Thu·Mar 18, 2021Thursday·March 18, 2021

1. 01*

   New experimental ${}^{23}$Na($\alpha ,p$)${}^{26}$Mg Reaction Rate for Massive Star and Type-Ia Supernova models

   N. J. Hubbard · C. Aa. Diget🇬🇧 · S. P. Fox🇬🇧 · H. O. U. Fynbo🇩🇰 · A. M. Howard · O. S. Kirsebom · A. M. Laird🇬🇧 · M. Munch🇩🇰 · A. Parikh🇪🇸 · M. Pignatari🇬🇧 · J. R. Tomlinson

   The ${}^{23}$Na($\alpha ,p$)${}^{26}$Mg reaction has been identified as having a significant impact on the nucleosynthesis of several nuclei between Ne and Ti in type-Ia supernovae, and of ${}^{23}$Na and ${}^{26}$Al in massive stars. The reaction has been subjected to renewed experimental interest recently, motivated by high uncertainties in early experimental data and in the statistical Hauser-Feshbach models used in reaction rate compilations. Early experiments were affected by target deterioration issues and unquantifiable uncertainties. Three new independent measurements instead are utilizing inverse kinematics and Rutherford scattering monitoring to resolve this. In this work we present directly measured angular distributions of the emitted protons to eliminate a discrepancy in the assumptions made in the recent reaction rate measurements, which results in cross sections differing by a factor of 3. We derive a new combined experimental reaction rate for the ${}^{23}$Na($\alpha ,p$)${}^{26}$Mg reaction with a total uncertainty of 30% at relevant temperatures. Using our new ${}^{23}$Na($\alpha ,p$)${}^{26}$Mg rate, the ${}^{26}$Al and ${}^{23}$Na production uncertainty is reduced to within 8%. In comparison, using the factor of 10 uncertainty previously recommended by the rate compilation STARLIB, ${}^{26}$Al and ${}^{23}$Na production was changing by more than a factor of 2. In type-Ia supernova conditions, the impact on production of ${}^{23}$Na is constrained to within 15%.

   nucl-exastro-ph.SRnucl-thApJ(2021)·2 citations
2. 02*

   Azimuthal anisotropy measurements of strange and multistrange hadrons in U+U collisions at $\sqrt{s_{NN}}=193$ GeV at the BNL Relativistic Heavy Ion Collider

   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

   We present systematic measurements of azimuthal anisotropy for strange and multistrange hadrons ($K_s^0$, $\Lambda$, $\Xi$, and $\Omega$) and $\varphi$ mesons at midrapidity ($|y|<$ 1.0) in collisions of U + U nuclei at $\sqrt{s_{NN}}=193$ GeV, recorded by the STAR detector at the Relativistic Heavy Ion Collider. Transverse momentum ($p_{\text{T}}$) dependence of flow coefficients ($v_2$, $v_3$, and $v_4$) is presented for minimum bias collisions and three different centrality intervals. Number of constituent quark scaling of the measured flow coefficients in U + U collisions is discussed. We also present the ratio of $v_n$ scaled by the participant eccentricity (${\epsilon }_n\left\{2\right\}$) to explore system size dependence and collectivity in U + U collisions. The magnitude of $v_2/{\epsilon }_2$ is found to be smaller in U + U collisions than that in central Au + Au collisions contradicting naive eccentricity scaling. Furthermore, the ratios between various flow harmonics ($v_3/v_2^{3/2}$, $v_4/v_2^{4/2}$) are studied and compared with hydrodynamic and transport model calculations.

   nucl-exPRC(2021)·24 citations
3. 03*

   Measurement of the Beam-Normal Single-Spin Asymmetry for Elastic Electron Scattering from ${}^{12}$C and ${}^{27}$Al

   QWeak Collaboration: D. Androic · D.S. Armstrong · A. Asaturyan · K. Bartlett · R.S. Beminiwattha · J. Benesch · F. Benmokhtar · J. Birchall · R.D. Carlini · M.E. Christy · J.C. Cornejo · S. Covrig Dusa and 72 other authors

   We report measurements of the parity-conserving beam-normal single-spin elastic scattering asymmetries $B_n$ on ${}^{12}$C and ${}^{27}$Al, obtained with an electron beam polarized transverse to its momentum direction. These measurements add an additional kinematic point to a series of previous measurements of $B_n$ on ${}^{12}$C and provide a first measurement on ${}^{27}$Al. The experiment utilized the Qweak apparatus at Jefferson Lab with a beam energy of 1.158 GeV. The average lab scattering angle for both targets was 7.7 degrees, and the average $Q^2$ for both targets was 0.02437 GeV${}^2$ (Q=0.1561 GeV). The asymmetries are $B_n$ = -10.68 $\pm$ 0.90 stat) $\pm$ 0.57 (syst) ppm for ${}^{12}$C and $B_n$ = -12.16 $\pm$ 0.58 (stat) $\pm$ 0.62 (syst) ppm for ${}^{27}$Al. The results are consistent with theoretical predictions, and are compared to existing data. When scaled by Z/A, the Q-dependence of all the far-forward angle (theta < 10 degrees) data from ${}^1$H to ${}^{27}$Al can be described by the same slope out to $Q\approx 0.35$ GeV. Larger-angle data from other experiments in the same Q range are consistent with a slope about twice as steep.

   nucl-exPRC(2021)·13 citations
4. 04*

   Three-body description of ${}^9$C: Role of low-lying resonances in breakup reactions

   Jagjit Singh🇯🇵 · Takuma Matsumoto🇯🇵 · Tokuro Fukui🇯🇵 · Kazuyuki Ogata🇯🇵

   The ${}^9$C nucleus and related capture reaction, ${}^8\mathrm{B}(p,\gamma ){}^9\mathrm{C}$, have been intensively studied with an astrophysical interest. Due to the weakly-bound nature of ${}^9$C, its structure is likely to be described as the three-body (${}^7\mathrm{Be}+p+p$). Its continuum structure is also important to describe reaction processes of ${}^9$C, with which the reaction rate of the ${}^8\mathrm{B}(p,\gamma ){}^9\mathrm{C}$ process have been extracted indirectly. We perform three-body calculations on ${}^9$C and discuss properties of its ground and low-lying states via breakup reactions. We employ the three-body model of ${}^9$C using the Gaussian-expansion method combined with the complex-scaling method. This model is implemented in the four-body version of the continuum-discretized coupled-channels method, by which breakup reactions of ${}^9$C are studied. The intrinsic spin of ${}^7$Be is disregarded. By tuning a three-body interaction in the Hamiltonian of ${}^9$C, we obtain the low-lying $2^{+}$ state with the resonant energy 0.781 MeV and the decay width 0.137 MeV, which is consistent with the available experimental information and a relatively high-lying second $2^{+}$ wider resonant state. Our calculation predicts also sole $0^{+}$ and three $1^{-}$ resonant states. We discuss the role of these resonances in the elastic breakup cross section of ${}^9$C on ${}^{208}$Pb at 65 and 160 MeV/A. The low-lying 2${}^{+}$ state is probed as a sharp peak of the breakup cross section, while the 1${}^{-}$ states enhance the cross section around 3 MeV. Our calculations will further support the future and ongoing experimental campaigns for extracting astrophysical information and evaluating the two-proton removal cross-sections.

   ↳ nucl-thnucl-exPRC(2021)·7 citations
5. 05*

   TMDlib2 and TMDplotter: a platform for 3D hadron structure studies

   N.A. Abdulov🇷🇺 · A. Bacchetta🇮🇹 · S. Baranov🇷🇺 · A. Bermudez Martinez🇩🇪 · V. Bertone🇫🇷 · C. Bissolotti🇮🇹 · V. Candelise🇮🇹 · L.I. Estevez Banos🇩🇪 · M. Bury🇩🇪 · P.L.S. Connor🇩🇪 · L. Favart🇧🇪 · F. Guzman🇨🇺 and 26 other authors

   A common library, TMDlib2, for Transverse-Momentum-Dependent distributions (TMDs) and unintegrated parton distributions (uPDFs) is described, which allows for easy access of commonly used TMDs and uPDFs, providing a three-dimensional (3D) picture of the partonic structure of hadrons. The tool TMDplotter allows for web-based plotting of distributions implemented in TMDlib2, together with collinear pdfs as available in LHAPDF.

   ↳ hep-phnucl-exnucl-thEPJC(2021)·100 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.