Wed·Jan 26, 2022Wednesday·January 26, 2022

1. 01*

   First direct measurement of the ${}^{13}$N($\alpha$,$p$)${}^{16}$O reaction relevant for core-collapse supernovae nucleosynthesis

   H. Jayatissa🇺🇸 · M. L. Avila🇺🇸 · K. E. Rehm🇺🇸 · R. Talwar · P. Mohr🇭🇺 · K. Auranen🇫🇮 · J. Chen🇺🇸 · D. A. Gorelov🇺🇸 · C. R. Hoffman · C. L. Jiang · B. P. Kay🇺🇸 · S. A. Kuvin · D. Santiago-Gonzalez🇺🇸

   Understanding the explosion mechanism of a core-collapse supernova (CCSN) is important to accurately model CCSN scenarios for different progenitor stars using model-observation comparisons. The uncertainties of various nuclear reaction rates relevant for CCSN scenarios strongly affect the accuracy of these stellar models. Out of these reactions, the ${}^{13}$N($\alpha$,$p$)${}^{16}$O reaction has been found to affect various stages of a CCSN at varying temperatures. This work presents the first direct measurement of the ${}^{13}$N($\alpha$,$p$)${}^{16}$O reaction performed using a 34.6 MeV beam of radioactive ${}^{13}$N ions and the active-target detector MUSIC (MUlti-Sampling Ionization Chamber) at Argonne National Laboratory. The resulting total ${}^{13}$N($\alpha$,$p$)${}^{16}$O reaction cross sections from this measurement in the center-of-mass energy range of 3.26 - 6.02 MeV are presented and compared with calculations using the Hauser-Feshbach formalism. Uncertainties in the reaction rate have been dramatically reduced at CCSN temperatures.

   nucl-exPRC(2022)·11 citations
2. 02*

   Activation cross section measurement of the 14N(p,gamma)15O astrophysical key reaction

   Gy. Gyürky · Z. Halász · G.G. Kiss🇭🇺 · T. Szücs🇩🇪 · Fülöp

   14N(p,gamma)15O is one of the key reactions of nuclear astrophysics playing a role in various stellar processes and influencing energy generation of stars, stellar evolution and nucleosynthesis. For a reliable reaction rate calculation the low energy cross section of 14N(p,gamma)15O must be known with high accuracy. Owing to the unmeasurable low cross sections, theoretical calculations are unavoidable. High precision experimental cross section data are needed in a wide energy range in order to provide the necessary basis for low energy extrapolations. In the present work the total 14N(p,gamma)15O cross section was measured with a method complementary to the available data sets. The cross section was measured with activation, based on the detection of the annihilation radiation following the beta+ decay of the reaction product 15O. This method, which provides directly the astrophysically important total cross section, was never used for the 14N(p,gamma)15O cross section measurement in the studied energy range. The non-resonant cross section was measured between 550 keV and 1400 keV center-of-mass energies with total uncertainty of about 10%. The results were compared with literature data using an R-matrix analysis. It is found that the cross sections measured in this work are in acceptable agreement with the two recent measurements only if the weak transitions - not measured in those works - are included. The present data set, being largely independent from the other available data, can be used to constrain the extrapolated cross sections to astrophysical energies and helps to make the astrophysical model calculations more reliable.

   nucl-exastro-ph.SRPRC(2022)·14 citations
3. 03*

   Collision-System and Beam-Energy Dependence of Anisotropic Flow Fluctuations

   STAR Collaboration: M. S. Abdallah🇪🇬 · J. Adam🇺🇸 · L. Adamczyk🇵🇱 · J. R. Adams🇺🇸 · J. K. Adkins🇺🇸 · G. Agakishiev🇷🇺 · I. Aggarwal🇮🇳 · M. M. Aggarwal🇮🇳 · Z. Ahammed🇮🇳 · I. Alekseev🇷🇺 · D. M. Anderson🇺🇸 · A. Aparin🇷🇺 and 382 other authors

   Elliptic flow measurements from two-, four- and six-particle correlations are used to investigate flow fluctuations in collisions of U+U at $\sqrt{s_{\mathrm{NN}}}$= 193 GeV, Cu+Au at $\sqrt{s_{\mathrm{NN}}}$= 200 GeV and Au+Au spanning the range $\sqrt{s_{\mathrm{NN}}}$= 11.5 - 200 GeV. The measurements show a strong dependence of the flow fluctuations on collision centrality, a modest dependence on system size, and very little if any, dependence on particle species and beam energy. The results, when compared to similar LHC measurements, viscous hydrodynamic calculations, and T$R$ENTo model eccentricities, indicate that initial-state-driven fluctuations predominate the flow fluctuations generated in the collisions studied.

   nucl-exPRL(2022)·26 citations
4. 04*

   Investigating the predicted breathing-mode excitation of the Hoyle state

   K. C. W. Li🇿🇦 · F. D. Smit🇿🇦 · P. Adsley🇿🇦 · R. Neveling🇿🇦 · P. Papka🇿🇦 · E. Nikolskii · J. W. Brümmer🇿🇦 · L. M. Donaldson🇿🇦 · M. Freer🇬🇧 · M. N. Harakeh🇳🇱 · F. Nemulodi🇿🇦 · L. Pellegri🇿🇦 and 16 other authors

   Knowledge of the low-lying monopole strength in ${}^{12}\mathrm{C}$ $-$ the Hoyle state in particular $-$ is crucial for our understanding of both the astrophysically important $3\alpha$ reaction and of $\alpha$-particle clustering. Multiple theoretical models have predicted a breathing mode of the Hoyle State at $E_x\approx 9$ MeV, corresponding to a radial in-phase oscillation of the underlying $\alpha$ clusters. The ${}^{12}\mathrm{C}(\alpha ,{\alpha }^{\prime }){}^{12}\mathrm{C}$ and ${}^{14}\mathrm{C}(p,t){}^{12}\mathrm{C}$ reactions were employed to populate states in ${}^{12}$C in order to search for this predicted breathing mode. A self-consistent, simultaneous analysis of the inclusive spectra with R-matrix lineshapes, together with angular distributions of charged-particle decay, yielded clear evidence for excess monopole strength at $E_x\approx 9$ MeV which is highly collective. Reproduction of the experimentally observed inclusive yields using a fit, with consistent population ratios for the various broad states, required an additional source of monopole strength. The interpretation of this additional monopole resonance as the breathing-mode excitation of the Hoyle state would provide evidence supporting a ${\mathcal{D}}_{3h}$ symmetry for the Hoyle state itself. The excess monopole strength may complicate analysis of the properties of the Hoyle state, modifying the temperature dependence of the $3\alpha$ rate at $T_9\gtrsim 2$ and ultimately, the predicted nucleosynthesis in explosive stars.

   nucl-exnucl-thPLB(2022)·12 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.