Determination of the spin and parity of all-charm tetraquarks

TL;DR

This study measures the quantum numbers of all-charm tetraquarks, confirming their spin and parity, and providing insights into their internal structure using advanced angular analysis techniques at the LHC.

Contribution

First measurement of quantum numbers of all-charm tetraquarks, applying Higgs boson analysis methods to exotic states at the LHC.

Findings

Quantum numbers for parity and charge conjugation are +1.

The spin is consistent with 2ħ, excluding 0ħ and 1ħ.

The $J^{PC} = 2^{++}$ assignment constrains internal structure models.

Abstract

The traditional quark model 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. The exact nature of their internal structure remains uncertain. This paper reports the first measurement of quantum numbers of the recently discovered family of three all-charm tetraquarks, using data collected by the CMS experiment at the Large Hadron Collider from 2016 to 2018. The angular analysis techniques developed for the discovery and characterization of the Higgs boson 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 consistent with 2$\hbar$, while 0$\hbar$ and 1$\hbar$ are excluded at 95% and 99% confidence level, respectively. The $J^{PC} = 2^{++}$ assignment implies particular configurations of constituent spins and orbital angular momenta, which constrain the possible internal structure of these tetraquarks.