On 4 July this year – following the announcement of the new particle discovery from CERN – European Physical Society president Luisa Cifarelli interviewed Guido Tonelli, former spokesperson of CERN’s CMS Collaboration.
With respect to today’s exciting announcement, how are you feeling?
It is very difficult for me to describe today’s emotions. For people that have been searching for the Higgs boson for over 20 years, today is like living out a dream. The unambiguous signals – shown by ATLAS and CMS – are now so strong that we can abandon any sort of prudence: we are observing a new, narrow resonance and it will not fade away with additional data.
To be frank: when, last year, I presented our first results at CERN – together with Fabiola Gianotti, ATLAS spokesperson – very few people were convinced that the excess of events around a mass of 125 GeV/c2 we both reported would be soon considered the first experimental evidence of the presence of the Higgs boson in LHC data.
Today the statistical significance is so large that even the most prudent of our colleagues seem to be fully convinced: the new-born baby that we first saw just a few months ago has quickly become a robust child. I have no doubt that he will soon become a young adult.
Tell us about your relationship with this long-awaited discovery.
When – in the early nineties – I joined a very small group of physicists who were aiming to design the scientific instruments that would allow for the discovery of the Higgs boson, a large fraction of the scientific community was highly sceptical. Many colleagues did consider us completely crazy.
They were partly right since, at that time, most of the proposed technologies did not exist; the costs seemed to be prohibitive and looking for such an elusive particle in the hostile environment of high luminosity LHC collisions was simply considered by everybody to be a sort of “mission impossible”.
In fact it took more than 20 years and a patient, strenuous effort of thousands of people to build and then operate our detectors; and then to record and analyse the data. The full credit for today’s result goes to these people.
What do you think will be the implications of this discovery?
The role the Higgs boson plays in nature is so important that there will be profound implications for our vision of matter and the universe.
A series of questions are already on the table: Is this light scalar playing some role in the inflation mechanism? Has it an invisible width due to decays in dark matter particles? What is the mechanism eventually protecting the Electroweak Vacuum from instability up to the Planck scale?
On one hand, today we celebrate the triumph of the Standard Model of elementary interactions; the last missing piece has finally been found. On the other hand, since a light Higgs boson is extremely sensitive to any kind of new physics, we have now at hand a sort of new laboratory to be fully explored. Are the properties of this particle exactly the ones predicted by the theory? Can we measure precisely all its quantum numbers, width and couplings to check that indeed there is no anomaly?
As we close this 48-year-long hunt since the first theoretical predictions, we find ourselves on the verge of a new era. This is a great day for physics.