LHCb observes an exceptionally large group of particles

16 - 03 - 2017


The image above shows the data (black dots) of the reconstructed mass distribution resulting from the combination of the Ξc+ and K- particles. The five particle states are the five narrow peaks standing out from the data distribution. (Image: LHCb collaboration)

In what is an exceptional observation, the LHCb experiment at CERN has discovered a new system of five particles in a single analysis.

The LHCb experiment at CERN is a hotbed of new and outstanding physics results. In just the last few months, the collaboration has announced the measurement of a very rare particle decay and evidence of a new manifestation of matter-antimatter asymmetry, to name just two examples.

In a paper released today, the LHCb collaboration announced the discovery of a new system of five particles all in a single analysis. The exceptionality of this discovery is that observing five new states all at once is a rather unique event.

The particles were found to be excited states – a state that has a higher energy than the absolute minimum configuration (or ground state) – of a particle called Ωc0. This Ωc0 is a baryon, a particle with three quarks, containing two “strange” and one “charm” quark. Ωc0decays via the strong force.

The ground state has been known about for quite some time. But little is known about the excited states, where the quarks are in a higher energy configuration. Eighteen such states are predicted by theory models but yet undiscovered. Today LHCb announces the observation of five of them, corresponding to narrow peaks in the figure on the right.

“This discovery demonstrates the capabilities of the LHC to produce new yet unknown particles,” said Nikhef researcher Patrick Koppenburg. These observations are tests of the theoretical description of the strong nuclear force. While it is known that quarks usually come in packs of three, nobody knows exactly why and how the strong force binds them together. Other such states are expected to be discovered in the future, including hopefully new types of pentaquarks.”

“The next step will be the determination of the quantum numbers of these new particles – characteristic numbers used to identify the properties of a specific particle – and the determination of their theoretical significance”, adds Antimo Palano, LHCb scientist from Bari university. “It will contribute to understanding how the three constituent quarks are bound inside a baryon”.

More information
More information on this result can be found on the LHCb website and in the scientific paper.