Is this the end of particle physics as we know it? Let’s hope not
Physicists around the world (myself included) are hoping that this week will usher in a new era of discovery. And not, as some fear, the end of particle physics as we know it.
After 27 months of shutdown and return to service, the Large Hadron Collider has begun its long-awaited “Season 2”. Deep under the Franco-Swiss border, the first physics data is now being collected in CERN’s newly upgraded detector temples at the record collision energy of 13 teraelectronvolts (TeV).
Much has been written about the accelerator upgrade, experiments and computing infrastructure needed to handle the new deluge of data from the new energy frontier. Much attention has also – rightly – been given to the crowning achievement of Exploit 1: the discovery of the Higgs boson.
But the “elephant in the collider” is this: we knew Run 1 had to find the Higgs boson – or something, and it did. With Run 2 we don’t know what we are looking for.
OK, so maybe that’s a little oversimplified. We certainly have some good guesses about what is beyond the Standard Model of particle physics, our current best understanding of matter and forces at the fundamental level which was essentially completed in July 2012.
One of the main contenders is supersymmetry, a theory that provides a candidate for dark matter that would make up about 23% of our universe. My thesis happened to be based on early results from LHC phase 1 which indicated that we had found no evidence of supersymmetry.
To date, I haven’t had to write an embarrassing addendum to my thesis. But, if there are many convincing arguments in favor of supersymmetry, it is not mandatory the same way the Higgs boson was. The Higgs was a missing piece in our current physics puzzle; supersymmetry would represent a whole new puzzle.
Scientific wild goose hunting?
Does that make Run 2 a waste of time? Are we pouring money into an extra-dimensional wild goose chase? Are we, in fact, looking at the barrel of the end of collider-based particle physics?
You would be forgiven for thinking so, if you had no knowledge or understanding of the history of particle physics (or how science works, for that matter). After all, science is arguably the most boring when you 1) know exactly what you’re looking for and 2) find it.
It’s much more fun to consider physics in the middle of the 20th century. You could pretty much describe all known physics, chemistry, materials science, and biology with electrons, protons, neutrons, and photons. Yet advances in particle detector technology – Wilson’s cloud chamber, Blackett’s triggers, Powell’s photographic emulsions – have led to the discovery of completely new particles outside of this comfortable model of nature.
At the time, cosmic rays – particles bombarding our atmosphere from space – had energies far greater than those laboratory accelerators could produce. They represented a new energetic frontier for physics, explored by the heroic particle hunters of the 1930s and 1940s who climbed mountains, launched high-altitude balloons, and flew airplanes in search of their quantum careers.
They were rewarded for their efforts with, among other things, strange particles, a completely new type of matter that defied the predictions of the time and opened the door to a veritable zoo of subatomic building blocks.
The second half of the 20th century saw a transatlantic race to build ever larger particle accelerators to artificially produce cosmic rays under controlled laboratory conditions and tame the particle zoo. This race was undoubtedly won by the LHC. As we approach the new, unknown energy frontier of Run 2, so we again need a new generation of particle hunters. We need experimental physicists who can sift through every byte of data in search of “what’s next.”
Personally, I avoided supersymmetric searches (I went there, I did it) and, with the students of the Langton Star Center, I joined the MoEDAL collaboration. This experiment searches for Paul Dirac’s hypothetical magnetic monopole. Based in the LHCb cavern at Point 8, MoEDAL (LHC Monopoly and Exotic Species Detector) will use a number of new detection technologies to search for traces generated by heavy, highly ionizing magnetic monopoles that could, in theory, be produced in proton-proton collisions.
Magnetic monopoles are the magnetic equivalent of single electrical charges – like a magnet with only a north or south pole, not both – and their discovery would shake up physics down to its electromagnetic core. This is high risk and highly rewarding research, but by providing alternatives to traditional CMS and ATLAS detection methodologies, we ensure that as many bases are covered as possible.
We don’t know what we’ll find in Run 2. It could be monopoles, dark matter, micro black holes, extradimensional excitations, gravitons, or something else entirely. What is certain is that if we are going to find anything, we will have to be incredibly smart about how to do it. We may even need your help. If we don’t find anything, it could be the beginning of the end of what collider-based Earth physics can tell us about the Universe. But even a zero Run 2 result would still be a result, and an important result.
It is therefore the dawn of a new era for particle physics. It is time for the experimenters to eclipse their theorist friends once more. It’s open season for particle hunters.
You can find out more about the MoEDAL experiment at this year’s Royal Society Summer Science Exhibition, June 30-July 5, in London.