In this exploratory lattice study, low-energy scattering of the (DD * ) ± meson system is analyzed using lattice QCD with N f = 2 twisted mass fermion configurations with three pion mass values. The calculation is performed within single-channel Lüscher's finite-size formalism. The threshold scattering parameters, namely the scattering length a0 and the effective range r0, for the s-wave scattering in J P = 1 + channel are extracted. For the cases in our study, the interaction between the two charmed mesons is weakly repulsive. Our lattice results therefore do not support the possibility of a shallow bound state for the two mesons for the pion mass values we studied. This calculation provides some useful information on the nature of the newly discovered resonance-like structure Zc(3900) by various experimental groups.

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In this exploratory lattice study, low-energy near threshold scattering of the (D1D * ) ± meson system is analyzed using lattice QCD with N f = 2 twisted mass fermion configurations. Both swave (J P = 0 − ) and p-wave (J P = 1 + ) channels are investigated. It is found that the interaction between the two charmed mesons is attractive near the threshold in both channels. This calculation provides some hints in the searching of resonances or bound states around the threshold of (D1D * ) ± system. trum of B → Kπ ± ψ decays with indefinite quantum numbers. Later on, updated results indicate that the most favored quantum numbers is 1 + with significance of 6.4σ, while the second probable one is 0 − with significance 4.6σ [3]. In 2014, LHCb observed a resonant structure in B 0 → K + π − ψ decays with unambiguously determined quantum number of 1 + and also excluded the possibility ofD 1 D * threshold effect interpretation because of the positive parity [4]. Recently, LHCb confirms their results in a model-independent way [5].

We present an exploratory lattice study for the two-photon decay of η c using N f = 2 twisted mass lattice QCD gauge configurations generated by the European Twisted Mass Collaboration. Two different lattice spacings of a = 0.067 fm and a = 0.085 fm are used in the study, both of which are of physical size of 2 fm. The decay widths are found to be 1.025(5) KeV for the coarser lattice and 1.062(5) KeV for the finer lattice, respectively, where the errors are purely statistical. A naive extrapolation toward the continuum limit yields 1.122(14) KeV, which is smaller than the previous quenched result and most of the current experimental results. Possible reasons are discussed.