Determination of the spin and parity of all-charm tetraquarks.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41339507.
- Also identified by DOI 10.1038/s41586-025-09711-7 and PMC identifier 12675279.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The traditional quark model<sup>1,2</sup> accounts for the existence of baryons, such as protons and neutrons, which consist of three quarks, as well as mesons, composed of a quark-antiquark pair. Only recently has substantial evidence started to accumulate for exotic states composed of four or five quarks and antiquarks<sup>3</sup>. The exact nature of their internal structure remains uncertain<sup>4-29</sup>. Here we report the first measurement of quantum numbers of the recently discovered family of three all-charm tetraquarks<sup>30-32</sup>, using data collected by the CMS experiment at the Large Hadron Collider from 2016 to 2018 (refs. <sup>33,34</sup>). The angular analysis techniques developed for the discovery and characterization of the Higgs boson<sup>35-37</sup> have been applied to the new exotic states. Here we show that the quantum numbers for parity P and charge conjugation C symmetries are found to be +1. The spin J of these exotic states is determined to be consistent with 2ħ, while 0ħ and 1ħ are excluded at 95% and 99% confidence levels, respectively. The J<sup>PC</sup> = 2<sup>++</sup> assignment implies particular configurations of constituent spins and orbital angular momenta, which constrain the possible internal structure of these tetraquarks.