There are plenty of rumours that CERN may have accidentally split the time and space continuum. In this article the problem of general relativity is broken down by Berkeley Sychrotron scientist Petr Hoava, who theorises that if they could split time and space from each other, they would understand the pure relationship of gravity on objects better. The calculations made currently, in attempting to define the ‘graviton particle’ (the one physicists theorise exists but still can’t find) always result in an infinite number. This is one of the many fundamental issues the 5000 international scientists work on at CERN in Switzerland and other international facilities.
CERN and other synchrotrons specialise in the study of nuclear physics - study of the nucleus of the atom in context with matter and the universe. They also apply these experiments to broader commercial, geological, biological and defense fields. From the core experiments defining the standard model, anti-matter and radiation, other areas of research are wide ranging. These include macromolecular crystallography used in the Pharmaceutical industry to develop new drug candidates, microfocus spectroscopy (high energy X-rays) to study the composition of dust from comets, analysis of performance materials for engineering, identification of environmental pollutants, analysis and development of nanotechnology structures, and other solutions for radiotherapy, palaeontology, archaeology, art history and forensics.
To carry out these experiments, facilities at the synchrotrons dotted around the world are based on similar processes and designs. CERN’s facilities are recognised as some of the most sophisticated, as well as the largest, in the world. Below is a comprehensive diagram of the elements at the CERN site.
Ionising Energy
The oldest component of the CERN site is the Proton Synchrotron. As the name implies, this beam line accelerates or speeds up protons ready for collisions. Protons (positively charged particles), make up part of the nucleus of atoms. To prepare these protons for the Synchrotron, first the protons must be isolated. To strip the proton from a hydrogen-1 atom the electron it is bound with must be removed. This requires the use of ionising energy. Physicists work out, using mathematical calculations, the ionising energy required to split apart different atoms to produce different particle types - neutrons, protons etc. Different structures require different levels of energy to be split. The study of the interactions between energy and atom nuclei was key to the development of the nuclear bomb.
Nuclear Fission
The atom bomb, created by Manhattan Project scientists, worked on the principle that matter can become energy and energy can become matter. This was part of Einstein’s theory of relativity of E = mc2. 600 milligrams of Uranium was used in the Hiroshima Bomb. By introducing the correct ionising energy to cause a violent collision, all the uranium atoms contained in the core of the bomb would be subject to nuclear fission. Nuclear fission requires a neutron to split a heavy element (in this case uranium), to produce more neutrons to continue splitting the heavy element atoms. This chain reaction (or cascade) very quickly creates exponential amounts of energy, causing a nuclear explosion.
James Chadwick, a scientist from Cambridge University, discovered the neutron, receiving the Nobel Prize in 1932 for this work. He also spent much of his research career studying the behaviour of radioactive elements. Of particular interest ‘he looked at the nuclear charge of platinum, silver, and copper, and experimentally found that this was the same as the atomic number within an error of less than 1.5 per cent’. Chadwick worked under Ernest Rutherford (New Zealand born of a Scottish father and English mother). After some very interesting work on the magnetisation of iron, Rutherford researched at the Cavendish Laboratory in Cambridge, beginning his work on detection of ions and subsequently alpha and beta rays using magnet coils (now known as solenoids). Much of the work Rutherford and his ‘boys’ did focused on breaking apart the nucleus of the atom and identifying the different particles and waves that emitted from this process. The Cavendish Laboratory initially used oscillation techniques of detection, but moved to develop electrical methods. This work forms the basis of many of the particle detection facilities in CERN and other synchrotons.
Accelerators
Particle accelerators work by accelerating specific particles isolated using ionising energy. These are sped up through beam lines (precision engineered tubes filled with a vacuum, free of other particles) using electrical fields of alternating positive and negative energy. A series of dipole magnets (magnets charged with electrical current) keep the particle beams on track. Targets can be set up in experiment facilities for these particles to collide in to.
The Proton Synchrotron (PS) accelerates protons to enable detectors to assess what they are made of: matter (quarks), anti-matter (anti-quarks), gluons (the glue that holds them together) etc. The PS is also now used to accelerate ‘alpha particles (helium nuclei), oxygen, sulphur, argon, xenon and lead nuclei, electrons, positrons and antiprotons’. The PS has been engineered to become more efficient in the decades since the first acceleration of protons. It now provides many of the particles for experiments in the larger rings - the Super Proton Synchrotron (SPS) and the Large Hadron Collider.
Particle Detectors
ATLAS
The largest general particle detector at CERN is A Toroidal LHC ApparatuS. It uses a series of magnets and detectors along the length of the apparatus, to detect different particles according to the experiment being run. The particles from the accelerator are fired at a target inside the apparatus, causing a collision. The detectors pick up the various products of the collision, including different elemental particles (particles that cannot be broken down any further), heavy unstable particles, radiation emissions, anti-matter etc. The ATLAS experiment, involving 3000 physicists from around the world, focuses on working out why particles have mass, what is the rest of the 96% of the universe made up of, and why matter seems to be the preferred state of particles.
Image Key: 1) Muon Spectrometer: Forward regions (End-caps) and Barrel region. Magnet System: (2) Toroid Magnets (3) Solenoid Magnet. Inner Detector: (4) Transition Radiation Tracker (5) Semi-Conductor Tracker (6) Pixel Detector (7) Liquid Argon Calorimeter (8) Tile Calorimeter.
The Muon Spectrometer detects these heavy and unstable electron (or electron neutrino) particles that are not detected by other parts of the system. The Toroid (doughnut/star shaped) Magnet in Atlas is one of the largest magnets ever built for a particle detector. The Solenoid Magnet is a superconducting coil inside the detector, which delivers a solenoid field, which can then be mapped, allowing the positions of particles to be recorded with a precision error rate of 0.05%.
Every experiment involving acceleration and collision of particles in the circular Syncrotrons and Hadron Colliders produces radiation. Particles will at times collide with the outer edge of the beam as they are accelerated. This paper goes in to more detail of the design required to minimise radiation dose exposure from the beam lines at CERN.
The Transition Radiation Tracker is however part of the experiment. It measures the frequency and optical radiation emitted by charged particles as they pass through the detector. It operates together with the Semi-Conductor Tracker and Pixel Detector to measure the precise paths of these charged particles. The Liquid Argon and Tile Calorimeters are designed to absorb all of the particles from a collision, in order to measure the amount of energy (calories) produced by the collision.
Compact Muon Solenoid
The CMS is the second general purpose particle detector at CERN. It sits at the northern side of the LHC. This detector uses the largest 4-Tesla superconducting electromagnet solenoid ever made to detect particles. It is able to radically divert the path of the heavy electrons or Muons to measure their momentum and speed. The detector also senses other particles in a similar way to the ATLAS detector, but is approximately half the size.
The CMS and ATLAS experiment were run to confirm the existence of the Higgs Boson. They are fairly sure that the Higgs Boson existed as the experiment behaved as predicted, with muons being in the right place at the right time as predicted by calculations. The Higgs Boson weighed 125 billion electron volts, the heaviest boson discovered to date. Scientists believe it to be the force particle which allows the matter in our universe to form.
ALICE and LHCb
These two detectors are more specialist than the general particle detectors. ALICE is able to detect most particles like the other detects but it is also designed to measure collisions of massive ions such as lead. Lead is the most stable heavy ion at 208 times the size of a proton. Upon collision the quarks and gluons are released from the hadron (a composite particle that contains both matter particles and force particles). These then form a quark-gluon plasma (QGP). This plasma then reforms in to clumps and speeds off out of the centre of the collision. This process is a confined recreation of what the beginning of the Universe might have looked like, reaching temperatures of 100,000 times that of the sun on a very very small scale. The ALICE experiment also studies the confinement, or the holding together of matter, by force particles that can only be broken with superheating.
In the standard model of physics, particles are arranged symmetrically in sets of four. The LHCb or Large Hadron Collider Beauty studies the level of symmetrical violation occurring when b-hadron or very heavy particles (which have a bottom quark, the heaviest and most unstable of the quarks or matter particles) are collided. The purpose is to delve deeper into the symmetry, or lack of, between matter and anti-matter in the universe. The assumption is that every matter particle has a corresponding anti-matter particle. LCHb tests that assumption and looks at anomalies, exotic hadron spectroscopy, Charm and Electroweak physics.
That concludes the brief outline of the structure of CERN and the Large Hadron Collider.
Next we take a look at the global network of synchrotrons, their geographical positions, purpose and how these centres of nuclear physics excellence work together…
The Light Sources.