CERN’s pentaquark: The Large Hadron Collider continues to amaze the science world
With the recent discovery of the pentaquark, we are once again reminded of the pioneering work that’s being carried out at CERN in Geneva.
Pentaquarks are an exotic form of matter first predicted in 1979. Everything around us is made of atoms, but since the 1960s, we’ve also known that protons and neutrons are made up of even smaller particles known as “quarks,” bound together by “strong force,” the strongest known force in nature.
If protons are hit hard enough, the strong force can be overcome and the protons smashed apart. The quark model actually explains the existence of more than 100 particles, all known as “hadrons” and made up of different combinations of quarks. For example the proton is made of three quarks. All hadrons seem to be made up of combinations of either two or three quarks, but there is no obvious reason more quarks could not stick together to form other types of hadron. Behold the pentaquark: five quarks bound together to form a brand new type of particle. Until now, nobody knew for sure if pentaquarks actually existed – and, although there have been several discoveries claimed in the last 20 years, none had stood the test of time.
This concept image shows what the pentaquark looks like.
How does the Large Hadron Collider work?
The collision process begins with either hydrogen or lead. To produce a proton stream, operators strip electrons away from hydrogen atoms. To produce an ion stream, operators heat lead atoms to 550 degrees celsius and then pass the lead vapour through an electric current to ionise it. Once the particles are ready, the operators pass them through an accelerator chain outside the LHC track itself. This chain applies radio frequency electrical fields to energise the particles (get them up to high speed), before injecting them into the LHC’s circular “beam pipe” tracks. As the beams zip around the pipes, in a ultra-high vacuum, they pass through periodic radio frequency cavities. These cavities produce electrical fields that energise the particles, keeping them moving at top speed. The pipes intersect at various collision points around the LHC ring, and the particles collide. Detectors at the intersection points register what happens. The biggest engineering challenge is guiding the particles – that is, steering them along the circular track and focusing them into beams. The LHC does this with powerful electromagnets, which generate magnetic fields to push the particles in the right direction. There are a total of 9,300 magnets in the LHC, including 1,232 15-metre-long dipole magnets that bend the beams so they follow the track, and 392 five to seven-metre magnets that focus the beams.
See the different parts of the LHC with this helpful diagram.
A conventional electromagnet consists of a coil of wire, hooked up to a power source that produces an electrical current. The current in the wires generates a magnetic field, thanks to the electromagnetic effect. In the massive LHC, the energy consumption for this type of electromagnet would be prohibitively expensive. Instead, the LHC sports supercooled superconducting electromagnets made from niobium-titanium cable. Niobium-titanium is a superconductive metal, meaning that if you keep it cold enough, it offers no electrical resistance and sustains an electrical current indefinitely. In other words, you can use it to create electromagnets that continually carry a current (13,000 amps, in the case of the LHC), while consuming no power whatsoever. The catch is that you have to keep the magnets incredibly cold. To do this, engineers first cool the magnets to -193.2 degrees celsius, using liquid nitrogen. Next, they cool the magnets down to a steady -271 degrees celsius, using an advanced refrigeration system. This system, essentially the biggest fridge in the entire world, uses superfluid liquid helium as a coolant.
How fast is the Large Hadron Collider?
The Large Hadron Collider (LHC) uses an array of 9,300 supercooled electromagnets to guide and accelerate particles – namely protons, around the 27km underground ring at CERN, up to speeds extremely close to that of light. At their fastest, these particles travel at around 299.8 million metres per second completing 11,245 laps of this ring every second. This is equivalent to travelling around the circumference of the Earth seven and a half times in one second.
This image shows a simulation of a particle collision.
The LHC has two rings with beams of trillions of particles zooming around in opposite directions. Detectors are placed at certain points where the pipes intersect causing collisions to occur. As both the particles are travelling in opposite directions at nearly the speed of light, you might expect their combined collision speed to be almost twice the speed of light. However both particles would measure their collision speed to be less than the speed of light. This seems counter-intuitive but is accounted for by the slowing down of time and warping of space as explained by Einstein’s special theory of relativity. This theory explains why no particle with mass should be able to travel faster than light, as it would require an infinite amount of energy to get there!
Top 5 Facts: Peter Higgs
Prof Peter Higgs has won the world’s oldest scientific prize – the Royal Society’s Copley Medal – for his work on the theory of the Higgs boson.
1 High five – Physicists use standard deviation to determine an official discovery or not. At 5 sigma, the level reached when scientists pored over the Higgs boson experiments, there’s a one in 3.5 million chance the data is a fluke.
2 The ‘God particle’ – The Higgs boson has been nicknamed the ‘God particle’, attributed to the Nobel prize-winning physicist Leon Lederman, whose book originally referred to it as the ‘goddamn particle’, but this was later amended.
3 Need for speed – Two of the highest-energy particle accelerators in the world were employed to search for the Higgs boson. In addition to the LHC, the Fermilab’s Tevatron, near Chicago, IL, was used.
4 Big Bang – Conditions conducive to the creation of the Higgs boson – similar to those at the time of the Big Bang – were created by smashing elementary particles together at nearly the speed of light.
5 Humble Hawking – There were many who doubted the existence of the Higgs boson, including Professor Stephen Hawking, who bet Gordon Kane of Michigan University $100 that CERN would find nothing.
Can the LHC be used to create a black hole?
Image of a black hole. Credit: NASA
In theory, to make a black hole all we would need to do would be to compress a huge amount of matter and energy into a tiny amount of space. In practical terms, however, this is incredibly difficult. There is much disagreement about the minimum size a black hole can be, and standard physics offers different answers to more exotic ‘multi-dimensional’ physics. Einstein said that mass and energy are equivalent – you can turn mass into energy and energy into mass – so very high energy particles smashing together could potentially lead to the creation of a black hole. However, the energy required for this would be the equivalent to taking the mass of a mountain range and converting it into energy. For reference, a nuclear weapon only releases the energy of a few grams worth of matter. So even the Large Hadron Collider at CERN, with its particles traveling at close to the speed of light will not, under standard physics, be able to create a black hole.
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