Researchers working on the LHCb experiment at CERN’s Large Hadron Collider announced the discovery of a new particle, which they named the Xicc++ particle. The scientists announced their findings Thursday at the EPS Conference on High Energy Physics in Venice, Italy.
The discovery could help scientists probe their understanding of one of the four fundamental forces that rule the universe.
The Xicc++ particle is a baryon, which means is part of the family of particles that make up most of the ordinary matter in the universe and which includes the likes of protons and neutrons.
The Xicc++ particle was discovered by scientists of the LHCb experiment
Every baryon is made up of three quarks, a type of particle that comes in six different “flavors.” The theory claims that you can mix up these six flavors in a variety of combinations to produce a whole host of baryons. However, most of these combinations have yet to be observed in the universe.
“Obviously you want to discover all of the states so the picture is complete,” said LHCb member Abolhassan Jawahery at the University of Maryland, according to New Scientist. “It doesn’t represent new physics, but it does help fill the picture that we have of the quark model. It may resolve some outstanding puzzles.”
The new finding has amazed particle physicists because it is the first confirmed particle to contain two heavier quarks –known as charm quarks- and a third lighter up quark. That means that unlike in other baryons, in which the three quarks rotate each other equally, the two charm quarks are believed to be at the center of the Xicc++ particle, while the lighter up quark is thought to be orbiting around them.
The new particle will help physicists test quantum chromodynamics
The extra mass means that the Xicc++ particle weighs in at about 3621 megaelectronvolts, making it four times heavier than the proton. LHCb member Sheldon Stone at Syracuse University in New York noted that those results are in line with theorists’ expectations, unlike previous results.
In 2002, the SELEX experiment at the United States particle accelerator Fermilab found evidence for a similar particle. However, it had a different mass than expected, which puzzled theorists.
“It had a very strange mass that looked suspicious,” said Stone, according to New Scientist. “It would have done chaos to our model of how things are put together. So this is going to be very comforting to the theorists.”
The result announced today has a statistical significance of 7 sigma, a measure of how confident the scientists are in the find. Usually, physicists consider anything over 5 sigma as a firm discovery. The SELEX result of 2002 only reached 4.8 sigma, for instance.
Physicists expect that studying the new particle will aid them test quantum chromodynamics, the theory of the strong force responsible for holding quarks together in baryons. As the Xicc++ particle is the first baryon to contain two heavy charm quarks, it will push the existing theory in a new direction.
“It really tests the theory if you put two of them together with a light quark,” said Stone, according to New Scientist. “It’s a nice result.”
Source: New Scientist