The cutting edge of particle physics today is represented by the world- renowned Large Hadron Collider (LHC) of the European Organisation for Nuclear Research (much better known by the French acronym of its original name, the European Council for Nuclear Research – Cern). This circular instrument, which has a circumference of exactly 26 659 m, runs in a tunnel some 100 m below ground and straddles the border between France and Switzerland.

The LHC contains 9 300 magnets, all precooled to 80 ˚K (or –193.2 ˚C) with 10 800 t of liquid nitrogen, and then cooled again to their operational temperature of 1.9 ˚K (–271.3 ˚C). This latter temperature is colder than that of outer space. The vacuum within the instrument is the same as that found in interplanetary space. The pressure within it is ten times less than the pressure on the surface of the moon.

At current full power, the LHC can accelerate beams of protons around its circumference 11 245 times every second at 99.9999991% of the speed of light. (These beams are controlled by the magnets.) It accelerates two beams in opposite directions, each beam having a maximum energy of 7 tera-electron Volts (TeV). (An electron Volt is a measurement of energy; 1 TeV is 1 012 electron Volts or 1 000 000 000 000 electron Volts – 1 TeV is roughly the energy of motion of a mosquito in flight but the LHC condenses this energy into a volume about a million million times smaller than that of a mosquito.)

These beams are brought into head-on collision, creating temperatures exceeding 100 000 times those found in the core of the sun. About 600-million collisions happen every second. These events are monitored by six separate experiments, each of which is a sophisticated machine in its own right. These are Alice, Atlas, CMS, LHCb, LHCf and Totem. Each of these is fitted with arrays of incredibly sensitive detectors, which monitor and track the particle collisions and their aftermaths.

Alice is the acronym of A Large Ion Collider Experiment and is focused on the conditions that existed just after the Big Bang (the event which started our universe). It is 26 m long, 16 m wide and 16 m high and weighs 10 000 t. Atlas is a general-purpose detector, aimed at the Higgs boson, extra dimensions and dark matter. It is 46 m long, 25 m wide, 25 m high and weighs 7 000 t. CMS stands for Compact Muon Solenoid and this experiment is also a general-purpose detector, with the same goals as Atlas but using different technology – basically, Atlas and CMS complement each other. CMS is 21 m long, 15 m wide and 15 m high and weighs 12 500 t.

LHCb is the abbreviation for Large Hadron Collider beauty, and this experiment is aimed at investigating the puzzle of why there is so little antimatter in the universe. It does so by focusing on a particle known as a b quark or beauty quark. It is 21 m long, 13 m wide and 10 m high and weighs 5 600 t. LHCf means Large Hadron Collider forward, because it uses what are called forward particles, which are created within the LHC, to simulate cosmic rays under laboratory conditions. This will allow scientists to calibrate and interpret large scale experiments with naturally occurring cosmic rays. By LHC standards, LHCf is a tiny experiment, involving two detectors, each 30 cm (yes, centimetres) long by 10 cm wide and 80 cm high and each weighing just 40 kg. Totem is the acronym for TOTal Elastic and diffractive cross-section Measurement. This experiment also uses forward particles and is aimed at physics that cannot be handled by the general purpose detectors (Atlas and CMS), such as the size of the proton. It also measures the luminosity of the LHC. It is 440 m long, 5 m wide and 5 m high and weighs 20 t.

To process the staggering amount of data produced by these experiments – 15 petabytes or enough to fill some 1.7-million dual-layer DVDs annually – the LHC is linked to a global network of tens of thousands of computers, known simply as the Grid. This includes Cern’s own computing core, 11 large Tier 1 computing centres in Europe and North America and more than 160 Tier 2 centres in other countries.

This data is supplied to large international groups of scientists working in collaboration.
There are more than 1 000 scientists from 30 countries working on Alice, while Atlas has some 3 000 scientists from 37 countries, CMS more than 2 000 scientists also from 37 countries, LHCb has 650 scientists from 13 countries, LHCf just 22 scientists from four countries and Totem 50 scientists from eight countries.

One of these countries is South Africa. South African scientists are involved in the Alice and, in particular, the Atlas experiments, and South African computers form part of the Grid. The iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) and the University of Cape Town are involved in Alice, while the universities of Cape Town, Johannesburg, KwaZulu-Natal and the Witwatersrand are involved in Atlas (they form a group called SA Atlas).

The cost to South Africa? A mere R3.5-million a year. (For a comparison, Britain’s annual contribution to the LHC is about £95-million or some R1.33-billion; the LHC cost £3.5-billion to build, including infrastructure costs.)

Return on investment

The LHC is not only an incredible scientific instrument, it is also a technological wonder and an engineering triumph. And South Africa is benefiting from all three aspects.

“In Atlas alone, we have more than 30 South African scientists and postgraduate students involved,” highlights University of Johannesburg physics professor Simon Connell, a leading member of SA Atlas. “This figure has grown by a factor of three since 2010. Participation in the LHC has reversed the brain drain. The diaspora is returning. People from South Africa are coming back because they can participate in this.” So far, about ten South African PhDs and Masters degrees have been completed on the Alice experiment, while several are nearing completion on Atlas.

South Africa is also benefiting in tech- nology and engineering terms. “Cern is actually seeing itself as a knowledge and technology hub. They see themselves as placing experts in contact with each other in an environment that will stimulate innovation,” he points out. “They recently developed a website for Cern-related research to facilitate and record the innovation that is happening. There is an incredible technopark at Cern with all the spin-off companies. It is very easy to get involved at the moment. There are extremely generous Cern-related intellectual property sharing and technology transfer oppor- tunities. People are very welcome to participate. This is true of both software and new technologies.” And Cern is transferring technology to South Africa.

After operating since 2009, the LHC has now entered what is called Long Shutdown 1, which will last for nearly two years and will see the entire instrument upgraded, allowing it to be operated at higher energies than hitherto possible. The upgrade will include new detectors in the experiments. “We’re working on a detector component for Atlas,” he reports. “We’re participating in the development of new detector tech- nologies which can be used in the upgrade of Atlas. We will be participating in the radiation hardness testing of this detector. We are looking at using the neutrons [produced by the Safari-1 research reactor] at Necsa [the South African Nuclear Energy Corporation] and the ion beams [produced by the accelerators] of iThemba LABS.”

Cern is looking to build intelligence into each and every pixel of a detector – something that was not previously possible. This would allow each detector system to determine what data it wants to ignore and what it wants to store and pass on to the computer system (which in turn will “decide” what should be brought to the immediate notice of the human supervisors). This will have great benefits for medical imaging technology, astronomy, data processing and electronics.
“South Africa is developing detector expertise and there is talk about creating some manufacturing capacity here – it would be advanced manufacturing, funded by the Department of Science and Technology and, if we win a contract, by overseas investors as well,” he states.
Already, this work has resulted in the local development of a device that can clearly identify diamonds within rock in laboratory conditions. Based on several areas of technology transfer from Cern and in partnership with scientists and engineers who are collaborators at Cern, a South African-developed technology demonstrator has shown the ability to detect diamonds within kimberlite rocks up to 15 cm in diameter, in a scaled-down run-of-mine scenario.

It is now being further developed for possible commercialisation in cooperation with local mining equipment and services group Multotec and the commercialisation offices of the Universities of Johannesburg and the Witwatersrand. “The patent is South African,” he assures. “It is now patented in virtually every country that mines diamonds. This device will enable a waterless, low-energy, small-plant-size solution for diamond miners.”

Hunting the Higgs

Of course, the prime purpose of the LHC is scientific, and it is particularly associated with the hunt for the Higgs boson. Last July, scientists announced that data from the LHC had revealed a particle consistent with the Higgs boson. But that did not mean the search had ended. “It walks like a Higgs boson, it talks like a Higgs boson, but people are not certain it is the Higgs boson,” says Connell.

At the last high-level physics conference, the Hadron Collider Physics Symposium, held in Japan in November, only half the relevant data from the LHC had been analysed. Now, in several search cases, all the data has been analysed and an update is expected at the next such conference, the Moriond Conference, to be held in Italy next month. (All discoveries made by the large scientific teams working on each experiment may only be announced publicly at specific events like a conference; individual scientists and subteams cannot say anything until a formal paper has been presented at such an event.)

The concept of the Higgs boson was developed in 1964 by Peter Higgs and others to fill a gap in the dominant theory in particle physics, known as the Standard Model. The Standard Model sees all matter as being composed of two fundamental types of particle – quarks and leptons. (A hadron is a subatomic particle composed of two or more quarks, such as a proton or neutron.)

There are six quarks and six leptons, grouped, in each case, into three generations of two particles each. The first generation comprises the lightest and most stable of the quarks and leptons and these form the most stable matter in the universe. The second and third generations are each, in turn, heavier and less stable and decay rapidly to more stable particles.

The first generation quarks are the up quark and the down quark, the second generation is made up of the charm quark and the strange quark, while the third generation comprises the top quark and the bottom quark. The three generations of leptons are, first, the electron and the electron-neutrino, second, the muon and the muon-neutrino and third, the tau and the tau-neutrino. Each particle has an intrinsic angular momentum, known as spin, which exists even if the particle is at rest.

There are also four fundamental forces in the universe – the strong force, the weak force, the electromagnetic force and gravity. The strong and weak force are only effective over very short ranges and are dominant only at the subatomic level, while the electromagnetic force and gravity have infinite range. (The weak force, while weaker than the strong and electromagnetic forces, is considerably stronger than gravity.)

All but gravity are known to arise from the exchange of force carrier particles between the quarks and the leptons. These force carrier particles are called bosons. Each force has its own particular carrier boson – the gluon carries the strong force, the W boson and Z boson carry the weak force and the photon carries the electromagnetic force. Each boson carries a discrete amount of energy.

(It is presumed there is a graviton that carries gravity. Gravity is also strongly connected to spacetime, as it is manifested by the bending of the fabric of space-time. Recent years have seen the development of very sensitive large scale astronomy-based and particle physics-based experiments, in an effort to chase down the nature of gravity. It is expected that South Africa’s role in the Square Kilometre Array radio telescope project may ultimately lead to such experiments being attracted to Southern Africa.)

The Higgs boson was postulated to explain the existence of mass, which could not be explained by the known particles and forces. “In order for the apparent Higgs boson to be the boson predicted by Peter Higgs, it must have very specific properties. Its intrinsic spin and parity (its symmetry with its mirror image) as well as the strength of its interactions with other particles in the Standard Model are set down very specifically in the theory,” he explains. “People have been looking at how it interacts with the other particles. There is still some uncertainty about its spin and parity. At the moment, within error bars the Higgs-like boson seems to be the Higgs boson. There is intense interest in these developing analyses, as, for example, the amount of Higgs-like bosons decaying into two photons is a little larger than predicted by the Standard Model. There are also fluctuations in the background that may ultimately turn out to be other bosonic particles. But the error bars are still large. We hope that they will be diminished with the update at the next conference.”

The upgraded LHC will be able to produce millions of Higgs bosons a year. “It will basically become a Higgs boson factory. The Higgs boson will be deeply studied.”

Beyond the Standard Model

The Higgs is not only important in itself. It is also likely to provide a window, or portal, into really advanced physics, into phenomena that the Standard Model cannot explain. First of all, there may be other Higgs bosons. “If it materialises that there is more than one, that would be very significant,” avers Connell. “That would take us beyond the Standard Model.” Even if there is only the boson originally postulated by Higgs, that would also have a profound impact. Its confirmation would inject infinities into the equations of the Standard Model and render them meaningless. “New physics would be needed to tame these infinities.”

Nor is this all. Even though it has been, in many respects, fantastically successful, the Standard Model has always had problems. Most notably, it cannot account for gravity. “We don’t yet have a [quantum – that is, subatomic] theory of gravity,” he affirms. “This is a huge shortcoming. Basically, the whole issue of gravity is wide open.”

Neither can it explain why there are the number of families of fundamental particles that there are. Nor can it suggest what existed before the Big Bang. “You can’t formulate such questions mathematically within the Standard Model,” he points out.

Then there are dark matter and dark energy, which together are believed to comprise 95% of the universe, but are not found within the Standard Model. Another puzzle to be solved is that massive imbalance in the universe between matter (very much dominant) and anti-matter. Yet the Big Bang should have created equal quantities of both.

“The LHC is doing research into all these things in parallel to the Higgs boson research,” he clarifies. “It’s all sitting there in the data and these things are and will be searched for in the data. Some of the answers may be in the data already collected. With the upgrade, there will be much more data.” The data from the LHC could result in the discovery of higher dimensions, parallel universes, microscopic black holes (technically called singularities) and even stranger things.

The two major current alternatives or extensions to the Standard Model are String Theory and Supersymmetry. String Theory is an attempt to provide a single unified explanation of the underlying structure of the universe and is sometimes flippantly called the Theory of Everything. Very simply, String Theory regards all the fundamental particles as being minute loops of “string”, or tensions in the geometrical fabric of space-time, the different particles resulting from different oscillations of the string loops. Although this has produced good mathematical results, and can explain everything the Standard Model can, plus more (including gravity), there is still no experimental evidence to support it.

Supersymmetry doubles the number of fundamental particles. For each of the particles we know about, there is a “superpartner” with a spin that differs by one-half. Combining supersymmetry and Albert Einstein’s general relativity also leads to a situation in which gravity could be integrated with the other three fundamental forces in a single theory. Moreover, the first generation superpartners could form the mysterious dark matter that suffuses the universe. Unfortunately, Supersymmetry creates a number of fundamental new problems as well.

“There are lots of hypotheses, but we need experiments,” asserts Connell. That is what the LHC was built to provide. The journey has just begun and it is going to be a mind-bending trip.