Tag: extra dimensions

The Large Hadron Collider is back online, ready to shift from the “what” of reality to “why”

The world’s single largest science experiment will restart on March 23 after a two-year break. Scientists and administrators at the European Organization for Nuclear Research – known by its French acronym CERN – have announced the status of the agency’s upgrades on its Large Hadron Collider (LHC) and its readiness for a new phase of experiments running from now until 2018.

Before the experiment was shut down in late 2013, the LHC became famous for helping discover the elusive Higgs boson, a fundamental (that is, indivisible) particle that gives other fundamental particles their mass through a complicated mechanism. The find earned two of the physicists who thought up the mechanism in 1964, Peter Higgs and Francois Englert, a Nobel Prize in that year.

Though the LHC had fulfilled one of its more significant goals by finding the Higgs boson, its purpose is far from complete. In its new avatar, the machine boasts of the energy and technical agility necessary to answer questions that current theories of physics are struggling to make sense of.

As Alice Bean, a particle physicist who has worked with the LHC, said, “A whole new energy region will be waiting for us to discover something.”

The finding of the Higgs boson laid to rest speculations of whether such a particle existed and what its properties could be, and validated the currently reigning set of theories that describe how various fundamental particles interact. This is called the Standard Model, and it has been successful in predicting the dynamics of those interactions.

From the what to the why

But having assimilated all this knowledge, what physicists don’t know, but desperately want to, is why those particles’ properties have the values they do. They have realized the implications are numerous and profound: ranging from the possible existence of more fundamental particles we are yet to encounter to the nature of the substance known as dark matter, which makes up a great proportion of matter in the universe while we know next to nothing about it. These mysteries were first conceived to plug gaps in the Standard Model but they have only been widening since.

With an experiment now able to better test theories, physicists have started investigating these gaps. For the LHC, the implication is that in its second edition it will not be looking for something as much as helping scientists decide where to look to start with.

As Tara Shears, a particle physicist at the University of Liverpool, told Nature, “In the first run we had a very strong theoretical steer to look for the Higgs boson. This time we don’t have any signposts that are quite so clear.”

Higher energy, luminosity

The upgrades to the LHC that would unlock new experimental possibilities were evident in early 2012.

The machine works by using powerful electric currents and magnetic fields to accelerate two trains, or beams, of protons in opposite directions, within a ring 27 km long, to almost the speed of light and then colliding them head-on. The result is a particulate fireworks of such high energy that the most rare, short-lived particles are brought into existence before they promptly devolve into lighter, more common particles. Particle detectors straddling the LHC at four points on the ring record these collisions and their effects for study.

So, to boost its performance, upgrades to the LHC were of two kinds: increasing the collision energy inside the ring and increasing the detectors’ abilities to track more numerous and more powerful collisions.

The collision energy has been nearly doubled in its second life, from 7-8 TeV to 13-14 TeV. The frequency of collisions has also been doubled from one set every 50 nanoseconds (billionth of a second) to one every 25 nanoseconds. Steve Myers, CERN’s director for accelerators and technology, had said in December 2012, “More intense beams mean more collisions and a better chance of observing rare phenomena.”

The detectors have received new sensors, neutron shields to protect from radiation damage, cooling systems and superconducting cables. An improved fail-safe system has also been installed to forestall accidents like the one in 2008, when failing to cool a magnet led to a shut-down for eight months.

In all, the upgrades cost approximately $149 million, and will increase CERN’s electricity bill by 20% to $65 million. A “massive debugging exercise” was conducted last week to ensure all of it clicked together.

Going ahead, these new specifications will be leveraged to tackle some of the more outstanding issues in fundamental physics.

CERN listed a few–presumably primary–focus areas. They include investigating if the Higgs boson could betray the existence of undiscovered particles, the particles dark matter could be made of, why the universe today has much more matter than antimatter, and if gravity is so much weaker than other forces because it is leaking into other dimensions.

Stride forward in three frontiers

Physicists are also hopeful for the prospects of discovering a class of particles called supersymmetric partners. The theory that predicts their existence is called supersymmetry. It builds on some of the conclusions of the Standard Model, and offers predictions that plug its holes as well with such mathematical elegance that it has many of the world’s leading physicists enamored. These predictions involve the existence of new particles called partners.

In a neat infographic by Elizabeth Gibney in Nature, she explains that the partner that will be easiest to detect will be the ‘stop squark’ as it is the lightest and can show itself in lower energy collisions.

In all, the LHC’s new avatar marks a big stride forward not just in the energy frontier but also in the intensity and cosmic frontiers. With its ability to produce and track more collisions per second as well as chart the least explored territories of the ancient cosmos, it’d be foolish to think this gigantic machine’s domain is confined to particle physics and couldn’t extend to fuel cells, medical diagnostics or achieving systems-reliability in IT.

Here’s a fitting video released by CERN to mark this momentous occasion in the history of high-energy physics.

Featured image: A view of the LHC. Credit: CERN

Update: After engineers spotted a short-circuit glitch in a cooled part of the LHC on March 21, its restart was postponed from March 23 by a few weeks. However, CERN has assured that its a fully understood problem and that it won’t detract from the experiment’s goals for the year.

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.