All Results

Quark Spin in Proton from Anomalous Ward Indentity

CLQCD CollaborationSubjects: Physics >> Nuclear Physics

We report a quark spin calculation from the anomalous Ward identity with overlap fermions on 2+1 flavor dynamical fermion configurations with light sea quark masses. Such a formulation decomposes the divergence of the flavor-singlet axial-vector current into a quark pseudoscalar term and a triangle anomaly term, flavor by flavor. A large negative contribution from the anomaly term is observed and it is canceled within errors by the contribution from the pseudoscalar term in the disconnected insertion in the heavy quark region. On the other hand, net negative contributions are obtained for the light and strange quarks in the disconnected insertion, since their quark pseudoscalar terms are smaller than that of the heavy quark. Our results are obtained from the 2+1 flavor domain wall fermion configurations on the 24^3*64 lattice with a-1 = 1.78(5) GeV and the light sea quark at m_{\pi} = 330 MeV. We use the overlap fermion for the valence and the quark loop so that the renormalization constants Z_m and Z_P cancel in the pseudoscalar operator 2mP. In addition, the overlap Dirac operator is used to calculate the local topological charge in the anomaly so that there is no renormalization for the anomaly term either. In this study, we find the total quark spin to be small mainlyly due to the large negative anomaly term which could be the source for the 'proton spin crisis'. |

Phase transition in finite density and temperature lattice QCD

CLQCD CollaborationSubjects: Physics >> Nuclear Physics

We investigate the behavior of the chiral condensate in lattice QCD at finite temperature and finite chemical potential. The study was done using two flavors of light quarks and with a series of?β?and?ma?at the lattice size?24×122×6. The calculation was done in the Taylar expansion formalism. We are able to calculate the first and second order derivatives of??ψ?ψ??in both isoscalar and isovector channels. With the first derivatives being small, we find that the second derivatives are sizable close to the phase transition and the magnitude of?ψ?ψ?decreases under the influence of finite chemical potential in both channels. |

Spectrum and Bethe-Salpeter amplitudes of $\Omega$ baryons from lattice QCD

Liang, Jian and Sun, Wei and Chen, Ying and Qiu, Wei-Feng; and Gong, Ming and Liu, Chuan and Liu, Yu-Bin and Liu,; Zhaofeng and Ma, Jian-Ping and Zhang, Jian-BoSubjects: Physics >> Nuclear Physics

The?Ω?baryons with?JP=3/2±,1/2±?are studied on the lattice in the quenched approximation. Their mass levels are ordered as?M3/2+ |

Low-energy Scattering of $(D^*\barD^*)^\pm$ System and the Resonance-like Structure $Z_c(4025)$

Chen, Ying and othersSubjects: Physics >> Nuclear Physics

In this paper, low-energy scattering of the?(D?D??)±?meson system is studied within L\"uscher's finite-size formalism using?Nf=2?twisted mass gauge field configurations. With three different pion mass values, the?s-wave threshold scattering parameters, namely the scattering length?a0?and the effective range?r0, are extracted in?JP=1+channel. Our results indicate that, in this particular channel, the interaction between the two vector charmed mesons is weakly repulsive in nature hence do not support the possibility of a shallow bound state for the two mesons, at least for the pion mass values being studied. This study provides some useful information on the nature of the newly discovered resonance-like structure?Zc(4025)?observed in various experiments. |

A Lattice Study of $(\barD_1 D^*)^\pm$ Near-threshold Scattering

Chen, Ting and othersSubjects: Physics >> Nuclear Physics

In this exploratory lattice study, low-energy near threshold scattering of the (D?1D?)± meson system is analyzed using lattice QCD with Nf=2 twisted mass fermion configurations. Both s-wave (JP=0?) and p-wave (JP=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 (D?1D?)± system. |

Two-photon decays of $\eta _c$ from lattice QCD

Chen, Ting and othersSubjects: Physics >> Nuclear Physics

We present an exploratory lattice study for the two-photon decay of?ηc?using?Nf=2?twisted mass lattice QCD gauge configurations generated by the European Twisted Mass Collaboration. Two different lattice spacings of?a=0.067fm and?a=0.085fm are used in the study, both of which are of physical size of 2fm. 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 towards the continuum limit yields?Γ?1.122(14)KeV which is smaller than the previous quenched result and most of the current experimental results. Possible reasons are discussed. |

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