We describe an experiment to search for a new vector boson A′ with weak coupling α′ & 6×10−8α to electrons (α = e/4π) in the mass range 65 MeV < mA′ < 550 MeV. New vector bosons with such small couplings arise naturally from a small kinetic mixing of the “dark photon” A′ with the photon — one of the very few ways in which new forces can couple to the Standard Model — and have received considera...

First data on coherent threshold π electroproduction from the deuteron taken by the A1 Collaboration at the Mainz Microtron MAMI are presented. At a four-momentum transfer of q = −0.1GeV/c the full solid angle was covered up to a centerof-mass energy of 4 MeV above threshold. By means of a Rosenbluth separation the longitudinal threshold s wave multipole and an upper limit for the transverse th...

We report on the current status of the technical design and results of tests of some components of a compact racetrack microtron (RTM) which is under construction at the Universitat Politècnica de Catalunya (UPC). The RTM end magnets are four-pole systems with the magnetic field created by a rare-earth permanent magnet material. As a source of electrons a 3D off-axis electron gun is used. These...

First data on coherent threshold π electroproduction from the deuteron taken by the A1 Collaboration at the Mainz Microtron MAMI are presented. At a four-momentum transfer of q = −0.1GeV/c the full solid angle was covered up to a centerof-mass energy of 4 MeV above threshold. By means of a Rosenbluth separation the longitudinal threshold s wave multipole and an upper limit for the transverse th...

A simple control system has been developed for the commissioning of a compact 12 MeV race-track microtron which is under construction at the Technical University of Catalonia. It is of modular structure and is based on LabView programs at a conventional PC and ATmega microcontrollers. Apart from modules to monitor different RTM systems it also includes an Automatic Frequency Control of the magn...

The study of baryon resonances via meson photoproduction reactions on the free proton and on nucleons in the nuclear medium is discussed. Special emphasis is laid on the production of neutral mesons which due to the suppression of nonresonant backgrounds are particularly well suited for the study of excited states of the nucleon. Experiments carried out during the last ten years with the TAPSde...

We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the γ[over →]p[over →]→ηp reaction up to a center-of-mass energy of W=1.9  GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indica...