Nobel 2013 Physics

Endowing particles with mass

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As the recipients of the 2013 science Nobel prizes gather in Stockholm to celebrate and be celebrated, News & Views shares some expert opinions on the achievements honoured.

François Englert and Peter W. Higgs were awarded the Nobel Prize in Physics for the theoretical discovery of a mechanism that bestows mass on fundamental particles (see figure).

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The triumph of a theory

The proposal of the mass-giving mechanism was a coup for theoretical physics, and will remain a landmark for centuries to come. The standard model of particle physics successfully predicts a panoply of experimental data, some of them extremely precise, in very different contexts. Without the ideas of Robert Brout, Englert1, Higgs2 and a few others, there is a fatal flaw in the standard model: it predicts that particles are massless, in clear contradiction to measurements. The mechanism that the researchers invented was the missing piece in a jigsaw puzzle, and the experimental detection of the Higgs boson at the Large Hadron Collider (LHC) at CERN, near Geneva, Switzerland, demonstrated that their ideas were correct.

As is often the case with scientific discoveries, this completed puzzle forms just one piece of a still larger one concerning quantum corrections to the Higgs-boson mass that occur at high energy scales. All particles receive quantum corrections to their masses from a boiling sea of other particles that pop in and out of existence, but normally the corrections are small and unproblematic. But for the Higgs boson, we have several corrections that are billions upon billions of times heavier than its measured mass (about 126 times the mass of a proton). So either quantum theory, which works so well in other contexts, is wrong, or we are missing a jigsaw piece.

There are exciting ideas for the missing piece that could solve this problem. One prominent idea, called supersymmetry, mathematically cancels the huge corrections, and predicts a host of new particles to be discovered. We therefore await the restart of experiments at the LHC in 2015 with bated breath.

Experimental endorsement

The first meeting to discuss what would become the LHC took place in 1984 in Lausanne, Switzerland. The 27-kilometre tunnel that now houses it was built for a previous accelerator, the Large Electron–Positron collider, which ran from 1989 to 2000. But as a result of even earlier discussions, the tunnel was built as large as possible to allow for future options3. These included later installation of a hadron collider, which became the LHC. In the 1990s, when researchers conceived the LHC's ATLAS and CMS particle detectors, with one of their major goals being to search for the Higgs boson, the required technology did not exist. A lengthy research and development programme was instigated to make sure that, when the time came, they could be built. Thousands of people have worked on them. These are just examples of the kind of long-term vision and investment needed to — using particle physicist David Miller's analogy4 — set off a rumour powerful enough to be heard.

In the end, the result of this endeavour is simple5,6. In a subset of recorded collisions between protons, there is a bump in the mass spectrum of pairs of photons and in the mass spectrum of four leptons (electrons and/or muons). That is the sign that we have managed to hit the background energy field of the Universe hard enough to make a wave in it. That wave is the Higgs boson. Many beautiful theoretical ideas have been proposed but consigned to oblivion, because they don't correspond to how the Universe works. Not so the mass mechanism proposed by Brout, Englert, Higgs and others — the boson is there!

References

  1. 1

    Englert, F. & Brout, R. Phys. Rev. Lett. 13, 321–323 (1964).

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  2. 2

    Higgs, P. W. Phys. Rev. Lett. 13, 508–509 (1964).

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  3. 3

    LEP design report. CERN-LEP-84-01 (CERN, 1984).

  4. 4

    www.hep.ucl.ac.uk/djm/higgsa.html

  5. 5

    The ATLAS Collaboration. Phys. Lett. B 716, 1–29 (2012).

  6. 6

    The CMS Collaboration. Phys. Lett. B 716, 30–61 (2012).

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Correspondence to Ben Allanach or Jonathan Butterworth.

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Allanach, B., Butterworth, J. Endowing particles with mass. Nature 504, 99 (2013). https://doi.org/10.1038/504099a

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