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Register a new userStudy of the doubly charmed tetraquark $T_{cc}^+$
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An exotic narrow state in the $D^0D^0pi^+$ 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 $ccbar{u}bar{d}$ 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 $D^0pi^+$ 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.
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The isospin breaking effect plays an essential role in generating hadronic molecular states with a very tiny binding energy. Very recently, the LHCb Collaboration observed a very narrow doubly charmed tetraquark $T_{cc}^+$ in the $D^0D^0pi$ mass spectrum, which lies just below the $D^0D^{*+}$ threshold around 273 keV. In this work, we study the $D^0D^{*+}/D^+D^{*0}$ interactions with the one-boson-exchange effective potentials and consider the isospin breaking effect carefully. We not only reproduce the mass of the newly observed $T_{cc}^+$ very well in the doubly charmed molecular tetraquark scenario, but also predict the other doubly charmed partner resonance $T_{cc}^{prime+}$ with $m=3876~text{MeV}$, and $Gamma= 412~text{keV}$. The prime decay modes of the $T_{cc}^{prime+}$ are $D^0D^+gamma$ and $D^+D^0pi^0$.
The mass and coupling of the doubly charmed $J^P=0^{-}$ diquark-antidiquark states $T_{cc;bar{s} bar{s}}^{++}$ and $T_{cc;bar{d} bar{s}}^{++}$ that bear two units of the electric charge are calculated by means of QCD two-point sum rule method. Computations are carried out by taking into account vacuum condensates up to and including terms of tenth dimension. The dominant $S$-wave decays of these tetraquarks to a pair of conventional $ D_{s}^{+}D_{s0}^{ast +}(2317)$ and $D^{+}D_{s0}^{ast +}(2317)$ mesons are explored using QCD three-point sum rule approach, and their widths are found. The obtained results $m_{T}=(4390~pm 150)~mathrm{MeV}$ and $Gamma =(302 pm 113~mathrm{MeV}$) for the mass and width of the state $T_{cc;bar{ s} bar{s}}^{++}$, as well as spectroscopic parameters $widetilde{m} _{T}=(4265pm 140)~mathrm{MeV}$ and $widetilde{Gamma }=(171~pm 52)~ mathrm{MeV}$ of the tetraquark $T_{cc;bar{d} bar{s}}^{++}$ may be useful in experimental studies of exotic resonances.
A highly significant structure is observed in the $Lambda_c^+K^-pi^+pi^+$ mass spectrum, where the $Lambda_c^+$ baryon is reconstructed in the decay mode $pK^-pi^+$. The structure is consistent with originating from a weakly decaying particle, identified as the doubly charmed baryon $Xi_{cc}^{++}$. The difference between the masses of the $Xi_{cc}^{++}$ and $Lambda_c^+$ states is measured to be $1334.94 pm 0.72 (mathrm{stat}) pm 0.27 (mathrm{syst}~mathrm{MeV}/c^2$, and the $Xi_{cc}^{++}$ mass is then determined to be $3621.40 pm 0.72 (mathrm{stat}) pm 0.27 (mathrm{syst} pm 0.14 , (Lambda_c^+)~mathrm{MeV}/c^2$, where the last uncertainty is due to the limited knowledge of the $Lambda_c^+$ mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 $mathrm{fb}^{-1}$, and confirmed in an additional sample of data collected at 8 TeV.
The doubly charmed exotic state $T_{cc}$ recently discovered by the LHCb Collaboration could well be a $DD^{*}$ molecular state long predicted in various theoretical models, in particular, the $DD^*$ isoscalar axial vector molecular state predicted in the one-boson-exchange model. In this work, we study the $DDD^*$ system in the Gaussian Expansion Method with the $DD^*$ interaction derived from the one-boson-exchange model and constrained by the precise binding energy of $273pm63$ keV of $T_{cc}$ with respect to the $D^{*+}D^0$ threshold. We show the existence of a $DDD^*$ state with a binding energy of a few hundred keV and spin-parity $1^-$. Its main decay modes are $DDDpi$ and $DDDgamma$. The existence of such a state could in principle be confirmed with the upcoming LHC data and will unambiguously determine the nature of the $T_{cc}^+$ state and of the many exotic state of similar kind, thus deepening our understanding of the non-perturbative strong interaction.
A search for the doubly charmed baryon $Xi_{cc}^{+}$ is performed through its decay to the $Lambda_c^+ K^- pi^+$ final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13$mathrm{,Tekern -0.1em V}$. The data correspond to a total integrated luminosity of $9,mathrm{fb}^{-1}$. No significant signal is observed in the mass range from 3.4 to 3.8$mathrm{,Gekern -0.1em V}/c^2$. Upper limits are set at $95%$ credibility level on the ratio of the $Xi_{cc}^{+}$ production cross-section times the branching fraction to that of $Lambda_c^+$ and $Xi_{cc}^{++}$ baryons. The limits are determined as functions of the $Xi_{cc}^{+}$ mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15$mathrm{,Gekern -0.1em V}/c$.
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