e~+e~- →charm cross sections via ISR

We discuss recent measurements of exclusive e+e-cross sections for charmed hadron final states near threshold performed by Belle and BABAR.The results are based on a study of events with initial-state-radiation photons in a large data sample collected with the Belle and BABAR detectors at the Υ(4S) resonance and nearby continuum.     

Production of charmonium(like) states in e+e- interactions

We present a search for new charmonium like states in e+e- annihilation using the initial-state radiation and the process e+e-→J/ψ D(*)D(*). The analyses are based on a huge data sample recorded near the T(4S) resonance with the Belle detector at the KEKB e+e- asymmetric-energy collider.     

QCD physics at hadron storage rings: From COSY to FAIR

As a result of the rapid rise of the coupling constant α_s at low momentum transfers, perturbation theory is not an appropriate method to describe the strong interaction. In this kinematic regime other methods such as lattice QCD or effective field theories are more appropriate to investigate the appearance of a still unsettled phenomena: confinement and chiral symmetry breaking. Furthermore, the confinement of quarks and gluons to hadrons allows crucial tests of fundamental symmetries that are inherent to the QCD Lagrangian but are broken in hadronic systems. Thus, high precision measurements of the production and decay of specific hadronic states provides decisive benchmarks to investigate the properties of QCD in this regime. A new series of experiments are being prepared using nearly full acceptance detectors for neutral and charged particles around internal targets in high intensity, phase-space-cooled hadronic beams. Later this year, it is planned to transfer the WASA detector from the CELSIUS to the COSY ring in order to measure the production and various decay channels of the η and η′ mesons, thereby investigating the violation of P, C, T, and combinations thereof, as well as isospin violation. The experimental and theoretical techniques employed here will provide an important basis to extend these investigations to the static and dynamical properties of hadrons with charm quark content with the high energy storage ring for antiprotons at the new GSI/FAIR facility. Additional related perspectives will be opened at the new facility ranging from the properties of hadrons in dense nuclear matter to measurements of the nucleon’s transverse spin distribution in the valence quark region using polarized antiprotons     

J/ψ→重子+反重子衰变的HOWL产生子的效率修正

发展了一种基于跃迁振幅信息的Monte-Carlo产生子来研究纯相空间产生子(HOWL)的效率修正. 对,J/ψ→pp, ΛΛ, pX衰变作了Monte-Carlo模拟,结果表明, 这种产生子能够很好地实现末态粒子的角分布. 与HOWL产生子比较, 发现末态粒子的角分布会对效率产生很大的修正. 所以, 对于长链的级联衰变, 推荐这种基于跃迁振幅信息的产生子.     

Open charm mesons and charmonia in magnetized strange hadronic matter

We investigate the in-medium masses of open charm mesons (D(\begin{document}$ D^0 $\end{document}, \begin{document}$ D^+ $\end{document}), \begin{document}$ \bar{D} $\end{document}(\begin{document}$ \bar{D^0} $\end{document}, \begin{document}$ D^- $\end{document}), \begin{document}$ D_s $\end{document}(\begin{document}$ {D_{s}}^+ $\end{document}, \begin{document}$ {D_{s}}^- $\end{document})) and charmonium states (\begin{document}$ J/\psi $\end{document}, \begin{document}$ \psi(3686) $\end{document}, \begin{document}$ \psi(3770) $\end{document}, \begin{document}$ \chi_{c0} $\end{document}, \begin{document}$ \chi_{c2} $\end{document}) in strongly magnetized isospin asymmetric strange hadronic matter using a chiral effective model. In the presence of a magnetic field, the number and scalar densities of charged baryons have contributions from Landau energy levels. The mass modifications of open charm mesons result from their interactions with nucleons, hyperons, and the scalar fields (the non-strange field σ, strange field ζ, and isovector field δ) in the presence of a magnetic field. The mass modifications of the charmonium states result from the modification of gluon condensates in a medium simulated by the variation in the dilaton field (χ) in the chiral effective model. The effects of finite quark masses are also incorporated in the trace of the energy-momentum tensor in quantum chromodynamics to investigate the mass shifts of charmonium states. The in-medium masses of open charm mesons and charmonia are observed to decrease with an increase in baryon density. The charged \begin{document}$ D^+ $\end{document}, \begin{document}$ D^- $\end{document}, \begin{document}$ {D_{s}}^+ $\end{document}, and \begin{document}$ {D_{s}}^- $\end{document} mesons have additional positive mass shifts due to Landau quantization in the presence of a magnetic field. The effects of the strangeness fraction are observed to be more dominant for \begin{document}$ \bar{D} $\end{document} mesons compared with D mesons. The mass shifts of charmonia are observed to be larger in hyperonic media compared with nuclear media when the effect of the finite quark mass term is neglected. These medium mass modifications can have observable consequences on the production of the open charm mesons and charmonia in high-energy asymmetric heavy-ion collision experiments.     

Using X(3823)→J/ψπ+π− to identify coupled-channel effects

Very recently, the Belle and BESIII experiments observed a new charmonium-like state X(3823), which is a good candidate for the D-wave charmonium ψ(1³D₂). Because the X(3823) is just near the D ¯D^∗ threshold, the decay X(3823)→ J/ψπ⁺π⁻ can be a golden channel to test the significance of coupled-channel effects. In this work, this decay is considered including both the hidden-charm dipion and the usual quantum chromodynamics multipole expansion (QCDME) contributions. The partial decay width, the dipion invariant mass spectrum distribution dΓ[X(3823) → J/ψπ⁺π⁻]/dm_π⁺_π⁻, and the corresponding dΓ[X(3823) → J/ψπ⁺π⁻]/d cos θ distribution are computed. Many parameters are determined from existing experimental data, so the results depend mainly only on one unknown phase between the QCDME and hidden-charm dipion amplitudes.     

Experimental review of e~+e~-→ππh_c

We review the recent BESIII measurement of e~+e~-→ππh_c in which its line shape is studied between the center-of-mass energies of 3.9 to 4.42 Ge V and an iso-vector charmonium-like state Z_c(4020) is observed in the invariant mass of πhc at the BESIII experiment. The charged Z_c(4020)~± is the second observed Z_c state following Z_c(3900), while the Z_c(4020)~0 is the first observed neutral Z_c state. The line shape of σ(e~+e~-→ππh_c) is also reanalyzed in view of searching for the Y state and the existence of the Y(4220) state is confirmed and compared with the previous work of the BESIII experiment.     

Study of charmonium(-like) states via ISR at Belle

The cross sections for e⁺e－→π⁺π^－J/ψ, π⁺π^－ψ(2S), K⁺K^－J/ψ, DD, D⁰D^－+π⁺+c.c., D^*D+c.c., and D^*D^* are measured using data sample collected on or near the Υ(4S) resonance with the Belle detector at KEKB. A peak near 4.25GeV/c², corresponding to the so called Y(4260), is observed in π⁺π^－J/ψ final state. In addition, there is another cluster of events at around 4.05GeV/c². Two resonant structures are observed in the π⁺π^－ψ(2S) invariant mass distribution, one at 4361±9±9MeV/c² with a width of 74±15±10MeV/c², and another at 4664±11±5MeV/c² with a width of 48±15± 3MeV/c². The rich structures observed in all these final states indicate that our understanding of the vector charmonium states above the open charm threshold is still poor, let alone the other possible dynamics such as charmonium hybrids or final state re-scattering and so on.