The Hunt for the Higgs Boson
Professor David Saxon and Professor Tony Doyle of the University of Glasgow are contributing to the largest ever collaboration of scientists, driven by a need to understand the nature of mass. Along with over 1800 other scientists from around the world, Professor Saxon and Professor Doyle are working on the ATLAS project at the CERN installation in Switzerland. A 27km circular underground tunnel, located at the foot of the Jura mountains near Geneva will be the location for an experiment where protons will be made to collide…
LHC, the Large Hadron Collider, is the particle accelerator that will be used in the ATLAS experiment. Higher energy is the key to development in this area and the (LHC) provides the most powerful instrument ever built to investigate the fundamental properties of particles.
Just as important, however, are the detectors that will record what happens when the particles collide. ATLAS is one of four major detection projects that will use LHC. The sheer scale of the collaboration is an achievement in itself, with 1800 scientists participating from more than 150 universities and laboratories in over thirty countries. And the purpose of the experiment? To shed new light on the fundamental nature of matter and reach a new understanding of what mass is. By causing protons to collide at such high energy, it is anticipated that the existence of the Higgs particle may finally be proved.
About the Higgs Boson
The Higgs boson is named after Peter Higgs, the Edinburgh University physicist who predicted its existence as long ago as 1964. His work was not immediately recognised, leading him to comment to a colleague, "This summer I have discovered something totally useless." A now famous analogy was used by Prof David J. Miller of University College London, to explain the theory to William Waldegrave, the UK Science Minister in 1993. "Imagine a cocktail party of political party workers who are uniformly distributed across the floor, all talking to their nearest neighbours. The ex-Prime-Minister enters and crosses the room. All of the workers in her neighbourhood are strongly attracted to her and cluster round her. As she moves she attracts the people she comes close to, while the ones she has left return to their even spacing. Because of the knot of people always clustered around her she acquires a greater mass than normal, that is, she has more momentum for the same speed of movement across the room. Once moving she is harder to stop, and once stopped she is harder to get moving again because the clustering process has to be restarted. In three dimensions, and with the complications of relativity, this is the Higgs mechanism."
"The greatest unsolved mystery in Physics is that we do not know what mass is," says Professor David Saxon, who leads the Particle Physics Experimental Group in the Department of Physics and Astronomy at the University of Glasgow. Over the years, Professor Saxon has focused his work in the area of particle tracking. "Think of a jet trail left in the sky after the plane has gone," he says by way of analogy. "We can find out about the nature of the particles that make up protons from the trail that they leave." Professor Saxon designed the original layout concept for the ATLAS tracking detector and will also be involved in the analysis of data once the experimental stage is reached.
When LHC is switched on in 2007 the ATLAS project can get under way. The Glasgow group have responsibility within the UK-Valencia forward cluster for contributions to the construction (ultrasonic wire-bonding) and testing on the forward tracker silicon microstrip modules. Using this array of 1000 modules, ATLAS will detect and analyse debris from the proton collisions to reveal fundamental detail about the constituent particles. The energy density in these highenergy collisions is similar to the particle collision energy in the early universe less than a billionth of a second after the Big Bang.
One of the main goals of the ATLAS program is to discover and study the Higgs particle. The Higgs boson or particle is of critical importance in particle theories and is directly related to the concept of particle mass and therefore to all masses.
"It is most likely that the Higgs boson remains only just undiscovered," says Saxon. "There are candidates, but at present no clinching evidence. Higgs events are so rare, it’s like looking for a needle in a haystack…or would be if it were not for the incredibly sophisticated data analysis techniques that are being developed."Professor Tony Doyle, also a member of the Particle Physics Experimental group in Glasgow, heads up the team that is responsible for delivering the computational power needed to make sense of the haystack of data created by the ATLAS experiments. The scale of this project, known as GridPP, means that Doyle and his team are operating at the edge of development in the area of data management and resource sharing.
CERN already lays claim to the World Wide Web as a spin-off invention. Around 1990, CERN, along with a few other particle physics labs, constituted the entire World Wide Web. At CERN the web provided the facilities required to exchange information between scientists working on different computers, perhaps at different sites.
The UK played a leading role in these developments and continues to operate at the forefront of the GridPP project. Where the web operates successfully on an anarchic basis, the Grid is a highly structured approach to managing data, organising the computational resources required and making them available to the huge number of people involved in over seventy institutes across the world. The Grid is concerned with the exchange of computer power, data storage, and access to large databases, without users having to search for these resources manually.
More recently, as a PPARC Senior Research Fellow and member of the ATLAS Collaboration, he has been working on analysis methods to search for the Higgs boson at the LHC. This task requires significant data and computational resources and led to an interest in Grid Data Management as part of the EU DataGrid project.
To return to the particle at the centre of all this activity, the Higgs boson, if it exists, is reckoned to be the particle that will explain the mass of the other types of particles that make up the atom, and therefore provide an explanation for the mass of everything. The scale of the numbers in this project is astonishing. A proton is approx 10-15 metres in length, but in order to make it travel at near the speed of light, a tunnel 27km in length is required.
During an experiment, one billion collisions will take place every second and a building that is 45m wide and 22m high is required to hold the detector that will be used to monitor the collisions of these sub-atomic particles. Then the equivalent of 10,000 PCs will be formed into a massive wide area network to deal with the data that is generated by the project. The 1800 scientists will need to collaborate closely at every stage in the process of constructing the experiment and analysing the data.
Even then, for the Higgs to appear, the "right kind" of collision needs to take place. Despite the billion collisions per second it could take many months for the type of incident that will reveal the evidence. "It does feel like trying to win the lottery," admits Professor Saxon, "but a £3bn international project does narrow the odds."