Studies Of The η And η[sup ʹ] Mesons At MAMI-C

Abstract

The Mainz Microtron MAMI has delivered a high quality electron beam with maximum energy of 880 MeV for many years. Recently the MAMI C stage with its maximum energy of 1.5 GeV was put into operation successfully and is delivering beam routinely now. The Al collaboration is doing electron scattering experiments with the ‘Three Spectrometer Setup’. A first experiment using the MAMI C beam to measure the ‘Recoil polarisation and beam‐recoil double polarization of eta electroproduction on the proton in the region of the S11(1535) resonance’ has been finished. The A2‐collaboration is measuring photon absorption cross section using circularly and linearly polarized photons up to energies of 1.4 GeV. The photons are produced in the ‘Bremsstrahlungs’ process. In the GDH experiment there where taken data for helicity dependent η production with the DAPHNE detector. In the year 2004 the Crystal Ball detector with its unique capability to cope with multi photon final states was set up in Mainz. The experimental apparatus will be completed by polarized targets and a recoil polarimeter. A new high‐statistics measurement of neutral η′ decays is underway at the upgraded Mainz Microtron Facility, MAMI‐C. Next year a series of experiments with the Crystal Ball detector and polarized targets will start.