Wed·Oct 5, 2016Wednesday·October 5, 2016

1. 01*

   Direct measurement of low-energy ${}^{22}$Ne(p,$\gamma$)${}^{23}$Na resonances

   R. Depalo🇮🇹 · F. Cavanna🇮🇹 · M. Aliotta🇬🇧 · M. Anders · D. Bemmerer🇩🇪 · A. Best🇮🇹 · A. Boeltzig🇮🇹 · C. Broggini🇮🇹 · C.G. Bruno🇬🇧 · A. Caciolli🇮🇹 · G. F. Ciani🇮🇹 · P. Corvisiero🇮🇹 and 21 other authors

   The ${}^{22}$Ne(p,$\gamma$)${}^{23}$Na reaction is the most uncertain process in the neon-sodium cycle of hydrogen burning. At temperatures relevant for nucleosynthesis in asymptotic giant branch stars and classical novae, its uncertainty is mainly due to a large number of predicted but hitherto unobserved resonances at low energy. Purpose: A new direct study of low energy ${}^{22}$Ne(p,$\gamma$)${}^{23}$Na resonances has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA), in the Gran Sasso National Laboratory, Italy. Method: The proton capture on ${}^{22}$Ne was investigated in direct kinematics, delivering an intense proton beam to a ${}^{22}$Ne gas target. $\gamma$ rays were detected with two high-purity germanium detectors enclosed in a copper and lead shielding suppressing environmental radioactivity. Results: Three resonances at 156.2 keV ($\omega \gamma$ = (1.48\,$\pm$\,0.10)\,$\cdot$\,10${}^{-7}$ eV), 189.5 keV ($\omega \gamma$ = (1.87\,$\pm$\,0.06)\,$\cdot$\,10${}^{-6}$ eV) and 259.7 keV ($\omega \gamma$ = (6.89\,$\pm$\,0.16)\,$\cdot$\,10${}^{-6}$ eV) proton beam energy, respectively, have been observed for the first time. For the levels at 8943.5, 8975.3, and 9042.4 keV excitation energy corresponding to the new resonances, the $\gamma$-decay branching ratios have been precisely measured. Three additional, tentative resonances at 71, 105 and 215 keV proton beam energy, respectively, were not observed here. For the strengths of these resonances, experimental upper limits have been derived that are significantly more stringent than the upper limits reported in the literature. Conclusions: Based on the present experimental data and also previous literature data, an updated thermonuclear reaction rate is provided in tabular and parametric form. The new reaction rate is significantly higher than previous evaluations at temperatures of 0.08-0.3 GK.

   nucl-exastro-ph.SRPRC(2016)·55 citations
2. 02*

   Empirical parametrizations of the resonance amplitudes based on the Siegert's theorem

   G. Ramalho🇧🇷

   We present parametrizations of the ${\gamma }^{\ast }N\to N(1535)1/2^{-}$, ${\gamma }^{\ast }N\to N(1520)3/2^{-}$ and ${\gamma }^{\ast }N\to \Delta (1232)3/2^{+}$ transition amplitudes that are compatible with the analytic constraints at the pseudothreshold (Siegert's theorem). The presented parametrizations also provide a fair description of the experimental data. For the case of the ${\gamma }^{\ast }N\to \Delta (1232)3/2^{+}$ transition, we discuss how the pion cloud parametrizations of the electric and the Coulomb quadrupole form factors can be adjusted according to the Siegert's theorem.

   ↳ nucl-thhep-exhep-phnucl-exJPS Conf.Proc.(2017)·0 citations
3. 03*

   Background model for the MAJORANA DEMONSTRATOR

   C. Cuesta🇺🇸 · N. Abgrall🇺🇸 · I.J. Arnquist🇺🇸 · F.T. Avignone III🇺🇸 · A.S. Barabash🇷🇺 · F.E. Bertrand🇺🇸 · A.W. Bradley🇺🇸 · V. Brudanin🇷🇺 · M. Busch🇺🇸 · M. Buuck🇺🇸 · T.S. Caldwell🇺🇸 · Y-D. Chan🇺🇸 and 55 other authors

   The MAJORANA Collaboration is constructing a system containing 44 kg of high-purity Ge (HPGe) detectors to demonstrate the feasibility and potential of a future tonne-scale experiment capable of probing the neutrino mass scale to ~15 meV. To realize this, a major goal of the MAJORANA DEMONSTRATOR is to demonstrate a path forward to achieving a background rate at or below 1 count/(ROI-t-y) in the 4 keV region of interest (ROI) around the Q-value at 2039 keV. This goal is pursued through a combination of a significant reduction of radioactive impurities in construction materials and analytical methods for background rejection, for example using powerful pulse shape analysis techniques profiting from the p-type point contact HPGe detectors technology. The effectiveness of these methods is assessed using simulations of the different background components whose purity levels are constrained from radioassay measurements. Preliminary background results obtained during the engineering runs of the Demonstrator are presented.

   ↳ physics.ins-detnucl-exJ.Phys.Conf.Ser.(2017)·12 citations
4. 04*

   $\bar{D}D$ meson pair production in antiproton-nucleus collisions

   R. Shyam🇮🇳 · K. Tsushima🇧🇷

   We study the $\bar{D}D$ (${\bar{D}}^0{D}^0$ and $D^{-}{D}^{+}$) charm meson pair production in antiproton ($\bar{p}$) induced reactions on nuclei at beam energies ranging from threshold to several GeV. Our model is based on an effective Lagrangian approach that has only the baryon-meson degrees of freedom and involves the physical hadron masses. The reaction proceeds via the $t$-channel exchanges of ${\Lambda }_c^{+}$, ${\Sigma }_c^{+}$, and ${\Sigma }_c^{++}$ baryons in the initial collision of the antiproton with one of the protons of the target nucleus. The medium effects on the exchanged baryons are included by incorporating in the corresponding propagators, the effective charm baryon masses calculated within a quark-meson coupling (QMC) model. The wave functions of the bound proton have been determined within the QMC model as well as in a phenomenological model where they are obtained by solving the Dirac equation with appropriate scalar and vector potentials. The initial- and final-state distortion effects have been approximated by using an eikonal approximation-based procedure. Detailed numerical results are presented for total and double differential cross sections for the ${\bar{D}}^0{D}^0$ and $D^{-}{D}^{+}$ production reactions on ${}^{16}$O and ${}^{90}$Zr targets. It is noticed that at $\bar{p}$ beam momenta of interest to the $\bar{P}ANDA$ experiment, medium effects lead to noticeable enhancements in the charm meson production cross sections.

   ↳ nucl-thhep-exhep-phnucl-exPRD(2016)·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.