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SPEAKER 1: I'd like to give the introduction to Dr. Fabiola Gianotti's talk. And I'd like to start with a brief introduction to Hans Bethe. Hans Bethe arrived at Cornell as a refugee from Nazi Germany at age 28 in 1935. And before the Second World War, whilst at Cornell, he conducted his groundbreaking work on energy production in stars, for which he was awarded the Nobel Prize in 1967.
He was, of course, a key figure on the Manhattan Project as Head of Theoretical Division. And he was productive through his 90s, and he was held in great estimation at Cornell, so much so that in addition to this lecture series, he was granted a permanent parking spot outside [INAUDIBLE], which he actually used through his 90s here. So his career in association with Cornell spanned almost seven decades, when he died at age 98 in 2005.
In the decade following the Second World War, Hans Bethe and Richard Feynman, who he had attracted to Cornell following Los Alamos, played a central role in the development of quantum electrodynamics, which contributes to today's talk as well. Feynman, by the way-- he occasionally babysat for the Bethe family. And Monica Bethe relates that she and her brother Henry looked forward to Feynman's visit, as he was most entertaining.
[LAUGHTER]
So Bethe's impact transcends the Cornell physics department. For example, in 1984, he, together with Richard Garwin, Kurt Gottfried, and Henry Kendall argued that Star Wars program would not, in fact, protect the United States from a nuclear attack, but in fact would expand the arms race. So now I turn to a slightly different topic, that of Brout, Englert, and Higgs.
So Brout, after receiving his PhD from Columbia University in '53, joined Cornell University as a faculty member. In '59 Francois Englert visited from Belgium and came to join Cornell as a research associate with Brout. So Brout and Englert then went back to Belgium in '61 to the Free University in Brussels.
In '64, Brout and Englert presented the results in Physical Review Letters that was cited this year as "the theoretical discovery of the mechanism that contributes to understanding of the origin of mass of subatomic particles." Peter Higgs and another group led by Kibble came to the same conclusion as Brout and Englert. Three papers were separately written on this discovery, and this year's Nobel Prize is to be awarded to Higgs and Englert. Brout died in 2011.
So the third player that I'd like to introduce is the instrument, the LHC. That was conceived of in the 80s and saw first light in 2008. It is, of course, a massive project, and it required, and still demands, international collaboration on an unprecedented scale. We'll be hearing much more about this in Fabiola's talk. We should note that the project took some 20 years from inception to turn on and then another four years to the announcement of the discovery of Higgs boson.
The common thread, then, that couples these players is time. Hans Bethe dedicated his whole life to physics and Cornell. Higgs, Brout, and Englert were proven to be correct some 50 years after they placed their ideas into print. And the LHC and ATLAS/CMS detectors that you'll be hearing of are projects that the scientists have worked and dedicated much of their lives towards.
These timescales are both humbling and inspirational for all of us in this room. So now, finally, I come to tonight's speaker, Dr. Fabiola Gianotti. Fabiola received her PhD from the University of Milan. She joined CERN in 1987 as a graduate student and continued with the ATLAS collaboration from its inception in '92.
She's involved with detector R&D, software development, both of which are critical to the discovery that you will hear about right now. She's the ATLAS experiment's former spokesperson and coordinator. She's also an accomplished pianist, and she's on record as saying there are many links between physics and art. So welcome to all of you.
The schooling in Italy was focused almost exclusively to classical humanities. So she's, in fact, really a Renaissance woman. The British newspaper The Guardian listed her as one of the Most Influential Women in 2011.
She's the runner-up, as you've heard on Monday, for Time Magazine's Person of the Year last year. And she was also awarded a Niels Bohr Institute Medal of Honor for her contribution to ATLAS this year. Again, one sees that persistence and inspiration are really essential ingredients to success. So please join me in welcoming Dr. Gianotti.
[APPLAUSE]
FABIOLA GIANOTTI: Thank you very much to department chair. And I'm very honored to be here and to have the chance to give such a prestigious lecture. So the topic will be the discovery of the Higgs boson. And I will try also to tell you what is the impact of this very tiny particle in our life.
And, of course, I'm very pleased to have the chance to discuss this topic just a few weeks after the Nobel Prize in Physics was awarded to Peter Higgs and Francois Englert for their theoretical discoveries, it was mentioned before, of the so-called Brout-Englert-Higgs mechanism and the theoretical prediction of the Higgs boson. So the Higgs boson has been discovered at the Large Hadron Collider at CERN.
So let me first tell you a few words about CERN. CERN is the European laboratory for particle physics. It is actually the biggest laboratory in the world for particle physics, or also called an ion energy physics accelerator-based particle physics. It's a place where over the past 60 years scientists from all over the world have been doing fundamental research, awarded by discoveries and Nobel Prizes.
It's a place where the scientific goals require the development of cutting-edge technologies in many fields, in many domains-- technologies that are then also transferred to society to the advantage of everyday life. One very famous example is the world wide web, which was introduced at CERN in the 90s by Sir Tim Berners-Lee in order to facilitate the exchange of information among the physicists involved in the laboratory's activities.
And then since then, it has changed the way society accesses information. It's also a place where we train people, we form young people, tomorrow's scientists, but also school students and teachers through a large number of initiatives. And it's also a fantastic place to bring people and nations together by attracting scientists from all over the world. Actually, more than 11,000 scientists work at CERN coming from more than 60 countries.
So just one historical slide to remind you that CERN was founded in 1954, so almost 60 years ago, by 12 European nations, with a two-fold goal of, first of all, giving back prestige to European research after World War II by creating a center of excellence and, second, mitigating the first symptoms of the Cold War by creating a place where European countries could work together peacefully. Today, CERN has 20 member states, all of them from Europe, plus other nations contributing to the activities there-- in particular, several observer states, including the United States.
The budget corresponds to about $1 billion US dollar per year, and it's contributed by each member states in proportion to their income. So this budget corresponds on average to one cappuccino per European citizen per year-- on average. Because a cappuccino is very cheap and good in southern Europe, and then you move north and it becomes very expensive.
[LAUGHTER]
So this is important. I would like to stress that. So this budget, $1 billion US dollars, is used to pay the salaries of the about 2,200 CERN employees. And the rest of it is used to develop the infrastructure-- accelerators, workshop detectors-- that are used by the worldwide community to do research at CERN. And this worldwide community, as I mentioned before, consists of more than 11,000 users from more than 60 countries.
So you can see here the world map of nations, the various countries involved in CERN activity, from Europe to the US, Russia, et cetera, South Africa, South America, Australia. And actually, there is also very strong contingent of physicists from the US, more than 1,000, so that CERN can be considered the second US lab in the world. First one is Fermilab, and the second one is-- in terms of physicists.
So apart from these sociological considerations, which are of course important-- I will come back to back to them later on-- CERN's primary mission is science. So what we do at CERN is to study the elementary particles, among which the building blocks of matter, so the quarks and the electrons, and the forces that control their behavior at the most fundamental level. So we all know today that matter is made of atoms.
Atoms are in turn made of a central nucleus surrounded by cloud of electrons. And nuclei are made of neutrons and protons. And neutrons and protons are made of smaller particles called the quarks. As far as we know today, quarks and electrons are elementary particles, so they cannot be cut into smaller pieces. And they are the fundamental constituent of matters.
So everything-- you, me, everything in this room, this floor and this laser pointer-- everything is made of electrons and quarks. You are perhaps disappointed, but that's it. And a lot of empty space, because atoms have a very, very big radius. So particle physics at modern accelerators, and the Large Hadron Collider is the most powerful accelerator built by mankind, allow us to scrutinize matter down to the size of the quarks, so down to scale, smaller then 10 to the minus 18 meters, which is 1 billionths of a billionths of a meter.
So these accelerators can be seen as a very powerful microscope that allows us to study not the cells, but to scrutinize matters at this level. At the same time, these studies give us insight into the structure and evolution of the universe. So the very small allows us to understand also the very big.
And the reason is that we know today from cosmology, but also from several experimental observations, that the universe had origins about 40 billion years ago from a big explosion called the Big Bang. And so at the beginning, at the time of the Big Bang, the universe was extremely dense and extremely hot. And then with time, it expanded and cooled down.
At the beginning, it was a gas of elementary particles, an ensemble of elementary particles. And then with time, the elementary particles start to stick together to form the nuclei, then the atoms, so the hydrogen atoms, and then heavier elements. And then with time, the star and the galaxies and the microstructure that we know today. But because the beginning of the universe was essentially gas of elementary particles, by studying the elementary particles and their interaction, their behavior, we can infer a lot of information about the behavior of the universe at the beginning of its existence.
So what do we do in practice? To do these very nice things. So what I'm going to say now is scientifically not rigorous. So I hope that it remains between you and me.
And there is a camera there, so this is scary for me. It's worrying. Because otherwise I'm going to be fired. But I will try to explain things to you in a very simple way.
So we do the following things. We accelerate two beams of particles-- for instance, two beams of protons as we do in the LHC, up to the speed or very close to the speed of light. And then we smash them.
And in this collision at very high energy, essentially three things happen. So first of all, protons goes in 2,000 pieces. It's like when you drive your Ferrari, which I'm sure you do every day, and you crash it against the Ferrari of your neighbor at high speed. And the neighbor also does the same thing every day.
And then the higher the speed, the velocity, the more the two Ferraris breaks into two smaller pieces and the smallest possible piece. And then you can study how a Ferrari is made. Similar way here.
Sorry, I told you it was not rigorous scientifically, so don't laugh now. So protons-- again, we mash those proteins. Proteins goes into 1,000 of pieces. And so you can study the elementary constituents of the protons, the quarks and the gluons that keep the quarks bound together inside the protons. So you can study how the elemental constituents of the proteins behave at high energy.
Second, in the collision, a lot of energy is produced. And we know from Einstein's equation E equal mc squared that this energy can transform itself into matter, into particles. Because energy and matter are two different manifestations of the same entity. And the higher the collision energies, so the more powerful the accelerator, the heavier the particles that can be produced.
So particles that could not be observed at past previous accelerators, perhaps because too heavy, become accessible today at the Large Hadron Collider because it has a higher energy. And this is what happened with the Higgs boson, which is not really so heavy. However, it's heavy enough and interacts relatively weakly, so that it requires a lot of energy and a lot of data to be produced.
And the third thing that we do, the energy that we produce in the collision corresponds to the temperature-- the energy or the temperature-- that the universe had very close, just a few instants after the Big Bang. And with the LHC, we are able to produce the energies and the temperatures that the universe had 10 to the minus 11 seconds after the Big Bang, so one-hundredths of a billion of a second after the Big Bang.
So we can go back in time up to this point. Beyond that, earlier than that, we don't know. We can't really produce such an energy in the lab. And if you ask yourself, what was the temperature of the universe at that time, it was 10 to the 16 degrees Kelvin, so 10 to 14 times the temperature in this room. This is the energy we are producing.
So this is what happens in the collision. And then in order to study the phenomena, what we do, we surround the collision point with big instruments called particle detectors-- high tech and very powerful instruments, very, very big-- which are used to detect ideally all the particles produced in the collision, all the particles coming out of this big smash. And therefore reconstruct the collision event and then understand what happened-- I mean, interpret what happened in the collision, what kind of particles have been produced, et cetera.
So essentially, we need three things. Well, we need four things. First of all, we need the brain, the human brain. Then, of course, from the instrumental point of view, we need three things. We need accelerator, we need particle detectors, and we need computing, to have very powerful computers.
So accelerators are usually underground rings. Well, you have one here in the Cornell campus, but the LHC is much bigger. And they are made of essentially two elements-- electric field, which are used to accelerate the particles incrementally at each turn.
So particles, at each turn they pass through some electrical field and they get the kink. And at each turn they get some acceleration until they reach the top energy. And magnetic fields that are used to keep the particles, the beams inside the ring and guide them into collisions.
So this is a view of the LHC underground ring. So it is 27-kilometer ring. And these blue tubes contain very powerful magnets used to guide the beams and bring them into collisions. So detectors, as I said before, surround the collision point, and they are used to detect and measure ideally every single particles emerging from the collision and reconstruct the trajectory, measure the energy of this particle, identify the particles, et cetera, so that we have a full picture of the event. And finally, the computing power is used to store, distribute, and analyze the huge amount of data that these detectors produce.
Now, the most powerful accelerator and the most high tech and complex detectors of the history of particle physics have been developed in the framework of the Large Hadron Collider project, which actually is one of the most ambitious scientific projects in general-- science in general. And that's required the development of most innovative concept and technologies in a huge number of domains, from cryogenics, materials science, superconducting magnets, electronics, data transfer and treatment, et cetera, and, as it was mentioned before, more than 20 years of efforts of the worldwide community, from first ideas, from first conceptual ideas to the first collisions and the data taking, which started at the end of 2009.
So the LHC is a 27-kilometer underground ring, 100 meters below ground, at the border between Switzerland and France. So this is an aerial view of the region. So the little white dots here shows the border between Switzerland, here, and France, here.
So this is Geneva Airport. This is the CERN main site where the main offices and buildings are. Lake Geneva is down here. And this circle shows the position location of the LHC ring, 27 kilometers.
It's not visible on the surface. It's underground. Over the past four years, two high energy proton beams have been circulating, accelerated and brought into collision, accelerating in the opposite direction and then colliding at four points of the accelerator, where these four little yellow stars are located, where we had excavated four big caverns and where four big particle detectors have been installed.
And so these four experiments are called ATLAS and CMS. These are the two biggest experiments and the two that have reported the discovery of the Higgs boson. And two smaller experiments, but a lot less important, called [INAUDIBLE] and ATLAS And the US has made very important, very significant contributions to the four experiments and to the accelerator itself. And, in particular, there is a very strong team of physicists here at Cornell University involved in the CMS experiment.
So I mentioned that we need three main elements. We need accelerator, detectors, and computers. So starting with the accelerator, the LHC is producing collisions between beams of protons at unprecedented energy.
Until now, it has been operating at an energy that I will call eight TeV. I will explain what it means in a few seconds. But in 2015, in two years from now, we will reach the design energy of these accelerators, 14 TeV. 14 TeV means seven times more energy than the most powerful colliders, previous most powerful collider.
And this was the Tevatron Collider at Fermilab here in the US. 14 TeV is a lot of energy. It corresponds to 10 to 14 times the temperature in this room. But there's a lot of energy on the microscopic scale. Because on the microscope scale, 14 TeV corresponds to something like few megajoules.
And a few megajoules is the energy of a mosquito, so it's not really that much on the microscopic level. But on the microscopic level is a huge amount of energy concentrated on a very small point. So the single most crucial element to achieve such high energy is a set of 1,200 superconducting magnets.
Because what is difficult in an accelerator, in a proton accelerator, is not to accelerate the protons themselves. This is quite easy, relatively speaking. What is difficult is to keep them inside a ring of-- big ring, but still of finer dimensions.
Again, when you drive your Ferrari, the same Ferrari as before, of course, if you're going a very high speed and you have to keep it on a circular track, of course, it's very difficult. The higher the velocity, the speed of the Ferrari, the more difficult is to keep it inside a circular ring.
And the same thing for the protons. If they run at very high speed, it's very difficult to keep them in an accelerator ring, which is big but still of finer dimensions. So we had to develop 1,200 high tech superconducting magnets providing very high magnetic fields, never achieved before. And in order to provide such a high magnetic field, we need to use superconducting material.
So this accelerator is made of 8,000 kilometers of niobium titanium superconducting cable. And because these magnets are superconducting, they have to work at low temperatures. So they operate at 1.9 degrees Kelvin, minus 271 degrees Celsius.
And I'll let you transform into Fahrenheit, because I always get confused. So anyway, it's very cold. I will show you in a slide what it means exactly, in one slide.
So detectors. Detectors are also quite impressive. And they are much more complex, much more high tech, and much more performing than their predecessors. So ATLAS is actually the biggest of the four detectors. It's 45 meters long, 25 meters high.
So you can see the dimensional here compared to two human beings. And I will repeat the joke I made on Monday. So those of you were here Monday, please, apologies. So we always put the woman and the man in our drawing, because we promote equal opportunity in our experiments.
So we always put the men and women in our drawing. So it's a big detector. So why so big? Because you need big volumes to absorb and to measure the very high energy particles produced in the collision.
You can't really measure a very high energy particle in just a little material like that. You need a big, big volume in order to absorb it and to measure it in detail. At the same time, in these big collisions, high energy collisions, thousands of particles are produced, and they need to be measured with very high precision, micrometric precision.
And the micron is one millionths of a meter. So this [INAUDIBLE] is actually made of a huge number, 100 million individual sensors that are used to reconstruct the trajectory of these particles. So, for instance, to give you an example, this is a collision between the two LHC beams registered by the same experiment. Not all the particles produced in the collision are shown in this figure. Otherwise, the figures would be much more complex.
But you see that from the collision point, a lot of particles are produced. And this particle releases signals in these little dots here in the individual sensitive elements of the detector. And starting from these individual dots, individual signals, you can reconstruct the trajectory of the individual particles and therefore have a full picture of this collision event.
So these detectors can be considered as giant digital camera that take pictures of the collisions. And then you develop your photograph, and you can see the picture, the image, and understand what happened in the collision. The problem is that the two beams are colliding 40 million times a second.
So these detectors have to take picture 40 million times a second. So these detectors have to be extremely fast. Of course, we do not store all these pictures, because it would be impossible to analyze them. We only store a few hundred a second. But nevertheless, they're clearly working at a very high pace.
Also impressive is the size and the geographical spread of the collaboration of the scientists involved in these experiments. So this, again, is the example of ATLAS. ATLAS consists of 3,000 scientists from 38 countries.
So here you can see the map. So in yellow, the countries involved in the ATLAS experiment. They come from Europe, from Australia, South Africa, China, Russia, South America, the US, et cetera.
And the nice thing also is that out of these 3,000 scientists, 1,000 are-- sorry, first I wanted to remind the contribution of the US. So we have 41 universities and laboratories working in ATLAS, with 600 scientists and 250 students. Actually, you see about 1/3, or more than 1/3, of the 3,000 collaborators, 2,000 scientists in ATLAS, are actually PhD students.
And if you add on top the young post-doc, then you see that most of the ATLAS population is young. So this plot shows-- this figure shows the distribution in age of the ATLAS population, for boys in blue and girls in red. And you see that most of the collaboration is young.
Most of the people are below 35. I'm here in this first bin, and I will not move from this first bin. Sorry. Don't laugh. It's not nice.
And you can also see an important thing. About 20% of the collaboration is made of women, so it's quite good. And you see that the fraction of women actually increases in the younger generations.
So there are more and more young women involved in fundamental research in particle physics, which, of course, is very good. I will skip the computing in the interest of time. And before going to [INAUDIBLE], I would like to show you another slide to summarize a few more numbers related to this very complex and challenging project.
So I mentioned already that the magnets work at very low temperature, 1.9 degree Kelvin, which corresponds to minus 271 degrees Celsius. Now, this makes the LHC the coldest place of the universe. Because, remember, I mentioned before the Big Bang, the big explosion, which gave origin to the universe.
And then with time, the universe expanded and cooled down. If you ask yourself, what is the temperature of the universe today? The answer is 3 Kelvin. So the LHC actually is colder than the universe, the outer space. So it's the cooler place of the universe, and also it's the coolest project in the world.
Then these beams contains a lot of protons. So the accelerator has been operating at maximum power until now. Typically 100,000 billion protons were circulating in one direction and 100 billion protons in the other direction. And because these protons have an energy close to the speed of-- a velocity close to the speed of light, the energy stored in these beams is very, very large-- 350 megajoules.
So if you want to know what this corresponds to, I found on the web that this corresponds to the energy of a British aircraft carrier traveling at 12 knots. Why it has to be British, I don't know. But this is what I found on the web, and so I will report it.
So the CMS experiment has more iron than the Eiffel Tower in Paris and weighs more than [INAUDIBLE]. And in ATLAS, we need 3,000 kilometer of cables to bring the signals from the underground cavern to the control room. And because I skipped the computing part, let me just mention that every year, each one of the [INAUDIBLE] experiments produces something like 10 petabytes of data. And you all know what petabyte is, but if you wanted to write this data on DVDs, you will need a pile of about 20 kilometers. So it's quite a lot.
So the question is, why? So the reason is that we know elementary particles and their interactions quite well, thanks to a huge amount of experimental work over the last 40 years and the results from experiments made at various accelerators and various laboratories from all over the world. And also, we have a theory, which is called the Standard Model, that describes these particles and their interactions pretty well.
This theory has been extremely successful, because all the particles predicted by the theories, except one, actually. Well, all of the particles have been discovered. The last one is the Higgs boson, which was discovered about one year ago. And all the predictions of the theories, in terms of the way this particle interacts, have been verified experimentally by experiments from all over the world.
The problem is that in spite of the fact that this theory is very successful, it is not able to address and answer all the questions for which we have evidence to date. The first question, which was a puzzle until one year ago, and now it has been understood and it is related to the Higgs boson, is what is the origin of the particle masses? And so now this has been understood.
So the question is ticked off, at least a large part understood. And then we come back to this later in the next slide. Then there is another problem that we don't understand. Unfortunately, today, for us, 96% of the universe is dark, meaning that only 4% of the universe is made of the matter I was describing before, the matter of which all of us are made, ordinary matter-- so atoms, chemical elements, what we know today.
The rest is dark, dark meaning that, A, we don't know what it's made of. And second, dark because it does not interact with our instrument. We can't see it. We can only infer the existence of dark matter and dark energy indirectly from the motion of the galaxies from other measurements.
But we don't know what is the constitution of dark matter, what is the origin of dark energy. So in particular, 23% of the universe is made of a form of matter which we don't know, meaning that none of these particles that we have observed so far has the good feature to explain dark matter and its feature as we observe it through astronomical observation.
So there must be a new particle beyond those predicted by the standard model and beyond those observed so far that explain 23% of the universe. But today this is a question mark, and dark energy is even a bigger question mark. We know today that in the universe there is a lot of matter and very little anti-matter. Thank goodness. Otherwise we would not be here.
But we don't know why there is this imbalance, and so on, so forth. We don't know why gravity is so weak in the world of elementary particles compared to the other forces that act among elementary particles, like the electromagnetic force, the weak force, and the stronger force. So the LHC has been conceived and built to address some of these questions, and perhaps others, and to try to answer them.
And actually, we managed to address and explain the first one. So the adventure of the LHC started in March 2010, when first proton beams of unprecedented energy had been circulating in the accelerator and brought into collisions. And so since then, we have achieved the following things.
So first of all, the three important fundamental components-- accelerator, detectors, and computing-- have been performing extremely well, beyond the most optimistic expectations. So a huge amount of collisions have been delivered by the accelerator to ATLAS and CMS, LHTB and ATLAS. So we have recorded a huge amount of data. ATLAS and CMS have recorded 5 billion collisions each.
With this data, we have measured the known particles, those that you have seen in the previous slide, the Standard Model particles already known, already discovered at previous accelerator. But we have measured them again in this new energy regime. And we also looked for new particles and new physics which could explain the questions I mentioned in the previous slide. And we have found unfortunately nothing, no sign for new physics that could allow us to explain at least, for instance, the origin of that matter, et cetera.
But the most important results is that in July 2012, the two biggest experiments, ATLAS and CMS, have reported observation of a new particle. That time, we called Higgs-like, because it looked very much like the Higgs boson. But we were not sure it was the Higgs boson, whereas today we are sure it is the Higgs boson. A massive particle, mass 125 GeV, means 130 times the mass of the proton.
So why is this particle so important? And I have one slide with which I will try to explain the importance of the question and the Brout-Englert-Higgs mechanism. So again, I will be extremely simple and scientifically not rigorous. So I hope the physicists in the room will forgive me.
So until the 4th of July of last year, we didn't know why some of the elementary particles have no mass. They are pure energy, like the photon. And we are all familiar with the photon, which is the quantum of light. I mean, this room is full of photons.
Whereas other particles, like electrons or, for instance, the W and Z particles, which are responsible for transmitting the weak force, which is responsible in turn for radioactive decays or the thermonuclear interaction in the sun-- the W and the Z particle are massive. They have mass corresponding to 100 times the mass of the proton. We didn't understand why the top quark, which is the earliest elementary particle observed so far, has a mass compatible with that of a gold atom, is so heavy, whereas the electron is 350,000 times less massive.
So in the original formulation of the theory of the Standard Model, all particles are massless, which of course contradicts experimental observation. We know that the electron has a mass. We know that the W and the Z particles have a mass, et cetera.
So in order to solve these problems, some physicists at the beginning of the 60s-- well, the number of physicists who contributed to solving the puzzle is larger than that. But the key work was done in 1964, as mentioned earlier, by three physicists, Peter Higgs from Edinburgh and Robert Brout and Francois Englert from Brussels, although both of them have been here in Cornell. And actually, Robert Brout was faculty for several years, but then was convinced by Francois Englert to move to Belgium.
And so in '61, they both moved to Belgium. So these three physicists-- unfortunately, Brout passed away in 2011; otherwise he would have shared a Nobel Prize with Peter Higgs and Francois Englert-- introduced a mechanism called Brout-Englert-Higgs, which explains how elementary particles get mass. So I will try to explain to you the mechanism in a very simple and non-rigorous way. So it went like that.
At the time of the Big Bang, all particles were massless. They were pure energy, and they were moving in the universe at the speed of light. And imagine that the universe was filled with a kind of medium. But this medium was transparent, a kind of, I would say, ether or something very, very light.
And so the particles could not see it. And therefore, they were ignoring it. And then the temperature goes down.
After the big explosion, the temperature goes down. And then at some point, some time-- and this time, again, is 10 to the minus 11 seconds after the Big Bang-- a phase transition occurs. Phase transition is a complicated term that we use-- expression we use in physics to indicate a change of status. Like, when water becomes ice, it's a phase transition. It's a changed state.
So imagine that this medium, which was transparent, at this time becomes more consistent, become something more solid. I would say something like a sticky medium, some glue or some marmalade, something disgusting like that. Now, the elementary particles see that something has changed.
Uh-oh. There is something. The universe is not empty any longer. There is some medium.
And imagine that the elementary particles are little balls. It's not difficult to imagine. And some of them have a smooth surface. This is the photon. And a particle with a smooth surface can go through the marmalade without essentially seeing it.
So the photon doesn't change its status and continues to travel happily at the speed of light. On the other hand, if the surface of the little ball is rough, then imagine something rough going through the glue. It starts to stick some glue and becomes more massive and is slowed down.
So this is the Higgs mechanism. Elementary particles interacting with the medium, actually emitted with what we call a field in physics, get a mass. And this mass is proportional to the strength of interaction.
The photon does not interact at all, so it remains massless. Photons are massless. And other particles interact more, and they get mass. So I can anticipate your question.
The question is, who cares about the elementary particles, the Higgs Field, et cetera? Well, the problem is that if the elementary particles did not have a mass, we will not be here, because atoms will not stick together. And if there are no atoms, there are no chemical elements. There is no ordinary matter.
Also, if the elementary particles add the mass, but did not have exactly the mass they have, also we have things screwed up. And the proton may decay. If the proton decays, there is no hydrogen atom.
Again, there is no chemistry. There is nothing in the universe. And so ourselves, we will not exist. Or perhaps we would exist in a completely different form.
So we are what we are because the elementary particles have exactly the masses they have. The problem is that until the 4th of July of last year, we didn't know how this could happen. And with the discovery of the Higgs boson, which is a manifestation of this field and this medium, we know that the mechanism is the one that has been invented, introduced by these three gentlemen.
So what did we observe in practice? The theory predicts that the Higgs boson-- once it is produced, it decays. So it disintegrates immediately, for instance, in two photons.
So ATLAS and CMS, the ATLAS and CMS physicists have looked among all the collisions and recorded those that contained two photons. So, for instance, this is one of the collisions registered by the CMS experiment. And you see the two beams arrive from these two directions. These are indicated by the yellow arrows.
This is the collision point. You see many particles going out of the collision. And then you see here these two green lights indicates two big energy depositions due to two photons. So CMS and ATLAS have analyzed events like this and looked at the spectrum of these two photons.
And if you just have some background phenomena, you expect to see a steeply falling spectrum. But if you have a particle with a given mass that disintegrates itself into two photons, then you expect to see a peak corresponding to the mass of that particle. And you can see here from the ATLAS data a peak on top of the background.
And when you subtract the background, you see clearly this peak coming out very clearly. This is the Higgs boson, or the signal due to the Higgs boson. It was not easy to find, because these particles is produced very rarely.
For instance, a Higgs boson decaying into four electrons, which is another possibility, another possible decay mode of this particle, is produced every 10,000 billion proton collisions. So it was very hard work to extract such a tiny signal, these little, so important, so special particles out of the huge amount of proton collisions. And I must say that it required a lot of ingenuity, ideas, and analysis of the data. And most of the work actually was done by young people. And we have discovered it so fast also because we have many good young people, students and post-doc, who are brilliant and introduced very nice ideas to find this object.
So I will anticipate three frequently asked questions. Question number one, is this new particle the Standard Model Higgs boson? Well, today we can say that it is type A Higgs boson.
And the measurement of this particle that we've been doing since the 4th of July over last year indicates that it behaves very much like the Standard Model Higgs boson predicted by the minimal Higgs mechanism-- Higgs-Brout-Englert mechanism. However, we don't know yet if it is really-- this particle perhaps is a particle that belongs to a more exotic physics beyond the Standard Model. Of course, we will be much happier if this second hypothesis is the right one. Because this means that there is physics beyond the Standard Model and this particle is the first manifestation of new physics.
The second question is, is the task of the LHC over? And, of course, the answer is no, you know very well. Because remember that I show you a long list of questions that we want to address.
And for the moment, we have been able to answer the first one. But the others, of course-- the origin of dark matter, matter/anti-matter symmetry, and many other things-- we will have to continue to explore and hopefully give an answer. And the final question is, will the Higgs boson change our day by day life?
And my answer to this question is that it did already. And the reason is that in order to discover this tiny particle, we had to develop a huge amount of cutting-edge technologies in many fields in order to be able to build a very powerful accelerator and very powerful and unprecedented instruments and detectors to be able to produce the Higgs boson and detect it. And this has been done at CERN in collaboration and together with the institutes and institutional laboratories working together with CERN, like Cornell University.
And here on the campus, you have a very good example of these very cutting-edge developments of, for instance, accelerators and similar instruments. And these technologies have been, then, transferred to society. For instance, today that are something like 30,000 particle accelerators in the world, and only a few dozen of them are used in particle physics in fundamental research.
Most of them are used in other fields-- material science and medicine, for instance, to bombard the tumor tissue and to destroy it. But all of them have been built on-- are based on technologies developed at CERN or Cornell or other contributing institutions. Likewise, we have been developing the instruments.
The detectors that we've been developing in order to build these big instruments are now used in medicine, for instance in medical imaging, like the famous PET, positron emission tomography, which is one of the scanners which is mostly used today. So the Higgs boson already changed our life.
So in conclusion, at CERN, in particular with the LHC, we look for, we seek answers to very important questions about the elementary constituents of matter and the structure and evolution of the universe. In order to achieve this goal, this scientific goal, we have to develop high tech technologies, cutting-edge technologies in a huge number of domains, which then we transfer to society to the benefit of everyday life.
CERN and the LHC are also excellent places to train and to form students and young scientists and wonderful places to promote peace by bringing together scientists from all over the world. We have seen more than 60 different countries. And with the advent of the LHC, a new era of discoveries started, with aspiration of a new energy scale. And actually, this era has been already-- these efforts have been already awarded by the observation of the discovery of a new particle, which is a very special one, as I hope I've been able to convey to you.
I would like to conclude with a couple of remarks. I've been stressing, of course, the importance and the applications of what we are doing and the spin off of our research. However, I would like to stress that, first of all, fundamental research and fundamental knowledge is the fuel of progress.
Without fundamental research, without new ideas, at some point even applied research and even progress becomes sterile, stagnates. The light bulb is not just the evolution of the candle. It has required a step. It has required new ideas to go from the candle to electricity and to light. So fundamental research is really important in order to be able to-- for progress and also for economical progress.
Second, knowledge, I will say, is art. And so we go back to the discussion before about the fact that, for me, art, and knowledge are very close to each other, art and science. Knowledge and art are among the highest expression of the human being as clever beings, are perhaps the two things that differ and that distinguish us from animals. Also, animals are clever, but not as clever as we are. And this is nature.
And so not supporting and not funding art and fundamental knowledge, because perhaps they don't bring us tomorrow a little bit more bread, I think is like, in some sense, distorting the essence of mankind and, in some sense, killing the highest expression of women and men. Thank you.
[APPLAUSE]
SPEAKER 1: Yes?
AUDIENCE: So I've heard that a lot of people mention that finding the Higgs boson could be the final piece of filling in the Standard Model. However, on your slide of the Standard Model, you also featured the graviton, which I know has yet to be observed. So why have we not considered finding the graviton essential to completing the Standard Model?
FABIOLA GIANOTTI: Because what we define, what we call the Standard Model is the ensemble of the elementary particles and their interaction through the forces that are relevant at the microscopic level-- so the little magnetic force, the strong force, and the weak force. So on that point of view, now we are complete. The problem, of course-- one of the problems that I list in one of my slides-- is that we don't know how to fit the gravity in this context. Because we know that gravity is extremely weak compared to the other forces at the level of elementary particle.
So this is still one big question. And we will have to understand how to reconcile the two things. For the moment, there are some ideas.
There are string theories. There are many ideas, but nothing really experimentally, I would say, conclusive. So, of course, people are looking for gravitons. People are looking for many phenomena like that.
But for the moment, we have no clue. I'm sorry to my friend theorists, but I think that you can contradict me if I'm wrong. So in some sense, gravity is something that is not in the Standard Model. Actually, the Standard Model is called the Standard Model of electroweak and strong interactions because the theory describes this kind of force. But your remark is very good. Yes?
AUDIENCE: I was wondering if there were other ways to find these particles besides the Collider, if there's other experiments going on besides the [INAUDIBLE].
FABIOLA GIANOTTI: Of course. So very good question. Yeah, absolutely there are. There are.
There are complimentary approaches to particle physics and to find a solution to this question. So one way is to accelerate beams and to smash them. Another possibility is to observe the particles that come from the universe, from outer space.
They cost less than an accelerator. They are for free, because they just come from cosmic rays or from outer space. There are complementary approaches.
For instance, I was mentioning before dark matter. We don't know what is the particle that constitutes dark matter. And so the approach to the matter is actually two-fold.
On one end-- well, there are several approaches, but to remain simple, two given kinds of dark matter. What we do, we hope to produce this particle by smashing the LHC beams. But at the same time, we also build detectors in underground cavern where we hope to observe dark matter particles interacting with the detector coming from outer space.
So these are [INAUDIBLE]. And, of course, in order to give a definite answer to the dark matter problem, we hope to observe both-- I mean, to observe it in both ways. And we get complementary information from these two observations.
So yes. You are well-prepared, I see. Very good. Questions are working. Yes?
AUDIENCE: It's a very good question. I'm not a physicist. So does that mean that it has always existed? This [INAUDIBLE] always exist? It doesn't change?
FABIOLA GIANOTTI: Same standard. Same 10 to the minus 11 seconds after the Big Bang. Means that it's here. This field is in this room.
AUDIENCE: But you cannot, for example, take a piece of the room and just take [INAUDIBLE] particle beams.
FABIOLA GIANOTTI: No. So the question is about if the Higgs field has always existed and-- what is it? This is what you ask?
AUDIENCE: Yeah, yeah. Can we modify it or interact with it? [INAUDIBLE].
FABIOLA GIANOTTI: No. I don't think we can modify it. So the Higgs field exists-- the Higgs mechanism, the Higgs field came into action 10 to the minus 11 seconds after the Big Bang, before it was not there. And then it started to be active 10 to the minus 11 seconds after the Big Bang. And since then, it's here, all over the place, in this room.
AUDIENCE: How did it originate?
FABIOLA GIANOTTI: Sorry?
AUDIENCE: How did it originate?
FABIOLA GIANOTTI: It originates because-- well, I have to go through then to the mathematical question. But essentially, there is a potential associated with the Higgs field, which has a shape that is a function of the temperature of energy. So at some point, the temperature goes down below a certain level, and then this makes this potential become active.
So I am sure it is not more clear than it was before, but anyway. I don't know if my friend theorists here can help. So in some sense, the Higgs field now is here everywhere in this room. Otherwise, the electrons and the quarks in your body would not have a mass-- in your body and my body as well. I'm not special in that.
I'm sorry. It's here. We can't see it. Actually, we did not discover the Higgs field. We have discovered Higgs field indirectly through the manifestation through the Higgs boson, which is excitation of the Higgs field itself, which is produced in the equation.
SPEAKER 1: Yes?
AUDIENCE: So very recently, we heard some news which said that the dark matter was not found by [INAUDIBLE] experiments in the large underground xenon-based experiments [INAUDIBLE]. So can you comment on that?
FABIOLA GIANOTTI: So I think you are alluding to an experiment which is called LUX, which is an underground experiment made of xenon. So this is one of the experiments which has produced very nice results. There have been also previous results which did not observe dark matter particle yet. So they put limits on the way the dark matter particles interact.
So it means their interaction with matter is even weaker that we could test until now. Doesn't mean that dark matter doesn't exist. It means that if it exists, as weaker interaction or perhaps different mass. So we will continue to search.
But it's also true that there is no single-- today, there is no interpretational single of what are the features of the particle making up dark matter. It could be a massive particle with very weak interactions. It could be another sort of particle living in a hidden sector, wit, again, weaker interaction. So we don't know. So that's why we are approaching the problems with different experiments. Because at some point, we have to find a solution. It's quite embarrassing that we don't know 96% of the universe.
AUDIENCE: How do you plan to [INAUDIBLE]?
FABIOLA GIANOTTI: So we would need to build more massive detectors. Because this particle has very weak interaction, so it can go through your detector without interacting, you need very massive detector to increase the probability to observe at least one interaction. So this is the way that people are doing for underground experiments.
From the point of view of the collider, of course, colliding beams at higher energy and with more intensity in order to produce-- I mean, try to produce at least a few events in which dark matter particles are produced. So this is the way we are approaching the problem. So, yes, what you heard is correct.
There is a very nice results from this LUX experiment, but it's the most recent result of a long series of results that gave null experiment. Nothing was observed, but we will continue. Research is a very difficult thing. It's a very long path, and you need to have a lot of patience.
SPEAKER 1: I think with that, let's conclude this evening's lecture. And before we thank Fabiola, I'd like to invite all of you to a reception that's in 401 PSP immediately following. But now, let's please thank Fabiola again.
FABIOLA GIANOTTI: Thank you.
Physicist Fabiola Gianotti announced in July 2012 that a team at CERN had discovered a particle consistent with the Higgs boson, predicted by the Standard Model of particle physics, that is crucial to understanding physics and the structure and evolution of the universe.
Gianotti discussed the unprecedented challenges that were overcome to find the once-theoretical elementary particle, Nov. 13, 2013 as part of the Hans Bethe Lecture Series at Cornell.
The Hans Bethe Lectures, established by the Department of Physics and the College of Arts and Sciences, honor Bethe, a Cornell professor of physics from 1936 until his death in 2005 who won the Nobel Prize in physics in 1967 for his description of the nuclear processes that power the sun.
