Study of the doubly charmed tetraquark [Formula: see text]

New insight into the exotic states strongly coupled with the DD‾∗ from the Tcc. Sci Bull (Beijing) 2024:S2095-9273(24)00490-0. [PMID: 39142944 DOI: 10.1016/j.scib.2024.07.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

We have investigated the internal structure of the open- and hidden-charmed (DD∗/D¯D∗) molecules in the unified framework. We first fit the experimental lineshape of the Tcc+ state and extract the DD∗ interaction, from which the Tcc+ is assumed to arise solely. Then we obtain the DD‾∗ interaction by charge conjugation. Our results show that the DD‾∗ interaction is attractive but insufficient to form X(3872) as a bound state. Instead, its formation requires the crucial involvement of the coupled channel effect between the DD¯∗ and cc¯ components, although the cc¯ accounts for approximately 1% only. Besides X(3872), we have obtained a higher-energy state around 3957.9 MeV with a width of 16.7 MeV, which may be a potential candidate for the X(3940). In JPC=1+- sector, we have found two states related to the iso-scalar X̃(3872) and hc(2P), respectively. Our combined study provides valuable insights into the nature of these DD∗/DD¯∗ exotic states.

Shallow Bound States and Hints for Broad Resonances with Quark Content b[over ¯]c[over ¯]ud in B-D[over ¯] and B^{*}-D[over ¯] Scattering from Lattice QCD

We present the first determination of the energy dependence of the B-D[over ¯] and B^{*}-D[over ¯] isospin-0, S-wave scattering amplitudes both below and above the thresholds using lattice QCD, which allows us to investigate rigorously whether mixed bottom-charm b[over ¯]c[over ¯]ud tetraquarks exist as bound states or resonances. The scattering phase shifts are obtained using Lüscher's method from the energy spectra in two different volumes. To ensure that no relevant energy level is missed, we use large, symmetric 7×7 and 8×8 correlation matrices that include, at both source and sink, B^{(*)}-D[over ¯] scattering operators with the lowest three or four possible back-to-back momenta in addition to local b[over ¯]c[over ¯]ud operators. We fit the energy dependence of the extracted scattering phase shifts using effective-range expansions. We observe sharp peaks in the B^{(*)}-D[over ¯] scattering rates close to the thresholds, which are associated with shallow bound states, either genuine or virtual, a few MeV or less below the B^{(*)}-D[over ¯] thresholds. In addition, we find hints for resonances with masses of order 100 MeV above the thresholds and decay widths of order 200 MeV.

Doubly Charmed Tetraquark T_{cc}^{+} from Lattice QCD near Physical Point

The doubly charmed tetraquark T_{cc}^{+} recently discovered by the LHCb Collaboration is studied on the basis of (2+1)-flavor lattice QCD simulations of the D^{*}D system with nearly physical pion mass m_{π}=146  MeV. The interaction of D^{*}D in the isoscalar and S-wave channel, derived from the hadronic spacetime correlation by the HAL QCD method, is attractive for all distances and leads to a near-threshold virtual state with a pole position E_{pole}=-59(_{-99}^{+53})(_{-67}^{+2})  keV and a large scattering length 1/a_{0}=0.05(5)(_{-2}^{+2})  fm^{-1}. The virtual state is shown to evolve into a loosely bound state as m_{π} decreases to its physical value by using a potential modified to m_{π}=135  MeV based on the pion-exchange interaction. Such a potential is found to give a semiquantitative description of the LHCb data on the D^{0}D^{0}π^{+} mass spectrum. Future study is necessary to perform physical-point simulations with the isospin-breaking and open three-body-channel effects taken into account.

Role of Left-Hand Cut Contributions on Pole Extractions from Lattice Data: Case Study for T_{cc}(3875)^{+}

We discuss recent lattice data for the T_{cc}(3875)^{+} state to stress, for the first time, a potentially strong impact of left-hand cuts from the one-pion exchange on the pole extraction for near-threshold exotic states. In particular, if the left-hand cut is located close to the two-particle threshold, which happens naturally in the DD^{*} system for the pion mass exceeding its physical value, the effective-range expansion is valid only in a very limited energy range up to the cut and as such is of little use to reliably extract the poles. Then, an accurate extraction of the pole locations requires the one-pion exchange to be implemented explicitly into the scattering amplitudes. Our findings are general and potentially relevant for a wide class of hadronic near-threshold states.

Observation of a Resonant Structure near the D_{s}^{+}D_{s}^{-} Threshold in the B^{+}→D_{s}^{+}D_{s}^{-}K^{+} Decay

An amplitude analysis of the B^{+}→D_{s}^{+}D_{s}^{-}K^{+} decay is carried out to study for the first time its intermediate resonant contributions, using proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. A near-threshold peaking structure, referred to as X(3960), is observed in the D_{s}^{+}D_{s}^{-} invariant-mass spectrum with significance greater than 12 standard deviations. The mass, width, and the quantum numbers of the structure are measured to be 3956±5±10  MeV, 43±13±8  MeV, and J^{PC}=0^{++}, respectively, where the first uncertainties are statistical and the second systematic. The properties of the new structure are consistent with recent theoretical predictions for a state composed of cc[over ¯]ss[over ¯] quarks. Evidence for an additional structure is found around 4140 MeV in the D_{s}^{+}D_{s}^{-} invariant mass, which might be caused either by a new resonance with the 0^{++} assignment or by a J/ψϕ↔D_{s}^{+}D_{s}^{-} coupled-channel effect.

Revealing the nature of hidden charm pentaquarks with machine learning

We study the nature of the hidden charm pentaquarks, i.e., the P_c4312,P_c4440 and P_c(4457), with a neural network approach in pionless effective field theory. In this framework, the normal χ² fitting approach cannot distinguish the quantum numbers of the P_c(4440) and P_c(4457). In contrast to that, the neural network-based approach can discriminate them, which still cannot be seen as a proof of the spin of the states since pion exchange is not considered in the approach. In addition, we also illustrate the role of each experimental data bin of the invariant J/ψp mass distribution on the underlying physics in both neural network and fitting methods. Their similarities and differences demonstrate that neural network methods can use data information more effectively and directly. This study provides more insights about how the neural network-based approach predicts the nature of exotic states from the mass spectrum.

An updated review of the new hadron states

The past decades witnessed the golden era of hadron physics. Many excited open heavy flavor mesons and baryons have been observed since 2017. We shall provide an updated review of the recent experimental and theoretical progresses in this active field. Besides the conventional heavy hadrons, we shall also review the recently observed open heavy flavor tetraquark statesX(2900) andTcc+(3875)as well as the hidden heavy flavor multiquark statesX(6900),Pcs(4459)0,Zcs(3985)-,Zcs(4000)+, andZcs(4220)+. We will also cover the recent progresses on the glueballs and light hybrid mesons, which are the direct manifestations of the non-AbelianSU(3) gauge interaction of the Quantum Chromodynamics in the low-energy region.

The role of multi-parton interactions in doubly-heavy hadron production

Beauty and charm quarks are ideal probes of pertubative Quantum Chromodymanics in proton–proton collisions, owing to their large masses. In this paper the role of multi-parton interactions in the production of doubly-heavy hadrons is studied using simulation samples generated with Pythia, a Monte Carlo event generator. Comparisons are made to the stand-alone generators BcVegPy and GenXicc. New methods of speeding up Pythia simulations for events containing heavy quarks are described, enabling the production of large samples with multiple heavy-quark pairs. We show that significantly higher production rates of doubly-heavy hadrons are predicted in models that allow heavy quarks originating from different parton–parton interactions (within the same hadron–hadron collision) to combine to form such hadrons. Quantitative predictions are sensitive to the modelling of colour reconnections. We suggest a set of experimental measurements capable of differentiating these additional contributions.

Prediction of a Narrow Exotic Hadronic State with Quantum Numbers J^{PC}=0^{--}

Lots of charmonium-like structures have been observed in the last two decades. Most of them have quantum numbers that can be formed by a pair of charm and anticharm quarks, thus it is difficult to unambiguously identify the exotic ones among them. In this Letter, by exploiting heavy quark spin symmetry, we present a robust prediction of the hadronic molecular scenario, where the ψ(4230), ψ(4360) and ψ(4415) are identified as DD[over ¯]_{1}, D^{*}D[over ¯]_{1}, and D^{*}D[over ¯]_{2}^{*} bound states, respectively. We show that a flavor-neutral charmonium-like exotic state with quantum numbers J^{PC}=0^{--}, denoted as ψ_{0}(4360), should exist as a D^{*}D[over ¯]_{1} bound state. The mass and width of the ψ_{0}(4360) are predicted to be (4366±18)  MeV and less than 10 MeV, respectively. The ψ_{0}(4360) is significant in two folds: no 0^{--} hadron has been observed so far, and a study of this state will enlighten the understanding of the mysterious vector mesons between 4.2 and 4.5 GeV, as well as the nature of previously observed exotic Z_{c} and P_{c} states. We propose that such an exotic state can be searched for in e^{+}e^{-}→ηψ_{0}(4360) and uniquely identified by measuring the angular distribution of the outgoing η meson.

Signature of a Doubly Charm Tetraquark Pole in DD^{*} Scattering on the Lattice

The doubly charm tetraquark with flavor ccu[over ¯]d[over ¯] and isospin I=0 is investigated by calculating the DD^{*} scattering amplitude with lattice QCD. The simulation is done on CLS ensembles with dynamical u/d, s quarks and m_{π}≃280  MeV for two charm quark masses, one slightly larger and one slightly lower than the physical value. The scattering amplitudes for partial waves l=0, 1 are extracted near threshold via the Lüscher method by considering systems with total momenta PL/(2π)=0,1,sqrt[2],2 on two spatial volumes. A virtual bound state pole in the DD^{*} scattering amplitude with l=0 is found 9.9_{-7.1}^{+3.6}  MeV below the DD^{*} threshold for the charm quark mass closer to the physical value. This pole is likely related to the doubly charm tetraquark discovered by LHCb less than 1 MeV below the D^{0}D^{*+} threshold. Future lattice simulations closer to the continuum limit and physical quark masses would be valuable to establish this connection systematically.

Study on hadron-hadron interaction with femtoscopic technique

We study the method to study the exotic hadrons using the femtoscopic correlation function in the high-energy collisions. The formula for the correlation function extended to the coupled-channel case is employed. We see that how the coupled-channel effect works for the correlation function from the different hadron emitting sources with the case of the K−p correlation function. The method is applied to the prediction for the DD*/DD̅* correlation function for the study of the Tcc/X(3872) state.

Impact of clustering inside compact tetraquarks

Due to the reducibility of tetraquark operators into mesonic clusters, a strong interplay exists in tetraquarks between compact and molecular structures. This issue is studied within an effective field theory approach, where the compact tetraquark is treated as an elementary particle. Under the influence of the coupling to the mesonic clusters, an initially formed compact tetraquark bound state is deformed towards a new structure of the molecular type, having the attributes of a shallow bound state.

Triangle Singularity in the Production of T+cc(3875) and a Soft Pion at Hadron Colliders

If the double-charm tetraquark meson T+cc(3875) is a loosely bound molecule, it can be produced in high-energy proton-proton collisions by the creation of the charm mesons D∗+D0 at short distances followed by their binding into T+cc. It can also be produced by the creation of D∗+D∗+ at short distances followed by their rescattering into T+ccπ+ through a charm-meson triangle loop. A charm-meson triangle singularity produces a narrow peak in the T+ccπ+ invariant mass distribution 6.1 MeV above the threshold with a width of about 1 MeV. The fraction of T+cc that are accompanied by π+ with E < mπ is estimated to be roughly 3%. The fraction of T+cc events with T+ccπ+ in the narrow peak from the triangle singularity could be comparable.