Higgs Live Blogging 3 - Fundamental Bits To Decrypt The Seminars
    By Tommaso Dorigo | July 4th 2012 12:02 AM | 5 comments | 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 first two entries of this live blogging series are available here (part 1) and here (part 2) ]

    7 AM. In thirty minutes the doors of the Main auditorium will open, and people will flood in. I have no idea whether it will be a tidy flow or a wild rush, but I suspect that the latter is more probable, given the strong feelings involved (people losing a night of sleep; the historical importance of the event; the young age and varied nationality of the people queueing up; the absence of suitable infrastructure to guide the queue).

    7.20AM Will it be a model-independent discovery or a model-dependent one ? Answering this question is not easy at all. First of all, when we search for a particle in a certain final state we are already making assumptions on the way it is produced. For instance, looking at two-photon final states one might say "oh, I am just making a model-independent search of a narrow resonance decaying to two photons", but then why should one include in one of the subcategories events which feature two very high-energy, very-forward hadronic jets -those that provide the "forward tag" of a vector-boson-fusion production mode ?

    The model dependence is everywhere. It is built in the test statistics which we use to quantify the confidence level, the p-values, everything. If the particle had a different spin than zero, there would be a significant difference in the discrimination power of our selection tools.

    So, claiming a discovery is a must - we have very large significances in two experiments that see basically the same thing. But claiming a discovery of the standard model Higgs boson requires to attach some disclaimers at the end. Surely, we have looked for the standard model Higgs boson and we have found something which looks like the real thing. But it could be a SUSY Higgs, or even something different, like a graviton. It could. We certainly will never be sure, in some sense. I think the fair thing to do is to say we discovered a particle whose properties agree with those expected from a Higgs, and that more studies will clarify beyond reasonable doubt the exact nature of the particle.


    Thanks for the updates. I am sure many of us who are not as lucky as you to be on the scene will be reading every word you write........Its really an exciting moment!

    Here is a real-time Twitterfeed so readers can see what people around the world are saying about the discovery
    Just dropped in to say Good Morning, and with a hope that you have far more than 125 GeV energy stored in you to make it through this day ;).

    Has Dr. Dorigo made it into the auditorium?

    "or even something different, like a graviton. It could. "

    I know very little of these matters, but your statement conflicts with what Wikipedia implies:

    Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, is impossible with any physically reasonable detector.[12] The reason is the extremely low cross section for the interaction of gravitons with matter. For example, a detector with the mass of Jupiter and 100% efficiency, placed in close orbit around a neutron star, would only be expected to observe one graviton every 10 years, even under the most favorable conditions. It would be impossible to discriminate these events from the background of neutrinos, since the dimensions of the required neutrino shield would ensure collapse into a black hole.[12]

    I found this imagery memorable and it came to mind at the mention of a graviton.

    Then has our Wikipedia made (another) overstatement?