Where Is the Lightest Charmed Scalar Meson?

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.

Axial-Vector D_{1} Hadrons in D^{*}π Scattering from QCD

We present I=1/2 D^{*}π scattering amplitudes from lattice QCD and determine two low-lying J^{P}=1^{+} axial-vector D_{1} states and a J^{P}=2^{+} tensor D_{2}^{*}. Computing finite-volume spectra at a light-quark mass corresponding to m_{π}≈391  MeV, for the first time, we are able to constrain coupled J^{P}=1^{+} D^{*}π amplitudes with ^{2S+1}ℓ_{J}=^{3}S_{1} and ^{3}D_{1} as well as coupled J^{P}=2^{+}  Dπ(^{1}D_{2}} and D^{*}π(^{3}D_{2}} amplitudes via Lüscher's quantization condition. Analyzing the scattering amplitudes for poles we find a near-threshold bound state, producing a broad feature in D^{*}π{^{3}S_{1}}. A narrow bump occurs in D^{*}π{^{3}D_{1}} due to a D_{1} resonance. A single resonance is found in J^{P}=2^{+} coupled to Dπ and D^{*}π. A relatively low mass and large coupling are found for the lightest D_{1}, suggestive of a state that will evolve into a broad resonance as the light-quark mass is reduced. An earlier calculation of the scalar D_{0}^{*} using the same light-quark mass enables comparisons to the heavy-quark limit.

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.

QCD confronts heavy-flavor and exotic hadrons

A review of QCD-based theory approaches to study the heavy-flavor and exotic hadrons is given. The focus is on the results from lattice QCD and from lattice QCD complemented by effective field theories. Both approaches are first briefly introduced and applied in few examples. Then the status of various hadrons sectors is presented.