A newly discovered subatomic particle will provide opportunities to learn about how the most powerful of nature's forces operates.
It takes a big team to investigate the very small. In the case of the new meson Ds3*(2860),- that meant 800 authors on the papers in Physical Review Letters and Physical Review D announcing its discovery.
At an everyday level we are familiar with the forces of gravity and electromagnetism. However, at a subatomic level the strong and weak nuclear forces control the behavior of particles.
The strong force holds protons and neutrons together to form atomic nucleii, but it is also responsible for these particles existing at all, binding quarks together; two up quarks and one down quark to make a proton. The force “is so strong that the binding energy of the proton gives a much larger contribution to the mass, through Einstein's equation E = mc2, than the quarks themselves,” says co-author Professor Tim Gershon of the University of Warwick.
Other types of quarks are much heavier and unstable. However, they can be created using the Large Hadron Collider (LHC) at CERN. Mesons are particles made up of a quark and an antiquark bound by the strong force and Ds3*(2860)- is the latest example.
While much progress has been made on understanding the weak and electromagnetic forces, the strong force is more mysterious. “Calculations are done with a computationally intensive technique called Lattice QCD," says Gershon. "In order to validate these calculations it is essential to be able to compare predictions to experiments. The new particle is ideal for this purpose because it is the first known that both contains a charm quark and has spin 3." The authors state, “This is the first observation of a heavy flavoured spin-3 resonance, and the first time that any spin-3 particle has been seen to be produced in beta decays.”
Spin in this case refers to the quantum mechanical property with some parallels to angular momentum on a macroscopic scale. High spin particles have faster orbiting quarks. “Because it has spin 3, there can be no ambiguity about what the particle is," says Gershon. Where lower spins can be produced with different quark formations, there is only one way to make a spin value of 3. This helps physicists know exactly what they are dealing with and it makes the calculations to model it manageable.
Collisions often produce multiple particles that can be hard to distinguish. In the case of Ds3*(2860)-, another particle, DsJ*(2860)- appears at the same energy peak but with spin 1. The peak was spotted in 2006, but it is only now that the particles have been differentiated.