Dawn News

March, 29 2015

No Higgs breakthrough

SCIENTISTS working at the Large Hadron Collider have found no evidence that the new particle discovered earlier this year is anything but the simplest — and most boring — variety of Higgs boson.

Staff at Cern, the particle physics lab near Geneva, celebrated in July after they found what looked like the elusive boson amid the debris of scores of high-energy collisions inside the huge machine.

At the time, preliminary results from the two main experiments, Atlas and CMS, hinted that the particle might be something more exciting than the singular beast originally described in equations nearly 50 years ago. A more exotic Higgs could pave the way to a profound new understanding of nature.

But fresh data released by both teams at a conference in Kyoto shows that — so far at least — there is nothing peculiar about the particle's behaviour. The results do not completely rule out a more exotic Higgs particle, though. Some versions would look so much like the so-called Standard Model Higgs boson they could take years to identify.

“The particle is still there, and it's certainly staying consistent with the Standard Model,” said Joe Incandela, head of the CMS detector team.

The Higgs particle was first postulated in 1964 as a single entity whose existence betrays an invisible field that spreads through space and gives mass to fundamental particles, including the basic building blocks of matter.

But some theories that go beyond the Standard Model — a mathematical framework that describes the known particles and their interactions — call for families of Higgs particles, where each sibling plays a role in conferring mass on elementary particles.

One reason the Higgs boson took more than two decades to find is that it is spectacularly unstable. As soon as the boson is created, it disintegrates into more familiar particles, including quarks, electrons and photons. To find the Higgs, scientists looked for an excess of these particles, which would imply that the Higgs boson had been created.

When Cern first reported the discovery of a Higgs-like particle in July, both teams saw what might have been the first signs of an exotic variety of Higgs boson.

The particle seemed to disintegrate too often into energetic photons called gamma particles, and into taus, the heavy cousins of electrons, not often enough. The numbers were too small to stoke excitement, but if the discrepancies had grown, the case for an exotic Higgs would become more convincing.

The new results, based on far more collisions than were gathered in July, show that all the decays fall in line with the Standard Model. However, neither team updated their results for Higgs particles disintegrating into gamma particles, which may still harbour signs of an unusual Higgs at work.

The discovery of a more exotic Higgs boson would thrill particle physicists and mark a huge leap forward in human knowledge. Some versions of a theory called supersymmetry anticipate five different Higgs bosons.

The theory doubles the number of particle types in the universe, shows how common forces of nature once combined as one, and hints at the make-up of dark matter, the invisible substance that clumps around galaxies.— The Guardian, London

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