The "God particle," what exactly does it research?

Recently, the latest findings from the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) were published in Physical Review Letters. The research reveals rare signs of the decay of the Higgs boson. Chinese scientists played a crucial role as co-leaders and main contributors to this joint measurement. The anonymous peer review process described the observation of a new decay channel of the Higgs boson as highly anticipated news within the physics community. The Higgs boson, often referred to as the "God particle," is responsible for endowing all fundamental particles with mass. In 2021, researchers detected evidence of the Higgs boson decaying into a photon and a "virtual photon" in two detectors at the LHC, namely the ATLAS and CMS experiments. Now, for the first time, the two detector teams have jointly searched for signals of the Higgs boson decaying into a Z boson and a photon, successfully observing this rare decay. What significance do these studies hold? Why are particle physicists so captivated by studying the "decay" of the Higgs boson? And how will the construction of the "Higgs Factory," which requires substantial investment, contribute to these research efforts? To address these questions, the relevant Chinese scientists involved in this joint measurement were interviewed by the Chinese Science Bulletin. What is the significance of studying the rare decay of the Higgs boson? The Higgs boson is the last basic particle discovered in the Standard Model of particle physics. Its rarity is due to its extremely low production rate and its spontaneous decay into other particles within an extremely short timeframe. On July 4, 2012, CERN announced the discovery of the Higgs boson to the world, marking the beginning of new research endeavors for many scientists. One such scientist is Dr. Huang Yanping, a researcher at the Institute of High Energy Physics, Chinese Academy of Sciences. Since 2013, Dr. Huang has been engaged in various experiments related to the Higgs boson, including the search for the decay of the Higgs boson into a Z boson and a photon. "This is a rare decay," Dr. Huang told the Chinese Science Bulletin. The rarity stems from the fact that out of 1000 Higgs bosons, only 1 to 2 decay into a Z boson and a photon. Due to limited experimental data and measurement resolution, current scientists primarily focus on the decay of the Z boson into electron pairs or muon pairs. Dr. Huang considers this research to be exceptionally challenging yet crucial. Particle physicists believe that studying the decay of the Higgs boson will help determine important parameters and understand how "mass is generated." The reason they put in so much effort to search for the decay of the Higgs boson into a Z boson and a photon is that this rare decay process might shed light on the "loop effects" of the Higgs boson's interactions with other particles. "Many theories predict the existence of new particles such as additional color-charged scalar particles, leptons, or vector bosons in the 'loop effects,' where the Higgs boson decays into Z bosons and photons," explained Dr. Huang Yanping."Circle diagram effect" is derived from the standard model of particle physics and is considered to be a complex quantum process. According to the explanation of the basic model of particle physics, elementary particles acquire mass by interacting with the Higgs particle. However, since photons have no mass, there is no direct interaction between the Higgs particle and photons in principle. However, in reality, the Higgs particle decays into photons. The only consistent explanation is the "circle diagram effect", which means that the Higgs particle does not directly interact with photons, but rather through quantum interaction with other particles, ultimately producing photons. "Our observation of the rare decay phenomenon of the Higgs boson provides a new window for deeper understanding of the 'circle diagram effect' mechanism involving the Higgs particle, testing the standard model, and exploring new physics," said Huang Yanping. "Why collaborate on research?" ATLAS and CMS are two important detectors at the LHC. As early as the first run of the LHC, the corresponding experimental groups of the two detectors had collaborated in measuring the mass of the Higgs particle. Chen Mingshui told "China Science News" that particle physicists are studying various decay processes of the Higgs particle, such as the decay of the Higgs particle into bottom quark and antiquark, diphoton, and muon pairs, etc. Huang Yanping said that observing signs of rare decay is only the first step in studying this rare decay. "In the future, we hope to increase the significance of experimental results to 5 standard deviations and hopefully discover experimental results that match or exceed expectations." However, their research on the Higgs particle is not limited to its decay processes. "The ultimate goal of Higgs particle research is to discover and test the mass origin of the Higgs particle itself, or you could say, dissecting the 'God'," said Chen Mingshui. Huang Yanping spent nearly 6 years and finally completed the precise energy calibration of the ATLAS detector, thus improving the precision of Higgs mass measurement. In addition to continuously improving research "tools", the self-interaction of the Higgs particle is also the most important issue of concern for scientists. Currently, the interactions between the Higgs particle and fermions, bosons, and other particles have been verified one by one, while the specific mechanism of the self-interaction of the Higgs particle is still unclear. "The standard model predicts that the Higgs particle can acquire mass through self-interaction," explained Chen Mingshui. The question they have been trying to figure out is "the Higgs particle provides mass to all elementary particles, but where does its own mass come from?" Because of this, studying the production process of double Higgs particles and measuring the self-interaction of the Higgs particle has become a research hotspot. "Why build a 'Higgs factory'? Currently, many particle physicists who hope to conduct research on the Higgs particle have high expectations for the "Higgs factory". Representative plans include Japan's International Linear Collider (ILC), Europe's Future Circular Collider (FCC), and China's Circular Electron-Positron Collider (CEPC) projects.Please scan the QR code below for 3 seconds to recognize.Chinese scientistsEuropean Organization for Nuclear Research (CERN)Large Hadron Collider (LHC)Higgs particlerare decayHiggs factory.