First evidence of rare Higgs Boson decay revealed.

According to the Standard Model, if the Higgs boson has a mass of approximately 125 billion electronvolts, roughly 0.15% of Higgs bosons will decay into a Z boson and a photon. However, extensions of the Standard Model propose alternative decay rates. Therefore, accurately measuring the decay rate is a treasure trove of knowledge, shedding light on physics beyond the Standard Model and the true nature of the enigmatic Higgs boson.

Before this groundbreaking discovery, the ATLAS and CMS teams independently scoured through data collected from proton-proton collisions at the LHC. They meticulously combed through collision events, searching for a telltale sign of the Higgs boson decay into a Z boson and a photon. Their strategies involved identifying the Z boson through its decay into pairs of electrons or muons (heavier cousins of electrons), which occurs in approximately 6.6% of cases.

The key to the success

The key to their success recognized a distinctive feature—a narrow peak amidst a smooth background—in the distribution of the combined mass of the decay products. To enhance sensitivity, the teams categorized events based on the characteristics of the production processes of the Higgs boson. They harnessed advanced machine-learning techniques to differentiate between genuine signals and background noise.

This collaboration has significantly boosted their search's statistical precision and reach, leading to the first compelling evidence of the Higgs boson decay into a Z boson and a photon.

Although the result falls just shy of the conventional requirement of 5 standard deviations for a definitive observation, the discovery boasts a statistical significance of 3.4 standard deviations. Furthermore, the measured signal rate exceeds the prediction of the Standard Model by 1.9 standard deviations, sparking further excitement among physicists.

Pamela Ferrari, the ATLAS physics coordinator, expressed her enthusiasm, stating, "Each particle has a special relationship with the Higgs boson, doing the search for rare Higgs decays a high priority. Through a meticulous combination of the individual results of ATLAS and CMS, we have made a step towards unraveling yet another riddle of the Higgs boson."

This groundbreaking discovery propels us closer to unlocking the secrets of the universe, challenging our current understanding of particle physics. The ongoing endeavors at the LHC promise even more profound revelations as scientists continue to push the boundaries of human knowledge, delving deeper into the enigmatic realm of particle interactions. As we embark on this extraordinary journey, we eagerly anticipate the next chapter in our quest to understand the fundamental building blocks of our existence.