The big ring gets an even bigger ring as an upgrade. Universe, beware!
The gigantic LHC particle accelerator is a major success, but the ambitious physics experiment has failed to identify dark matter. Now, scientists aim to build a new device to collide particles so forcefully that the Big Bang is recreated.
Asmall bundle of protons are heading for a violent death. By means of radio waves, scientists pump ever more energy into the bundle, which travels through the narrow tube at a speed close to that of the light. few cm away, an identical bundle is speeding through a second tube in the opposite direction. As the bundles pass through huge detectors, physicists make them collide with a force that cannot be matched by any other device in the world. The protons are pulverized, and the detectors now try to identify any new, exotic particles that might originate in the cloud of shattered protons.
This is how physicists from the European Organization for Nuclear Research, CERN, have studied the tiniest building blocks of the universe for decades. Since 2009, they have used the tremendous LHC accelerator, which has been a major success in many ways, but even the world’s largest particle accelerator has failed to do one thing.
Already when the experiments began, physicists hoped that the high-energy LHC collisions would result in the theoretical dark matter, which is vital for astronomers being able to explain how the galaxies can rotate so fast without ejecting their stars in all directions. But the particles of darkness have not been identified, and so, CERN and 70 research institutions throughout the world plan to build the accelerator of the future, the Future Circular Collider (FCC). The huge device will have a circumference of 100 km and be able to collide protons seven times more forcefully than the LHC. Invisible twins save theory In 2012, when LHC scientists identified the Higgs boson, it was a monumental discovery. The existence of the particle is the definitive proof that history’s most comprehensive and successful physics theory, the standard model, is correct. The standard model is a classification of elementary particles, that can be divided into two types – atomic building blocks and power-carrying particles.
Among the atomic building blocks, you will find 12 particles: six different types of quarks, three types of electrons, and three
types of neutrinos. With these basic ingredients, all atoms in the universe can be produced. The standard model also describes three of the four fundamental forces of nature – the electromagnetic force, the strong nuclear force, and the weak nuclear force, which each have their own force-carrying particles. The most well-known is the photon, which is the force-carrying particle of the electromagnetic force. However, scientists have not been able to find a force particle, which carries the fourth force, gravity.
So, physicists have developed quantum gravitational theories, in which the mass attraction between bodies is produced via exchange of force-carrying particles known as gravitons. But the theory only works out right mathematically, if each elementary particle has an invisible twin. This means that the standard model’s atomic building blocks such as quarks must have force-carrying twins known as squarks, whereas force-carrying particles such as photons must have atomic building block partners known as photinos. Those were the twin particles that physicists hoped the LHC would find. Twin particle discoveries would not only pave the way for a theory that can explain all phenomena in the universe, but rather also be the proof that dark matter exists, solving a major problem for astronomers, who cannot explain how stars can orbit the centres of galaxies so fast without being chucked away – unless gravity from invisible dark matter hold them in place.
LHC is not sufficiently powerful
In physics, mass and energy are two sides of the same coin. The heavier the particles are, the higher their energy, and so, particles’ mass is often measured in gigaelectron volts (GeV). After analysing billions of LHC proton collisions, physicists have concluded that the twin particles must at least have a mass of 1-2,000 GeV. But the heavier the particles, the more energy is requires to produce them in accelerators. The LHC might not be able to produce such heavy particles – the Higgs boson only weighs 125 GeV. So, physicists need a new huge accelerator which can generate much more energy.
Higgs boson to be studied
The FCC accelerator will be completed in 2035, but already now, CERN project staff is working on its design. Very few details have been revealed at this point, but there is every indication that the accelerator will be built in a tunnel with a circumference of 100 km. The huge size is due to the fact that charged particles such as protons emit radiation, when their paths are bent, causing them to lose energy. The large circumference minimizes the bend and so the energy loss, reducing the quantity of energy to be pumped into the particles, as they circulate in the ring.
According to FCC Deputy Study Leader Frank Zimmermann, the tunnel will most likely end up including more than one accelerator. First of all, engineers will probably be asked to build an electron accelerator, in which electrons will collide with their antiparticles, known as positrons. Collisions between electrons and positrons are simple, as they are not made up of smaller particles. In the collisions, the electrons are converted into pure energy, which is subsequently converted into particles with corresponding energy, which the detectors pick up. So, the collisions are purer and easier to analyse, making an electron accelerator perfect for accurate measurements.
The new device will be able to generate millions of Higgs bosons, whereas the LHC will only generate abut 1,000 up until 2035. A Higgs boson is the elementary particle responsible for everything in the universe having mass. Physicists know that a Higgs boson combines with the other elementary particles and that the particle’s mass depends on the strength of the coupling. Electrons combine with Higgs bosons with a modest force, and hence, they have a small mass, whereas quarks are heavier, as they have more powerful couplings. With the new device, physicists will be able to take a closer look at the coupling mechanism.
After a few years, the electron accelerator will be scrapped and replaced by a proton accelerator. Protons have a 2,000 times larger mass than electrons and can provide much more high-energy collisions. And unlike the electron accelerator, it can be used to spot new particles. Proton collisions can provide physicists with a record high collision energy of 100,000 GeV, which might be necessary to produce the twin particles. The disadvantage of proton accelerators is that it is difficult to analyse the collisions. Protons are made up of small atomic building blocks known as quarks and the force- carrying particles of gluons, and so, the cloud of particles that spreads in the wake of a proton collision is much more complex than in the case of electrons.
If the accelerator spots twin particles, it will be the discovery of the century, as it would solve a series of physics and astronomy problems. And if the FCC does not identify dark matter, scientists will know that twin particles do not exist, as in that case they will be too heavy. So even another failed attempt will make scientists wiser.