A new LHC: 10 things to look out for

Through an extraordinary routine, the most powerful machine built by humankind is slowly but surely gearing up for its relaunch in March 2015. The Large Hadron Collider (LHC), straddling the national borders of France and Switzerland, will reawaken after two years of upgrades and fixes to smash protons at nearly twice the energy it did during its first run that ended in March 2012. Here are 10 things to look out for: five upgrades and five possible exciting discoveries.

Technical advancements

1. Higher collision energy – In its previous run, each beam of protons destined for collision with other beams was accelerated to 3.5-4 TeV. By May 2015, each beam will be accelerated to 6.5-7 TeV. By doubling the collision energy, scientists hope to be able to observe higher-energy phenomena, such as heavier, more elusive particles.
2. Higher collision frequency – Each beam has bunches of protons that are collided with other oncoming bunches at a fixed frequency. During the previous run, this frequency was once every 50 nanoseconds. In the new run, this will be doubled to once every 25 nanoseconds. With more collisions happening per unit time, rarer phenomena will happen more frequently and become easier to spot.
3. Higher instantaneous luminosity – This is the detectability of particles per second. It will be increased by 10 times, to 1 × 10³⁴ per cm² per second. By 2022, engineers will aim to increase it to 7.73 × 10³⁴ per cm² per second.
4. New pixel sensors – An extra layer of pixel sensors, to handle the higher luminosity regime, will be added around the beam pipe within the ATLAS and CMS detectors. While the CMS was built with higher luminosities in mind, ATLAS wasn’t, and its pixel sensors are expected to wear out within a year. As an intermediate solution, a temporary layer of sensors will be added to last until 2018.
5. New neutron shields – Because of the doubled collision energy and frequency, instruments could be damaged by high-energy neutrons flying out of the beam pipe. To prevent this, advanced neutron shields will be screwed on around the pipe.

Research advancements

1. Dark matter – The LHC is adept at finding particles both fundamental and composite previously unseen before. One area of physics desperately looking for a particle of its own is dark matter. It’s only natural for both quests to converge at the collider. A leader candidate particle for dark matter is the WIMP: weakly-interacting massive particle. If the LHC finds it, or finds something like it, it could be the next big thing after the Higgs boson, perhaps bigger.
2. Dark energy – The universe is expanding at an accelerating pace. There is a uniform field of energy pervading it throughout that is causing this expansion, called the dark energy field. The source of dark energy’s potential is the vacuum of space, where extremely short-lived particles continuously pop in and out of existence. But to drive the expansion of the entire universe, the vacuum’s potential should be 10120 times what observations show it to be. At the LHC, the study of fundamental particles could drive better understanding of what the vacuum actually holds and where dark energy’s potential comes from.
3. Supersymmetry – The Standard Model of particle physics defines humankind’s understanding of the behavior of all known fundamental particles. However, some of their properties are puzzling. For example, some natural forces are too strong for no known reason; some particles are too light. For this, physicists have a theory of particulate interactions called supersymmetry, SUSY for short. And SUSY predicts the existence of some particles that don’t exist in the Model yet, called supersymmetric partners. These are heavy particles that could show themselves in the LHC’s new higher-energy regime. Like with the dark matter WIMPs, finding a SUSY particle could by a Nobel Prize-winner.
4. Higgs boson – One particle that’s too light in the Standard Model is the Higgs boson. As a result, physicists think it might not be the only Higgs boson out there. Perhaps there are others with the same properties but weigh lesser or more.
5. Antimatter reactions – Among the class of particles called mesons, one – designated B⁰ – holds the clue to answering a question that has astrophysicists stymied for decades: Why does the universe have more matter than antimatter if, when it first came into existence, there were equal amounts of both? An older result from the LHC shows the B⁰ meson decays into more matter particles than antimatter ones. Probing further about why this is so will be another prominent quest of the LHC’s.

Bonus: Extra dimensions – Many alternate theories of fundamental particles require the existence of extra dimensions. The way to look for them is to create extremely high energies and then look for particles that might pop into one of the three dimensions we occupy from another that we don’t.