Ten years ago, the discovery of the Higgs boson was world news. KIJK looks back – and looks ahead – with particle physicist Stan Bentvelsen.
Since 2014, Stan Bentvelsen has been director of the Dutch Particle Physics Institute Nikhef† Before that, for many years he was ultimately responsible for the Dutch contribution to the ATLAS experiment, which investigates collisions in the European Union particle accelerator LHC studies. On July 4, 2012, spokespersons for ATLAS and the competing CMS experiment announced that they had a discovered a new particle† And it seemed that this was the Higgs boson, predicted as early as 1964, which gives other particles their mass.
WATCH: Let’s go back to the summer of 2012. How far in advance did you know: we are going to announce to the world that we have found a new particle?
Stan Bentvelsen: “That must have been a week or a half before 4 July. We’ve been seeing with ATLAS for a while a signal that got stronger and stronger† But within particle physics we have agreed that something must have a sigma of at least 5 to be allowed to speak of a discovery. (A sigma of 5 means that the chance that you would have seen the same signal if the Higgs boson had not existed, is less than 1 in 3.5 million – ed.) This involves the sum of many different analyses, and that addition was only completed very shortly beforehand.
We ourselves were particularly curious about what our competitor was going to say: the LHC experiment CMS, which studies the same physical phenomena as ATLAS. We had no idea what that team would announce. But that turned out to see the same signals as us. That is why, after our presentations, the then CERN director Rolf Heuer was able to say: “Ladies and gentlemen, I think we have it.“That was a very special moment that really changed physics research.”
How has research changed with the discovery of the Higgs boson?
“After the discovery of the Higgs boson, research has become much broader, much more open. Before 2012, we mainly wondered: does the Higgs boson exist or not? As a result, we hardly dared to ask all kinds of other questions. Such as: why is the Higgs boson so light? And what exactly is the Higgs field that belongs to that Higgs boson? If you put that into the universe, it should curl up to the size of a football. Why doesn’t that happen?”
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In 2012, the CERN press release still called it ‘a particle consistent with the Higgs boson’ instead of simply ‘the Higgs boson’. Why the blow to the arm?
“There is no flag on such a particle that says: ‘I am a Higgs particle.’ We saw a spike in our charts that clearly indicated a new particle. But you still have to ask yourself: is this really the Higgs boson that we expect from the Standard Model of particle physics? The Higgs boson is the exponent of the Higgs field, a kind of substance that is supposed to give all other particles mass. That is a very curious concept. It is very surprising that nature indeed behaves this way. And we are actually still busy determining whether the Higgs boson really has all the properties that it should have according to the standard model.”
What are the most important measurements of the Higgs boson over the past ten years?
“The following applies to particles: the heavier they are, the easier they feel the Higgs field – and the easier it is to measure the interaction between such a particle and the Higgs field. So far we have been able to measure that interaction for some of the heaviest particles: the top quark, the bottomquark, the charm quark… (Quarks are elementary particles that are, among other things, the building blocks of protons and neutrons, in turn the building blocks of atomic nuclei. There are six different ones in total – ed.) It is always a surprise to see that the standard model, which describes these interactions, appears to be correct. At the same time, we know that the standard model cannot be the whole story. For example, there is no particle in it where you put it dark matter problem you can solve.”
Will the particle accelerator LHC teach us even more about the Higgs boson?
“I think there is still a lot that can be done with the LHC. So far, we have only analyzed a few percent of the expected total number of particle collisions. It becomes exciting with the so-called self-interaction of the Higgs boson. In extremely rare cases, the Higgs boson can, according to the predictions, disintegrate into two new Higgs particles. But the experimental challenge of being able to measure that signal is enormous. We really need all the data that the LHC will collect over its entire lifespan.
Does the knowledge about the Higgs boson also have practical applications?
“Well, the techniques we needed to find the Higgs boson have led to a lot of innovation. Proton therapy as a treatment method against cancer, for example. But the Higgs boson itself? Your imagination has to go very far to find an application for that. This kind of research is mainly about pure, fundamental curiosity.”
After the Higgs boson, no other new particles have been discovered with the LHC. Disappointed?
“Well, that’s a case of ‘do you see the glass as half full or half empty?’ Before this discovery, I couldn’t imagine finding the Higgs boson at all. Now we see that we’re really starting to understand this new particle, and I think that’s a very nice result. In that regard, the past ten years have been very satisfactory.
Of course you can also say that the results are disappointing. We had all hoped a bit for supersymmetry (a theory in which all particles have heavier partners – ed.) or extra dimensions or so. We don’t see any of that at the moment. But that also means that the question of what lies beyond the standard model is only becoming more pressing.”
Opening image: ATLAS/CERN
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