Experimental constraints on the $\ddot{I}‰$-nucleus real potential

Abstract

In a search for $\ddot{I}‰$ mesic states, the production of $\ddot{I}‰$-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 $\ddot{I}{€}^0{\hat{I}}^3$ pairs from decays of bound or quasi-free $\ddot{I}‰$-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 $\ddot{I}{€}^0{\hat{I}}^3$ pairs, which would indicate the population and decay of bound $\ddot{I}‰{}^{11}$B states, are not observed. The $\ddot{I}{€}^0{\hat{I}}^3$ 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 $\ddot{I}‰$-meson. A comparison of the measured total energy distribution with calculations suggests the real part $V_0$ of the $\ddot{I}‰{}^{11}$B potential to be small and only weakly attractive with $V_0(\ddot{I}=\ddot{I}{}_0)=-15\pm$ 35(stat) $\pm$20(syst) MeV in contrast to some theoretical predictions of attractive potentials with a depth of 100 - 150 MeV.

13 pages, 8 figures