According to scientists from CERN’s LHCb experiment, the discovery of a new type of meson, named Ds3*(2860)ˉ, will transform our understanding of the strong interaction, the fundamental force of nature found within the protons of an atom’s nucleus.
Ds3*(2860)ˉ was discovered in the decay chain Bs0→D0K–π+ , where the Bs0, D0, K– and π+ mesons contain respectively a bottom anti-quark and a strange quark, a charm anti-quark and an up quark, an up anti-quark and a strange quark, and a down anti-quark and an up quark. The particle is observed as a peak in the mass of combinations of the D0 and K– mesons. The distributions of the angles between the D0, K– and π+ particles allow the spin of Ds3*(2860)ˉ to be unambiguously determined. Image credit: LHCb.
Ds3*(2860)ˉ is a meson that contains a charm anti-quark and a strange quark.
The subscript 3 denotes that it has spin 3, while the number 2860 in parentheses is the mass of the particle in the units of MeV/c2. The value of 2,860 MeV/c2 corresponds to approximately 3 times the mass of the proton.
Ds3*(2860)ˉ is bound together in a similar way to protons. Due to this similarity, the LHCb team argues that physicists will now be able to study the particle to further understand strong interactions.
Along with gravity, the electromagnetic interaction and weak nuclear force, strong-interactions are one of four fundamental forces.
“Gravity describes the Universe on a large scale from galaxies to Newton’s falling apple, whilst the electromagnetic interaction is responsible for binding molecules together and also for holding electrons in orbit around an atom’s nucleus,” explained team member Prof Tim Gershon of the University of Warwick, UK.
“The strong interaction is the force that binds quarks, the subatomic particles that form protons within atoms, together.”
“It 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.”
Due in part to the forces’ relative simplicity, scientists have previously been able to solve the equations behind gravity and electromagnetic interactions, but the strength of the strong interaction makes it impossible to solve the equations in the same way.
“Calculations of strong interactions are done with a computationally intensive technique called Lattice QCD. In order to validate these calculations it is essential to be able to compare predictions to experiments,” Prof Gershon said.
“Ds3*(2860)ˉ is ideal for this purpose because it is the first known that both contains a charm quark and has spin 3.”
There are six quarks known to physicists: Up, Down, Strange, Charm, Beauty and Top. Protons and neutrons are composed of up and down quarks, but particles produced in accelerators such as CERN’s Large Hadron Collider can contain the unstable heavier quarks.
In addition, some of these particles have higher spin values than the naturally occurring stable particles.
“Because Ds3*(2860)ˉ contains a heavy charm quark it is easier for theorists to calculate its properties. And because it has spin 3, there can be no ambiguity about what the particle is,” Prof Gershon said.
“Therefore it provides a benchmark for future theoretical calculations. Improvements in these calculations will transform our understanding of how nuclei are bound together.”
The discovery is detailed in two papers that will be published in the journals Physical Review Letters (arXiv.org preprint) and Physical Review D (arXiv.org preprint).
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R. Aaij et al. 2014. Observation of overlapping spin-1 and spin-3 D¯¯¯0K− resonances at mass 2.86GeV/c2. Physical Review Letters, accepted for publication; arXiv: 1407.7574
R. Aaij et al. 2014. Dalitz plot analysis of B0s→D¯¯¯0K−π+ decays. Physical Review D, accepted for publication; arXiv: 1407.7712
