A new neutron polarimeter for measuring the neutron's electric form factor was designed and constructed to complement the A1 spectrometer setup at the Mainz Microtron (MAMI). The design is based on a previous polarimeter with significant improvements to halve the error of the extracted form factor. A higher granularity of the polarimeter sections and a deeper first section on the one hand, and a faster readout employing Time-over-Threshold methods to measure the signal amplitudes combined with a high-precision FPGA-based TDC on the other hand will allow to achieve this goal. The performance of the new polarimeter during a first measurement campaign in 2019 using liquid hydrogen and deuterium targets will be discussed.

In this paper, we describe an experiment measuring low -Q2 elastic electron-proton scattering using a newly developed cryogenic supersonic gas jet target in the A1 three-spectrometer facility at the Mainz Microtron. We measured the proton electric form factor within the four-momentum transfer range of 0.01 Q2 0.045 (GeV/c)2. The experiment showed results consistent with the existing measurements. The data we collected demonstrated the feasibility of the gas jet target and the potential of future scattering experiments using high-resolution spectrometers with this gas jet target.

M. Christmanna,b,†,∗, P. Achenbacha,b,c, S. Aulenbachera, M. Birotha, S. Caiazzaa, A. Deniga,b,c, L. Doriaa,c, J. Geimera, P. Gülkera, P. Klaga, M. Laußa,b, M. Litticha, S. Lunkenheimera, T. Manoussosa, D. Markusa, M. Maucha,b, H. Merkela,c, J. Müllera, J. Schlaadta, B. S. Schlimmea, C. Sfientia,c, S. Stengela,b and C. Szyszkaa for the MAGIX collaboration Institute for Nuclear Physics, Johannes Gutenberg University Mainz, Johann-Joachim-Becher-Weg 45, 55128 Mainz, Germany Helmholtz Institute Mainz, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Johannes Gutenberg University Mainz, 55099 Mainz, Germany PRISMA Cluster of Excellence, Johannes Gutenberg University Mainz, Staudingerweg 9, 55128 Mainz, Germany

A cryogenic supersonic gas jet target was developed for the MAGIX experiment at the high-intensity electron accelerator MESA. It will be operated as an internal, windowless target in the energy-recovering recirculation arc of the accelerator with different target gases, e.g., hydrogen, deuterium, helium, oxygen, argon, or xenon. Detailed studies have been carried out at the existing A1 multi-spectrometer facility at the electron accelerator MAMI. This paper focuses on the developed handling procedures and diagnostic tools, and on the performance of the gas jet target under beam conditions. Considering the special features of this type of target, it proves to be well suited for a new generation of high-precision electron scattering experiments at high-intensity electron accelerators.

The light collection properties of several wavelength-shifting fiber configurations embedded in a box-shaped plastic scintillating counter were studied by scanning with minimum ionizing electrons. The light was read out by silicon photomultipliers at both ends. The light yield produced by the 855-MeV beam of the Mainz Microtron showed a strong dependence on the transverse distance from ∗Corresponding author at: Institut für Kernphysik, Johannes Gutenberg-Universität, 55099 Mainz, Germany. Email address: achenbach@uni-mainz.de (P. Achenbach) 1Part of master thesis. Preprint submitted to Nucl. Instrum. Methods Phys. Res. A January 18, 2021 ar X iv :2 10 1. 06 12 2v 1 [ ph ys ic s. in sde t] 1 5 Ja n 20 21 its position to the fibers. The observations were appropriately modeled by attributing the total light yield to the collection of diffuse light inside the counter and of direct light reaching a fiber. This was compared to the light collection properties of a scintillating counter without fibers. These studies were carried out within the development of plastic scintillating detectors as an active veto system for the DarkMESA electron beam-dump experiment that will search for light dark matter particles in the MeV mass range.

The light collection of several fiber configurations embedded in a box-shaped plastic scintillating counter was studied by scanning with minimum ionizing electrons. The light was read out by silicon photomultipliers at both ends. The light yield produced by the 855-MeV beam of the Mainz Microtron showed a strong dependence on the transverse distance from the beam position to the fibers. The observations were modeled by attributing the collection of indirect light inside of the counter and of direct light reaching a fiber to the total light yield. The light collection with fibers was compared to that of a scintillating counter without fibers. These studies were carried out within the development of plastic scintillating detectors as an active veto system for the DarkMESA electron beam-dump experiment that will search for light dark matter particles in the MeV mass range.

Various physics observables can be determined from the localization of distinct edge-like features in distributions of measurement values. In this paper, we address the observation that neither differentiating nor fitting the measured distributions is robust against significant fluctuations in the experimental data. We propose the application of Finite Impulse Response (FIR) filters instead . To demonstrate the method, we consider the typical case in particle physics in which the precise localization of kinematic edges, often blurred by e.g. background contributions and detector effects, is crucial for determining particle masses. We show that even for binned data, typical for high energy physics, the optimal FIR filter kernel can be approximated by the first derivative of a Gaussian (FDOG). We study two highly complementary supersymmetric scenarios that, if realized in nature, could be observed at a future high-energy e(+)e(-) collider such as the International Linear Collider (ILC) or the Compact Linear Collider (CLIC). The first scenario considers the production of (e) over tilde (+/-)-pairs while the second focuses on the (chi) over tilde (+/-)(1) and (chi) over tilde (0)(2)-pair production. We demonstrate that the FIR filter method for edge extraction is superior to previously employed methods in terms of robustness and precision.

P. Achenbach,a,b,c,∗ S. Aulenbacher,a M. Biroth,a S. Caiazza,a M. Christmann,a,b,† A. Denig,a,b,c L. Doria,a J. Geimer,a P. Gülker,a P. Klag,a M. Lauß,a,b M. Littich,a S. Lunkenheimer,a T. Manoussos,a D. Markus,a M. Mauch,a,b H. Merkel,a,c J. Müller,a J. Schlaadt,a B.S. Schlimme,a C. Sfienti,a,c S. Stengela,b and C. Szyszkaa for the MAGIX Collaboration Institute of Nuclear Physics, Johannes Gutenberg University Mainz, Johann-Joachim-Becher-Weg 45, 55128 Mainz, Germany Helmholtz Institute Mainz, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Johannes Gutenberg University Mainz, 55099 Mainz, Germany PRISMA+ Cluster of Excellence, Johannes Gutenberg University Mainz, Staudingerweg 9, 55128 Mainz, Germany

We report on a new measurement of the beam-normal single spin asymmetry A_n in the elastic scattering of 570 MeV transversely polarized electrons off ^28Si and ^90Zr at Q^2=0.04 GeV^2/c^2. The studied kinematics allow for a comprehensive comparison with former results on ^12C. No significant mass dependence of the beam-normal single spin asymmetry is observed in the mass regime from ^12C to ^90Zr.

A study of the detector response of PbF, crystals and three different types of lead glass blocks to electrons from a 14-MeV beam of the Mainz Microtron MAMI is presented. For the first time, signal height, signal width, and homogeneity of the response of these Cherenkov radiators were determined for energies between 10 and 14 MeV. To complement the beam tests, optical properties of the materials, in particular measured transmittances in the near UV and visible spectrum, were studied. The measured detector responses were also compared to Monte Carlo simulations of energy-loss, light production, transport, and detection. These Cherenkov radiators are considered as active material of a low-energy calorimeter for the detection of light dark matter particles recoiling off electrons behind the beam-dump of the Mainz Energy Recovering Superconducting Accelerator MESA.

MAGIX is a planned experiment that will be implemented at the upcoming accelerator MESA in Mainz. Due to its location in the energy-recovering lane of the accelerator beam-currents up to 1mA with a maximum energy of 105 MeV will be available for precision experiments. MAGIX itself consists of a jet-target and two magnetic spectrometers. Inside the spectrometers GEM-based detectors will be used in the focal plane for track reconstruction. The design goals for the detector modules are a spatial resolution of 50 um, a size of 1.20 m x 0.3 m and a minimal material budget. To accomplish these goals we started developing several GEM-prototypes to study different behaviors and techniques to optimize the final detector design. The GEM foils used are provided by CERN and are trained, stretched and framed in our laboratory. The readout is done with an SRS based system. In this contribution the requirements, achievements and the ongoing developments are presented.