Large Hadron Collider Detects Evidence of a Rare Higgs Boson Process: God Particle Decaying Into a Pair of Muons
The Compact Muon Solenoid (CMS) is a general-purpose detector at the Large Hadron Collider (LHC). It has a broad physics programme ranging from studying the Standard Model (including the Higgs boson) to searching for extra dimensions and particles that could make up dark matter. The CMS detector is built around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a field of 4 tesla, about 100,000 times the magnetic field of the Earth. The field is confined by a steel “yoke” that forms the bulk of the detector’s 14,000-tonne weight.
The ATLAS and CMS collaborations at the Large Hadron Collider have seen evidence of a new type of decay not yet observed: the Higgs boson decaying into a pair of muons.
US CMS — the United States contingent of the global CMS collaboration — played a crucial role in this result, contributing to the excellent performance of CMS detector. US CMS members have been instrumental in the design, construction and upgrades of detector components that capture the particle tracks and help filter potential signals from the background noise: the tracker detector, the muon detectors, the muon trigger system and the computing system. They continue to lead the successful maintenance and operations of these systems.
“US CMS is very proud to acknowledge the significant impact made by its members in deploying innovative analysis techniques, including cutting-edge AI methods, which were critical in establishing the evidence for Higgs boson decays into a muon and antimuon pair,” said Brown University physicist Meenakshi Narain, chair of the US CMS collaboration. “This is a rare process, and finding evidence for it is a vital step toward understanding the Higgs particle and the Standard Model.”
CMS is an international collaboration with members from 238 institutes across 55 countries. US CMS, hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory, makes up about a third of the CMS collaboration.
“The achievement, reached significantly ahead of what was expected, relies on the excellent performance of our detector, on the large data set provided by LHC and on advanced analysis techniques,” said Roberto Carlin, spokesperson for the CMS experimental collaboration.
The ATLAS and CMS experiments at CERN have announced new results that show that the Higgs boson decays into two muons. The muon is a heavier copy of the electron, one of the elementary particles that constitute the matter content of the universe. While electrons are classified as a first-generation particle, muons belong to the second generation. The physics process of the Higgs boson decaying into muons is a rare phenomenon as only about one Higgs boson in 5,000 decays into muons. These new results have pivotal importance for fundamental physics because they indicate for the first time that the Higgs boson interacts with second-generation elementary particles.
Physicists at CERN have been studying the Higgs boson since its discovery in 2012 to probe the properties of this very special particle. The Higgs boson, produced from proton collisions at the Large Hadron Collider, disintegrates – referred to as decay – almost instantaneously into other particles. One of the main methods of studying the Higgs boson’s properties is by analyzing how it decays into the various fundamental particles and the rate of disintegration.
CMS achieved evidence of this decay with 3 sigma, which means that the chance of seeing the Higgs boson decaying into a muon pair from statistical fluctuation is less than one in 700. ATLAS’ two sigma result means the chances are one in 40. The combination of both results would increase the significance well above 3 sigma and provides strong evidence for the Higgs boson decay to two muons.
“CMS is proud to have achieved this sensitivity to the decay of Higgs bosons to muons and to show first experimental evidence for this process. The Higgs boson seems to interact also with second-generation particles in agreement with the prediction of the Standard Model, a result that will be further refined with the data we expect to collect in the next run,” says Roberto Carlin, spokesperson for the CMS experiment.
The Higgs boson is the quantum manifestation of the Higgs field, which gives mass to elementary particles it interacts with, via the Brout-Englert-Higgs mechanism. By measuring the rate at which the Higgs boson decays into different particles, physicists can infer the strength of their interaction with the Higgs field: the higher the rate of decay into a given particle, the stronger its interaction with the field. So far, the ATLAS and CMS experiments have observed the Higgs boson decays into different types of bosons such as W and Z, and heavier fermions such as tau leptons. The interaction with the heaviest quarks, the top and bottom, was measured in 2018. Muons are much lighter in comparison, and their interaction with the Higgs field is weaker. Interactions between the Higgs boson and muons had, therefore, not been seen at the LHC.