TA2-Transnational Access to MAMI

In addition to MAMI, a new accelerator, the Mainz Energy Recovering Superconducting Accelerator (MESA), a compact CW linear accelerator using superconducting cavities and the energy-recovering linac (ERL) design, is currently under construction. It will run in parallel to MAMI. The commissioning of the MESA accelerator and the experiments are foreseen in 2020/21. The field of research pursued at MAMI and MESA is the study of the structure of hadrons with the electromagnetic probes. It can be summarised by the notion "From Quarks and Gluons to Hadrons and Nuclei". Moreover, a facility for applied research in the field of the production and usage of coherent x-rays exists.

The beam of MAMI excels by its reliability (> 80% beam on target, about 6600 beam hours per year on the long-term average), a very small diameter (0.1 mm), a tiny halo (only about 10-5 of the intensity is outside a diameter of 1 mm of the actual beam), and a very good energy definition (10-6 long-term stability). The most important quality, however, is the effectively direct current beam (continuous wave) with up to 100 μA, which allows to measure small cross-sections with simultaneous detection of several coincident particles. Besides MAMI, such a beam quality is achieved only by the CEBAF (Continuous Beam Electron Accelerator Facility) of the Thomas Jefferson Laboratory in Newport News, Virginia, USA, however in the complementary energy range from 1.5 to 12 GeV.

MESA will accelerate electrons to a maximum energy of approximately 200 MeV, however with a beam intensity, which will be an order of magnitude higher than what is already achievable at MAMI.

Three-spectrometer setup - A1 collaboration: The A1 collaboration operates a setup of various magnetic spectrometers. The core components of the setup are three big spectrometers of 300 tons each, turning around a common pivot. They have maximum momentum coverage of up to 870 MeV/c, a spatial acceptance of 28 msr, and an excellent momentum resolution of 10-4. The focal planes of these spectrometers comprise drift chambers, scintillators as timing detectors, Cherenkov detectors, and a proton polarimeter. A highly segmented large solid angle neutron detector is under construction. In 2017 a cryogenic gas jet target with target densities of up to 1019 atoms /cm2 came into operation at A1. Crystal Ball/TAPS detector – A2 collaboration: The A2 collaboration runs a facility for energy tagging of bremsstrahlung photons designed by physicists from the Glasgow and Edinburgh Universities and financed by the UK Engineering and Physical Science Research Council. An additional end point tagger was built to cover the high-energy part of the photon energy spectrum and to access the "threshold". The primary detector arrangement consists of the Crystal Ball and TAPS detectors. This setup is particularly suitable for the detection of photons with a solid angle of almost 4π with high resolution and count rate capability. A polarised frozen-spin target for protons and deuterons with longitudinal and transverse polarisation is operating successfully.

Coherent x-rays - X1 collaboration: The X1 collaboration is using several methods to produce coherent x rays: parametric x-rays, Smith-Purcell effect, undulators, and transition radiation for applications in several fields of science and medicine.

P2 spectrometer for MESA: The MESA accelerator can be operated in an extracted beam mode, serving the P2 experiment, which is designed with the primary goal to measure the electroweak mixing angle, sin2W, at low momentum transfer in the parity-violating elastic ep-scattering process. A high precision measurement of the electroweak mixing angle offers the possibility to test new physics models on a mass scale of up to 50 TeV. The P2 setup will consist of a large superconducting magnet, centered on a high-power liquid hydrogen target. The scattered electrons will be measured in a quartz bar detector.

MAGIX spectrometer for MESA: The operation of a high-intensity ERL beam with intensities of at least 1 mA in conjunction with an internal gas target is a novel experimental approach and will yield competitive luminosities of 1035 cm-2s-1. To fully exploit the physics opportunities of such a setup, the MAGIX high-resolution double-arm spectrometers is under construction. MAGIX will allow to continue the search for a hypothetical gauge boson (dark photon), which is predicted in the context of dark matter models. Services currently offered by the infrastructure.

In the last years MAMI has played a decisive role in the study of hadrons in the low energy domain with electromagnetic probes and is used by a large number of international researchers. The domain of low momentum transfers is particularly suited to study the Quantum Chromo Dynamics (QCD) in its most challenging region, i.e. at low energies. MAMI offers unique research capabilities in high-precision electron- and photon scattering, parity-violating electron scattering, meson production and decays, and hypernuclear physics.

Ever since the start of the Transnational Access program in 2004, an ever increasing demand by European researchers is documented. There are now a total of about 200 users at MAMI, 70 of them were participating in the HadronPhysics3 Integrating Activity of FP7.