Fri·Aug 12, 2016Friday·August 12, 2016

1. 01*

   Study of $(\mathbf{\alpha },\mathbf{p})$ and $(\mathbf{\alpha },\mathbf{n})$ reactions with a Multi-Sampling Ionization Chamber

   M. L. Avila · K. E. Rehm · S. Almaraz-Calderon🇺🇸 · A. D. Ayangeakaa🇺🇸 · C. Dickerson🇺🇸 · C. R. Hoffman · C. L. Jiang · B. P. Kay🇺🇸 · J. Lai · O. Nusair🇺🇸 · R. C. Pardo🇺🇸 · D. Santiago-Gonzalez · R. Talwar🇺🇸 · C. Ugalde🇺🇸

   A large number of $(\alpha ,p)$ and $(\alpha ,n)$ reactions are known to play a fundamental role in nuclear astrophysics. This work presents a novel technique to study these reactions with the active target system MUSIC whose segmented anode allows the investigation of a large energy range of the excitation function with a single beam energy. In order to verify the method, we performed a direct measurements of the previously measured reactions ${}^{17}$O$(\alpha ,n{)}^{20}$Ne, ${}^{23}$Na$(\alpha ,p{)}^{26}$Mg, and ${}^{23}$Na$(\alpha ,n{)}^{26}$Al. These reactions were investigated in inverse kinematics using ${}^4$He gas in the detector to study the excitation function in the range of about 2 to 6 MeV in the center of mass. We found good agreement between the cross sections of the ${}^{17}$O$(\alpha ,n{)}^{20}$Ne reaction measured in this work and previous measurements. Furthermore we have successfully performed a simultaneous measurement of the ${}^{23}$Na$(\alpha ,p{)}^{26}$Mg and ${}^{23}$Na$(\alpha ,n{)}^{26}$Al reactions.

   nucl-exNucl.Instrum.Meth.A(2017)·26 citations
2. 02*

   Study of the astrophysically important ${}^{23}\mathrm{Na}(\mathbf{\alpha },\mathbf{p}{)}^{26}\mathrm{Mg}$ and ${}^{23}\mathrm{Na}(\mathbf{\alpha },\mathbf{n}{)}^{26}\mathrm{Al}$ reactions

   M. L. Avila · K. E. Rehm🇺🇸 · S. Almaraz-Calderon🇺🇸 · A. D. Ayangeakaa🇺🇸 · C. Dickerson🇺🇸 · C. R. Hoffman · C. L. Jiang · B. P. Kay🇺🇸 · J. Lai · O. Nusair🇺🇸 · R. C. Pardo🇺🇸 · D. Santiago-Gonzalez · R. Talwar🇺🇸 · C. Ugalde🇺🇸

   The ${}^{23}$Na$(\alpha ,p{)}^{26}$Mg and ${}^{23}$Na$(\alpha ,n{)}^{26}$Al reactions are important for our understanding of the ${}^{26}$Al abundance in massive stars. The aim of this work is to report on a direct and simultaneous measurement of these astrophysically important reactions using an active target system. The reactions were investigated in inverse kinematics using ${}^4$He as the active target gas in the detector. We measured the excitation functions in the energy range of about 2 to 6 MeV in the center of mass. We have found that the cross sections of the ${}^{23}$Na$(\alpha ,p{)}^{26}$Mg and the ${}^{23}$Na$(\alpha ,n{)}^{26}$Al reactions are in good agreement with previous experiments, and with statistical model calculations.

   nucl-exPRC(2016)·21 citations
3. 03*

   Can Ab Initio Theory Explain the Phenomenon of Parity Inversion in ${}^{11}$Be?

   Angelo Calci🇨🇦 · Petr Navrátil🇨🇦 · Robert Roth🇩🇪 · Jérémy Dohet-Eraly🇨🇦 · Sofia Quaglioni🇺🇸 · Guillaume Hupin🇫🇷

   The weakly bound exotic ${}^{11}$Be nucleus, famous for its ground-state parity inversion and distinct n+ ${}^{10}$Be halo structure, is investigated from first principles using chiral two- and three-nucleon forces. An explicit treatment of continuum effects is found to be indispensable. We study the sensitivity of the ${}^{11}$Be spectrum to the details of the three-nucleon force and demonstrate that only certain chiral interactions are capable of reproducing the parity inversion. With such interactions, the extremely large E1 transition between the bound states is reproduced. We compare our photodisintegration calculations to conflicting experimental data and predict a distinct dip around the $3/2_1^{-}$ resonance energy. Finally, we predict low-lying $3/2^{+}$ and $9/2^{+}$ resonances that are not or not sufficiently measured in experiments.

   ↳ nucl-thnucl-exPRL(2016)·113 citations
4. 04*

   Parametrization of the nucleus-nucleus gamma-ray production cross sections below 100 GeV/nucleon: Subthreshold pions and Hard photons

   Ervin Kafexhiu🇩🇪

   "Subthreshold pions" and so-called "hard photons" are two important channels for producing less than 1 GeV $\gamma$-rays and $e^{\pm }$ pairs from nuclear collisions with energy per nucleon below the $\pi$-meson production threshold. I use publicly available experimental data to parametrize these two channels' $\gamma$-ray and $e^{\pm }$ production cross sections and extend the pion contribution to these particles spectra at higher energies using their corresponding spectra from $pp$ interactions. These parametrizations are valid for collision energy $T_p\le 100$ A GeV and agree reasonably well with the available experimental data. The new parametrizations allow, for the first time, accurate studies of astrophysical $\gamma$-rays below 1 GeV.

   ↳ astro-ph.HEnucl-exPRC(2016)·13 citations
5. 05*

   Dynamical freeze-out criterion in a hydrodynamical description of Au + Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV and Pb + Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2760$ GeV

   Saeed Ahmad🇮🇳 · Hannu Holopainen🇩🇪 · Pasi Huovinen🇩🇪

   In hydrodynamical modeling of ultrarelativistic heavy-ion collisions, the freeze-out is typically assumed to take place at a surface of constant temperature or energy density. A more physical approach is to assume that freeze-out takes place at a surface of constant Knudsen number. We evaluate the Knudsen number as a ratio of the expansion rate of the system to the pion scattering rate, and apply the constant Knudsen number freeze-out criterion to ideal hydrodynamical description of heavy-ion collisions at RHIC ($\sqrt{s_{\mathrm{NN}}}=200$ GeV) and the LHC ($\sqrt{s_{\mathrm{NN}}}=2760$ GeV) energies. We see that once the numerical values of freeze-out temperature and freeze-out Knudsen number are chosen to produce similar $p_T$ distributions, the elliptic and triangular anisotropies are similar too, in both event-by-event and averaged initial state calculations.

   ↳ nucl-thhep-phnucl-exPRC(2017)·15 citations
6. 06*

   Toward establishing low-lying $\Lambda$ and $\Sigma$ hyperon resonances with the $\bar{K}+d\to \pi +Y+N$ reaction

   H. Kamano🇯🇵 · T.-S. H. Lee🇺🇸

   A model for the $\bar{K}d\to \pi YN$ reactions with $Y=\Lambda ,\Sigma$ is developed, aiming at establishing the low-lying $\Lambda$ and $\Sigma$ hyperon resonances through analyzing the forthcoming data from the J-PARC E31 experiment. The off-shell amplitudes generated from the dynamical coupled-channels (DCC) model, which was developed in Kamano et al. [Phys. Rev. C 90, 065204 (2014)], are used as input to the calculations of the elementary $\bar{K}N\to \bar{K}N$ and $\bar{K}N\to \pi Y$ subprocesses in the $\bar{K}d\to \pi YN$ reactions. It is shown that the cross sections for the J-PARC E31 experiment with a rather high incoming-$\bar{K}$ momentum, $|{\vec{p}}_{\bar{K}}|=1$ GeV, can be predicted reliably only when the input $\bar{K}N\to \bar{K}N$ amplitudes are generated from a $\bar{K}N$ model, such as the DCC model used in this investigation, which describes the data of the $\bar{K}N$ reactions at energies far beyond the $\bar{K}N$ threshold. We find that the data of the threefold differential cross section $d\sigma /(d{M}_{\pi \Sigma }d{\Omega }_{p_n})$ for the $K^{-}d\to \pi \Sigma n$ reaction below the $\bar{K}N$ threshold can be used to test the predictions of the resonance poles associated with $\Lambda (1405)$. We also find that the momentum dependence of the threefold differential cross sections for the $K^{-}d\to {\pi }^{-}\Lambda p$ reaction can be used to examine the existence of a low-lying $J^P=1/2^{+}$ $\Sigma$ resonance with a pole mass $M_R=1457-i39$ MeV, which was found from analyzing the $K^{-}p$ reaction data within the employed DCC model.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2016)·19 citations
7. 07*

   Measurement of the low-energy quenching factor in germanium using an ${}^{88}$Y/Be photoneutron source

   B.J. Scholz🇺🇸 · A.E. Chavarria🇺🇸 · J.I. Collar🇺🇸 · P. Privitera🇺🇸 · A.E. Robinson🇺🇸

   We employ an ${}^{88}$Y/Be photoneutron source to derive the quenching factor for neutron-induced nuclear recoils in germanium, probing recoil energies from a few hundred eV${}_{nr}$ to 8.5keV${}_{nr}$. A comprehensive Monte Carlo simulation of our setup is compared to experimental data employing a Lindhard model with a free electronic energy loss $k$ and an adiabatic correction for sub-keV${}_{nr}$ nuclear recoils. The best fit $k=0.179\pm 0.001$ obtained using a Monte Carlo Markov Chain (MCMC) ensemble sampler is in good agreement with previous measurements, confirming the adequacy of the Lindhard model to describe the stopping of few-keV ions in germanium crystals at a temperature of $\sim$77 K. This value of $k$ corresponds to a quenching factor of 13.7 % to 25.3 % for nuclear recoil energies between 0.3 keV${}_{nr}$ and 8.5 keV${}_{nr}$, respectively.

   ↳ physics.ins-detastro-ph.COastro-ph.IMhep-ex+2PRD(2016)·70 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.