27 research outputs found
Particle tracking in kaon electroproduction with cathode-charge sampling in multi-wire proportional chambers
Wire chambers are routinely operated as tracking detectors in magnetic
spectrometers at high-intensity continuous electron beams. Especially in
experiments studying reactions with small cross-sections the reaction yield is
limited by the background rate in the chambers. One way to determine the track
of a charged particle through a multi-wire proportional chamber (MWPC) is the
measurement of the charge distribution induced on its cathodes. In practical
applications of this read-out method, the algorithm to relate the measured
charge distribution to the avalanche position is an important factor for the
achievable position resolution and for the track reconstruction efficiency. An
algorithm was developed for operating two large-sized MWPCs in a strong
background environment with multiple-particle tracks. Resulting efficiencies
were determined as a function of the electron beam current and on the signal
amplitudes. Because of the different energy-losses of pions, kaons, and protons
in the momentum range of the spectrometer the efficiencies depend also on the
particle species
Differential cross section measurement of the 12C(e,e’pp)10Beg.s. reaction
The differential cross section was measured for the 12C(e, e
pp)10Beg.s. reaction at energy and
momentum transfers of 163MeV and 198MeV/c, respectively. The measurement was performed at the
Mainz Microtron by using two high-resolution magnetic spectrometers of the A1 Collaboration and a
newly developed silicon detector telescope. The overall resolution of the detector system was sufficient to
distinguish the ground state from the first excited state in 10Be. We chose a super-parallel geometry that
minimizes the effect of two-body currents and emphasizes the effect of nucleon-nucleon correlations. The
obtained differential cross section is compared to the theoretical results of the Pavia reaction code in which
different processes leading to two-nucleon knockout are accounted for microscopically. The comparison
shows a strong sensitivity to nuclear-structure input and the measured cross section is seen to be dominated
by the interplay between long- and short-range nucleon-nucleon correlations. Microscopic calculations based
on the ab initio self-consistent Green’s function method give a reasonable description of the experimental
cross section.
A highly segmented neutron polarimeter for A1
International audienceA 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
Electric and magnetic form factors of the proton
The paper describes a precise measurement of electron scattering off the proton at momentum transfers of \ GeV. The average point-to-point error of the cross sections in this experiment is 0.37%. These data are used for a coherent new analysis together with all world data of unpolarized and polarized electron scattering from the very smallest to the highest momentum transfers so far measured. The extracted electric and magnetic form factors provide new insight into their exact shape, deviating from the classical dipole form, and of structure on top of this gross shape. The data reaching very low values are used for a new determination of the electric and magnetic radii. An empirical determination of the Two-Photon-Exchange (TPE) correction is presented. The implications of this correction on the radii and the question of a directly visible signal of the pion cloud are addressed
Strange hadrons – strangeness in strongly interacting particles
In 2007 the Mainz Microtron MAMI has been upgraded to 1.5 GeV electron beam energy, crossing the energy threshold for open strangeness production. The strangeness quantum number, as carried by the strange quark, provides valuable information on the contribution of individual quark flavours to hadronic processes. Theoretically, the strange quark with its rest energy of order 150 MeV is particularly interesting because it can neither be treated as a massless nor as a heavy quark. Experimentally, an instrument of central importance for the charged kaon electro-production off the proton or light nuclei at MAMI is the magnetic spectrometer Kaos that was installed recently and is now routinely operated by the A1 collaboration
Measurement of the -particle monopole transition form factor challenges theory: a low-energy puzzle for nuclear forces?
We perform a systematic study of the -particle excitation from its ground state to the resonance. The so-called monopole transition form factor is investigated via an electron scattering experiment in a broad -range (from to fm). The precision of the new data dramatically superseeds that of older sets of data, each covering only a portion of the -range. The new data allow the determination of two coefficients in a low-momentum expansion leading to a new puzzle. By confronting experiment to state-of-the-art theoretical calculations we observe that modern nuclear forces, including those derived within chiral effective field theory which are well tested on a variety of observables, fail to reproduce the excitation of the -particle
The proton charge radius extracted from the Initial State Radiation experiment at MAMI
We report on a comprehensive reinterpretation of the existing cross-section data for elastic electron-proton scattering obtained by the initial-state radiation technique, resulting in a significantly improved accuracy of the extracted proton charge radius. By refining the external energy corrections we have achieved an outstanding description of the radiative tail, essential for a detailed investigation of the proton finite-size effects on the measured cross-sections. This development, together with a novel framework for determining the radius, based on a regression analysis of the cross-sections employing a polynomial model for the form factor, led us to a new value for the charge radius, which is
Measurement of the -particle monopole transition form factor challenges theory: a low-energy puzzle for nuclear forces?
We perform a systematic study of the -particle excitation from its ground state to the resonance. The so-called monopole transition form factor is investigated via an electron scattering experiment in a broad -range (from to fm). The precision of the new data dramatically superseeds that of older sets of data, each covering only a portion of the -range. The new data allow the determination of two coefficients in a low-momentum expansion leading to a new puzzle. By confronting experiment to state-of-the-art theoretical calculations we observe that modern nuclear forces, including those derived within chiral effective field theory which are well tested on a variety of observables, fail to reproduce the excitation of the -particle
The proton charge radius extracted from the initial-state radiation experiment at MAMI
International audienceWe report on a comprehensive reinterpretation of the existing cross-section data for elastic electron-proton scattering obtained by the initial-state radiation technique, resulting in a significantly improved accuracy of the extracted proton charge radius. By refining the external energy corrections we have achieved an outstanding description of the radiative tail, essential for a detailed investigation of the proton finite-size effects on the measured cross sections. This development, together with a novel framework for determining the radius, based on a regression analysis of the cross sections employing a polynomial model for the form factor, led us to a new value for the charge radius, which is $(0.878 \pm 0.011_\mathrm {stat.}\pm 0.031_\mathrm {sys.}\pm 0.002_\mathrm {mod.})\,\mathrm {fm}