Higgs: why we care


The media was recently in turmoil about the confirmed sighting of the Higgs boson, an unusual event not just for the discovery of the particle, but also because hard science does not often make headlines in the popular press.

It is tempting to think the mainstream media picked up on the excitement – bordering on fervour – that greeted the discovery in scientific circles, but it is more likely due to the Higgs boson’s controversial nickname: the God particle.

Although that nickname is widely despised among scientists, the importance of the discovery really cannot be overstated: the discovery of the Higgs boson is probably the most important scientific event of our time. So much of our current scientific thinking rests on an underlying theory, which would fall apart in spectacular fashion if the Higgs boson was proved to be nothing more than a scientific fantasy.

Also, the success is more than just a scientific one. The discovery is also a triumph of the first order for information technology – the volume of data processed, and the network connecting the many institutions involved, is an engineering feat worthy of its own accolades.

A question which baffles many observers is why so much rested on a particle which we didn’t even know existed or not. And in fact, we still do not – the evidence looks good, but it’s not definitive and will need a great deal of corroboration and peer review before anyone wins a Nobel Prize.

The Higgs boson was theorised in 1964 by Peter Higgs, along with the Higgs Mechanism. Bosons are subatomic particles, which along with quarks and leptons, are believed to combine to form the elementary particles we learn about in school – electrons, protons, and so on – as well as giving rise to fundamental forces such as electromagnetism. The Higgs boson in particular is believed to interact with other particles in a way that causes them to have mass, an obviously fundamental property of matter.

Those quarks, leptons and bosons come in several flavours, which are predicted (and required) by the Standard Theory of particle physics. The Standard Theory is a framework which attempts to explain the interaction we see in the universe in terms of particles and interactions, such as magnetic and nuclear forces. The theory is far from perfect – gravity does not fit the theory, for example – and may, in fact, be completely wrong, but it is currently about the best option on the table.

To test the Standard Theory, experiments are conducted to detect the presence of the various particles. If a particle is found where it is expected, that is chalked up as confirmation that the Standard Theory still holds water. The Higgs boson stood apart from its neighbours in that it eluded discovery for many years. Repeated experiments narrow the focus on the area where the particle was expected to be found, with no positive results.

Lacking a Higgs boson – if experimentation had ever concluded it was not there to be found at all – the Standard Theory would simply fall apart. Sans Higgs, it fails to explain a fundamental phenomenon of the universe – why particles have mass – and would have to be scrapped and replaced with a new theory (there are alternative theories available that do not need the Higgs boson). Enormous amounts of research and money would have been, not wasted – the march of science always includes exploring dead ends – but fruitlessly misplaced.

If the evidence does hold up, and the Higgs boson is indeed where we think it is, it will confirm a critical piece of the current understanding of the Standard Theory. So our entire understanding of the universe, from one point of view, relied on that confirmation of the Higgs boson’s existence.

The search for the Higgs boson was one of the principle goals behind the construction of the Large Hadron Collider (LHC) at CERN in Switzerland. The LHC accelerates particles to near light-speed and then smashes them together, breaking off constituent particles, which can be identified by the traces they leave behind on the LHC’s sensor arrays.

By tuning the exact energies and particles involved in each collision, specific particles can be targeted – if the predicted traces show up on the sensors, that is taken as proof of the particle’s existence. Particle colliders have grown in power and sensitivity as the energies required for deeper analysis continue to grow.

As the sensitivity of the tools grows, so does the volume of data produced by each experiment. The LHC generates terabytes of data from every collision, data which must be gathered, stored, and then disseminated at speed to research institutions around the world for number-crunching analysis. That task, beyond the capabilities of regular computing environments, is the job of the Worldwide LHC Computing Grid (WLCG).

The LHC’s detectors can produce over 15 petabytes of data every year. Terabytes of data stream from the LHC’s sensors after every collision, containing minute details of the trajectories, speeds and energies of millions of particles from the collisions.

At CERN, Tier 0 of the WLCG is a data centre connected to the counting room (where particle data is collected) via a 10Gbps fibre link. The information is filtered to identify “interesting” data, which is then transmitted to 11 Tier 1 institutions around the world via dedicated 10Gbps links of their own, together forming the LHC Optical Private Network. Those centres perform additional processing, operate data backups for the LHC, and then provide subsets of the data to Tier 2 centres, numbering about 150, where scientists receive the specific slices of data needed for their research. A combination of private fibre links and high-speed Internet connections are used to share the data, and then gather the results.

A key participant in the WLCG is the European Grid Infrastructure project, which operates grid computing resources across hundreds of scientific centres, including many involved in LHC research.

Crunching the numbers is not just a job for massive computing centres – your humble home PC can contribute to the efforts as well. CERN runs the LHC@home computing initiative, which uses computing cycles of volunteers to study particle collisions and contribute data back to the LHC project. LHC@home is similar in concept to SETI@home and Folding@home, which use home PCs to advance the search for extraterrestrial life and the science of protein folding respectively.

The discovery of the Higgs boson is a tremendous success for science, but also for the engineering involved at the LHC at CERN, and in the grid computing network constructed to analyse the data. Next-generation networking, computing, and analysis tools have been driven through our relentless quest for tiny, elusive particles.