Ready for the jump

| 19 March 2015

A simulated event at 13 TeV in the CMS detector at the LHC. Animation: Thomas McCauley, Copyright: CERN, for the benefit of the CMS Collaboration

The LHC’s so-called Run 2 kicks off when first beam circulate in the 27-kilometre tunnel. After a period of getting to know the consolidated and improved LHC, the machine operators think they can deliver first collisions at 13 TeV to the LHC’s experiments in late May or early June. This is a 60% increase in energy, opening up doors to new physics territory. “The start of Run2 represents a jump forward almost as significant as the transition from the Tevatron to LHC’s Run 1, and it promises the biggest extension of the discovery reach of the whole future of the LHC programme,” says CERN theorist Michelangelo Mangano. “We can expect spectacular surprises. It opens the door to a very very exciting period.

The discovery potential is high. Not only will scientists look at the Higgs boson in more detail to get a clearer picture of its properties, maybe even spot discrepancies with the Standard Model of particle physics. They will also look for signs of supersymmetry (SUSY) or new particles that could hint at forces we did not know before. The theory of supersymmetry says that all known particles have heavier superpartners, new particles that bring a new dimension to the subatomic world. The lightest superpartner is a likely candidate to be dark matter, and could thus also explain the structure of the cosmos. The candidate for the lightest superpartner (the so-called neutralino) could appear in the decays of the gluon’s superpartner (the gluino), and Mangano says that he is “ready to bet the SUSY will show up one way or another.”

While many collisions are needed to confirm a discovery, Mangano says that signs of as yet undiscovered and unexpected things could show up in the data already after the first few months of Run 2. One contender for physics beyond the Standard Model is a force carrier particle called Zˈ – a heavy version of the Z boson, carrier of the weak force and well known to particle physicists. A new force carrier particle means there must be a new force we did not know about – a discovery that would rewrite textbooks.

Hitoshi Murayama agrees: within a year the data should reveal what is lurking in the new energy realm, he says. Murayama, who is a theoretical physicist at Berkeley, Director of the Kavli Institute for the Physics and Mathematics of the Universe (IPMU) and Deputy Director of the LCC, also has the gluino and the Zˈ on top of his wish list for discoveries at the LHC, with the gluino being “our best shot” at detecting dark matter. “However, we would of course not know right away what it is – it would take years to learn about its spin, its mass and other properties,” he says. “That’s where the ILC would excel, nailing all the properties of the new finds and of course of the Higgs.” Even if the LHC does not discover anything new beyond the Higgs, he considers the ILC a crucial machine to study its precise nature – “it’s a new brand of particle, we need to learn more about it, and even the long-term LHC programme couldn’t reveal as much as the linear collider could.”

In a recent paper, he pitches the idea of a new model of dark matter that is nearly an exact copy of QCD, the theory associated with the strong force that relies on the gluon. What if dark matter also interacts strongly? A detailed study of the Zˈ, if produced at the LHC, may show it decays into these strongly interacting dark matter particles and would help answer parts of these questions. More answers could come from electron-positron collisions by measuring the coupling of Z’ to dark matter particles.

The LHC programme is mapped out until the year 2035, by which time it will have collected a massive 3000 inverse femtobarns of data, where one inverse femtobarn corresponds to approximately 100 trillion – 1012 – proton-proton collisions. “There’s plenty of room for a deeper exploration of nature,” says Mangano.

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