Wed·Mar 2, 2022Wednesday·March 2, 2022

1. 01*

   Observation of an ultra-low $Q$-value electron-capture channel decaying to ${}^{75}$As via high-precision mass measurement

   M. Ramalho🇫🇮 · Z. Ge🇫🇮 · T. Eronen🇫🇮 · D. A. Nesterenko🇫🇮 · J. Jaatinen · A. Jokinen · A. Kankainen🇫🇮 · J. Kostensalo🇫🇮 · J. Kotila🇫🇮 · M. I. Krivoruchenko🇷🇺 · J. Suhonen🇫🇮 · K. S. Tyrin🇷🇺 · V. Virtanen🇫🇮

   A precise determination of the atomic mass of ${}^{75}$As has been performed utilizing the double Penning trap mass spectrometer, JYFLTRAP. The mass excess is measured to be -73035.519(42) keV/c${}^2$, which is a factor of 21 more precise and 1.3(9) keV/c${}^2$ lower than the adopted value in the newest Atomic Mass Evaluation (AME2020). This value has been used to determine the ground-state-to-ground-state electron-capture decay $Q$ value of ${}^{75}$Se and ${\beta }^{-}$ decay $Q$ value of ${}^{75}$Ge, which are derived to be 866.041(81) keV and 1178.561(65) keV, respectively. Using the nuclear energy-level data of 860.00(40) keV, 865.40(50) keV (final states of electron capture) and 1172.00(60) keV (final state of ${\beta }^{-}$ decay) for the excited states of ${}^{75}$As${}^{\ast }$, we have determined the ground-state-to-excited-state $Q$ values for two transitions of ${}^{75}$Se $\to$ ${}^{75}$As${}^{\ast }$ and one transition of ${}^{75}$Ge $\to$ ${}^{75}$As${}^{\ast }$. The ground-state-to-excited-state $Q$ values are determined to be 6.04(41) keV, 0.64(51) keV and 6.56(60) keV, respectively, thus confirming that the three low $Q$-value transitions are all energetically valid and one of them is a possible candidate channel for antineutrino mass determination. Furthermore, the ground-state-to-excited-state $Q$ value of transition ${}^{75}$Se $\to$ ${}^{75}$As${}^{\ast }$ (865.40(50) keV) is revealed to be ultra-low (< 1 keV) and the first-ever confirmed EC transition possessing an ultra-low $Q$ value from direct measurements.

   nucl-exPRC(2022)·20 citations
2. 02*

   Measurement of the helicity dependence for single ${\pi }^0$ photoproduction from the deuteron

   The A2 collaboration at MAMI: F. Cividini · M. Dieterle · S. Abt · P. Achenbach · P. Adlarson · F. Afzal · Z. Ahmed · J.R.M. Annand · H.J. Arends · M. Bashkanov · R. Beck · M. Biroth and 63 other authors

   The helicity-dependent single ${\pi }^0$ photoproduction cross section on the deuteron and the angular dependence of the double polarisation observable $E$ for the quasi-free single ${\pi }^0$ production off the proton and the neutron have been measured for the first time from the threshold region up to the photon energy 1.4 GeV. The experiment was performed at the tagged photon facility of the MAMI accelerator and used a circularly polarised photon beam and longitudinally polarised deuteron target. The reaction products were detected using the large acceptance Crystal Ball/TAPS calorimeter, which covered 97% of the full solid angle. Comparing the cross section from the deuteron with the sum of free nucleon cross sections provides a quantitative estimate of the effects of the nuclear medium on pion production. In contrast, comparison of $E$ helicity asymmetry data from quasi-free protons off deuterium with data from a free proton target indicates that nuclear effects do not significantly affect this observable. As a consequence, it is deduced that the helicity asymmetry $E$ on a free neutron can be reliably extracted from measurements on a deuteron in quasi-free kinematics.

   nucl-exEPJA(2022)·9 citations
3. 03*

   Transport coefficients of the quark-gluon plasma at the critical point and across the first-order line

   Joaquin Grefa🇺🇸 · Mauricio Hippert🇺🇸 · Jorge Noronha🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸 · Israel Portillo🇺🇸 · Claudia Ratti🇺🇸 · Romulo Rougemont🇺🇸

   A bottom-up Einstein-Maxwell-Dilaton holographic model is used to compute, for the first time, the behavior of several transport coefficients of the hot and baryon-rich strongly coupled quark-gluon plasma at the critical point and also across the first-order phase transition line in the phase diagram. The observables under study are of the shear and bulk viscosities, baryon diffusion, thermal conductivity, the jet quenching parameter $\hat{q}$, as well as the heavy-quark drag force and Langevin diffusion coefficients. These calculations provide a phenomenologically promising estimate for these coefficients, given that our model quantitatively reproduces lattice QCD thermodynamics results, both at zero and finite baryon density, besides naturally incorporating the nearly-perfect fluidity of the quark-gluon plasma. We find that the diffusion of baryon charge, and also the shear and bulk viscosities, are suppressed with increasing baryon density, indicating that the medium becomes even closer to perfect fluidity at large densities. On the other hand, the jet quenching parameter and the heavy-quark momentum diffusion are enhanced with increasing density. The observables display a discontinuity gap when crossing the first-order phase transition line, while developing an infinite slope at the critical point. The transition temperatures associated with different transport coefficients differ in the crossover region but are found to converge at the critical point.

   ↳ nucl-thhep-phnucl-exPRD(2022)·66 citations
4. 04*

   The importance of Fe fragmentation for LiBeB analyses: Is a Li primary source needed to explain AMS-02 data?

   D. Maurin🇫🇷 · E. Ferronato Bueno🇳🇱 · Y. Génolini🇫🇷 · L. Derome🇫🇷 · M. Vecchi🇳🇱

   High-precision data from AMS-02 on Li, Be, and B provide the best constraints on Galactic cosmic-ray transport parameters. We re-evaluate the impact of Fe fragmentation on the Li, Be, and B modelling. We discuss the consequences on the transport parameter determination and reassess whether a primary source of Li is needed to match AMS-02 data. We renormalised several cross-section parametrisations to existing data for the most important reactions producing Li, Be, and B. We used the USINE code with these new cross-section sets to re-analyse Li/C, Be/C, and B/C AMS-02 data. We built three equally plausible cross-section sets. Compared to the initial cross-section sets, they lead to an average enhanced production of Li ($\sim 20-50\%$) and Be ($\sim 5-15\%$), while leaving the B flux mostly unchanged. In particular, Fe fragmentation is found to contribute to up to 10\% of the Li and Be fluxes. Used in the combined analysis of AMS-02 Li/C, Be/C, and B/C data, the fit is significantly improved, with an enhanced diffusion coefficient ($\sim 20\%)$. The three updated cross-section sets are found to either slightly undershoot or overshoot the Li/C and B/C ratios: this strongly disfavours evidence for a primary source of Li in cosmic rays. We stress that isotopic cosmic-ray ratios of Li (and to a lesser extent Be), soon to be released by AMS-02, are also impacted by the use of these updated sets. Almost no nuclear data exist for the production of Li and B isotopes from Ne, Mg, Si, and Fe, whereas these reactions are estimated to account for $\sim 20\%$ of the total production. New nuclear measurements would be appreciated and help to better exploit the high-precision AMS-02 cosmic-ray data.

   ↳ astro-ph.HEnucl-exAstron.Astrophys.(2022)·21 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.