Rare Higgs boson decay observed in Large Hadron Collider experiments

Scientists at CERN have discovered evidence of the Higgs boson decaying into a Z boson and a photon, providing indirect evidence of particles beyond those predicted by the Standard Model, which could one day even change our understanding of how everything in the universe works.

By: Science Desk
Kochi | Updated: June 6, 2023 09:18 AM IST

3 min read

Large Hadron Collider at the European Organisation for Nuclear Research

A 3D cut-out of the Large Hadron Collider's magnetic dipole. (Image credit: CERN)

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The European Organization for Nuclear Research (CERN), which hosts the Large Hadron Collider,(LHC) announced on Friday that scientists at the organisation found the first evidence of the rare process by which the Higgs boson decays into a Z boson and a photon.

The discovery of the Higgs boson, what some call the “god particle,” in 2012 marked a major milestone in the study of particle physics. Since that discovery, scientists working with the ATLAS and CMS experiments at LHC have been investigating the properties of the particle, trying to understand the ways in which it is produced and how it decays into other particles.

At the Large Hadron Collider Physics (LHCP) conference last month, ATLAS and CMS teams reported how they discovered evidence of the Higgs boson decaying into a Z boson and a photon. The Z boson is the electrically neutral carrier of the weak force and the photon is the carrier of the electromagnetic force.

More hints beyond the standard model

According to CERN, this decay could provide indirect evidence of the existence of particles beyond those predicted by the Standard Model of particle physics. The Standard Model is the current best theory that can explain all phenomena associated with elementary particles, or the building blocks of the universe.

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“We already know that there must be something that the standard model does not predict because we have indirect evidence of it. We cannot formulate a theory if we do not know what basic mechanism is responsible for those effects. That is why we are looking for something beyond this model. If we do discover something like that, it would be a change of paradigm. It would be a revolution in the field,” Nicola Neri, senior scientist at the LHCb (LHC beauty) experiment, said to indianexpress.com in a July 2022 interview, when asked about why physicists are looking beyond the standard model.

According to Neri, once scientists get a direct signal that goes beyond the standard model, there would be a need to rewrite part of the physics that is currently accepted. For example, physicists currently recognise four fundamental forces— the strong force, the weak force, the electromagnetic force and the gravitational force. There could be a fifth force that they do not yet know of. Of course, this is just an example proved by Neri to illustrate how going beyond the standard model would change the fundamentals of physics as scientists understand them.

Decay of the Higgs boson

The Higgs boson particle’s decay into a Z boson and photon is similar to that of a decay into two photons, according to CERN. In these cases, the particle does not directly decay into these pairs of particles. Instead, it happens through, and “intermediate loop of virtual particles” that come into and out of existence but cannot be detected directly. These “virtual” particles could include new and so far unknown particles that interact with the Higgs boson.

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