Charmonium Energy Region Research Articles

Charmonium χc0 and χc2 resonances in coupled-channel scattering from lattice QCD

In order to explore the spectrum of hidden-charm scalar and tensor resonances, we study meson-meson scattering with JPC=0++,2++ in the charmonium energy region using lattice QCD. Employing a light-quark mass corresponding to mπ≈391 MeV, we determine coupled-channel scattering amplitudes up to around 4100 MeV considering all kinematically relevant channels consisting of a pair of open-charm mesons or a charmonium meson with a light meson. A single isolated scalar resonance near 4000 MeV is found with large couplings to DD¯, DsD¯s and the kinematically closed D*D¯* channel. A single tensor resonance at a similar mass couples strongly to DD¯, DD¯* and D*D¯*. We compare the extracted resonances to contemporary experimental candidate states, previous lattice results and theoretical modeling. In contrast to several other studies, we do not find any significant feature in the scalar amplitudes between the ground state χc0(1P) and the resonance found around 4000 MeV. Published by the American Physical Society 2024

Scalar and Tensor Charmonium Resonances in Coupled-Channel Scattering from Lattice QCD

We determine JPC=0++ and 2++ hadron-hadron scattering amplitudes in the charmonium energy region up to 4100 MeV using lattice QCD, a first-principles approach to QCD. Working at mπ≈391 MeV, more than 200 finite-volume energy levels are computed and these are used in extensions of the Lüscher formalism to determine infinite-volume coupled-channel scattering amplitudes. We find that this energy region contains a single χc0 and a single χc2 resonance. Both are found as pole singularities on the closest unphysical Riemann sheet, just below 4000 MeV with widths around 70 MeV. The largest couplings are to kinematically closed D*D¯* channels in S-wave, and couplings to several decay channels consisting of pairs of open-charm mesons are found to be large and significant in both cases. Above the ground state χc0, no other scalar bound states or near-DD¯ threshold resonances are found, in contrast to several theoretical and experimental studies. Published by the American Physical Society 2024

The Y(4260) and Y(4360) enhancements within coupled-channels

Puzzling structures have been observed in the charmonium energy region, namely the Y(4260) and the Y(4360), that cannot be easily accommodated within quark model frameworks. The proximity of nearby dominant hadronic thresholds suggests that they play an important role in the formation of the enhancements. We present results of an unitarized effective Lagrangian model, where mesonic loops, equivalent to coupled-channels, and charmonium vectors ψ interplay to generate line-shapes and poles.

Hadron Spectroscopy at BESIII

The BESIII experiment, hosted at the IHEP of Beijing, has collected the world largest data sample in the charmonium energy region. One of the most important physics goals of BESIII is the investigation of the QCD prediction. QCD can be accessed in a unique way by means of hadron spectroscopy, which was extensively studied and many important progresses were achieved in the last years. Charmonium decays provide an excellent scenario for studying nucleons, hyperons and their excited states, XYZ resonances, as well as light hadrons. Some of the most recent results for hadron spectroscopy from BESIII will be reported.

Open charm scenarios

We discuss possibilities of identifying open charm effects in direct production processes, and propose that direct evidence for the open charm effects can be found in e+e− → J/ψπ0. A unique feature with this process is that the DD̄* + c.c. (where c.c. stands for charge conjugation) open channel is located in a relatively isolated energy, i.e. ~ 3.876 GeV, which is sufficiently far away from the known charmonia ψ(3770) and ψ(4040). Due to the dominance of the isospin-0 component at the charmonium energy region, an enhanced model-independent cusp effect between the thresholds of D0D̄*0 + c.c. and D+D*− + c.c. can be highlighted. An energy scan over this energy region in the e+e− annihilation reaction can help us to understand the nature of X(3900) recently observed by Belle Collaboration in e+e− → DD̄ + c.c, and establish the open charm effects as an important non-perturbative mechanism in the charmonium energy region.

Puzzles in charmonium decays

The open charm effects via intermediate hadron loop transitions seem to play a crucial role in the understanding of several existing "puzzles" in charmonium exclusive decays, such as the $\psi(3770)$ non-$D\bar{D}$ decays, and "$\rho\pi$ puzzle" etc. In the charmonium energy region, non-perturbative mechanisms could be still sizeable, and as a consequence the intermediate hadron loop transitions also provide a mechanism for the helicity-selection-rule (HSR) violation. We report our recent progress on those existing puzzles.