E. Klempt

First observation of X-rays from antiprotonic hydrogen

Abstract We have observed the Balmer series of antiprotonic hydrogen atoms formed in gaseous hydrogen at 4 atm. The yield of L X-rays was determined to be (6 ± 3)% per stopped antiproton. The 2P state is dominantly depopulated via p p annihilation and not by radiative transitions to the 1S state.

The LEAR Crystal Barrel Detector

The features of the Crystal Barrel Detector which is in preparation for LEAR at CERN, are discussed. The physics aims include qq‐ and exotics‐spectroscopy and a detailed investigation of yet unknown pp‐anihilation channels. An eventual later use on the PSI‐B‐Meson‐Factory is discussed. The paper finishes with a description of the present status of the project.

Scrutinizing the evidence for N(1685)

The helicity-dependent observable E for the reaction γd → ηn(p) with a spectator proton was recently measured by the A2 Collaboration at MAMI in Mainz. The data were interpreted as further evidence for a narrow resonance with spin and parity J = 1/2 (P11 wave). However, a full partial wave analysis without any narrow resonance leads to an excellent description of the data; imposing a narrow resonance with the properties suggested by the A2 Collaboration leads to a significant deterioration of the fit quality: there is no need for a narrow resonance.