Scientists working at the CERN laboratory’s Large Hadron Collider (LHC) in Geneva announced last night that two independent experiments have shown signs that the hypothesised Higgs boson, AKA the “god particle”, might exist.
Researchers have been accelerating protons into each other at almost the speed of light using the highest energy levels achieved in a laboratory, 7 tera-electron Volts (TeV), in an attempt to recreate Big Bang conditions and in doing so create the Higgs boson – the missing link in the Standard Model of elementary particle physics.
Elementary particles are the smallest fundamental units of matter, and all such units predicted by the Standard Model have been observed, except for the Higgs boson. If it is found, then physicists will have a sound theory for what gives elementary particles their mass. Plus, British physicist Peter Higgs, who proposed the existence of the particle in 1964, will be proven right.
Professor Geoff Taylor, Director of the ARC Centre of Excellence for Particle Physics at the Terascale, University of Melbourne
During 2011 the much-anticipated Large Hadron Collider (LHC) at CERN, Geneva, operated successfully beyond all hopes, collecting data far in excess of that expected. Scientists across the world are sifting this data for evidence of new physics, looking for the possible “smoking gun” signals of Higgs bosons – if they exist, and if they are being created at the LHC, that is.
Many interactions occur in the LHC collisions but these don’t necessarily represent products of exotic particles, and are from more common or garden-variety interactions. Our experimenters carefully calculate how many observed interactions (“events”) are expected from the properties of known processes and particles (“background events”) and then determine if an excess remains in the data. A discovery requires a statistical excess of events of specific characteristics over background events. A statistical measure that is beyond the realms of an “accidental excess” is required.
The status of the searches for the Standard Model Higgs boson, by both ATLAS and CMS experiment collaborations, were presented at a special seminar at CERN, on 13 December. CERN Director General, Rolf Heuer says “These results will be based on the analysis of sufficient data to make significant progress in the search for the Higgs boson, but not enough to make any conclusive statement on the existence or non-existence of the Higgs.”
At midnight last night (Australian Eastern Standard time), ATLAS Collaboration spokesperson, Fabiola Gianotti, and CMS Collaboration spokesperson Guido Tonelli, presented their experiments first analysis of the 2011 data, carried out in search of the Higgs boson. Enticing hints at a signal consistent with that expected by the Higgs boson are being seen in each experiment, however, the statistical “significance” of these results is still not sufficient to call either a discovery of this much sought after particle, nor of its exclusion.
CERN Director-General, Rolf Heuer, stated that “we had a fantastic year, much better than expected” and that the experiments “extremely good progress”, but that we still need many more collisions next year in order to get a definite answer … to the question on the Higgs: to be or not to be?“
The allowed mass range of the Higgs boson has been significantly narrowed with the search homing on the same low-mass region of 115-130 GeV/c2. Tantalizing as these results may be, we will have to wait for the additional data expected in the first half of 2012 for the "conclusive” result. In fact this may well coincide with the ICHEP2012 conference (International High Energy Physics Conference, 2012) to be held in Melbourne from 4-11 July 2012. We are definitely in for a very exciting program of results.
Australian researchers from ARC Centre of Excellence for Particle Physics at the Terascale (CoEPP) play a key role in the search for the Higgs boson, with Centre researchers working on the ATLAS experiment at CERN for a number of years. The ATLAS experiment involves around 3000 scientists from 37 countries. ATLAS is the general-purpose detector used at the Large Hadron Collider (LHC) — the world’s largest and highest-energy particle accelerator. 2012 will see the LHC providing the experiments with the collisions required to make a definitive statement. Stay tuned.
The expert reactions below are provided by the Australian Media Science Centre.
Dr Philip Schuster, Perimeter Institute for Theoretical Physics, Canada
For 40 years, physicists have searched for the origin of the weak interactions, and the mechanism that generates mass for fundamental particles in the Universe. These phenomena are responsible for basic features of our world ranging from the long lifetime of the Sun to the very existence of atoms. Today, it looks like we have promising evidence that there is actually a Higgs mechanism in Nature, and the particle associated with that mechanism may finally be showing itself. Going forward, physicists will gather more evidence needed to prove that a Higgs particle exists. Understanding the properties of the Higgs mechanism and where it comes from will be an important goal for the next decade.
Dr Alan Barr, Oxford University’s Department of Physics, ATLAS UK Physics Coordinator
It is a testament to the superb performance of the LHC that we are already finding hints that might be indicative of Higgs bosons so early in the machine’s lifetime. The results are not yet conclusive, but during the next year we will know whether the Higgs boson exists in the form predicted by the “Standard Model” of particle physics. The analysis has to be done very carefully, since in scientific research the most interesting results are often found in unexpected places.
We must bear in mind that the Standard Model is known to be incomplete, since it describes only that 5% of the universe that is made of atoms. What the LHC will tell us about the other 95% of the universe is likely to be an open question for many years to come.
Dan Tovey, Professor of Particle Physics, University of Sheffield and ATLAS spokesman
While these results do not provide conclusive proof of the existence of the Higgs boson the fact that broadly similar hints have been seen by two competing experiments using several different complementary techniques is very suggestive. With much more data due next year it won’t be long before we can answer this question once and for all.
Geoff Hall, Professor of Physics, Imperial College London, UK spokesperson for CMS
At the beginning of this year, we had little idea of what mass the Higgs boson might have, assuming it really existed. Now the situation is completely changed, as a result of less than one year of LHC data, and the region where the Higgs may be found has been narrowed from about 500 GeV to 10-20 GeV. There are also strong hints that the Higgs may really exist in that narrow range. This is quite remarkable. The successful and rapid analysis shows how well the experiments work and how ready for the complex studies the scientists are, after about twenty years of building and preparation. It has been a huge effort. It is too soon to draw conclusions but it certainly begins to feel as though we are on the verge of momentous progress, confirming the Standard Model and shedding new light on deeper ideas. Of course, it is tempting to speculate how particle physics will change with a Higgs discovery but most of us are still focused on verifying that it is really found and, if so, to prove what kind of Higgs it is – eg Standard Model or supersymmetric. This will require a lot more data in the coming year, and even after that for some years to come.
Professor Themis Bowcock, Head of Particle Physics, University of Liverpool
The CERN results on the Higgs boson have the scientific world agog. Have they or have they not seen the elusive particle sometimes called the God Particle? First proposed in the 1960s, this particle plays a crucial role in the evolution of the Universe from the Big Bang to the way we see it today.
Our understanding of nature and its fundamental forces is known as the Standard Model. For the last 40 years it has allowed us to understand phenomena such as light, the way the sun burns, and how atoms and nuclei are held together.
The Standard Model relies on a particle called the Higgs boson which interacts with other particles making some very heavy whilst leaving others light. This shapes the Universe we know today. However to date no-one has found direct evidence of the Higgs.
The ATLAS and CMS experiments at the LHC have come as close as anyone to observing the Higgs and now both have presented small but significant signals. It is possible that each observation is simply a statistical fluke, a fluctuation in the background, mimicking a Higgs signal. But the fact that ATLAS and CMS independently agree on the possible Higgs mass substantially increases the overall significance of the results.
If the Higgs observation is confirmed, through analysis of data to be collected next year, this really will be one of the discoveries of the century. Physicists will have uncovered a keystone in the makeup of the Universe – one whose influence we see and feel every day of our lives.
Dr Alan Barr, physics coordinator of the ATLAS UK collaboration
Our understanding of physics at the microscopic level is described by a beautiful piece of mathematics known as the “Standard Model”. For that mathematical model to work correctly, various pieces must work together, like a well-engineered machine. The Higgs boson is a crucial part of the machinery of the subatomic world.
This evidence of the existence of a Higgs boson suggests that the mathematically beautiful theory of the subatomic world is more than just an elegant model, and that it really does seem to describe the universe around us.
Dr Stephen Haywood, Head of the Atlas Group at the STFC Rutherford Appleton Laboratory
This is what many of us have been working towards for the best part of 20 years. If the first inklings of the Higgs boson are confirmed, then this is just the start of the adventure to unlock the secrets of the fundamental constituents of the Universe.
Dr Claire Shepherd-Themistocleus, Head of the CMS Group at the STFC Rutherford Appleton Laboratory
“We are homing in on the Higgs. We have had hints today of what its mass might be and the excitement of scientists is palpable. Whether this is ultimately confirmed or we finally rule out a low mass Higgs boson, we are on the verge of a major change in our understanding of the fundamental nature of matter.
Professor Stephan Söldner-Rembold, Head of the Particle Physics Group, University of Manchester
ATLAS and CMS have presented an important milestone in their search for the Higgs particle, but it is not yet sufficient for a proper discovery given the amount of data recorded so far. Still, I am very excited about it, since the quality of the LHC results is exceptional. The Higgs particle seems to have picked itself a mass which makes things very difficult for us physicists. Everything points at a mass in the range 115-140 GeV and we concentrate on this region with our searches at the LHC and at the Tevatron.
The results indicate we are about half-way there and within one year we will probably know whether the Higgs particle exists with absolute certainty, but it is unfortunately not a Christmas present this year. The Higgs particle will, of course, be a great discovery, but it would be an even greater discovery if it didn’t exist where theory predicts it to be. This would be a huge surprise and secretly we hope this might happen. If this is case, there must be something else that takes the role of the "standard” Higgs particle, perhaps a family of several Higgs particles or something even more exotic. The unexpected is always the most exciting.