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The mystery of the J/ψ meson: How did this particle change the history of particle physics?
In the vast universe of particle physics, the appearance of J/ψ meson is like a dazzling star, illuminating researchers' understanding of the microscopic world. On November 11, 1974, Burton Richter of the Stanford Linear Accelerator Center and Samuel Ting of the Brookhaven National Laboratory independently discovered the new particle. It opened a whole new chapter on the structure of quarks and triggered the subsequent "November Revolution".
J/ψ meson: the union of quarks and antiquarks
The J/ψ meson is a flavor-neutral meson consisting of a charm quark and a charm antiquark. According to quark theory, this type of meson formed by the binding of quarks is called a "charmonium". J/ψ is the most common charon, with a spin of 1 and a relatively low mass, with a rest mass of 3.0969 GeV/c2, which is slightly higher than ηc sub>'s mass is 2.9836 GeV/c2. Surprisingly, the average lifetime of J/ψ is 7.2×10−21 seconds, which is about a thousand times longer than expected.
This discovery not only challenged the theory of particle physics, but also paved the way for subsequent research.
Theoretical and experimental background
The discovery of J/ψ has a profound theoretical and experimental foundation. Since the 1960s, with the proposal of the quark model, scientists have begun to explore the structure of particles such as protons and neutrons. Early models suggested that all mesons were made of three different kinds of quarks. However, as SLAC's Deep Internal Energy Scattering experiments progressed, researchers discovered that there seemed to be smaller particles inside the protons.
The nature of these sub-mass components is hotly debated in the scientific community. By 1974, as theoretical predictions about charm quarks became clear, Ding and Richter's discovery confirmed those theories.
Uniqueness of decay patterns
As a subatomic particle, the J/ψ meson shows unique behavior in decay, and its hadronic decay mode is strongly suppressed by the OZI rule, which extends its lifetime. Therefore, the decay width of J/ψ is only 93.2±2.1 keV, showing its stability. As hadronic decays gradually decrease, electromagnetic decays begin to increase, causing the probability of J/ψ mesons decaying into leptons to increase significantly.
The academic significance of quantum chromodynamics and J/ψ
When discussing the J/ψ meson, one topic that cannot be ignored is its role in quantum chromodynamics (QCD). As the research deepened, scientists found that the stability of J/ψ would face challenges in a high-temperature QCD environment. When the temperature exceeds the Hagedorn temperature, J/ψ and its excited states may collapse, a phenomenon that foreshadows the formation of quark-gluon plasma.
These studies have put heavy ion collision experiments at the forefront of exploring elementary particle physics.
Interesting facts about naming
Due to the almost simultaneous discovery of J/ψ, this particle has a unique two-letter name. Richter originally wanted to name it "SP", but this was not popular with the team members. Since there were still available Greek letters, "ψ" was finally chosen, and Ding gave it the name "J". Their naming demonstrated the unique insights of physicists at that time into particle naming.
ConclusionThe discovery of the J/ψ meson became a milestone in particle physics, which not only promoted the understanding of the microscopic world, but also simplified the complex theoretical framework. It carries the hard work of many scientists and has become the cornerstone of subsequent research. In future scientific exploration, what unexpected discoveries will the J/ψ meson bring?
