Seeing Beyond the Higgs: What’s next for the Large Hadron Collider?

Burried layers deep in the ground, about 330 feet below the Franco-Swiss border, lies a marvelous machine, one that has been pushing the boundaries of our knowledge of the universe since its activation in 2008. Thus far, the Large Hadron Collider is the biggest machine ever built and the largest experiment ever attempted. About 27 km in circumference and comprising 1296 superconducting magnets, the LHC has been churning out the smallest bits of matter in the universe to reveal our origins and answer the most fundamental questions about our universe.

The LHC’s job is to recreate the conditions that were present in the universe less than a billionth of a second after the Big Bang. What it does is that it accelerates protons at 99.999999% the speed of light (two beams of protons in opposite directions) around a circular tunnel before colliding them together head-on inside four giant detectors. The protons simply come from hydrogen gas. Each beam consists of 2808 bunches of protons. Each bunch of protons consists of 1.15×1011  protons (that is a 100 billion protons)! Each bunch of protons is also separated by no less than 25 feet (27 metres). The protons are accelerated to energies of 7 million million electron-volts (7 TeV) per beam and then are collided together at a combined total energy of 14 million million electron volts (14 TeV). 1,296 superconducting dipole magnets (each 13.5 metres long) and more than 2,500 other magnets are used to bend and guide the high energy beams at precise curved paths. The superconducting dipole magnets must have a field strength of 200,000 times the strength of the Earth’s magnetic field. To accomplish this, the magnets must conduct electricity efficiently without loss of energy, so they are operated at 1.9 kelvins (even colder than the space between the stars!). A distribution system supplying liquid helium is actually connected to the LHC for that purpose.

But why do this? The new particles produced as a result of these proton collisions are quite different than the particles originally collided together. They are particles that we can no longer see in the world around us. And despite that fact that these new particles are only short-lived, they played a fundamental role in building the universe. So, to understand the origin of the universe, we need to understand these very fleeting particles that have disintegrated when the universe began. They are the ingredients of the universe. The high energy collisions take us back to the beginning of the Big Bang, when all the particles in the universe were there, but before they had coalesced to form protons and neutrons. The LHC will also help us understand how gravity works.

All the matter that we know and can see accounts for only 4 percent of the universe. The rest (96 %) is “dark matter” and “dark energy” which are not what they sound and which we cannot see or detect but which scientists believe guide the movements of stars and galaxies. That was also one of the reasons why the LHC was built. Supersymmetry is one of the theories which could explain dark matter. Supersymmetry predicts that every particle in the Standard Model of Particle Physics has a yet-to-be-discovered partner particle. And one of those particles could well be the one that makes up dark matter. And if they do exist, they will be detected by ATLAS and CMS. The LHCb detector will help us understand the matter-antimatter difference and the evolution of our matter-dominated universe. There are huge complexities which we do not understand from string theory to the nature of spacetime to wormholes and the LHC will take us onto a voyage of discovery into these unknown lands in order to revolutionize our understanding of the universe.

How the LHC works
How the LHC works: Protons pass through a chain of accelerators. First, hydrogen nuclei from hydrogen gas are stripped off their electrons and then sent to the Lina2 accelerator, where they are accelerated at 50 Mega-electron volts. The beam is then injected into the Proton Synchrotron Booster (Booster) where they are accelerated to 1 Giga-electron volts and afterwards sent off to the Proton Synchrotron where they are accelerated 25 Giga-electron volts. The beam is then pushed to 450 Giga-electron volts by the Superproton Synchrotron and finally to 7 TeV by the LHC main ring, where two proton beams are injected in opposite directions. Photo credit: CERN
The beam pipes must maintain a vaccuum, even emptier than that of intergalactic space! Or, the gas molecules will scatter/deflect proton collisions. Photo credit: CERN

As previously discussed, the four collision points are giant detectors that capture the instant of particle collisions. Two such detectors are CMS (Compact Solenoid Magnet) and ATLAS (A Toroidal LHC Apparatus). The CMS detector takes a 100 Mega-pixel photo at a rate of 40 million times per second! 21 metres long, 15 metres wide, and 15 metres high, it is the heaviest instrument ever built and is built around a massive superconducting solenoid. At the center of the CMS, conditions that were present a trillionth of a second at the Big Bang are recreated. After the protons are collided, new particles are created, at which point signals are sent to over a 1000 computers at a rate of millions of gigabytes per second!

LHC Collision points  Source: University of Washington
LHC Collision points
Source: University of Washington

At 46 metres long, 25 metres in diameter, and 7000 tonnes, the ATLAS is the largest volume particle detector ever built and it is designed to capture proton collisions at 600 million times a second. Its sensors contain as many transistors as there are many stars in our whole galaxy! This is a detector that is 20 metres high but yet is built to the precision of the diameter of a human hair!

The ALICE detector does not collide protons but observes collisions of complex lead or gold nuclei in order to recreate conditions that were present less than a millionth of a second after the Big Bang when the high energy state of matter ruled the universe.

ATLAS Detector  Source: CERN
ATLAS Detector
Source: CERN

In 2012, both the CMS and ATLAS detectors were reported to have seen excesses of particles that fit the profile of a Higgs boson with a mass of 125 and 126 GeV respectively. In other words, the Higgs boson was discovered! The Higgs boson is one of the tiny units of matter that make up the fundamental building blocks of the universe. Empty space is supposedly not empty at all, but rather it is full of the Higgs field. The Higgs boson was theorized in order to explain why some force-carrying particles like the W and Z bosons (which were discovered in the 1980’s) have mass while other particles such as photons do not. It was also theorized that W boson interactions would be impossible without the Higgs boson. These were bosons that demanded a Higgs. But, such a scenario of W bosons scattering off each other is a very rare occurrence at the Large Hadron Collider and ATLAS has seen evidence for 34 of these events among billions of collisions. It was definitely a milestone discovery that put the last critical piece of the Standard Model of Physics in place.

The LHC was shut down for upgrades in 2013 but just a few days ago on June 3rd, this legendary machine was restarted at double the energy (13 TeV) of its first run (which began with a collision energy of 7 Tev), in order to optimize particle collisions for potential new physics. The aim at the moment is to look for new physics, new elementary particles, search for dark matter and dark energy, and even to search for extra dimensions — all remarkable possibilities which may revolutionize the world of science. This remarkable endeavor will certainly will take us onto a voyage of discovery into uncharted realms of physics. What a time to be alive!

Featured image courtesy of: CERN


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