There鈥檚 a new particle in town, and it鈥檚 a double-charmingly heavy beast. Researchers working on the LHCb experiment at CERN鈥檚 Large Hadron Collider have announced the discovery of the esoterically named聽Xicc++ particle. The find could help us probe our understanding of one of the four fundamental forces that govern the universe.
罢丑别听齿颈cc++聽is a baryon, the family of particles that make up most ordinary matter and includes the likes of protons and neutrons.聽All baryons are made up of three quarks, a type of fundamental particle that comes in six different flavours. Theory suggests you can mix up these six in a variety of combinations to produce a whole host of baryons, but many of these combinations have yet to be observed in the real world.
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鈥淥bviously you want to discover all of the states so the picture is complete,鈥� says LHCb member at the University of Maryland. 鈥淚t doesn鈥檛 represent new physics, but it does help fill the picture that we have of the quark model. It may resolve some outstanding puzzles.鈥�
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This latest find is exciting particle physicists because it is the first confirmed to contain two heavier quarks known as charm quarks 鈥� the third constituent is an up quark. That means unlike in other baryons, where the three quarks rotate around each other equally, the two charm quarks are thought to sit at the centre of the Xicc++ with the lighter up quark orbiting around them.
A firm discovery
All this extra mass means聽Xicc++聽weighs in at around 3621 megaelectronvolts, four times heavier than the proton.聽That鈥檚 in line with theorists鈥� expectations, says聽LHCb member at Syracuse University, New York, unlike previous results.
In 2002, the SELEX experiment at US particle accelerator Fermilab found evidence for a similar particle, but with a different mass that puzzled theorists. 鈥淚t had a very strange mass that looked suspicious,鈥� says Stone. 鈥淚t would have done chaos to our model of how things are put together. So this is going to be very comforting to the theorists.鈥�
The result announced today, at the聽 in Venice, Italy, has聽a statistical significance聽of over 7 sigma 鈥� a聽measure of how confident the researchers are in the find. Traditionally, physicists treat anything over 5 sigma as a firm discovery. The SELEX result only reached .
Physicists hope studying the new particle will help them test quantum chromodynamics, the theory of the strong force, which is responsible for holding quarks together in baryons.聽As the聽Xicc++聽is the first baryon to contain two heavy quarks, it will push the theory in a new direction. 鈥淚t really tests the theory if you put two of them together with a light quark,鈥� says Stone. 鈥淚t鈥檚 a nice result.鈥�
