Determination of the spin and parity of all-charm tetraquarks

The traditional quark model $^{1,2}$ 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 $^{3}$ . The exact nature of their internal structure remains uncertain $^{4–29}$ . Here we report the first measurement of quantum numbers of the recently discovered family of three all-charm tetraquarks $^{30–32}$ , using data collected by the CMS experiment at the Large Hadron Collider from 2016 to 2018 (refs. $^{33,34}$ ). The angular analysis techniques developed for the discovery and characterization of the Higgs boson $^{35–37}$ 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 2 ħ , while 0 ħ and 1 ħ are excluded at 95% and 99% confidence levels, respectively. The J $^{ P C }$ = 2 $^{++}$ assignment implies particular configurations of constituent spins and orbital angular momenta, which constrain the possible internal structure of these tetraquarks.