ATLAS and CMS to present Higgs search results

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A couple of weeks ago, I posted about the rumors that were flying around the internet concerning the presumed discovery of the Higgs boson. At the time, those rumors were unfounded: nobody really knew what the results of the analysis were. But no longer! The LHC experiments will be presenting those results tomorrow, July 4, at 9 AM Zurich time — that’s 3 AM on the east coast of the US. There will be a live webcast of the presentation if you want to see the results as they happen.

So what exactly is going to be presented? Officially the results from ATLAS and CMS are being kept under wraps, but the rumors going around this time (which should be a little more reliable) suggest that the new data from both experiments support the bump at \(\SI{125}{GeV}\) that was last announced in December. It’s also been suggested that, while neither experiment individually has achieved the \(5\sigma\) significance physicists are waiting for to claim a “discovery,” when you combine the results from the two experiments together, they do exceed that \(5\sigma\) threshold.

Despite all the excitement, I think these rumors reflect exactly what most people in the field have been expecting — certainly, it’s what I’ve been expecting all long, at least since December, although it was (and still is, for the next 11 hours) far from certain. On one hand, this is great, because it would prove that the Higgs mechanism (which gives particles mass) is valid, but on the other hand, it makes particle physics kind of boring after this. What we really wanted was for the LHC to discover something brand new, something which would suggest that we might find even more particles at higher energies, like supersymmetric partner particles. But that hasn’t happened at all. In fact, the LHC has searched the entire mass range \(\SI{90}{GeV}\) to \(\SI{600}{GeV}\) and pretty solidly ruled out any new particles existing anywhere in that range. (A quick reminder for those who may not know: the gigaelectronvolt, \(\si{GeV}\), is actually a unit of energy, but \(\si{GeV}/c^2\) is a unit of mass. We like to leave off the \(/c^2\) for brevity.)

With that in mind, what happens next? Well, something else I’ve heard through the rumor mill is that, even though the LHC experiments are confident that they have discovered a particle with a mass of \(\SI{125}{GeV}\), they’re not yet sure that it is the standard model Higgs boson. Verifying whether it is or isn’t will take a lot more detailed investigation of the particle’s properties, in particular what it decays to, than just figuring out that it exists and has a certain mass. So the LHC is definitely not out of a job yet.

Even beyond that, though, the LHC is not even up to its maximum design energy! In the long run, the collider is intended to collide particles such that the total energy of each pair is \(\SI{14}{TeV}\). Right now it’s only up to \(\SI{8}{TeV}\). When the LHC is eventually upgraded to its full energy, it will be able to look for new particles at even higher masses than its current \(\SI{600}{GeV}\) limit, and it’s still possible that we might find something there. If not, the future of particle physics doesn’t look promising — it’s really hard to get funding when you don’t have anything in mind to discover.

But I shouldn’t get ahead of myself. For now, let’s just sit back and appreciate the LHC’s success. I’ll definitely be posting something about the results announced at ICHEP after they come out, perhaps even right afterwards since I’ll probably still be awake at 4 AM.