and it would be something different so up to some Maximum and that maximum is called

the plunk Mass it is not a very large Mass it's neither a very large mass nor a very small Mass it happens to be about

100,000th of a gram a small dust mode but that is the heaviest that a Char that a um that an elementary particle can be without turning into a black hole

and if you ask now where on this chart from zero this is called mlan up to the maximum where are the ordinary particles the electrons the

photons the um quarks they are way way down here the largest mass of a known

elementary particle is about 10-7 of the plunk Mass why are the particles so light well one answer is in order to detect massive particles you

have to have a lot of energy in order to have a lot of energy you need a big accelerator we've only made accelerators up to some uh size and so for all we know the rest of this is filled with

particles and that's probably true that's probably true but what is special about these particles well first of all let me name them and then I'll tell you what's special about them that makes

them Clump up at zero Mass let's name them the particles of the standard model they come in two varities it is not important that you know the difference well I'll give you a rough idea of what

the difference is they come in two varieties called firion and bosons the firmians are all the particles that make up matter in the

usual sense the electron which I'll just call E well the neutrino goes along with the electron that's a new the electron the neutrino quirks there's a variety of different

quirks incidentally there are several different kinds of electrons we call them electron mu on tow it doesn't matter but they're very electron likee and several kinds of

neutrinos the electrons have the electric charge the neutrinos don't and then there are quarks a variety of different kinds of quarks up quarks down quarks this kind of Quark that kind of

quark and those quarks several different kinds of quarks you know what the role of them are they make up the

proton and uh that's about it for um for Fons for bosons on the other hand and there first of all a photon gamma gamma

for a gamma ray Photon there's an object called the gluon G it's very much like a photon it's very much like a photon but

it doesn't have anything to do with atoms it has to do with nuclei and protons and neutrons it plays the same role in holding the nucleus or better

yet the proton together as the photon plays in creating electrical fields inside an atom so there's the gluon and then there are two others

called W bosons and Zebo for the most part we won't be interested in any of them except the photon here and there but mostly we'll

be interested in the Zebo Zone that's it that's the standard model that's all there is to it with one exception I've left something out it's a

thing you came to find out about tonight okay so will come to it if there was no Expos on then this would be it now what

is special about this set of particles what's special about them is for reasons that I'm going to come to reasons that I will come to all of these particles in

the standard model as I've laid it out here with nothing else in it would all have mass equal to zero they would be massless and explain why that is in a

little while we often hear that it's the role of the higs bosan to create mass for particles or to give the particles their

Mass that's the expression that I've heard over and over the higs gives particles why do why do the particles have to be given Mass why can't they have mass of their

own why do they have to be given Mass well as it turns out for reasons we'll explain this set of particles is exact the set of particles which would have no

Mass if this was all there was now in part that explains in part it explains why the particles why these particles

are so very light it's because they're massless they have no Mass well not quite we can't live with that because we know that particles really do have

mass next question I'm going to draw some figures over here what do these particles do what kind of processes that they are they involved in all right the

basic process of the standard model this is an over simplification but it's qualitatively right is that the firion there's a firon moving along and

I will describe a firon by a solid line solid because it's what makes up stuff solid line that's moving from one point in

SpaceTime to another point of space time what the standard model does is it causes the emission of bosons a electron moving along can emit

a photon electron moving along can emit a photon and that's connected with the electric

charge any electrically charged particle can emit a photon a photon that's the first thing that the standard model does now this of course is just Quantum

electrodynamics it does not have could be the electron it could be any electrically charged particle next The

Quirk let's see do we have room here yeah we'll just do it the Quark Quark let's just call it Q The Quirk can emit a

gluon precisely the same pattern The Quirk emits a gluon now the Quark can also emit a photon if it happens to be electrically charged and quarks are

electrically charged but electrons cannot emit gluons gluons are the things that bind quirks together to hold them together into protons and neutrons and then there's one more

important process for me tonight there are two more processes but I'll just write down one here and it is either an electron oh incidentally a

neutrino cannot emit a photon it has no electric charge it cannot emit a gluon it's not a quark

okay both electrons and neutrinos and quirks for that matter can emit the Zebo on where's the Zebo on here's the Zebo on right here and when

they do so the Zebo on being electrically neutral the electric charge of whatever is here doesn't change so this is another process that

the standard model describes now first of all why are the Bon's

massless well the photon's massless we know that it travels with a speed of light now could we make a theory in which the photon had some Mass yes we

could but the more important thing is that we can make a theory in which the photon doesn't have a mass why because the photon doesn't have a

mass using the same kind of theory the ZB Boon would not have a mass and the gluon would not have a mass everything would be

massless these would be the processes that could happen these would be the particles they would all be

massless okay now how do Fields how do Fields give particles mass or better yet more simply a simple example I'm going

to show you a simple example now the simple example is how a field can affect the mass of a particle we'll come back in a moment to how it can give something

which didn't have mass mass but let's take a more modest question how may Fields affect the mass or better yet how

might they make different masses for different particles so I'm going to show you an example this example is a little bit contrived but it's a real

example a water molecule water molecules have the basic property that they're little dumbbells they have a plus end and a minus end electrically

charge plus end and minus end uh they're actually not they're more like y's you know y with three ends but we can think of them as having a plus end dumbbells

and a minus end now the mass of a water molecule water molecules have mass the mass of a

water molecule doesn't depend on its orientation if we turned it over and made a water molecule with its minus end here and the plus end here it would have

exactly the same mass why it's the symmetry of space space is the same in every direction and so by symmetry we would say that the water

molecule standing up straight has exactly the same mass as the water molecule standing on its head let's not worry for tonight about whether it's lying on its side quantum mechanics tells us we don't have

to worry about anything but standing up straight and lying on its head all right so that's uh that's true about water molecules their mass is the same if they're standing up straight and think

of water molecules now as particles think of them just as particles we don't know what they are they're just little Elementary particles we can't see them and so we have two kinds of particles

the upstanding and a standing on his head particle with exactly the same mass now I thought I had a purple no purple I told them to put

purple I'll have to use orange where over here underneath the board you mean under here oh

good all right I have my color coding in my notes here and if I blow it I'll be terrible Okay so that looks Brown to

me it is brown okay let's create a region in which there's an electric field we're going to make a field it could be between two capacitor plates the capacitor plates could be far apart

it doesn't matter but let's put them the capacitor plates here and here and inside that region let's create an electric field the electric field in this case

pointing up that means it pushes plus charges up and minus charges down if I have my signs right and let's take one of these water

molecules and insert it in here once I insert the water molecule in here the energy of the upstanding water

molecule and the upside down water molecule are different which one has less energy the

one with the plus up has less energy and the one turn turned over has larger energy the water molecule itself is

electrically neutral it has no electric charge but it's a little dipole it has a pair of charges and which one has more

energy depends on the sign of the electric field okay so there we are we have two water molecules two types of water molecules two different particles we

could give them different names we could call it water and um uh scotch and the water molecule has one

one energy the scotch molecule has another uh energy and there they are well by e equal

mc² this also tells us that the two molecules have different mass now in practice this would be a tiny different Mass between them but they would have

different Mass so the same effect of this field which exerts itself on charged particles does something to neutral water molecules incidentally notice that it doesn't exert any net

force on the water molecule the water molecule moves smoothly through it with no Force no net force acting on it but there was a difference in the up uh in

the uh two configurations of the water molecule and so it's as if we had particles of two different Mass so this is just an example of how a field

creates mass in this case it increases one mass and decreases the other Mass incidentally if you read some of the literature and they'll tell you

about how the um Hig field gives a mass I've read any number of places that it's something like space being filled with molasses it is not like space being

filled with molasses the vacuum is not sticky and one of the things that molasses would do well the the idea is

that massive particles move slower than massless particles so the idea is that molasses slows them down but Fields

don't slow particles down if you give the particle a push in this direction it will just continue to move because there's no net force on it it'll just slide right through this

thing frictionlessly no uh no impedance no uh no friction no molasses there's not the other the other analogy I once heard is

um that it was like trying to push a snow plow through a heavy snow in the Arctic uh it's got nothing to do with it whatever that's a that's a that's a lazy

way to explain it and it's a wrong way to explain it okay so there we are but now let's think of this in a slightly different

way the electric field in here can also be pictured in terms of photons a field is another way of

talking about a collection a condensate of photons an electric field we can replace the electric field

by a condensate the same kind of condensate the same kind of condensate of photons Let's uh draw photons by just a little squiggly lines fill this up

with photons how does it know which way the electric field is pointing well photons have a polarization they could be up or they could be down so just imagine this thing being filled with

photons but not filled in the usual way but filled in a condensate what does a condensate mean a condensate means that if I pull one out it doesn't make any difference if I put an extra one in it

doesn't make any difference that's the meaning of the condensate so it's an indefinite number of photons that's what a field is indefinite and if you pull

one out nothing happens and now let's reintroduce the um the water molecule let's just draw the water molecule moving through here now I'm going to make the water molecule

red I've already blown my uh my color coding here's a water molecule moving through here and what is it going to do it has charged particles inside it the

charged particles can Emit and absorb photons they Emit and absorb photons we've made the photons green now so it emits photons but when it emits a photon

putting an extra Photon in doesn't matter and so we usually draw that by just putting a cross at the end a cross simply means that throwing an extra

Photon in doesn't affect anything photon is emitted and just is absorbed or is

just um disappears into the condensate as this object the dumbbell moves through the electric field it's

constantly emitting and absorbing these photons which get lost in the condensate that is another way of

talking about how the field affects the particle and depending on whether the photons are polarized up or down this effect of constantly being

absorbing and emitting photons will have the effect of Shifting the energy of the two configurations of the uh of the dumbell that's simply an example of how

a field can affect the mass of a particle and how it can be thought of in terms of particles and condensates that's what I want you to

keep in mind that picture okay now come to Elementary particles not dumbbells not

molecules first question is there any reason why a particle or an object just can't have a mass does it need an excuse

to have a mass uh does it need anything called the higs phenomena to have a mass well there are lots of things in nature that have mass and have nothing whatever to do with the higs phenomena let me give you an

example imagine you had a box and let's make that box at out of extremely light stuff the lightest stuff you can think of but it's a box with good reflecting

walls and fill it with lots of high energy radiation bouncing off the walls but never getting out it's made out of massless stuff the

photons are massless they have no Mass the Box we're imagining is made out of stuff which is exceedingly light doesn't have much mass but there's plenty of energy in

there lots and lots of energy well e equal mc² and so this box will behave exactly

as if it had a mass we didn't need anything to give Mass Just Energy that's all it took are there any particles which are like this which get Mass

having nothing to do with uh higs or anything else yes the proton the proton is a particle which is

made out of quarks quarks three quarks and a bunch of gluons G's a bunch of gluons a large number of

gluons quarks and gluons in the standard model are massless does that mean that the proton would be massless if the quarks and

gluons were massless not at all if the quarks and gluons were massless the effect on the proton would be about a 1%

or even less change in its mass not much at all where does its mass come from it comes from the kinetic energy of these

massless particles rattling around in a box the Box being created by the proton so Mass doesn't have to come from black

holes are another example black holes have mass it doesn't come from the higs phenomenon doesn't have anything to do with higs so what is it about

the models of the St the particles of the standard model which require us to introduce a new ingredient all right so I'm going to concentrate on the electron let's concentrate on the

electron we don't need all of this and what I need to tell you about is the direct theory of electrons but really we don't have to know very much about the direct Theory

all we have to know is that electrons have in and furthermore if an electron was moving very fast down the axis here let's say with close to the speed of

light we really accelerate that electron then there's two possibilities the spin of the electron can be right-handed like that think of my thumb as the direction

of motion of the electron it can be going that way like my right hand or it can be going that way like my left hand

oh I didn't realize I could do that now two kinds of electrons right-handed and left-handed okay now do right-handed

electrons always stay right-handed can they flip and become left-handed can the right-handed become a left-handed left-handed become a right-handed yeah

that's exactly what the direct Theory says but if it was moving with a speed of light it couldn't why not because if a thing is moving with a speed of light

time is infinitely slowed down and nothing can happen to the object it just moves along but nothing can happen internally to the object so if its mass

was Zero it couldn't flip but in the direct Theory this flipping back and forth between I I tend to do it this way but that's not right this way this way this way this way that

is intimately associated with the mass of the particle and in fact the mass of a direct particle is simply proportional

to the rate at which it flips from left to right that's the direct theory in a nutshell mass is the rate for the electron to flip back and forth from

left to right okay of course the faster it's going the slower it will flip but that's all right you take that into account so

mass is left to right to left to right and we could draw the motion of an electron in the following way here's the

electron moving down the axis at first it's right-handed so it's going this way and then it's left-handed it's going this way and then it's right

hand can you tell the difference maybe not but that's okay and in between it jumps from one to the other the probability or the rate at

which it jumps is a measure of the mass of the electron so it jumps back and forth and back and forth now I'm going to ask you to believe something really crazy do you

remember this zebon where's the zosan the zosan was Associated was emitted it could be emitted from electrons it could be

emitted from neutrinos but let's concentrate on electrons it is not the same as the photon and the thing which emits it is

not the same as the electric charge it is another kind of charge a completely separate kind of charge it's like charge

but it emits Zebo we need a name for it we don't have a name for it well we do have a name for it's a very awkward name it's called the weak hypercharge I don't

like that because it's the thing which emits the Zebo zons I call it zilch zilch zilch is like electric

charge but it's not electric charge when a particle which has zilch accelerates it emits a zebon it may also emit a photon if it

also happens to have electric charge now electrons both right-handed and left-handed have the same electric

charge okay but left-handed and right-handed electrons do not have the same Z in the standard model this is part of

the mathematics of the standard model the the left-handed and the right-handed electrons have different zilch the left-handed electron has zilch of plus

one and the right-handed electron has zero zilch I didn't make this up in fact my friend Steve Weinberg didn't make it

up if anybody made it up he's up there or down there I don't know where but uh and uh it is just the way it is it is the way the mathematics of the standard model

works that the left-handed and the right-handed particles have different zil and now we have a puzzle when the electron moves

along and it flips from left to right that means the zilch goes from plus one to zero but zilch is like electric charge it's

conserved how can the zilch go from zero to one it can't it can't and that's the reason that the electron in the standard model doesn't have a mass because the

left-handed and the right-handed have different value of a conserved quantity and so left can't go to right period no Mass okay how do we get around

this we get around this by introducing a new ingredient and the new ingredient is called the zigs bosan it's not the higs bosan not yet we

haven't gotten to the higsbo on yet we've gotten to the zigs boson the zigs Bon is one new

ingredient it is closely connected with this Mexican Hat type configuration here it's a kind of

particle but it forms a condensate you can't tell how many are there you can put one in you can take one out and so forth without changing

the vacuum so we have one more ingredient it's a condensate that space is filled

with and the nature of the condensate is that doesn't have electric charge it has zilch and it's a condensate meaning that if you put a zilch in nothing happens if

you take one out nothing happens and let's ask now what that

means the left-handed electron coming in has a zilch of one let's call it a z of

one the right-handed has Z equal Z back to the left-handed Z equal 1 is that possible

only if you emit something at this point which carries off that Z equals 1 a

zigs the zigs Bon gets emitted it carries a z = 1 both what happens to it where does it

go it goes into the condensate it gets lost in the condensate you put a you put one in and it just gets absorbed into the

condensate and so the electron goes on its merry way the condensate absorbs the zilch and it goes from one to zero but then it can borrow a particle back from

the condensate borrow one back it doesn't even have to borrow it if you pull one out nothing changes again and so it goes on its merry way

from left-handed to right-handed from left-handed to right-handed every time it switches it emits a particle carrying this zil quantum number which then just

gets absorbed into the condensate that's the mechanism by which a field and in this case it's a field

which forms a condensate by itself it doesn't require capacitor plates it just requires the energy to be such that the field naturally gets

shifted and that's the mechanism by which electrons quirks and the various partners of those particles the me

particle the um too lepton all those ordinary ordinary and extraordinary particles the Fons get their Mass by this phenomenon

here phenomenon doesn't really have a name it's called the spontaneous breaking of chyro symmetry but uh it does have a name but this is what it is

okay what about the zebon I told you before the zebon is like a photon photons are massless how does a zebon get a mass so I'll just show you

something very similar happens to the zeban let's remind ourselves what a zosan can do it can take any particle which has a zilch and in particular this

green zigs particle it can take the zigs particle and the zigs particle can emit a Zebo

on it has charge not real charge but zilch and zilch emits Zeos all right so now let's ask what that means that means that a Zebo on

moving along can do something a little bit similar to this it can

absorb some zilch out of the condensate condensate but now it has zil originally it was just a Zebo on zebon don't have

zilch it absorbs some zilch and it becomes a zigs Zebo on becomes a zigs but then it can emit the zigs which gets

lost in the condensate again and the Zebo on just moves on its merry way constantly going back and forth from being

a Zebo on to being one of these imaginary not imaginary uh zigs particles that's the nature

of the way particles get Mass from Fields this phenomenon of the zosan getting a mass is called the brout

angare higs phenomenon this is the one that's called the higs phenomenon the zebon getting a mass now this could have

happened to the photon had there been a condensate of ordinary charged particles the photon would have become massive we would all be dead if that were the case

massive photons would not be healthy for us and so we are very lucky that uh that this phenomenon here did not apply to ordinary electric

charge will we ever discover the zigs particle sure we discovered it long

ago it's just part of the zosan zosan was discovered I mean was postulated 1967 but or even before that by many

people but it was discovered I don't even remember around 1980 I forgot when the uh when the experiment uh slack first discovered the existence

experimentally but when it was discovered that there was a Zebo on that it had a mass and that when its properties were studied the properties were not only consistent but required

that it was a thing which went back and forth and back and forth and back back and forth between pure zebon and the zigs particle so they've existed we're not in doubt about them

and we never were at least not for many years so far I have not mentioned the higs boson so what is the higs

boson well the higs boson has to do with this condensate it has to do with this condensate but it's a different kind of

exit ation than sliding around the uh the edge of the sombrero here does not have to move it's not something which has to do

with sliding around here it has to do I'll tell you two different ways to think about it you have a condensate and you can imagine the condensate has a

density a density of these uh fictitious particles in the condensate imagine something which changes the density of them kind of like a sound wave a

compression wave of some kind which squeezes them closer and further and closer apart makes it more and more less dense that kind of vibration is what a

higs higsbo on is another way to think about it is that it doesn't have to do with sliding around the uh periphery of the

sombrero it's it go to a place in space and start the field also ating this way in and

out this way the further away it is the stronger the condensate the closer to the center the weaker the condensate so when it soses back and forth It's Kind

of a compressional wave in the condensate that mode that phenomena that oscillation is

what is called a higs boson the Boon is like the sound wave propagating through the uh through the condensate the reason it is been so

important is because it was the one element that had not yet been discovered as I said the zigs was discovered long ago the Z and the W the

electrons and all the others were discovered long ago and so the next question which I'll try to answer in a couple of in five minutes is why it was

so hard hard to discover the higs what we discovered about it and very very quickly what the future

might or might not bring try to do this in a couple of minutes okay so what kind of thing does the higs BOS on itself do now we're talking about the

higs BOS on not the zigs BOS on not the zos on the higs itself the one the one that's been so elusive all these years it's called

H and what it can do with some probability is for example create we read this from left to right higs bosz

on moving along in time time is now to the left can create an electron and a

positron it can create a pair of quirks it can also create other things a me particle or a top Quark or a bottom

Quark all of the different quarks electrons also neutrinos all the various Fons can be created in pairs

when a higs boson decays you say if it's like a sound wave why does it decay well believe me sound waves Decay if they didn't Decay you'd continue to hear my voice ring forever and ever wouldn't you

so sound waves do Decay and it is possible to think of sound waves as decaying by creating particles so the higs bosan decays it

decays quickly if it exists if it really exists it decays quickly either into an electron positron or a pair of quarks or maybe some other of the Fons that exist

in nature you can read this diagram in two different ways oh incidentally the probability that the higs decays like

this is proportional to the mass of the particle that it decays into the the heavier the mass the more

strongly that particle is coupled to the higs boson so heavy particles are favored and light particles are not favored now you can read this diagram in

either direction you can say the higs boson decays but you can also say an electron and a positron confused together to make a higs

boson well if we want to make higs bosons and see them in the laboratory we want to read the diagram from right to left and we want to say this is a process whereby a pair of electrons can

come together and make a higs BOS on we've been colliding electrons and positrons for a long long time almost as long as I've been a

physicist not quite we've been uh colliding electrons and positrons together and nobody was ever able to discover the higs now one reason in the early days is it turns out that the higs

is a fairly heavy particle I will tell you what its masses but it's a fairly heavy particle and unless you have enough energy you don't have enough energy to make the higs BOS on but

there's a more important reason in fact slack in the later days of Slack's life had plenty of energy to make the higs the problem was the weakness of the

coupling the smallness of the mass of the electron translated into a very weak improbable

cross-section too small in effect too unlikely to make the higs and so when you Collide electrons together at high energy electrons are just not favorable they're too light and because they're

light they tend to not make higs with any appreciable probability well how about quirks we can Collide quirks together

the usual quarks that make up the proton and neutron are also very light and because they are light also unlikely to ever make a higs BOS on well you you I'm

sure they were made in slack but never in appreciable numbers that it was possible to uh toh detect them so that was the main difficulty the lightness of

these particles was a thing that essentially prohibited us from making hig's in abundance at slack or in other

Laboratories where collisions took place what is the most favorable particle most likely

particle for the higs to decay in the heaviest the heaviest of the Fons and the heaviest of the firion is called the

top Quark the top Quark is hundreds and hundreds thousands of times heavier than the electron many thousand many many times heav many thousands of times heavier than the

electron and the higs preferentially will Decay into top quirks so we'll just call those the

quirks they are quirks but they're very heavy 170 times the mass of a proton basically which is heavy top and

anti-top top quirks and anti- quirks so you say well look now it's easy to make the higs bows on you just oh actually in fact not possible for the

higs to Decay the two top quirks because the two top quarks are too heavy but if you read it the other way and you take a pair of top quirks and Collide them together you can make a higs so it's

easy we just go in the laboratory take a pair of top quirks Collide them together and make a higs well the problem is that it's not so easy to find top quirks in

nature why not not they Decay very rapidly to the other quirks they're not sitting around you can't put them into the accelerator and accelerate them they

disappear in a tiny fraction of a second there are no top quirks sitting around uh not even buried inside protons and so

forth not even buried inside other kinds of particles there are no top quarks around so we have to make the top Quirk somehow in the Collision how do you make

a top quk all right so here's a way to make a top quk a gluon can come along this is a gluon now and remember what gluons do they

couple to quirks one possibility is that the gluon can make a top quark and an anti-top Quark well there's plenty of gluons

around as we'll see in a moment so why don't we just take a glue on and make a top quk and an anti-top Quark out of it the reason is because gluons are very light they're almost

they're almost massless they don't weigh very much top quirks are very heavy there's simply not enough energy in the gluon to create a pair of top quarks so

what we have to do is we have to take a pair of gluons now here's a process that you can imagine take a pair of gluons with a lot of energy moving toward each

other with a huge speed plenty of energy let one of them make a pair of top quarks for a short period of time and then let the other one come and be

absorbed by one of the top quarks there we have it a pair of top quarks created by a pair of gluons a pair of high energy gluons smashed

together and make a pair of top quirks once we've created those pair of top quarks the top quarks can come

together and make our higs bow on this is the way we usually draw this is to just draw gluon gluon and then a

triangle higs these are top quirks going around the loop here that's the most efficient process for making um for

making higs bosons but where do you get gluons from gluons aren't floating around well yes they are the proton is

filled with gluons the proton mass of the proton is maybe 50% and energy from gluons or something like

that it's filled with gluons and quirks you take two protons and you Collide them together and the gluons inside the protons can Collide during

the collision and do this that was what was detected at LHC LHC is a proton proton collider

it collides protons together and when protons a very indirect way to prot protons collide together a gluon from each one of them scatter Collide create a pair of

top quarks and then the top quarks then have plenty of come together and create the Hig BOS on that's the process that was

discovered at the LHC and it took a long time to get there it was a hard thing to do it was a very very hard thing to do but now it's done we know the mass of

the higs bosan it's 125 G about 127 time the mass of the proton and that's I think a finished

fact before I quit Let's uh talk about the near future what have we learned we've

learned that the standard model is essentially correct we've learn the standard model is essentially correct everything seems to fit together the higs bosz on fitting

together remember it's not the higs boson really that gives the particles their Mass it's the zigs boson but the higs boson is just what's left over when you think of these density oscillations it was the last remaining piece it is

now in place uh it's finished but is everything fitting together exactly right quantitatively right well that we don't

know we don't know there's one hint one hint of a discrepancy and I'll tell you what the hint of that discrepancy is Let's uh here's I drew this picture let

me draw it again over here it's the process of creating a higs by two gluons coming

together gluon gluon top Quark going around the loop and higs now this same process once the higs

is created also allows the higs to decay but it's not so easy to see gluons in the laboratory they're difficult to work

with that's not the best process for looking for the higs boson after you've created it the best process is to replace the gluons by photons I don't

have to even change the picture photons it's exactly the same process except with photons out here once the higs is created by whatever it can create it it

can DEC K into two photons it's an intricate process it involves a lot of theory and a lot of calculation a Fineman diagram not easy

to calculate but you can calculate it and it depends on the properties of the top Quirk going around here at the moment at the moment and I'm not an

expert at this I can only quote what I'm told a at the moment the higs bosan that was produced in the laboratory appears

to Decay into two photons a little too quickly about one and a half times too quickly now everybody agrees that that

is not a statistically really significant fact yet but what will it mean if it persists it doesn't seem like a big deal one and a half times too fast

but the point is the theorists have the ability to calculate that rate very accurately a one and a half times too big a rate is

serious it means something is going on the most likely thing that would be going on is that there's another kind of particle in addition to the top Quirk that has not been discovered yet that

can also participate in the same kind of it's called a triangle diagram some other kind of particle that of course would be big news if there's something there that is not described by the

standard model that would be big news it could be a super symmetric particle it could be anything all kinds of things if this this is something to watch for now

the buzzwords are the decay of the higs into a pair of photons and a excess of about one and a half I think it's a two Sigma effect whatever that means means something the

statisticians um it means that it's not so robust but it could be right right if it turns out to be right it means that we've discovered something

unexpected or it might be even something that's expected but something new beyond the standard model remember the standard model is over 50 years old well over 50

years old and so 1967 am I right 77 87 997 2007 no not K getting on 50 years old so discovering the hings bosone wasn't

really discovering anything was confirming something if this should be off by a factor of one and a half one will have discovered something absolutely new so if you want to watch if you know want to be a spectator in

the sport and you want to watch what happens this is the thing to watch for next whether the higs decays are consistent with the standard model okay that's uh we we're finished

uh thank you very much and uh I hope you all got something out of that one or two questions yeah uh what would cause two different ferons to have different rat of chyro

oscillation good the answer is going to be an unsatisfying one the answer is that the Fons

have what would cause different Fons to have different masses different masses essentially different different oscillation different rates of oscillation are the same as different masses the coupling strength the

coupling constant that couples the relevant particle to the uh to the higs

field what happens the particle moves has separ coupl yes each one has a separate coupling constant emits this what did I call it the the zigs midst

the zigs which gets lost there's a coefficient here which is basically a probability each one and we don't know why they are what they are we know how to parameterize it but we don't know how to

explain it for each kind of particle let's say the electron or the MU particle or whatever it happens to be there's a different constant there and that constant is the constant which

determines the rate and the mass it's the same constant which comes into telling you how rapidly the higs decays into these particles and

therefore the the heavier the particle the stronger the Decay so that's a good question I meant to say something about it I forgot

good do we know the value of the H mask do we know the value of the vacuum expectation value of the H field yeah we've known that for a long time 240 gev

the value of the expectation value is from one language it's simply the displacement of the field in another language it's the density of the

condensate can think of it either way the density of the condensate or as the value of the displacement of the field and that's why oscillation in the

magnitude of the field is the same as a density fluctuation what's that apparently not apparently not well yes I think it

does but there are many many other things that give it an energy density and for whatever reason they almost all cancel out this is one of the great mysteries of uh

you yeah right so that's that's a very good question to which we don't have an answer at the moment right okay I hope you got something out of that I had fun preparing it and figuring out how to try

to explain it uh some of you you probably got something others are just mystified and sitting why they talking about but

that's it [Applause]

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