The Summer of LHC

This summer has the potential to be among the most exciting in particle physics in quite some time. Why? Recall that last December, the ATLAS and CMS Experiments both unveiled their results in the search for the Higgs Boson [1]. This particle, which has long eluded detection (but which has also largely been out of the reach of even the highest-energy particle colliders, though we only know that with hindsight), is the last unverified prediction of the Standard Model of Particle Physics. Given its relationship to mass and its role as the “giver of mass” to all other known subatomic particles, there is hope that the Higgs holds a special place in experimental physics: as a gateway to a more encompassing and general description of nature.

So why is this summer exciting? Last December, the ATLAS and CMS experiments had just finished collecting their 2011 data set. This sample, the largest of its kind, was composed of about “5 inverse femtobarns” of proton-proton collision data taken at an energy of 7 TeV. SMU post-doctoral scholar Aidan Randle-Conde has an excellent explanation of these concepts (femtobarns, for instance) in his LHC Blog [2]. But, to put it in perspective, this means that this sample represented about 550,000,000,000,000 proton-proton collisions (using a total proton-proton interaction cross-section of 110 millibarns at 7 TeV).  That’s a lot of collisions.

But it was necessary to collect so much data for a simple reason: if the Higgs were easy to spot, it would be readily produced and we would have already seen it. But the Higgs is NOT readily produced, even at such an impressive machine at the Large Hadron Collider. In fact, the Higgs production cross-section (a measure of how readily its produced when colliding protons) is of the order of 1 picobarn. Compare that to the total proton-proton cross-section of 110 millibarns; that means that 99.999999999991% of the time, the collision of two protons at 7 TeV DOES NOT produce a Higgs boson.

A tremendous effort has been put in by thousands of people over two decades to make it possible to throw away as much of the uninteresting stuff and keep only the interesting stuff. That includes proton-proton collisions likely to contain a Higgs particle. I cannot stress enough what a convergence this requires, but from engineers, physicists, students, post-docs, faculty . . . everybody.

So, again, why does this summer matter? Because while the amount of data taken in 2011 is impressive, we’ve already taken MORE data in 2012 than in all of 2011 . . . and done it in less than half the time. Doubling the data means you increase your sensitivity to the presence of a Higgs particle quite significantly. By the end of 2012, we might have as much as 4-5 times the data taken in 2011. But, already, this summer marks a critical milestone.

In just a few weeks, the ATLAS and CMS experiments will present their latest results on the search for the Higgs Boson at the International Conference on High-Energy Physics (ICHEP 2012), a bi-annual conference that is the leading venue in the world for the presentation of new and hot results. This year, it’s in Australia, and our own Prof. Jodi Cooley from the SMU Physics Department and the SuperCDMS Dark Matter experiment will be convening a session of the conference. I hope we’ll also get some “live updates” from her and others on the happenings at ICHEP.

SMU has an involvement in a few key aspects of the search for the Standard Model Higgs Boson, including post-doctoral scholar Ryan Rios working on the “golden channel” for the Higgs search, H -> ZZ(*) -> 4 leptons. But many different SMU people are working on different aspects of Higgs physics, including graduate student Tingting Cao, post-doc Aidan Randle-Conde, and professors Ryszard Stroynowski, Robert Kehoe, Jingbo Ye, and myself. For more information about my own research, you can check out some of my own blog posts [3].

Meanwhile, there is work to be done at CERN. You can keep up with what the SMU group is doing by checking out Aidan’s LHC blog,, and my professional blog, I will cross-post things here as appropriate.

[1] “Higgs Seminar Discussion” (

[2] “What the L?!” (

[2] “In Pursuit of the Subatomic Chimera” ( and “An Overabundance of Tau and its Neutrino” (…d-its-neutrino)


About Stephen Sekula

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