We investigate the nature of the recently observed narrow resonance Z c (3900), which is assumed to be a D * D molecular state with quantum numbers I G J P = 1 + 1 + . Using QCD sum rules, we consider contributions up to dimension eight in the operator product expansion and work at the leading order in α s . The mass we arrived at is (3.88 ± 0.17) GeV, which coincides with the mass of Z c (3900).

We present the light-cone distribution amplitudes of the Ξ baryons up to twist six on the basis of QCD conformal partial wave expansion to the leading order conformal spin accuracy. The nonperturbative parameters relevant to the DAs are determined in the framework of the QCD sum rule. The light-cone QCD sum rule approach is used to investigate both the electromagnetic form factors of Ξ and the exclusive semileptonic decay of Ξ c as applications. Our estimations on the magnetic moments are µ Ξ 0 = −(1.92 ± 0.34)µ N and µ Ξ − = −(1.19 ± 0.03)µ N . The decay width of the process Ξ c → Ξe + ν e is evaluated to be Γ = 8.73 × 10 −14 GeV, which is in accordance with the experimental measurements and other theoretical approaches.

Based on QCD conformal partial wave expansion to leading order conformal spin accuracy, we present the light-cone distribution amplitudes (DAs) of Σ and Λ baryons up to twist 6. It is concluded that fourteen independent DAs are needed to describe the valence three-quark states of the baryons at small transverse separations. The nonperturbative parameters relevant to the DAs are determined within the framework of QCD sum rule method. With the obtained DAs, a simple investigation on the electromagnetic form factors of these baryons are given. The magnetic moments of the baryons are estimated by fitting the magnetic form factor with the dipole formula.

The semileptonic weak decay process of the Λ c baryon to the neutron Λ c → ne + ν e is examined. The transition form factors are investigated with light-cone QCD sum rules. The differential decay width is obtained in the dynamical region by fitting the sum rules-allowed results with the dipole formula. The total decay width and the branching ratio are estimated to be Γ(Λ c → ne + ν e ) = (8.89 ± 0.36) × 10 −15 GeV and Br(Λ c → ne + ν e ) = 0.27 ± 0.01%, respectively.

We present the light-cone QCD sum rules up to twist 6 for the electromagnetic form factors of the Λ baryon. To estimate the magnetic moment of the baryon, the magnetic form factor is fitted by the dipole formula. The numerical value of our estimation is µ Λ = −(0.64 ± 0.04)µ N , which is in accordance with the experimental data and the existing theoretical results. We find that it is twist 4 but not the leading twist distribution amplitudes that dominate the results.