Study of the doubly charmed tetraquark $T_{cc}^+$

TL;DR

This paper reports the discovery and detailed analysis of the $T_{cc}^+$ tetraquark, a narrow exotic state below the $D^{*+}D^0$ threshold, using LHCb data, providing insights into its structure and production.

Contribution

First detailed experimental study of the $T_{cc}^+$ tetraquark, including measurements of its mass, decay structure, and resonance parameters, revealing its nature and production characteristics.

Findings

Confirmed the $T_{cc}^+$ as an isoscalar $ccar{u}ar{d}$ tetraquark

Measured resonance parameters including pole position and scattering length

Observed an unexpected dependence of production rate on track multiplicity

Abstract

An exotic narrow state in the $D^0D^0\pi^+$ mass spectrum just below the $D^{*+}D^0$ mass threshold is studied using a data set corresponding to an integrated luminosity of 9 fb$^{-1}$ acquired with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The state is consistent with the ground isoscalar $T^+_{cc}$ tetraquark with a quark content of $cc\bar{u}\bar{d}$ and spin-parity quantum numbers $\mathrm{J}^{\mathrm{P}}=1^+$. Study of the $DD$ mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell $D^{*+}$ mesons is confirmed by the $D^0\pi^+$ mass distribution. The mass of the resonance and its coupling to the $D^{*}D$ system are analysed. Resonance parameters including the pole position, scattering length, effective range and compositeness are measured to reveal important information about the nature of the $T^+_{cc}$ state. In addition, an unexpected dependence of the production rate on track multiplicity is observed.