Omega Meson Mass Research Articles

Vector meson masses from a hidden local symmetry in a constant magnetic field

We discuss the magnetic responses of vector meson masses based on the hidden local symmetry (HLS) model in a constant magnetic field, described by the lightest two-flavor system including the pion, rho and omega mesons in the spectrum. The effective masses influenced under the magnetic field are evaluated according to the derivative or chiral expansion established in the HLS model. At the leading order $\mathcal{O}({p}^{2})$, the g factor of the charged rho meson is fixed to be 2, implying that the rho meson at this order is treated just like a pointlike spin-1 particle. Beyond the leading order, one finds anomalous magnetic interactions of the charged rho meson, involving the anomalous magnetic moment, which give corrections to the effective mass. It is then suggested that up to $\mathcal{O}({p}^{4})$ the charged rho meson tends to become massless. Of interest is that nontrivial magnetic dependence of neutral mesons emerges to give rise to the significant mixing among neutral mesons. Consequently, it leads to the dramatic enhancement of the omega meson mass, which is testable in future lattice simulations. Corrections from terms beyond $\mathcal{O}({p}^{4})$ are also addressed.

Measurement of neutral-meson masses in meson-nucleus interactions at a momentum of 7 GeV/c at the Hyperon-M setup

The π 0, η, K 0, ω, and f 2(1270) masses were measured at the HYPERON-Msetup in meson-nucleus interactions at a momentum of 7 GeV/c by using six nuclear targets: Be, C, Al, Cu, Sn, and Pb. The experiment in question proved to be insensitive to the expected effects of a modification to the omega-meson mass in nuclear matter. As for the f 2(1270) meson, its mass and width values averaged over all experimental data, $$m_{f_2 }$$ = 1275.8 ± 1.0(stat.) ± 0.4(syst.) MeV/c 2 and $$\Gamma _{f_2 }$$ = 190.3 ± 1.9(stat.) ± 1.8(syst.) MeV/c 2, agree well with the world-average values. At the same time, our experimental data do not rule out the possible effect of an in-medium modification to the f 2(1270)-meson mass for heavy nuclei at a level better than 0.4%.

SATURATION PROPERTIES OF NUCLEAR MATTER IN A RELATIVISTIC MEAN FIELD MODEL CONSTRAINED BY THE QUARK DYNAMICS

We have built an effective Walecka-type hadronic Lagrangian in which the hadron masses and the density dependence of the coupling constants are deduced from the quark dynamics using a Nambu–Jona-Lasinio model. In order to stabilize nuclear matter an eight-quark term has been included. The parameters of this Nambu–Jona-Lasinio model have been determined using the meson properties in the vacuum but also in the medium through the omega meson mass in nuclei measured by the TAPS collaboration. Realistic properties of nuclear matter have been obtained.

Saturation properties of nuclear matter in a relativistic mean field model constrained by the quark dynamics

We have built an effective Walecka-type hadronic Lagrangian in which the hadron masses and the density dependence of the coupling constants are deduced from the quark dynamics using a Nambu–Jona-Lasinio model. In order to stabilize nuclear matter an eight-quark term has been included. The parameters of this Nambu–Jona-Lasinio model have been determined using the meson properties in the vacuum but also in the medium through the omega meson mass in nuclei measured by the TAPS Collaboration. Realistic properties of nuclear matter have been obtained.

Effective Hadron Masses and Effective Interactions in Nuclear Matter

Relations among the effective hadron masses and the effective interactions in nuclear matter are studied by using the generalized relativistic mean field theory. We found that we can make the effective omega-meson mass smaller and the equation of state softer if we require that the omega-meson mean field is proportional to the baryon density. In this case, there is a simple and exact relation between the effective omega-meson mass and the effective omega-nucleon coupling. Because of this relation, the effective omega-nucleon coupling automatically decreases if the effective omega-meson mass decreases. Consequently, the equation of state becomes softer. A trial to embed the QCD sum-rule results into the hadron field theory is also shown.

Chiral Sigma Model with Pion Mean Field in Finite Nuclei

The properties of infinite matter and finite nuclei are studied by using the chiral sigma model in the framework of the relativistic mean field theory. We reconstruct an extended chiral sigma model in which the omega meson mass is generated dynamically by the sigma condensation in the vacuum in the same way as the nucleon mass. All the parameters of chiral sigma model are essentially fixed from the hadron properties in the free space. In nuclear matter, the saturation property comes out right, but the incompressibility is too large and the scalar and vector potentials are about a half of the phenomenological ones, respectively. This fact is reflected to the properties of finite nuclei. We calculate N = Z even-even mass nuclei between N = 16 and N = 34. The extended chiral sigma model without the pion mean field leads to the result that the magic number appears at N = 18 instead of N = 20 and the magic number does not appear at N = 28 due to the above mentioned nuclear matter properties. The latter problem, however, could be removed by the introduction of the finite pion mean field with the appearance of the magic number at N = 28. We find that the energy differences between the spin-orbit partners are reproduced by the finite pion mean field which is completely a different mechanism from the standard spin-orbit interaction.

Nuclear matter properties in relativistic mean-field model with σ- ω coupling

The possibility of extending the linear sigma-omega model by introducing a sigma-omega coupling phenomenologically is explored. It is shown that, in contrast to the usual Walecka model, not only the effective nucleon mass M* but also the effective sigma meson mass m*_sigma and the effective omega meson mass m*_omega are nucleon density dependent. When the model parameters are fitted to the nuclear saturation point (the nuclear radius constant r_0=1.14fm and volume energy a_1=16.0MeV) as well as to the effective nucleon mass M*=0.85M, the model yields m*_sigma=1.09m_sigma and m*_omega=0.90m_omega at the saturation point, and the nuclear incompressibility K_0=501MeV. The lowest value of K_0 given by this model by adjusting the model parameters is around 227MeV.

An effective lagrangian with broken scale and chiral symmetry applied to nuclear matter and finite nuclei

We study nuclear matter and finite nuclei in the mean field approximation with a chiral lagrangian which generalizes the linear σ model and also accounts for the QCD trace anomaly by means of terms which involve the σ and π fields as well as the glueball field φ. The scale invariant term which leads to an omega meson mass, after symmetry breaking, is strongly favored to be of the form ω μ ω μ φ 2 by the bulk properties of nuclei; they also rather strongly constrain the other parameters. A reasonable description of the closed shell nuclei oxygen, calcium and lead can be achieved and this can be improved by including a term( ω μm ω μm ) 2 in the lagrangian. This leads to a level of agreement with the data that is comparable to that of the nonlinear Walecka model.