On July 4, 2012, physicists from the ATLAS and CMS collaborations at CERN’s Large Hadron Collider announced the observation of a Higgs boson at a mass of around 125 gigaelectronvolts. Ten years later, and with the data corresponding to the production of a 30-times larger number of Higgs bosons, the ATLAS and CMS researchers have learned much more about the properties of the elementary particle. Their results, presented in two papers published in the journal Nature, show that the particle’s properties are remarkably consistent with those of the Higgs boson predicted by the Standard Model of particle physics. They also show that the particle is increasingly becoming a powerful means to search for new, unknown phenomena that — if found — could help shed light on some of the biggest mysteries of physics, such as the nature of the mysterious dark matter present in the Universe .
The Standard Model of particle physics describes the fundamental known particles and forces that make up our Universe, with the exception of gravity.
One of the central features of the Standard Model is a field that permeates all of space and interacts with fundamental particles.
The quantum excitation of this field, known as the Higgs field, manifests itself as the Higgs boson, the only fundamental particle with no spin.
In 2012, a particle with properties consistent with the Higgs boson was observed by the ATLAS and CMS experiments at the Large Hadron Collider (LHC).
Since then, more than 30 times as many Higgs bosons have been recorded by the experiments, enabling much more precise measurements and new tests of the theory.
“The Higgs boson is the particle manifestation of an all-pervading quantum field, known as the Higgs field, that is fundamental to describe the Universe as we know it,” the physicists said.
“Without this field, elementary particles such as the quark constituents of the protons and neutrons of atomic nuclei, as well as the electrons that surround the nuclei, would not have mass, and nor would the heavy particles (W bosons) that carry the charged weak force, which initiates the nuclear reaction that powers the Sun.”
To explore the full potential of the LHC data for the study of the Higgs boson, including its interactions with other particles, ATLAS and CMS combined numerous complementary processes in which the Higgs boson is produced and decays into other elementary particles.
Each of their full LHC Run 2 datasets (between 2015 and 2018) include over 10,000 trillion proton-proton collisions and about 8 million Higgs bosons.
The studies each combine an unprecedented number and variety of Higgs boson production and decay processes to obtain the most precise and detailed set of measurements to date of their rates, as well as of the strengths of the Higgs boson’s interactions with other particles.
All of the measurements are remarkably consistent with the Standard Model predictions within a range of uncertainties depending, among other criteria, on the abundance of a given process.
For the Higgs boson’s interaction strength with the carriers of the weak force, an uncertainty of 6% is achieved.
By way of comparison, similar analyzes with the full Run 1 data sets resulted in a 15% uncertainty for that interaction strength.
“After just ten years of Higgs boson exploration at the LHC, the ATLAS and CMS experiments have provided a detailed map of its interactions with force carriers and matter particles,” said Dr. Andreas Hoecker, spokesperson of the ATLAS Collaboration.
“The Higgs sector is directly connected with very profound questions related to the evolution of the early Universe and its stability, as well as to the striking mass pattern of matter particles.”
“The Higgs boson discovery has sparked an exciting, deep and broad experimental effort that will extend throughout the full LHC program.”
“Sketching such a portrait of the Higgs boson this early on was unthinkable before the LHC started operating,” said CMS spokesperson Dr. Luca Malgeri.
“The reasons for this achievement are manifold and include the exceptional performances of the LHC and of the ATLAS and CMS detectors, and the ingenious data analysis techniques employed.”
The new combination analyzes also provide, among other new results, stringent bounds on the Higgs boson’s interaction with itself and also on new, unknown phenomena beyond the Standard Model, such as on Higgs boson decays into invisible particles that may make up dark matter.
ATLAS Collaboration. A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery. Nature, published online July 4, 2022; must: 10.1038/s41586-022-04893-w
CMS Collaboration. A portrait of the Higgs boson by the CMS experiment ten years after the discovery. Nature, published online July 4, 2022; must: 10.1038/s41586-022-04892-x