Mon·Feb 5, 2024Monday·February 5, 2024

1. 01*

   The MESA physics program

   Sören Schlimme🇩🇪 · Kurt Aulenbacher🇩🇪 · Sebastian Baunack🇩🇪 · Niklaus Berger🇩🇪 · Achim Denig🇩🇪 · Luca Doria🇩🇪 · Alfons Khoukaz🇩🇪 · Frank Maas🇩🇪 · Harald Merkel🇩🇪 · Concettina Sfienti🇩🇪 · Michaela Thiel🇩🇪

   In the recent past, a comprehensive experimental program has been worked out at the Mainz Energy-Recovery Superconducting Accelerator, MESA, at the Institute of Nuclear Physics in Mainz. MESA is a high-intensity, low-energy electron accelerator presently under construction and will thereby provide great opportunities to perform a new generation of high-precision scattering experiments. The versatile MAGIX experiment will use MESA's innovative energy recovery technique, with a science focus on the study of hadron structure and few-body systems, dark sector searches, and investigations into reactions pertinent to nuclear astrophysics. An external beam line will supply spin-polarized electrons to the P2 experiment, enabling the performance of sensitive tests of the Standard Model through parity-violating electron scattering. The DarkMESA beam dump experiment, situated behind P2, is dedicated to the search for light dark matter particles.

   nucl-exEPJ Web Conf.(2024)·16 citations
2. 02*

   Direct cross-section measurement of the weak r-process 88Sr({\alpha},n)91Zr reaction in {\nu}-driven winds of core collapse supernovae

   C. Fougères🇫🇷 · M. L. Avila🇺🇸 · H. Jayatissa🇺🇸 · D. Santiago-Gonzalez🇺🇸 · K. Brandenburg🇲🇽 · Z. Meisel🇺🇸 · P. Mohr🇺🇸 · F. Montes🇺🇸 · C. Műller-Gatermann🇺🇸 · D. Neto🇺🇸 · W.-J. Ong🇺🇸 · J. Pereira🇺🇸 and 6 other authors

   About half of the heavy elements beyond iron are known to be produced by the rapid neutron capture process, known as r-process. However, the astrophysical site producing the r-process is still uncertain. Chemical abundances observed in several cosmic sites indicate that different mechanisms should be at play. For instance, the abundances around silver measured in a subset of metal-poor stars indicate the presence of a weak r-process. This process may be active in neutrino-driven winds of core collapse supernovae where ($\alpha$,n) reactions dominate the synthesis of Z ~ 40 elements in the expelled materials. Scarcely measured, the rates of ($\alpha$,n) reactions are determined from statistical Hauser-Feshbach calculations with $\alpha$-optical-model potentials, which are still poorly constrained. The uncertainties of the ($\alpha$,n) reaction rates therefore make a significant contribution to the uncertainties of the abundances determined from stellar modeling. In this work, the ${}^{88}$Sr($\alpha$,n)${}^{91}$Zr reaction which impacts the weak r-process abundances has been probed at astrophysics energy for the first time; directly measuring the total cross sections at astrophysical energies of 8.37 - 13.09 MeV in the center of mass (3.8 - 7.5 GK). Two measurements were performed at ATLAS with the electrically-segmented ionization chamber MUSIC, in inverse kinematics, while following the active target technique. The cross sections of this $\alpha$-induced reaction on ${}^{88}$Sr, located at the shell closure N = 50, have been found to be lower than expected, by a factor of 3, despite recent statistical calculations validated by measurements on neighboring nuclei. This result encourages more experimental investigations of ($\alpha$,n) reactions, at N = 50 and towards the neutron-rich side, to further test the predictive power and reliability of such calculations.

   nucl-exPRC(2024)·7 citations
3. 03*

   Constraining theoretical Corrections to Gamow-Teller Transition Rates

   L. Xayavong🇰🇷 · Y. Lim🇰🇷

   We propose two novel constraints for the theoretical corrections to Gamow-Teller transition rates. The first, derived from a two-level model, predicts forbidden regions within the plane defined by the isospin-mixing correction, ${\delta }_{C1}$, and the ratio, $\eta$, of the isospin-symmetry Gamow-Teller matrix elements between the upper and lower admixed states. It serves as a filter for the theoretical calculations, particularly effective for small values of $|\eta |$. The other employs experimental $ft$ values, incorporating the upper admixed states, and exploits mirror symmetry to eliminate isospin-invariant and nuclear structure-independent quantities. This approach not only offers an alternative mean for collectively testing theoretical corrections but also, as a byproduct, enables the extraction of ${\eta }^2$. This provides another sensitive test for the isospin-conserving component of nuclear Hamiltonian. Our investigation reveals a substantial cancellation of among radiative correction contributions in these tests.

   ↳ nucl-thnucl-exPRC(2025)·2 citations
4. 04*

   Directional Response of Several Geometries for Reactor-Neutrino Detectors

   Mark J. Duvall · Brian C. Crow · Max A. A. Dornfest · John G. Learned🇺🇸 · Marc F. Bergevin · Steven A. Dazeley🇺🇸 · Viacheslav A. Li🇺🇸

   We report simulation studies of six low-energy electron-antineutrino detector designs, with the goal of determining their ability to resolve the direction to an antineutrino source. Such detectors with target masses on the one-ton scale are well-suited to reactor monitoring at distances of 5--25 meters from the core. They can provide accurate measurements of reactor operating power, fuel mix, and burnup, as well as unsurpassed nuclear non-proliferation information in a non-contact cooperating reactor scenario such as those used by IAEA. A number of groups around the world are working on programs to develop detectors similar to some of those in this study. Here, we examine and compare several approaches to detector geometry for their ability not only to detect the inverse beta decay (IBD) reaction, but also to determine the source direction of incident antineutrinos. The information from these detectors provides insight into reactor power and burning profile, which is especially useful in constraining the clandestine production of weapons material. In a live deployment, a non-proliferation detector must be able to isolate the subject reactor, possibly from a field of much-larger power reactors; directional sensitivity can help greatly with this task. We also discuss implications for using such detectors in longer-distance observation of reactors, from a few km to hundreds of km. We have modeled six abstracted detector designs, including two for which we have operational data for validating our computer modeling and analytical processes. We have found that the most promising options, regardless of scale and range, have angular resolutions on the order of a few degrees, which is better than any yet achieved in practice by a factor of at least two.

   ↳ physics.ins-detastro-ph.IMhep-exnucl-exPhys.Rev.Applied(2024)·5 citations
5. 05*

   Baryon Spin and Emergent Hadron Mass

   Peng Cheng🇨🇳

   This thesis describes the use of Dyson-Schwinger equations (DSEs) to study baryon bound states in QCD. In this work, octet baryon axial form factors are calculated using a symmetry-preserving treatment of a vector $\times$ vector contact interaction (SCI). The baryons are considered as quark-plus-interacting-diquark bound states, whose structure (wave function) is obtained by solving a Poincaré-covariant Faddeev equation. Since it preserves symmetries, all consequences of partial conservation of the axial current are manifest. For instance, one finds that octet baryon axial properties are consistent with only minor violations of SU(3)-flavour symmetry, being interpreted as a dynamical consequence of emergent hadron mass (EHM). Considering neutral axial currents, the SCI delivers predictions for the flavour separation of octet baryon axial charges and, consequently, produces values for the associated SU(3) singlet, triplet, and octet axial charges. The results indicate that, at the hadron scale ${\zeta }_{\mathcal{H}}$, valence degrees of freedom carry approximately $50\%$ of an octet baryon's total spin. Proton structure is one of the principal topics in hadron physics. Its study is expected to reveal key features of both the origin of mass and strong interaction dynamics. This work therefore extended the above analyses to an examination of in-proton parton helicity (spin) distribution functions (DFs). Using Ansätze for hadron-scale proton polarised valence quark DFs, predictions are delivered for all proton polarised DFs at the measurement scale ${\zeta }_{\mathrm{C}}^2=3$GeV${}^2$. The pointwise behaviour of the predicted DFs and, consequently, their moments, shows good agreement with results inferred from data. Based on these results, one finds that experimental measurements of the proton flavour-singlet axial charge should return a value $a_0^{\mathrm{E}}({\zeta }_{\mathrm{C}})=0.35(2)$.

   ↳ hep-phhep-exhep-latnucl-ex+10 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.