News blog

HEP-2011: Higgs hunting at 144GeV

HiggsSim.jpgToday, the two big detectors at the Large Hadron Collider (LHC) delivered a plenary at the Europhysics Conference on High-Energy Physics in Grenoble. The results were largely the same as those given on Friday, but there was also a taste of what’s to come.

First, a quick recap: the LHC is a massive particle accelerator on the French-Swiss border. It’s smashing protons together to create heavier (and hopefully new) particles. Late last week, both the ATLAS and CMS detectors reported a faint signal between around 130-150 gigaelectronvolts. It could be the Higgs boson, which researchers believe is an essential part of what gives other particles their mass. Then again, it could be a random fluctuation.

To try and separate signal from noise, the two detectors are now going to combine their data. Today, William Murray, who heads the Higgs search at ATLAS, provided a hint of what a combined data set might look like. In his talk, Murray told the audience that most of the fluctuations between CMS and ATLAS cancelled out, except for one point at around 144 GeV. It’s compatible with a Higgs signal, and is currently at about 2.9 sigma significance (it has about a 99.63% chance of being right).

That may sound like a sure thing, but it’s not. There could be systematic errors in both detectors that have caused the excess. Or problems with theoretical predictions, meaning that there’s not an excess at all.

The fully combined data, which could be presented as early as next month, should take into account at least some of these possibilities. Ultimately, though, the collider will have to gather even more data before the Higgs can be discovered (or declared dead).

Image: ATLAS


  1. Report this comment

    Andre David said:


    […] except for one point at around 144 GeV. It’s compatible with a Higgs signal, and is currently at about 2.9 sigma significance […]


    This is not correct. The significance quoted above is local and does not take into account the fact that the searches were performed in a wide range of masses. The local significance can only be smaller than the significance that is translated into a “chance of being right”.

    This is the so-called “look elsewhere” effect or “trials factor”; the more places you look for the presence of a signal, the more likely it becomes that background (fluctuations) alone will fake that signal.

  2. Report this comment

    Geoff Brumfiel said:

    Thanks for that clarification. I agree that one shouldn’t take the confidence level of the measurements too seriously at this stage.

  3. Report this comment

    Brett A. Becker said:

    I am also curious as to the “cancelling out” of the data between CMS and ATLAS. for instance, how large are the anomalies that have been cancelled out? Are they on the same order of magnitude as the signal around 144GeV?

Comments are closed.