Momentum dependence of the imaginary part of the $ \omega$ - and $ \eta^{\prime}$ -nucleus optical potential

Abstract

Abstract. The photoproduction of ω and η mesons off carbon and niobium nuclei has been measured as a function of the meson momentum for incident photon energies of 1.2-2.9 GeV at the electron accelerator ELSA. The mesons have been identified via the ω → π 0 γ → 3γ and η → π 0 π 0 η → 6γ decays, respectively, registered with the CBELSA/TAPS detector system. From the measured meson momentum distributions the momentum dependence of the transparency ratio has been determined for both mesons. Within a Glauber analysis the in-medium ω and η widths and the corresponding absorption cross sections have been deduced as a function of the meson momentum. The results are compared to recent theoretical predictions for the in-medium ω width and η -N absorption cross sections. The energy dependence of the imaginary part of the ω-and η -nucleus optical potential has been extracted. The finer binning of the present data compared to the existing data allows a more reliable extrapolation towards the production threshold. The modulus of the imaginary part of the η nucleus potential is found to be about three times smaller than recently determined values of the real part of the η -nucleus potential, which makes the η meson a suitable candidate for the search for meson-nucleus bound states. For the ω meson, the modulus of the imaginary part near threshold is comparable to the modulus of the real part of the potential. As a consequence, only broad structures can be expected which makes the observation of ω mesic states very difficult experimentally.

Meson–nucleus potentials and the search for meson–nucleus bound states

“…Obviously, it is important to extract information on the in-medium width of the mesons for very low meson momenta, close to the production threshold. Therefore the CBELSA/TAPS Collaboration has studied the momentum dependence of the transparency ratio [213] and extracted the η absorption cross section and the in-medium width of the η meson. The inelastic cross sections σ inel has been derived, using Eq.…”

“…The resulting momentum dependence of the in-medium η width has been converted into the dependence of the imaginary part of the η -nucleus potential as a function of the available energy in the meson- 93 Nb system, as presented in [213] . The obtained spectrum is shown in Fig.…”

“…A comparison to Monte-Carlo calculations [95] and GiBUU simulations [94] gives an in-medium width of 130-150 MeV in the nuclear rest frame for ω mesons with an average 3-momentum of ≈ 1.1 GeV/c, indicating a strong in-medium broadening compared to the free ω width of 8.4 MeV [39]. More recently the momentum dependence of the transparency ratio has been studied in finer momentum bins [213]. The inelastic ω-nucleon cross sections deduced from Eq.…”

“…For hadron physics the study of these states provides a unique possibility Table 1: Compilation of theoretical predictions for the real (V 0 ) and imaginary (W 0 ) mesonnucleus potentials at normal nuclear matter density. [270,271], η [213,219,220], ω [213,233,229], and φ [254] mesons. Thick (thin) error bars correspond to statistical (systematic) errors.…”

Mass Modifications of Light Mesons in Nuclear Matter with the Three Flavor Extended Linear Sigma Model

“…Then, another experiment called E16 experiment is planned at J-PARC. Besides, the η mesic nuclei experiments at GSI [18][19][20] and at the University of Bonn [21][22][23][24], and pp → ppη reaction experiment at the COSY accelerator complex [25] have been operated, regarding the investigation of the change of U (1) A axial anomaly in nuclear matter. Another η mesic nuclei experiments is ongoing at SPring-8 [26] (see Ref.…”