Physicists Discover New Tetraquark Containing Two Charmed Quarks

A group of scientists from CERN (European Organization for Nuclear Research), the GI Budker Institute of Nuclear Physics SB RAS (INP SB RAS), the A.I. Alikhanov Institute of Theoretical and Experimental Physics "Kurchatov Institute" (ITEP), NSU, et al. discovered a new particle, an exotic tetraquark T+. The "cc" indicates there are two charmed quarks in the particle, a total positive charge (+), and the presence of anti-u-quark and anti-d-quark. The results of the study were presented at the European Physical Society conference on high energy physics 2021 and published on the CERN website.

Currently, physicists know about more than twenty tetraquarks, particles composed of two quarks and two antiquarks. As a rule, these particles don’t live long. The new particle is unusual because it is a doubly charmed tetraquark. In addition, the tetraquark lives for a rather long time on a time scale characteristic of a strong interaction, 500-1000 times longer than previously observed tetraquarks.

Alexander Bondar, LHCb collaborator, Head of INP SB RAS Laboratory, RAS Academician, and Professor at the NSU Physics Department, talks about the results,

I think this discovery confirms our assumptions that there are even more stable particles that are not built from charmed quarks, but from pretty quarks (b-quarks). B-quarks are about four times heavier than charmed ones. If we understand everything correctly, these tetraquarks should be stable with respect to strong and electromagnetic interactions and live already 10-13 seconds. This is a very long time in comparison with the characteristic lifetime of hadronic physics objects. Therefore, the experiments first task is to search for these objects. The parameters of the collider will improve, the intensity of the beams will increase, and, quite possibly, in a few years another of these objects will be discovered.

These experiments allow us to understand better the processes that took place with matter in the first moments of the Universe’s emergence. By predicting or explaining the properties of the observed particles, scientists have a better understanding of the strong force mechanism that was dominant at the time.

Experimental data was collected from 2011 to 2018 and based on this about 200 births of new particles were observed. The signal is confidently recorded with a statistical significance of more than 10 standard deviations, that is, the probability of observing this effect due to statistical fluctuations is negligible. A group of scientists, including representatives of the INP SB RAS and NSU, participated in the analysis and rechecking of the preliminary results, the discussion of physics, and possible instrumental effects that can have an impact on the results obtained.