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Fifty years ago, a team at SLAC National Accelerator Laboratory in Menlo Park made a discovery that turned the world of particle physics upside down; they discovered a particle, called J/Psi, that set the stage for the modern era of particle physics. On Nov. 8, SLAC hosted a symposium celebrating the monumental discovery, and the 50 years of particle physics achievements that have followed in its wake.
The 50th anniversary symposium was a testament, not only to the importance of the discovery itself, but also to the remarkable progress made in particle physics over the last five decades, said Michael Peskin, a professor of particle physics and astrophysics at Stanford, and the organizer of the symposium. Today, scientists at SLAC National Accelerator Laboratory are using the J/Psi particle to help answer even bigger questions in particle physics.
“Much of the work done (to discover J/Psi) is the foundation of what we are now doing for the Large Hadron Collider,” said Zhi Zheng, a research assistant at SLAC who is working with the ATLAS collaboration at the Large Hadron Collider at CERN in Switzerland.
In November 1974, Burton Richter, a physics professor at Stanford University, and his team had made their revolutionary discovery of what they called the “Psi” particle by smashing electrons and positrons (antielectrons) together in SLAC’s particle collider. They double checked what they thought was a minor statistical inconsistency in the data that they were collecting, but found that it wasn’t a flaw in the data, it was a new particle.
Another group, led by Samuel Ting at the Brookhaven National Laboratory, had incidentally made the same discovery at the same time. However, they called this particle “J.”
On Nov. 11, 1974, the two teams working at the two separate particle colliders on opposite sides of the country simultaneously announced their groundbreaking discoveries, launching rapid progress in humanity’s understanding of the basic building blocks of atoms and matter. The J/Psi particle that the two teams had jointly discovered was unlike anything that scientists had previously encountered.
“The suddenness of the discovery coupled with the totally unexpected properties of the particle are what make it so exciting,” wrote Richter in a press release at the time of the discovery.
The discovery was so disruptive, that the event is now known as the “November Revolution” in particle physics.
The discovery of the J/Psi particle by Richter and Ting’s teams verified the existence of an atomic building block called the charm quark, and led to the widespread acceptance of what is now known as the “Standard Model” of particle physics. This earned the two men the 1976 Nobel Prize in physics.
“The discovery of this particle, the J/Psi, was absolutely crucial, because it turned out, first of all, that no one’s theory had predicted it,” said Peskin. “So all of a sudden we go from many models, uncertainty and arguments … to now you have to say quarks are real, and we have to build our theory around that.”
The discovery of the J/Psi particle paved the way for many other breakthroughs in particle physics, including the detection of the famed Higgs boson by the ATLAS experiment at CERN, the particle that is thought to be responsible for creating mass.
The ATLAS collaboration is an international group of physicists conducting a large particle detection experiment at the Large Hadron Collider at CERN in Switzerland with ATLAS, one of the largest particle detectors at the collider. This is the group that achieved the first experimental observation of the Higgs boson. SLAC National Accelerator Laboratory has many physicists, computer scientists and other technicians involved in the ATLAS experiment.
Prajita Bhattarai, another research assistant with the ATLAS collaboration, said that since the J/Psi particle has now been measured extensively, it can be used to calibrate machines at the Large Hadron Collider that measure other particles that we know less about.
“It has been 50 years since the discovery (of the J/Psi particle), so it has been measured really, really well,” she said. “So we can use this resonance to calibrate for the objects where we don’t know precisely how well our detector will be able to measure them.”
Peskin said that SLAC’s physicists, as well as other scientists around the world, will continue to build upon the large leap in understanding that was gained through the discovery of the J/Psi particle in 1974.
“Now we can begin to get at the questions that the Standard Model (of particle physics) doesn’t answer,” said Peskin. “Things like, why are some particles heavier than others? … Why does the Higgs boson do what it does? These are the frontier questions in particle physics today, and … (the J/Psi) discovery gave us the tools to explore these questions.”
