Higgs News

by Nicholas Mee on August 20, 2014

It is two years since CERN made its momentous announcement of the discovery of the Higgs boson on 4th July 2012. The Large Hadron Collider is currently being upgraded and is expected to restart operations in April 2015. Before it was shut down the LHC was colliding protons with a total energy of 8 TeV. When it is switched back on the combined energy of the colliding protons will be increased to 13 TeV before it is stepped up to the full design energy of 14 TeV.

A New Study

This lull in operation has given physicists further opportunity to analyse the data that has already been collected. A new study of the data collected by the Compact Muon Solenoid (CMS) detector at the LHC was published recently in the leading science journal Nature Physics. I will explain its significance below.

United Forces

The Higgs boson plays a dual role in the Standard Model. Its existence was originally hypothesized as a way to unify two of the forces of nature – the electromagnetic and weak forces. Forces are explained in quantum theories by the exchange of particles known as bosons. (For more information about bosons see my article Bosons, Lasers and Superfluids.) For instance, the electromagnetic force is due to the exchange of the fundamental particles from which light is composed – particles known as photons. The standard model combines the electromagnetic and weak forces into a single electroweak force that is produced by the exchange of four types of boson. And this is where the Higgs mechanism comes in. In the 1960s several theorists, including Peter Higgs, speculated that there might be a quantum field that permeates the whole of space and gives mass to three of the four electroweak bosons.

The Higgs Field

This field is known as the Higgs field. Higgs bosons are propagating pulses of vibration of the Higgs field. According to the standard model photons are not affected by the Higgs field, so they race on across the universe at the speed of light. They are exchanged to produce the electromagnetic force which is a long range powerful force. But the other three electroweak bosons do feel the Higgs field and this interaction gives them a large mass. The exchange of these lumbering particles results in a very short range feeble force. In this way the Higgs field breaks the electroweak force into two components that we see as the electromagnetic and weak forces.

But in the standard model even more is expected from the Higgs field. And it is the secondary role of the Higgs boson that has come to define it in the public imagination. Other fundamental particles, such as electrons and quarks, are expected to interact with the Higgs field and this is, according to the standard model, the origin of their mass. These are the matter particles or fermions. (For more information about fermions see my article Fermions, Atoms and Neutron Stars. ) This is not the only conceivable way for fermions to become massive, but it is the way that masses are generated in the standard model.

Now You See It Now Your Don’t!

The Higgs boson is an uncharged particle that decays in an instant into other particles. So it is not directly seen in the detectors of the LHC. Its existence is deduced from the detection of the particles that it decays into. The first signs of the existence of the Higgs boson that were announced in 2012 were due to the appearance of its decays into bosons. But if the Higgs boson plays the role expected in the standard model, then it must decay into fermions as well, and the fermions with the biggest mass must interact most strongly with the Higgs field and they will therefore be the ones that the Higgs bosons decay into most often.

The recently published paper in Nature reveals that the CMS detector has spotted Higgs boson decays into the heaviest possible quark-antiquark pairs formed of bottom quarks and anti-bottom quarks. (The top quark is even heavier than the Higgs boson, so it is not possible for a Higgs boson to decay into a top anti-top pair as this would violate energy conservation.) The Higgs boson has also been spotted decaying into the heaviest cousins of the electron known as tauons and anti-tauons. This is great news as it means that theorists’ expectations of the Higgs boson have been confirmed again and it provides even more evidence that the LHC really has found the Standard Model Higgs boson.

Peter Higgs inside the CMS detector during maintenance.


Further Information

There is a lot more information about the Higgs mechanism and the search for the Higgs boson in my book Higgs Force: Cosmic Symmetry Shattered.


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