Experimental constraints on the ω –nucleus real potential

Abstract

In a search for ω mesic states, the production of ω-mesons in coincidence with forward going protons has been studied in photon induced reactions on 12 C for incident photon energies of 1250 -3100 MeV. The π 0 γ pairs from decays of bound or quasi-free ω-mesons have been measured with the CBELSA/TAPS detector system in coincidence with protons registered in the MiniTAPS forward array. Structures in the total energy distribution of the π 0 γ pairs, which would indicate the population and decay of bound ω 11 B states, are not observed. The π 0 γ cross section of 0.3 nb/MeV/sr observed in the bound state energy regime between -100 and 0 MeV may be accounted for by yield leaking into the bound state regime because of the large in-medium width of the ωmeson. A comparison of the measured total energy distribution with calculations suggests the real part V 0 of the ω 11 B potential to be small and only weakly attractive with V 0 (ρ = ρ 0 ) = −15± 35(stat) ±20(syst) MeV in contrast to some theoretical predictions of attractive potentials with a depth of 100 -150 MeV.

Experimental results on theω- andη′-nucleus potential - on the way to mesic states

“…6 (middle). in account the error in the peak determination [16]. Within the errors this result is consistent with the value of potential depth deduced from the ω excitation function.…”

“…The ω and η mesons are reconstructed in the ω → π 0 γ → 3γ and η → π 0 π 0 η → 6γ decay channels, respectively. A more detailed description of the detector setup and the running conditions has been given in [14][15][16][17].…”

“…Many theoretical model predictions are, however, limited to mesons at rest in the nucleus or to only low meson momenta. The in-medium properties of low momentum mesons are studied experimentally by requesting the meson to be in coincidence with a forward going participant nucleon which takes over most of the momentum of the incoming beam, leaving the meson almost at rest relative to the nucleus [16]. In this case, the kinetic energy distribution of the meson becomes sensitive to the real part of the mesonnucleus potential.…”

Determination of the real part of theη′-Nb optical potential

“…In recent photoproduction experiments, we studied the ω-and η ′ -nucleus interaction and deduced information on the real [22][23][24][25] and imaginary part [21,26,27] of the optical potential. For the latter, values of ≈−70 MeV and ≈−10 MeV were extracted for the ω and η ′ meson, respectively, at saturation density and for average recoil momenta of ≈ 1G e V /c from transparency ratio measurements by studying the attenuation of the meson flux in the photoproduction off various nuclei.…”

Determination of theω- andη′-nucleus optical potential

“…In case of a strongly repulsive (attractive) interaction one would expect the peak in the kinetic energy distribution to be shifted to higher (lower) energies for the C target. The sensitivity of the peak position in the kinetic energy distribution on the potential depth, studied in [22], can be exploited to deduce the depth of the real part of the ω-nucleus potential. The experimental data for the ω kinetic energy distribution have been compared with the theoretical calculations and a potential depth of -(15±35) MeV has been determined, which appears to be too small to allow for the formation of ω mesic states in view of the large in-medium width of ≈ 90 MeV (see Sec.…”