We perform a systematic study of the α-particle excitation from its ground state 0_{1}^{+} to the 0_{2}^{+} resonance. The so-called monopole transition form factor is investigated via an electron ...scattering experiment in a broad Q^{2} range (from 0.5 to 5.0 fm^{-2}). The precision of the new data dramatically supersedes that of older sets of data, each covering only a portion of the Q^{2} 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 that are well tested on a variety of observables, fail to reproduce the excitation of the α particle.
Nuclear fragmentation measurements are necessary when using heavy-ion beams in hadrontherapy to predict the effects of the ion nuclear interactions within the human body. Moreover, they are also ...fundamental to validate and improve the Monte Carlo codes for their use in planning tumor treatments. Nowadays, a very limited set of carbon fragmentation cross sections are being measured, and in particular, to our knowledge, no double-differential fragmentation cross sections at intermediate energies are available in the literature. In this work, we have measured the double-differential cross sections and the angular distributions of the secondary fragments produced in the (12)C fragmentation at 62 A MeV on a thin carbon target. The experimental data have been used to benchmark the prediction capability of the Geant4 Monte Carlo code at intermediate energies, where it was never tested before. In particular, we have compared the experimental data with the predictions of two Geant4 nuclear reaction models: the Binary Light Ions Cascade and the Quantum Molecular Dynamic. From the comparison, it has been observed that the Binary Light Ions Cascade approximates the angular distributions of the fragment production cross sections better than the Quantum Molecular Dynamic model. However, the discrepancies observed between the experimental data and the Monte Carlo simulations lead to the conclusion that the prediction capability of both models needs to be improved at intermediate energies.
Polarization transfer to a bound proton in polarized electron knock-out reactions, A(e→,e′p→), is a powerful tool to look for an in-medium modification of the bound proton. It requires comparison to ...calculations that consider the many-body effects accompanying the quasi-free process. We report here measured components Px′, Pz′, and their ratio Px′/Pz′, of polarization transfer to protons bound in Ca40, which is described well by the shell model and for which reliable calculations are available. While the calculations capture the essence of the data, our statistical precision allows us to observe deviations that cannot be explained by simple scaling, including by varying the proton electromagnetic form factor ratio GE/GM. We further explore the deviations of the ratio of the polarization transfer components from that of a free proton, (Px′/Pz′)A/(Px′/Pz′)H, and its dependence on the bound-proton virtuality.
A highly segmented neutron polarimeter for A1 Spreckels, R.; Hoek, M.; Müller, U. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2024, Letnik:
1062
Journal Article
Recenzirano
Odprti dostop
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.
Despite decades of studies which have seen the nuclear charge distribution being measured with increasing precision, the neutron distribution remains elusive. The difference between the neutron and ...proton distributions is often expressed as the difference of their root mean square radii: the neutron skin thickness. Recently, the A2 collaboration at MaMi has measured the skin thickness in lead through coherent pion photoproduction 1 with a very high precision. However, they do not include theoretical uncertainties, which can be significant for this process. A new reaction code in the distorted wave impulse approximation (DWIA) is developed to help the (ongoing) analysis of the recent measurement by the A2 collaboration at MaMi of the coherent pion photoproduction cross section on 116,120,124Sn isotopes 2 and to properly quantify the theoretical uncertainties.
We present the first measurements of the double ratio of the polarization-transfer components (Px′/Pz′)p/(Px′/Pz′)s for knock-out protons from the s and p shells in C12 measured by the C12(e→,e′p→) ...reaction in quasi-elastic kinematics. The data are compared to theoretical predictions in the relativistic distorted-wave impulse approximation. Our results show that the differences between s- and p-shell protons, observed when compared at the same initial momentum (missing momentum), largely disappear when the comparison is done at the same proton virtuality. We observe no difference in medium modifications between protons from the s and p shells with the same virtuality in spite of the large differences in the respective nuclear densities.
We present the findings of a study based on a new inelastic electron-scattering experiment on the
12
C nucleus focusing on the kinematic region of
Q
2
=
0.8
GeV
2
/
c
2
. The measured cross section ...is sensitive to the transverse response function and provides a stringent test of theoretical models, as well as of the theoretical assumptions made in Monte-Carlo event-generator codes developed for the interpretation of neutrino-nucleus experiments, such as DUNE and HyperK. We find that modern generators such as GENIE and GiBUU reproduce our new experimental data within 10
%
.
We measured the ratio Px/Pz of the transverse to longitudinal components of polarization transferred from electrons to bound protons in C12 by the C12(e→,e′p→) process at the Mainz Microtron (MAMI). ...We observed consistent deviations from unity of this ratio normalized to the free-proton ratio, (Px/Pz)C12/(Px/Pz)H1, for both s- and p-shell knocked out protons, even though they are embedded in averaged local densities that differ by about a factor of two. The dependence of the double ratio on proton virtuality is similar to the one for knocked out protons from H2 and He4, suggesting a universal behavior. It further implies no dependence on average local nuclear density.