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

The collaboration
Nature Commun. 13 (2022) 3351, 2022.

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.

• #### Fig 1

Fig. 1 of the LHCb-PAPER-2021-032

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Distribution of $D^0 D^0 \pi^+$ mass where the contribution of the non-$D^0$ background has been statistically subtracted. Uncertainties on the...

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Fig. 3 of the LHCb-PAPER-2021-032

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Mass distribution for $D^0 \pi^+$ pairs from selected $D^0 D^0 \pi^+$ candidates with a mass below the $D^{*+}D^0$ mass threshold...

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Left panel of Fig. 4 of the LHCb-PAPER-2021-032

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$D^0 D^0$~mass distributions for selected candidates with the $D^0$ background subtracted. Uncertainties on the data points are statistical only and...

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Right panel of Fig. 4 of the LHCb-PAPER-2021-032

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$D^+ D^0$~mass distributions for selected candidates with the $D^0$ background subtracted. Uncertainties on the data points are statistical only and...

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Left panel of Fig. 5 of the LHCb-PAPER-2021-032

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Mass distributions for selected $D^+ D^+$ candidates with the $D^0$ background subtracted. Uncertainties on the data points are statistical only...

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Right panel of Fig. 5 of the LHCb-PAPER-2021-032

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Mass distributions for selected $D^+ D^0 \pi^+$ candidates with the $D^0$ background subtracted. Uncertainties on the data points are statistical...

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Fig. 7 of the LHCb-PAPER-2021-032

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Background-subtracted distributions for the multiplicity of tracks reconstructed in the vertex detector for $T_{cc}^+\to D^0 D^0 \pi^+$ signal, low-mass $D^0\bar{D}^0$...

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Fig. 8 of the LHCb-PAPER-2021-032

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Background-subtracted transverse momentum spectra for $T_{cc}^+\to D^0 D^0 \pi^+$ signal, low-mass $D^0\bar{D}^0$ and $D^0D^0$ pairs. The binning scheme is chosen...

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Top panel of Fig. 9 of the LHCb-PAPER-2021-032

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Mass distributions for selected $D^0 \bar{D}^0$ candidates with the $D^0$ background subtracted. Uncertainties on the data points are statistical only...

• #### Fig 9b

Bottom panel of Fig. 9 of the LHCb-PAPER-2021-032

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Mass distributions for selected $D^0 D^0$ candidates with the $D^0$ background subtracted. Uncertainties on the data points are statistical only...

• #### Fig ED3a

Top panel of Fig. ED3 in extended data of the LHCb-PAPER-2021-032

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Mass distributions for selected $\bar{D}^0D^0\pi^+$ candidates with the $D^0$ background subtracted. Uncertainties on the data points are statistical only and...

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Bottom panel of Fig. ED3 in extended data of the LHCb-PAPER-2021-032

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Mass distributions for selected $D^0D^0\pi^+$ candidates with the $D^0$ background subtracted. Uncertainties on the data points are statistical only and...

• #### Fig ED4a

Top panel of Fig. ED4 in extended data of the LHCb-PAPER-2021-032

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Mass distributions for selected $D^0D^-$ candidates with the $D^0$ background subtracted. Uncertainties on the data points are statistical only and...

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Bottom panel of Fig. ED4 in extended data of the LHCb-PAPER-2021-032

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Mass distributions for selected $D^0D^+$ candidates with the $D^0$ background subtracted. Uncertainties on the data points are statistical only and...

• #### Fig 1 unbinned

Fig. 1 of the LHCb-PAPER-2021-032

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Distribution of $D^0 D^0 \pi^+$ mass where the contribution of the non-$D^0$ background has been statistically subtracted by assigning the...

• #### Fig 3 unbinned

Fig. 3 of the LHCb-PAPER-2021-032

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Mass distribution for $D^0 \pi^+$ pairs from selected $D^0 D^0 \pi^+$ candidates with a mass below the $D^{*+}D^0$ mass threshold...

• #### Fig 4a unbinned

Left panel of Fig. 4 of the LHCb-PAPER-2021-032

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$D^0 D^0$~mass distributions for selected candidates with the $D^0$ background subtracted by assigning the a weight to every candidate.

• #### Fig 4b unbinned

Right panel of Fig. 4 of the LHCb-PAPER-2021-032

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$D^+ D^0$~mass distributions for selected candidates with the $D^0$ background subtracted by assigning the a weight to every candidate.

• #### Fig 5a unbinned

Left panel of Fig. 5 of the LHCb-PAPER-2021-032

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Mass distributions for selected $D^+ D^+$ candidates with the $D^0$ background subtracted by assigning the a weight to every candidate.

• #### Fig 5b unbinned

Right panel of Fig. 5 of the LHCb-PAPER-2021-032

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Mass distributions for selected $D^+ D^0 \pi^+$ candidates with the $D^0$ background subtracted by assigning the a weight to every...