Confirmed: That Was Definitely the Higgs Boson Found at LHC

By Amir Aczel | June 25, 2014 8:28 am

higgs boson

Ever since the 2012 announcement of the discovery of the Higgs boson, researchers have been working to fill in a gap in their measurements—they never yet saw the particle’s telltale decay into “matter” particles. This observation was considered an important indicator of the particle’s true identity.

Now scientists have succeeded in that observation, confirming that the particle whose discovery was announced at CERN on July 4th 2012, is indeed the long-sought-after Higgs boson.

In a nutshell, researchers determined that the boson whose existence was detected at CERN indeed decays into fermions—as predicted by the standard model of particle physics. Until now, the decay modes discovered at CERN have been of a Higgs particle giving rise to two high-energy photons, or a Higgs going into two Z bosons or two W bosons.

Making the Model

The standard model of particle physics is a view of all the particles and forces in the universe that explains the connections among them. Its underlying logic consists of deep mathematical symmetries that are believed to rule the interactions among elementary particles. The model is explained through quantum field theory—an amalgam of quantum mechanics and Einstein’s special theory of relativity. (If the general theory of relativity were to also be incorporated into this framework, it should lead to an understanding of quantum gravity.)

It is according to the standard model that the Higgs boson (which could be called the Higgs-Brout-Englert-Guralnik-Hagen-Kibble boson, for the other physicists whose work contributed to its discovery) endows particles with mass.

Many of the massive particles are, in fact, fermions, and so the Higgs is believed to couple to them. But this could not be proved as long as the Higgs was not found to decay—directly—into any of them.

Enter the Tau

In the new research work, just published in the journal Nature Physics, physicists fired protons at each other (as the Large Hadron Collider does) and scrutinized the collision results to see if they could find leptons (fermions that are similar to the electron, including the electron itself). In particular, they were looking for the heaviest lepton known, called the tau particle. The reason for this is that the more massive a particle is, the stronger its coupling to the Higgs. The tau is 3,500 times more massive than the electron (weighing in at about 1.8 GeV). And indeed researchers spotted tau leptons with a high degree of certainty, proving a decay of the Higgs boson into leptons.

The new findings are at a level of 3.8 sigma. This means, roughly speaking, that there is a 1 in 10,000 chance that the results are a false positive. The physicists are now waiting to confirm the result at the more exacting (and standard in particle physics) 5-sigma level, which would mean the probability described above would be roughly 1 in two million.

More work will be necessary, in order to both obtain stronger statistical proof of the new findings, and further verify other properties of the boson. But it looks like we are finally getting pretty close to certainty that the Higgs particle exists, and it agrees with the theory that has launched the massive search for it.

CATEGORIZED UNDER: Space & Physics, top posts
MORE ABOUT: higgs boson, physics
  • RAJ

    higgs boson is imaginary one– because- lots of things can produce 2 photons. like according to feynman’s diagram- 1 electon and 1 positron can produce = 2 photons ; then is the elecctron higgs boson now?

    • RAJ

      higgs boson is imaginary one– because- it is not directly observed- lots of things can produce 2 photons. like according to feynman’s diagram- 1 electon and 1 positron can produce = 2 photons ; then is the elecctron higgs boson now? so the higgs boson is one of the fake boson ever we have yet. no one can explain how does the mass of higgs boson formed ?how can higgs boson explain the gravity? there is no answer– thats why higgs boson is created in mind by the images created by two photons in many computer screens .( doubt every thing- find your own light- this is the dictum of science). so i doubted here on so called -discovery of higgs boson.

      • Dante Prudente

        Hummmm… why no clarification from Discover? Perhaps Raj is right. Science “ASS-U-MEs” that the Higgs Boson MUST exist. This can lead to a serious bias of interpretation on data. Could it be that scientists are gasping at straws, seeing things that just aren’t there? After all is this not really all about atheists satisfying their egos and some how proving (or deluding themselves) that God does not exist. Is not faith and theology simply the trusting of then theorizing on God? Science (and reason) is just another kind of religion. Plato knew that all too well.

  • Gray

    Hey Discover Magazine. How about you actually cover the news about Higgs Boson. I’m speaking specifically about how scientists very recently found that within a second of the Big Bang, the particles would have collapsed and according to the science, we shouldn’t exist.

    • http://blogs.discovermagazine.com Amir D Aczel

      Gray, you are right on! I proposed such a story to the editors a few hours ago. Stay tuned!…

    • Jason Moors

      This is complete ignorance you project. Science doesn’t make a claim that we should not exist, nor does it base claims off of anything but evidence. Furthermore, the best feature of science is that it constantly evolves it’s understanding of reality as more data is collected, not stick it’s head in the mud. Not only all that, you completely and utterly neglect the possibility of other particles and occurrences which may have taken place to lead to the current state of the universe. Do the world and science a favor and stay out of it and any discussions relating to it, as you choose to misunderstand it with presumption and lack of research on your part.

  • Jason

    Something that I have found misleading or at least glossed over in a lot of articles like this is that the Higgs Field only gives *some* of the mass, in fact I think it is a small minority of mass. If I understand the physics correctly it is the strong interaction that supplies the lion’s share of the observable mass. Is my understanding correct Discover Magazine?

    • http://blogs.discovermagazine.com Amir D Aczel

      Jason, that’s a really tough question. The Higgs was proposed by 3 papers (hence the 6 names) in 1964. In 1967, Steven Weinberg wrote a landmark paper called “A model of leptons”–something like 2 pages only, but one of the greatest papers in the history of physics. In it–in addition to several other things–he made the first reference in history to what he called “The Higgs mechanism.” He used it to break a fourfold symmetry: photon-Z0-W+-W-. In the primeval universe (pre-Higgs action) these four BOSONS were all massless. When the Higgs interacted with them (they are called the electroweak field), it broke the symmetry, leaving the photon massless and GIVING MASS to the triple of “weak-interaction bosons”: Z0, W+, and W-. These three are now confined to act inside nuclei and are responsible for the weak force that control beta (a form of radioactivity) decay. Now, as Weinberg explained to me in 2009: If the Higgs exists (it was 3 years before the CERN discovery) we would know it gives mass to these three. “We suspect that it probably gives mass to other massive particles as well.” Now the Higgs has been found and we know for sure that the masses of WWZ is obtained from the Higgs. The great aspect of the new discovery (above) is that it makes it extremely likely–because the Higgs interacts with a “matter particle” (a lepton, here) that it also gives mass to all these massive ELEMENTARY particles. I highlight this word because I understand your question: The proton is much, much more massive than the sum of its three quarks. And so is the neutron. So what’s going on here? The answer is that probably all elementary particles get their mass from the Higgs. BUT: the difference between the massive proton (and neutron) and the sum of the (elementary) quarks’ masses is the KINETIC energy of motion of the quarks within the nucleon (proton, neutron)–and thus you could say that it is “caused” or at least controlled by the strong force–manifesting itself as mass. (This was explained, among others, also by an American Nobel physicist: Jerome Friedman.)

      • Jason

        Thank you for the excellent reply! I had never encountered this part of the science or line or reasoning before reading Sean Carroll’s excellent book on the Higgs discovery (and really just a great excuse for him to write about quantum field theory). Your remarks have helped solidify some of what he wrote, which I have been grappling with for the last couple of months since my reading.

  • Jonus Hk

    Im just trying to figure out how this is gonna feed that starving baby in Africa.

    • sbkw1983

      The real world applications are still decades away, however, without such fundamental scientific endeavors in the past, there would be no such thing as – for example – the internet, television, radio, etc. (among countless other modern comforts we take for granted).

    • q00lKat

      As a proud Christian conservative, I feel that once out of the womb, that baby is on its own.

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