92,755 research outputs found

    The role of qqˉq\bar q components in the N(1440) resonance

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    The role of 5-quark components in the pion and electromagnetic decays and transition form factors of the N(1440) is explored. The qqqqqˉqqqq\bar q components, where the 4-quark subsystem has the flavor-spin symmetries [4]FS[22]F[22]S[4]_{FS}[22]_F[22]_S and [4]FS[31]F[31]S[4]_{FS}[31]_F[31]_S, which are expected to have the lowest energy of all qqqqqˉqqqq\bar q configurations, are considered in detail with a nonrelativistic quark model. The matrix elements between the 5-quark components of the N(1440) and the nucleon, qqqqqˉ→qqqqqˉqqqq\bar q\to qqqq\bar q, play a minor role in these decays, while the transition matrix elements qqqqqˉ→qqqqqqq\bar q\to qqq and qqq→qqqqqˉqqq\to qqqq\bar q that involve quark antiquark annihilation are very significant. Both for the electromagnetic and strong decay the change from the valence quark model value is dominated by the confinement triggered qqˉq\bar q annihilation transitions. In the case of pion decay the calculated decay width is enhanced substantially both by the direct qqˉ→πq\bar q \to \pi and also by the confinement triggered qqˉ→πq\bar q\to \pi transitions. Agreement with the empirical value for the pion decay width may be reached with a ∼\sim 30% qqqqqˉqqqq\bar q component in the N(1440).Comment: 23 pages revte

    Resonant Interactions in Rotating Homogeneous Three-dimensional Turbulence

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    Direct numerical simulations of three-dimensional (3D) homogeneous turbulence under rapid rigid rotation are conducted to examine the predictions of resonant wave theory for both small Rossby number and large Reynolds number. The simulation results reveal that there is a clear inverse energy cascade to the large scales, as predicted by 2D Navier-Stokes equations for resonant interactions of slow modes. As the rotation rate increases, the vertically-averaged horizontal velocity field from 3D Navier-Stokes converges to the velocity field from 2D Navier-Stokes, as measured by the energy in their difference field. Likewise, the vertically-averaged vertical velocity from 3D Navier-Stokes converges to a solution of the 2D passive scalar equation. The energy flux directly into small wave numbers in the kz=0k_z=0 plane from non-resonant interactions decreases, while fast-mode energy concentrates closer to that plane. The simulations are consistent with an increasingly dominant role of resonant triads for more rapid rotation

    Five-quark components in Δ(1232)→Nπ\Delta(1232)\to N\pi decay

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    Five-quark qqqqqˉqqqq\bar q components in the Δ(1232)\Delta(1232) are shown to contribute significantly to Δ(1232)→Nπ\Delta(1232)\to N\pi decay through quark-antiquark annihilation transitions. These involve the overlap between the qqqqqq and qqqqqˉqqqq\bar q components and may be triggered by the confining interaction between the quarks. With a ∼\sim 10% admixture of five-quark components in the Δ(1232)\Delta(1232) the decay width can be larger by factors 2 - 3 over that calculated in the quark model with 3 valence quarks, depending on the details of the confining interaction. The effect of transitions between the qqqqqˉqqqq\bar q components themselves on the calculated decay width is however small. The large contribution of the quark-antiquark annihilation transitions thus may compensate the underprediction of the width of the Δ(1232)\Delta(1232) by the valence quark model, once the Δ(1232)\Delta(1232) contains qqqqqˉqqqq\bar q components with ∼\sim 10% probability.Comment: accepted versio

    Nuclear modification factor in intermediate-energy heavy-ion collisions

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    The transverse momentum dependent nuclear modification factors (NMF), namely RCPR_{CP}, is investigated for protons produced in Au + Au at 1AA GeV within the framework of the isospin-dependent quantum molecular dynamics (IQMD) model. It is found that the radial collective motion during the expansion stage affects the NMF at low transverse momentum a lot. By fitting the transverse mass spectra of protons with the distribution function from the Blast-Wave model, the magnitude of radial flow can be extracted. After removing the contribution from radial flow, the RCPR_{CP} can be regarded as a thermal one and is found to keep unitary at transverse momentum lower than 0.6 GeV/c and enhance at higher transverse momentum, which can be attributed to Cronin effect.Comment: 8 pages, 5 figures; aceepted by Physics Letters
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