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CERN | Geneva | Switzerland

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What’s keeping thousands of CERN physicists busy right now?

We made big promises in terms of potential discoveries with the Large Hadron Collider (LHC) but so far, nothing new has emerged. So what are the thousands of physicists involved in the various LHC experiments doing right now? Quite simple: we are inspecting every square centimeter of thousands of acres of new territory opened up by the LHC.

Theorists swear: we are bound to find something. They have been refining the Standard Model of particle physics for a few decades now and know what they are talking about. So far, every prediction based on this theoretical description of what’s happening in the micro world of particles has been verified, sometimes to the ninth decimal!

The Standard Model is quite simple and rests on two assumptions: first, all matter is made of elementary particles (so far, we have identified three families of quarks and leptons, the building blocks of matter) and second, these particles interact with each other through basic forces: the gravitational, electroweak and strong forces. This is done by exchanging other particles called “bosons” that are associated with these forces. For example, the electromagnetic force, which is part of the electroweak interaction, is mediated by photons. Gluons carry the strong force that binds quarks together within protons and neutrons. The Higgs boson, if it exists, would mediate a new force not yet discovered.

The Standard Model seems to be to particle physics what arithmetic is to mathematics: just the first layer of a more complex theory. Most of daily calculations can be done with the basic operations provided by arithmetic, but if you want to do something more complex than shopping or cooking, something like building a house with curved walls and angular rooms, geometry is necessary. That’s about where we stand now: although the Standard Model has answered nearly everything observed so far, we know its equations get unstable at high energy. And high energy is where the LHC brought us. So we are bound to see something happen since we know things will start getting incoherent and break apart.

For the last decades, experimental physicists have looked at millions of events, each one being a snap shot of what happened following the collision of protons or electrons in various particle accelerators. This allowed us to explore a large territory but in a painstaking way. With the LHC turned on, it is as if we went from exploring a vast cavern with a small headlight to having central lighting installed in the cavern. Not only the LHC produces more events, allowing us to see in all little corners, but also these events come at a higher energy, enabling us to explore new sections of this cavern never reached before.

Right now, the LHC physicists are frantically exploring every single nook and cranny of this space. We can already rule out with absolute certainty large areas where new particles could have been hiding. The Standard Model Higgs boson is not the only new particle we are looking for but there is also a whole zoo of particles postulated under different hypotheses. In case you would like one of these particles for yourself, check out the Particle Zoo site.

If something is hiding out there as theorists are convinced (and they have been getting it all right so far with the Standard Model) then we will find it. Meanwhile, the goal is to establish a number of facts that will serve as landmarks in the definition of new models or the retention of existing ones not yet confirmed. Every time experimentalists set new limits, it restricts the number of allowed models, as John Ellis explained in a recent article published in the CERN Bulletin. Eventually, the right solution will emerge, revealing what is this new theoretical layer that must be added on top of the Standard Model. With time, we should be able to figure out how it all works and keep our promises for discoveries!

Pauline Gagnon
To be alerted of new postings, follow me on Twitter: @GagnonPauline

To illustrate this point, here are the limits established by the CMS collaboration while searching for supersymmetric particles associated with a particular model, here the CMSSM model (the Constrained Minimal Supersymmetric Model). Without getting lost in the details, what is worth noting is that all the space below the various curves is ruled out, meaning particles predicted by this supersymmetric model are excluded. One should compare these curves with what had been previously achieved after twenty years of hard work at the Tevatron by CDF and D0 (red and hatched areas) or at LEP (areas in yellow and green). Note also the difference between the results established in 2010 by CMS (dotted lines) and this year (solid lines). The ATLAS collaboration obtains similar results. One can clearly see the progress accomplished by the LHC experiments.

  • http://sciencesprings.wordpress.com Richard Mitnick

    I hope that you and all the HEPcats* at CERN are attaching to the LHC@home 2.0 project running in Scientific Linux, your favorite language, on software from BOINC. PLease visit
    http://boinc01.cern.ch/test4theory/ and join the team. We are today over a TeraFLOP per second, and aiming for half a PetaFLOP.

    *Hepcats is originally a Jazz term. But here, HEPcats refers to High Energy Physics people.

  • Bent Rothenberg

    if the BB was an explosion of antimatter, that would explain the lack of antimatter in the universe today. Futhermore it could explain why this matter (anti antimatter) is not absorbed by the dark matter.

  • http://tran.nathalie.free.fr Nathalie Olivi-Tran

    Good luck! I think that geometry in direct space may be a solution…

  • Milky

    Any words on the neutrinos traveling faster than light?

  • Jacek

    hope to hear something to..

  • http://tran.nathalie.free.fr Nathalie Olivi-Tran

    photons are sensitive to the curvature of space, neutrinos are not that ‘s why neutrinos arrived before photons. Can we really compare the speeds with a different paths? and if the path is the same (measure of the speed of neutrinos witghout comparing with the speed of photons with the same path) read my articles and reflexions on my website
    http://tran.nathalie.free.fr (‘hobby’ and ‘publications’)

  • Marcel van Velzen

    The standard model is quite simple …
    The standard model is not simple at all!
    Did you read The Quantum Theory of Fields, books 1 and 2 of Weinberg?
    It is the triumph of physics and it is very likely that it will be confirmed at CERN and nothing more (which is a very honourable task).
    I think this is currently what we should expect at CERN: A Lagrangian has renormalizable and non renormalizable terms. The non-renormalizable terms are suppressed and we don’t see them. This in itself would be an empty statement if it were not for gravity. Gravity can be shown to have only non-renormalizable terms and therefore if the statement above is true it should be very weak. And indeed it is. It is currently our best understood force at the CERN energies: it is equal to zero!
    It is only that a spin 2 boson couples equally to all energy-momentum that gravity is observable.
    It can be shown that non-renormalizable terms get stronger at about > 10^16 GeV. So that is where we should expect to see something happening.
    HOWEVER the standard model gives a detailed description of nature given the ingredients. It does not explain the observed particle masses or charges and couplings, so we have no idea why there are not also particles with 1.3453 times the electron mass and 1.21 times its charge.
    Does anyone agree on the above view?

    On the neutrino speed: the faster than light neutrino speed is equivalent to saying that we cannot move the proton PDF of figure 11 of the original article by 0.2 mm, which in nonsense. Does anyone agree?

  • Sergio Blancato

    I’m not a professional physicist but I think that assuming that space and time are the same for light and for neutrinos (a type of quite different particles) is simply an assumption to be proved. Neutrinos might travel in a space-time different from that of light and not sensitive to gravitational space curvature: this could explain why neutrinos appear to go faster than light going from Geneve to Gran Sasso. At least this is my two cents explaination.

  • João Victor

    Have you forgot light’s dual behaviour, Nathalie?

  • Goran B.

    I have a question for the scientists. We all know Einstein’s theory of relativity. By that theory light speed is the ultimate speed. But, that theory also says that when two bodies traveling at same speeds, but in opposite directions, when passing each other, speeds are summed. Which means that in the moment of passing, relative speed is doubled.
    Now, my question is:
    What is the relative speed for the particles if they would travel at speed of half of the speed of light plus one? Wouldn’t than relative speed betwen them be more than speed of light?

  • http://www.hornsbyplastering.com John Hornsby

    Not a scientist myself, but my understanding of this is as follows:

    Just as the distance between two objects can be halved an infinite number of times, assuming these objects have no physical dimensions themselves, so can we infinitely accelerate without attaining the speed of light. The absolute speed of your two bodies vith respect to the speed of light should be the difference of each body’s speed from the speed of light, multiplied.

    For example, if c is the speed of light, (c-0.51c * c-0.51c) = 0.7599c. If the speed of light is 1c, then you’ll never get past 0.999999~ using this model.

  • Pauline Gagnon

    In response to Nathalie’s comments,

    the measurement was made using exactly the same path for light and neutrinos. To estimate the time taken by light, they measured the distance and divided by the speed of light. For the neutrinos, they measured the times elapsed between their time of departure at CERN and their detection in Gran Sasso. No real light traveled this distance since it goes through the Earth’s crust. Only neutrino can penetrate matter like this.

  • Pauline Gagnon

    Hello Sergio,

    to this day we have no reason to believe that neutrino should behave differently. So far, all matter had respected this speed limit…

  • Pauline Gagnon

    Hello Marcel,

    my point was to state that the basic and fundamental two principles of the Standard Model are indeed very simple:
    1. All matter can be built from elementary particles
    2 These interact by exchanging bosons, the force carriers.

    Now, granted, putting all tis in equations and getting all the details worked out, is another story…

  • Marcel van Velzen


    Hello Pauline,

    Point taken! What you say is right, these basic principles of the standard model are easy to pircture. I was just trying to follow a complicated standard model calculation and over reacted. Sorry for that!

  • Willem JC de Roon

    According to Einsteins theory of relativity, light speed is the ultimate speed. Nowadays in my opinion we can say that this is not quite correct. The ultimate speed ( C ) is the speed of neutrino’s or light when it is travelling as it’s maximum. Under ultimate conditions ( a.o.no atmosphere) light speed will be equal to the speed of neutrino’s. Neutrino’are not subject to any friction, light is. Though minimal our earth conditions can have a ( very very very tiny ) influence on the max.speed of light.
    The earth as our location does not offer the perfect lab. conditions to establish that neutrino’s are travelling faster than light.

    Under better measuring conditions we will see that the speed of light and neutrino’s are the same and that the relativity theory of Einstein still will hold.

  • Steve5150

    I hate to point out the obvious. A repeatable error has occurred with neutrino detection. Undertstanding relativity means understanding why nothing that has mass travels faster than light in a vacuum. The 60 nanosecond early detection would mean that the neutrinos, and therefore, “information” had to travel backward through time. Interesting and scary dream, but sorry folks…. It’s quite impossible.