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Register a new userThe d-dibaryon in a colored cluster model
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A. J. Buchmann
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The mass and wave function of a six-quark system with quantum numbers J^P=0^-, T=0, called d, are calculated. We use a colored diquark-tetraquark cluster model for the six-quark wave function. A constituent quark model Hamiltonian with a two-body confinement potential, and residual one-gluon, one-pion, and one-sigma exchange interactions is used. The complications due to the quark exchange interactions between tetraquark and diquark clusters (Pauli principle) are taken into account within the framework of the Resonating Group Method. The calculated d mass is some 350 MeV above the empirical value if the same two-body confinement strength as in the nucleon and Delta is used. This paper also examines the validity of the usual assumption of a universal two-quark confinement strength. We propose that the effective two-body confinement strength in an exotic six-quark system, such as the d, could be weaker than in a single baryon. The weaker confinement hypothesis leads to a d mass of M=2092 MeV and a d radius of r=1.53 fm.
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We calculate the mass and structure of a J^P=0^-, T=0 six-quark system using a colored diquark-tetraquark cluster wave function and a nonrelativistic quark model Hamiltonian. The calculated mass is some 350 MeV above the empirical value if the same confinement strength as in the nucleon is used. If the effective two-body confinement strength is weaker in a compound six-quark system than in a single baryon, as expected from a simple harmonic oscillator model, one obtains M_d = 2092 MeV close to experiment.
The narrow peak recently found in various pionic double charge exchange (DCX) cross sections can be explained by the assumption of a universal resonance at 2065 MeV, called d. We calculate the mass of a six-quark system with J^P=0^-, T=0 quantum numbers employing a cluster model and a shell model basis to diagonalize the nonrelativistic quark model Hamiltonian.
In arxiv: 2102.05575 a two-step process $pn to (pp) pi^- to (Delta N) pi^- to (d pi^+) pi^-$ was calculated by using experimental total cross sections for the single-pion production processes $pn to pp pi^-(I=0)$ and $pp to d pi^+$. As a result the authors obtain a resonance-like structure for the total $pn to dpi^+pi^-$ cross section of about the right size and width of the observed $d^*(2380)$ peak at an energy about 40 MeV below the $d^*(2380)$ mass. We object both the results of the sequential process calculation and its presentation as an alternative to the dibaryon interpretation.
We analyze dilepton emission from hot and dense matter using a hybrid approach based on the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model with an intermediate hydrodynamic stage for the description of heavy-ion collisions at relativistic energies. During the hydrodynamic stage, the production of lepton pairs is described by radiation rates for a strongly interacting medium in thermal equilibrium. In the low mass region, hadronic thermal emission is evaluated assuming vector meson dominance including in-medium modifications of the rho meson spectral function through scattering from nucleons and pions in the heat bath. In the intermediate mass region, the hadronic rate is essentially determined by multi-pion annihilation processes. Emission from quark-antiquark annihilation in the quark gluon plasma is taken into account as well. When the system is sufficiently dilute, the hydrodynamic description breaks down and a transition to a final cascade stage is performed. In this stage dimuon emission is evaluated as commonly done in transport models. Focusing on the enhancement with respect to the contribution from long-lived hadron decays after freezout observed at the SPS in the low mass region of the dilepton spectra, the relative importance of the different thermal contributions and of the two dynamical stages is investigated. We find that three separated regions can be identified in the invariant mass spectra. Whereas the very low and the intermediate mass regions mostly receive contribution from the thermal dilepton emission, the region around the vector meson peak is dominated by the cascade emission. Above the rho-peak region the spectrum is driven by QGP radiation. Analysis of the dimuon transverse mass spectra reveals that the thermal hadronic emission shows an evident mass ordering not present in the emission from the QGP.
The purpose of the present study was to explore the possibility of accommodating the $d^*(2380)$ and its flavor SU(3) partners in a diquark model. Proposing that $d^*(2380)$ is composed of three vector diquarks, its mass is calculated by use of an effective Hamiltonian approach and its decay width is estimated by considering the effects of quark tunneling from one diquark to the others and the decays of the subsequent two-baryon bound state. Both the obtained mass and decay width of $d^*(2380)$ are in agreement with the experimental data, with the unexpected narrow decay width being naturally explained by the large tunneling suppression of a quark between a pair of diquarks. The masses and decay widths of the flavor SU(3) partners of $d^*(2380)$ are also predicated within the same diquark scenario.
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