Script Of The TEDx Talk
    By Tommaso Dorigo | September 26th 2011 03:39 PM | Print | E-mail | Track Comments
    About Tommaso

    I am an experimental particle physicist working with the CMS experiment at CERN. In my spare time I play chess, abuse the piano, and aim my dobson...

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    The organizers of TEDx Flanders did produce in a very timely manner very professional videos of the event, so you can follow offline the talks, including mine. However, what I said is not exactly what I had planned to say. Further, you might not want to spend your time looking at a recording. So for the record, I am pasting here my unamended script. Later on I will also post here the slides I showed while talking, which cannot be seen in the video.

    Thousands of physicists, engineers, computer scientists, modern-age seers have worked at it for the last twenty years.

    It was a spectacularly hard endeavour, but it is finally over. Now it is happening, as we speak.

    At the CERN laboratories in Geneva the most gigantic and complex machine ever built by Man is working 24/7 to uncover the mystery of mysteries: Finding out what is the stuff that the world’s made of.

    We all remember from high school that atomic nuclei are made of protons and neutrons. But these are in turn made of tiny hard things we name quarks.

    Well, if you went to high school before 1975 you might not know about quarks –how about going back there for an update ?

    That’d be a good idea, because during the last fifty years we have made huge leaps forward in our understanding of matter. It’s all quarks, and leptons. And we know these bind together by exchanging force carriers, particles we call bosons. We have built a pretty scheme of all these particles, and we have learned to compute how they behave.

    But we are not satisfied, because we’ve studied the classics.  
    Indeed, the greek philosopher Socrates is related to have put it the right way 2400 years ago: en eida oti ouden eida, I know I don’t really know: we know there’s more out there than we’ve got to know so far. But we have little clues of what that is. 

    And further, we even know we have not understood yet a crucial property of matter: What is generating the mass of elementary particles?  
    To put it simply, why does a proton weigh so much more than an electron ?

    So let’s go back to the quarks in the proton. Nobody has ever seen these things, yet we know they are there. It’s actually a no-brainer: if I can kick it, it exists. We physicists are practical people!

    And we do kick them quarks! We throw a proton against another proton, and bang! A quarks hits another quark, and we get to infer their existence from the spectacular mess they create.

    Like, imagine you’re traveling on the highway, carrying a case of whiskey in the trunk, when you’re hit by a truck coming from the opposite direction. Bang. Not much remains of what was in the car, but those who’ll come and pick up the remains might be able to tell whether it was Jack Daniels or Glenfiddich you were carrying around!

    That’s what the Large Hadron Collider experiments do: they examine the remains of these powerful collisions, enabling us to see inside the proton. Like the scent of whiskey, the produced debris of a proton collision tells the tale.

    But there’s a difference!

    Energy can turn to matter, as Einstein predicted. So the LHC accelerates protons to the speed of light, and then creates these collisions which turn kinetic energy into new subatomic particles.

    Now, the funny thing is that these new particles can be of any kind. So if the collisions are energetic enough, they may produce new states of matter we’ve never seen before: ones we want to know all about, because they could revolutionize our world!

    So we built the LHC. A 27 kilometer-long tunnel 100 meters underground, tightly packed with powerful magnets and cutting-edge electronics surrounding a narrow vacuum pipe. That’s where trillions of protons run in opposite directions, hitting one another head-on forty million times a second in the core of humongous detectors.

    To give you the flavor of how complicated and marvelous are these giant things, let me show you the CMS detector components as they are assembled inside-out.

    CMS is built like an onion: layer on layer of precise devices capable of tracking and identifying the hundreds of particles emitted in the collision.

    The whole thing weighs in the whereabouts of 13,000 tons – that’s about the combined weight of all citizens of Geneva.

    Now I would love to explain you more of how this all works, but time is a tyrant. Instead, let’s look at a few pictures showing how the detector “sees” the particles coming out of the collision.

    We call these “event displays”, and we take pride in making them as cool and colored as possible. We draw curved lines to show the trajectory of charged particles bending in the strong magnetic field; where they then deposit their energy we draw colored blocks of size proportional to it.

    To you it may all look unintelligible and chaotic, but to trained eyes these graphs allow the instant understanding of what went on in the detector after the collision took place. And by collecting many of these events, we get to figure out whether new particles or other fancy processes have been created.

    Did we see any new things yet ? Let Peter tell you about that.

    (Here start Peter's part, after which I take on the stage again:)

    Indeed my experiment is already sitting on twice more data than were published at summer conferences, as you can see in the data collection graph behind me.

    So right now, there’s 3000 physicists in CMS (and as many in ATLAS) who are working feverishly to see the first hints of the Higgs boson... There is a number of possible ways to search for it, and all are being pursued. And maybe we are seeing the first hints of the darn particle…. Can I say whether it's there ?

    I hesitate... You all look trustworthy and I'm willing to buy that each of you would keep the secret within these walls, but Peter here is such a loudmouth with his blog!

    The problem is that when in my blog I write something I should keep secret, I  get my colleagues all angry at me. See, I could live with the standard punishments, such as a ban from presenting results at conferences (I did get that once)….
    But in 3000 people there's always a nuthead or two,  who are ready to scratch your car. Now that would be annoying.

    Instead, when Peter publicizes anonymous comments in his blog, reporting confidential information about new discoveries, he only gets the good press -experimentalists can do nothing to him, since he does not care about physics conferences…
    Plus, he does not own a car!

    So, before I get treated with some very good wine tonight, I am incapable of letting go with the news that the Higgs boson indeed has been found.
    Nope. But I'm not going to leave you like that: I can certainly tell you what the Higgs boson mass is, if it exists!

    See, the mass of this particle is all-important, because it determines both how energetic need to be the collisions to generate it, and what kind of signal it produces when it disintegrates.

    In the past, the LEP II experiment at CERN searched for the Higgs boson in electron-positron collisions by gradually increasing the energy up as much as they could. They did not see it, so they ruled out its existence if it is lighter than 114 Giga-electronVolts.

    Now don't worry about these funny units, they're more or less equivalent to proton masses. So, below 114 whatchamacallits, no Higgs.

    More recently, the Tevatron experiments at Fermilab managed to say that the uncatchable boson cannot have a mass in the 150-170 GeV range, because they would have seen it if it was right there.

    And finally, a month ago the LHC experiments declared that the Higgs, if it exists, must be lighter than 145 whatchamacallits, excluding all the high-mass region -which was anyway disfavoured by theoreticians.

    Before the end of the year, at the LHC we're going to shoot down still more of that, but excluding wrong mass hypotheses is starting to feel like explaining how to make the chocolate mousse by compiling a list of all the wrong ingredients.

    More exciting is that unlike previous experiments, at CERN we now have the sensitivity to find the darn thing, and maybe we are finally seeing it and measuring its mass.

    So before you learn it from the press, I can tell you that the Higgs mass is……..
    119 whatchamacallits, give or take a few whatchamacallits. You can tell your grandma if you like, but please don't tell Peter!