Global constraints on absolute neutrino masses and their ordering [CL]

http://arxiv.org/abs/1703.04471

Within the standard three-neutrino framework, the absolute neutrino masses and their ordering (either normal, NO, or inverted, IO) are currently unknown. However, the combination of current data coming from oscillation experiments, neutrinoless double beta decay searches, and cosmological surveys, can provide interesting constraints for such unknowns in the sub-eV mass range, down to O(0.1) eV in some cases. We discuss current limits on absolute neutrino mass observables by performing a global data analysis, that includes the latest results from oscillation experiments, neutrinoless double beta decay bounds from the KamLAND-Zen experiment, and constraints from representative combinations of Planck measurements and other cosmological data sets. In general, NO appears to be somewhat favored with respect to IO at the level of ~2 sigma, mainly by neutrino oscillation data (especially atmospheric), corroborated by cosmological data in some cases. Detailed constraints are obtained via the chi^2 method, by expanding the parameter space either around separate minima in NO and IO, or around the absolute minimum in any ordering. Implications for upcoming oscillation and non-oscillation neutrino experiments, including beta-decay searches, are also discussed.

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F. Capozzi, E. Valentino, E. Lisi, et. al.
Tue, 14 Mar 17
14/74

Comments: 17 pages, including 3 tables and 11 figures

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Cross section measurement of the astrophysically important 17O(p,gamma)18F reaction in a wide energy range [CL]

http://arxiv.org/abs/1703.03184

The 17O(p,g)18F reaction plays an important role in hydrogen burning processes in different stages of stellar evolution. The rate of this reaction must therefore be known with high accuracy in order to provide the necessary input for astrophysical models.
The cross section of 17O(p,g)18F is characterized by a complicated resonance structure at low energies. Experimental data, however, is scarce in a wide energy range which increases the uncertainty of the low energy extrapolations. The purpose of the present work is therefore to provide consistent and precise cross section values in a wide energy range.
The cross section is measured using the activation method which provides directly the total cross section. With this technique some typical systematic uncertainties encountered in in-beam gamma-spectroscopy experiments can be avoided.
The cross section was measured between 500 keV and 1.8 MeV proton energies with a total uncertainty of typically 10%. The results are compared with earlier measurements and it is found that the gross features of the 17O(p,g)18F excitation function is relatively well reproduced by the present data. Deviation of roughly a factor of 1.5 is found in the case of the total cross section when compared with the only one high energy dataset. At the lowest measured energy our result is in agreement with two recent datasets within one standard deviation and deviates by roughly two standard deviations from a third one. An R-matrix analysis of the present and previous data strengthen the reliability of the extrapolated zero energy astrophysical S-factor.
Using an independent experimental technique, the literature cross section data of 17O(p,g)18F is confirmed in the energy region of the resonances while lower direct capture cross section is recommended at higher energies. The present dataset provides a constraint for the theoretical cross sections.

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G. Gyurky, A. Ornelas, Z. Fulop, et. al.
Fri, 10 Mar 17
7/52

Comments: Accepted for publication in Phys. Rev. C. Abstract shortened in order to comply with arxiv rules

Quantum Nuclear Pasta and Nuclear Symmetry Energy [CL]

http://arxiv.org/abs/1703.01433

Complex and exotic nuclear geometries are expected to appear naturally in dense nuclear matter found in the crust of neutron stars and supernovae environment collectively referred to as nuclear pasta. The pasta geometries depend on the average baryon density, proton fraction and temperature and are critically important in the determination of many transport properties of matter in supernovae and the crust of neutron stars. Using a set of self-consistent microscopic nuclear energy density functionals we present the first results of large scale quantum simulations of pasta phases at baryon densities $0.03 \leq \rho \leq 0.10$ fm$^{-3}$, proton fractions $0.05 \leq Y_p \leq 0.40$, and zero temperature. The full quantum simulations, in particular, allow us to thoroughly investigate the role and impact of the nuclear symmetry energy on pasta configurations. We use the Sky3D code that solves the Skyrme Hartree-Fock equations on a three-dimensional Cartesian grid. For the nuclear interaction we use the state of the art UNEDF1 parametrization, which was introduced to study largely deformed nuclei, hence is suitable for studies of the nuclear pasta. Density dependence of the nuclear symmetry energy is simulated by tuning two purely isovector observables that are insensitive to the current available experimental data. We find that a minimum total number of nucleons $A=2000$ is necessary to prevent the results from containing spurious shell effects and to minimize finite size effects. We find that a variety of nuclear pasta geometries are present in the neutron star crust and the result strongly depends on the nuclear symmetry energy. The impact of the nuclear symmetry energy is less pronounced as the proton fractions increase. Quantum nuclear pasta calculations at $T=0$ MeV are shown to get easily trapped in meta-stable states, and possible remedies to avoid meta-stable solutions are discussed.

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F. Fattoyev, C. Horowitz and B. Schuetrumpf
Tue, 7 Mar 17
3/66

Comments: 23 pages, 18 figures, 8 tables

Short-baseline electron antineutrino disappearance study by using neutrino sources from $^{13}$C + $^{9}$Be reaction [CL]

http://arxiv.org/abs/1702.08036

To investigate the existence of sterile neutrino, we propose a new neutrino production method using $^{13}$C beams and a $^{9}$Be target for short-baseline electron antineutrino (${\bar{\nu}}_{e}$) disappearance study. The production of secondary unstable isotopes which can emit neutrinos from the $^{13}$C + $^{9}$Be reaction is calculated with three different nucleus-nucleus (AA) reaction models. Different isotope yields are obtained using these models, but the results of the neutrino flux are found to have unanimous similarities. This feature gives an opportunity to study neutrino oscillation through shape analysis. In this work, expected neutrino flux and event rates are discussed in detail through intensive simulation of the light ion collision reaction and the neutrino flux from the beta decay of unstable isotopes followed by this collision. Together with the reactor and accelerator anomalies, the present proposed ${\bar{\nu}}_{e}$ source is shown to be a practically alternative test of the existence of the $\Delta m^{2}$ $\sim$ 1 eV$^{2}$ scale sterile neutrino.

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J. Shin, M. Cheoun, T. Kajino, et. al.
Tue, 28 Feb 17
50/69

Comments: N/A

Ab initio calculations of the isotopic dependence of nuclear clustering [CL]

http://arxiv.org/abs/1702.05177

Nuclear clustering describes the appearance of structures resembling smaller nuclei such as alpha particles (4He nuclei) within the interior of a larger nucleus. While clustering is important for several well-known examples, little is known about the general nature of clustering in nuclei. In this letter we present lattice Monte Carlo calculations based on chiral effective field theory for the ground states of helium, beryllium, carbon, and oxygen isotopes. By computing model-independent measures that probe three- and four-nucleon correlations at short distances, we determine the effective number of alpha clusters in any nucleus as well as their shape compared to alpha particles in vacuum. We also introduce a new computational approach called the pinhole algorithm, which solves a long-standing deficiency of auxiliary-field Monte Carlo simulations in computing density correlations relative to the center of mass. We use the pinhole algorithm to determine the proton and neutron density distributions and the geometry of cluster correlations in 12C, 14C, and 16C. The structural similarities among the carbon isotopes suggest that 14C and 16C have excitations analogous to the well-known Hoyle state resonance in 12C.

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S. Elhatisari, E. Epelbaum, H. Krebs, et. al.
Mon, 20 Feb 17
17/37

Comments: 5 + 9 pages (main + supplemental materials), 4 + 6 figures (main + supplemental materials)

Measurement of the stellar $^{58}$Ni$(n,γ)^{59}$Ni cross section with AMS [SSA]

http://arxiv.org/abs/1702.03352

The $^{58}$Ni$(n,\gamma)^{59}$Ni cross section was measured with a combination of the activation technique and accelerator mass spectrometry (AMS). The neutron activations were performed at the Karlsruhe 3.7 MV Van de Graaff accelerator using the quasi-stellar neutron spectrum at $kT=25$ keV produced by the $^7$Li($p,n$)$^7$Be reaction. The subsequent AMS measurements were carried out at the 14 MV tandem accelerator of the Maier-Leibnitz-Laboratory in Garching using the Gas-filled Analyzing Magnet System (GAMS). Three individual samples were measured, yielding a Maxwellian-averaged cross section at $kT=30$ keV of $\langle\sigma\rangle_{30\text{keV}}$= 30.4 (23)$^{syst}$(9)$^{stat}$ mbarn. This value is slightly lower than two recently published measurements using the time-of-flight (TOF) method, but agrees within the uncertainties. Our new results also resolve the large discrepancy between older TOF measurements and our previous value.

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P. Ludwig, G. Rugel, I. Dillmann, et. al.
Tue, 14 Feb 17
60/71

Comments: 13 pages, 4 figures; accepted for publication in Phys. Rev. C (2017)

First On-Site True Gamma-Ray Imaging-Spectroscopy of Contamination near Fukushima Plant [CL]

http://arxiv.org/abs/1702.01484

We have developed an Electron Tracking Compton Camera (ETCC), which provides a well-defined Point Spread Function (PSF) by reconstructing a direction of each gamma as a point and realizes simultaneous measurement of brightness and spectrum of MeV gamma-rays for the first time. Here, we present the results of our on-site pilot gamma-imaging-spectroscopy with ETCC at three contaminated locations in the vicinity of the Fukushima Daiichi Nuclear Power Plants in Japan in 2014. The obtained distribution of brightness (or emissivity) with remote-sensing observations is unambiguously converted into the dose distribution. We confirm that the dose distribution is consistent with the one taken by conventional mapping measurements with a dosimeter physically placed at each grid point. Furthermore, its imaging spectroscopy, boosted by Compton-edge-free spectra, reveals complex radioactive features in a quantitative manner around each individual target point in the background-dominated environment. Notably, we successfully identify a “micro hot spot” of residual caesium contamination even in an already decontaminated area. These results show that the ETCC performs exactly as the geometrical optics predicts, demonstrates its versatility in the field radiation measurement, and reveals potentials for application in many fields, including the nuclear industry, medical field, and astronomy.

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D. Tomono, T. Mizumoto, A. Takada, et. al.
Fri, 10 Feb 17
6/46

Comments: 19 pages, 7 figures, 2 tables

Establishment of Imaging Spectroscopy of Nuclear Gamma-Rays based on Geometrical Optics [CL]

http://arxiv.org/abs/1702.01483

Since the discovery of nuclear gamma-rays, its imaging has been limited to pseudo imaging, such as Compton Camera (CC) and coded mask. Pseudo imaging does not keep physical information (intensity, or brightness in Optics) along a ray, and thus is capable of no more than qualitative imaging of bright objects. To attain quantitative imaging, cameras that realize geometrical optics is essential, which would be, for nuclear MeV gammas, only possible via complete reconstruction of the Compton process. Recently we have revealed that “Electron Tracking Compton Camera” (ETCC) provides a well-defined Point Spread Function (PSF). The information of an incoming gamma is kept along a ray with the PSF and that is equivalent to geometrical optics. Here we present an imaging-spectroscopic measurement with the ETCC. Our results highlight the intrinsic difficulty with CCs in performing accurate imaging, and show that the ETCC surmounts this problem. The imaging capability also helps the ETCC suppress the noise level dramatically by ~3 orders of magnitude without a shielding structure. Furthermore, full reconstruction of Compton process with the ETCC provides spectra free of Compton edges. These results mark the first proper imaging of nuclear gammas based on the genuine geometrical optics.

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T. Tanimori, Y. Mizumura, A. Takada, et. al.
Fri, 10 Feb 17
40/46

Comments: 22 pages, 8 figures

Radiogenic Neutron Yield Calculations for Low-Background Experiments [CL]

http://arxiv.org/abs/1702.02465

Nuclear recoil backgrounds are one of the most dangerous backgrounds for many dark matter experiments. A primary source of nuclear recoils is radiogenic neutrons produced in the detector material itself. These neutrons result from fission and $(\alpha,n)$ reactions originating from uranium and thorium contamination. In this paper, we discuss neutron yields from these sources. We compile a list of $(\alpha,n)$ yields for many materials common in low-background detectors, calculated using NeuCBOT, a new tool introduced in this paper, available at https://github.com/shawest/neucbot. These calculations are compared to computations made using data compilations and SOURCES-4A

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S. Westerdale and P. Meyers
Thu, 9 Feb 17
64/67

Comments: N/A

Concurrent application of ANC and THM to assess the $^{13}{\rm C}(α,n)^{16}{\rm O}$ absolute cross section at astrophysical energies and possible consequences for neutron production in low-mass AGB stars [SSA]

http://arxiv.org/abs/1702.01589

The $^{13}{\rm C}(\alpha,n)^{16}{\rm O}$ reaction is considered to be the main neutron source responsible for the production of heavy nuclides (from ${\rm Sr}$ to ${\rm Bi}$) through slow $n$-capture nucleosynthesis ($s$-process) at low temperatures during the asymptotic giant branch (AGB) phase of low mass stars ($\lesssim 3-4\;{\rm M}_{\odot}$, or LMSs). In recent years, several direct and indirect measurements have been carried out to determine the cross section at the energies of astrophysical interest (around $190\pm40\;{\rm keV}$). However, they yield inconsistent results causing a highly uncertain reaction rate and affecting the neutron release in LMSs. In this work we have combined two indirect approaches, the asymptotic normalization coefficient (or ANC) and the Trojan Horse Method (THM), to unambiguously determine the absolute value of the $^{13}{\rm C}(\alpha,n)^{16}{\rm O}$ astrophysical factor. Therefore, we have determined a very accurate reaction rate to be introduced into astrophysical models of $s$-process nucleosynthesis in LMSs. Calculations using such recommended rate have shown limited variations in the production of those neutron-rich nuclei (with $86\leq A\leq 209$) receiving contribution only by slow neutron captures.

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O. Trippella and M. Cognata
Tue, 7 Feb 17
37/64

Comments: N/A

Antonella: A nuclear-recoil ionization-efficiency measurement in silicon at low energies [CL]

http://arxiv.org/abs/1702.00873

We have measured the ionization efficiency of silicon nuclear recoils with kinetic energy between 1.8 and 20 keV. We bombarded a silicon-drift diode with a neutron beam to perform an elastic-scattering experiment. A broad-energy neutron spectrum was used and the nuclear recoil energy was reconstructed with the time-of-flight technique. The overall trend of the results of this work are well described by the theory of Lindhard et al. above 4 keV of recoil energy. Below this energy, the presented data shows a deviation from the model. The data indicates a faster drop than the extrapolation of the Lindhard theory to low energies.

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F. Izraelevitch, D. Amidei, A. Aprahamian, et. al.
Mon, 6 Feb 17
12/43

Comments: N/A

Impacts of nuclear-physics uncertainty in stellar temperatures on the s-process nucleosynthesis [SSA]

http://arxiv.org/abs/1701.06978

We evaluated the uncertainty relevant to s-process nucleosynthesis using a Monte-Carlo centred approach. We are based on a realistic and general prescription of temperature dependent uncertainty for the reactions. We considered massive stars for the weak s-process and AGB stars for the main s-process. We found that the adopted uncertainty for (n,$\gamma$) rates, tens of per cent on average, affect the production of s-process nuclei along the $\beta$-stability line, while for $\beta$-decay, for which contributions from excited states enhances the uncertainty, has the strongest impact on branching points.

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N. Nishimura, G. Cescutti, R. Hirschi, et. al.
Wed, 25 Jan 17
58/74

Comments: 3 pages, 3 figures, to be published in the Proceedings of “the 14th International Symposium on Nuclei in the Cosmos (NIC-XIV)”; see arXiv:1701.00489, for the completed results

The Sun as a probe of Fundamental Physics and Cosmology [CEA]

http://arxiv.org/abs/1701.03926

The high quality data provided by helioseismology, solar neutrino flux measurements, spectral determination of solar abundances, nuclear reactions rates coefficients among other experimental data, leads to the highly accurate prediction of the internal structure of the present Sun – the standard solar model. In this talk, I have discussed how the standard solar model, the best representation of the real Sun, can be used to study the properties of dark matter, for which two complementary approaches have been developed: – to limit the number of theoretical candidates proposed as the dark matter particles, this analysis complements the experimental search of dark matter, and – as a template for the study of the impact of dark matter in the evolution of stars, which possibly occurs for stellar populations formed in regions of high density of dark matter, such as stars formed in the centre of galaxies and the first generations of stars.

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I. Lopes
Tue, 17 Jan 17
77/81

Comments: 11 pages; 6 figures; Nuclear Physics in Astrophysics VI (NPA6)

Reduced $E$1 $S$-factor of $^{12}$C($α$,$γ_0$)$^{16}$O [CL]

http://arxiv.org/abs/1701.02848

The astrophysical $S$-factor of $E$1 transition for $^{12}$C($\alpha$,$\gamma_0$)$^{16}$O is discussed in the $R$-matrix theory. The reduced $\alpha$-particle widths of the 1$^-_1$ ($E_x= 7.12$ MeV) and 1$^-_2$ ($E_x= 9.59$ MeV) states are extracted from the result of the potential model. The formal parameters are obtained without the linear approximation to the shift function. The resultant $E$1 $S$-factor is not strongly enhanced by the subthreshold 1$^-_1$ state if the channel radius is 4.75 fm. The calculated $\beta$-delayed $\alpha$-particle spectrum of $^{16}$N and the p-wave phase shift of $\alpha$+$^{12}$C elastic scattering are also found to be consistent with the previous studies. The small channel radius leads to the low penetrability to the Coulomb barrier, and it makes the reduced $E$1 $S$-factor below the barrier. Owing to the large reduced width from the molecular structure, the $R$-matrix pole of the 1$^-_2$ state is shifted in the vicinity of 1$^-_1$. The proximity of the two poles suppresses the interference between the states. The weak coupling feature of the $\alpha$+$^{12}$C system appears to be expressed as the shrinking strong interaction region.

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M. Katsuma
Thu, 12 Jan 17
12/60

Comments: 17 pages, 8 figures, 2 tables. Submitted to PTEP

An analytical coalescence formula for particle production in relativistic heavy-ion collisions [CL]

http://arxiv.org/abs/1701.01935

Based on a covariant coalescence model with a blast-wave-like parametrization of the phase-space configuration for constituent particles at freezeout, we derive an approximate analytical formula for the yields of clusters produced in relativistic heavy-ion collisions. Compared to previous existing formulae, the present work additionally considers the longitudinal dimension in momentum space, the relativistic corrections, and the finite size effects of the produced clusters relative to the space distribution of constituent particles at freezeout. The new analytical coalescence formula provides a useful approach to evaluate the yield of produced clusters, such as light nuclei from nucleon coalescence and hadrons from quark coalescence, in heavy-ion collisions. As a first application of the new analytical formula, we explore the strangeness population factor $S_3 = ^3_{\Lambda}$H/($^3$He$\times \Lambda/$p) based on nucleon/$\Lambda$ coalescence as well as the production of exotic hadrons based on quark coalescence in central Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. The results are compared with the prediction from other models.

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K. Sun and L. Chen
Tue, 10 Jan 17
9/75

Comments: 12 pages, 0 figures, 3 tables

Search for Possible Solar Influences in Ra-226 Decays [CL]

http://arxiv.org/abs/1701.01783

Measurements of Ra-226 activity from eight HPGe gamma ray detectors at the NC State University PULSTAR Reactor were analyzed for evidence of periodic variations, with particular attention to annual variations. All measurements were made using the same reference source, and data sets were of varying length taken over the time period from September 1996 through August 2014. Clear evidence of annual variations was observed in data from four of the detectors. Short time periodograms from the data sets suggest temporal variability of both the amplitude and frequency of these variations. The annual variations in two of the data sets show peak values near the first of February, while surprisingly, the annual variations in the other two are roughly out of phase with the first two. Three of the four detectors exhibited annual variations over approximately the same time period. A joint statistic constructed by combining spectra from these three shows peaks approximating the frequencies of solar r-mode oscillations with $\nu_R = 11.74$ cpy, $m=1$, and $l=3,5,6.$ The fact that similar variations were not present in all detectors covering similar time periods rules out variations in activity as the cause, and points to differing sensitivities to unspecified environmental parameters instead. In addition to seasonal variations, the modulation of environmental parameters by solar processes remains a possible explanation of periodogram features, but without requiring new physics.

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D. Stancil, S. Yegen, D. Dickey, et. al.
Tue, 10 Jan 17
63/75

Comments: Results in Physics (2016)

Radiative 3He-alpha reaction in Halo Effective Field Theory [CL]

http://arxiv.org/abs/1612.08959

In this work we study the radiative capture of ${\rm {}^3He}$ on ${\rm {}^4He}$ within the halo effective field theory framework. At leading order the capture amplitude comprises the initial state s-wave strong and Coulomb interactions summed to all orders, and depends on four parameters that can, in principle, be extracted from elastic ${\rm {}^3He}$-$\alpha$ scattering alone. At next-to-leading order, $s$- to p-wave initial state radiation with non-perturbative Coulomb and two-body currents contribute, with two extra parameters from the latter that are fitted to capture data. We perform three different fits of our parameters to available scattering data and most recent capture data. Our astrophysical $S$-factor, $S_{34}\sim 0.60\,{\rm keV\cdot b}$, is slightly above the average in the literature, though consistent within current error bars.

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R. Higa, G. Rupak and A. Vaghani
Fri, 30 Dec 16
20/64

Comments: 24 pages, 8 figures

Triple parton scatterings in proton-nucleus collisions at high energies [CL]

http://arxiv.org/abs/1612.08112

A generic expression to compute triple parton scattering (TPS) cross sections in high-energy proton-nucleus (pA) collisions is derived as a function of the corresponding single-parton cross sections and an effective parameter encoding the transverse parton profile of the proton. The TPS cross sections are enhanced by a factor of $9\,A\approx 2000$ in pPb compared to those in proton-nucleon collisions at the same center-of-mass energy. Estimates for triple charm ($c\overline{c}$) and bottom ($b\overline{b}$) production in pPb collisions at LHC and FCC energies are presented based on next-to-next-to-leading order (NNLO) calculations for $c\overline{c}, b\overline{b}$ single-parton cross sections. At $\sqrt{s_{NN}} = 8.8$ TeV, about 10% of the pPb events have three $c\overline{c}$ pairs produced in separate partonic interactions. At $\sqrt{s_{NN}} = 63$ TeV, the pPb cross sections for triple-J$/\psi$ and triple-$b\overline{b}$ are ${\cal O}$(1–10 mb). In the most energetic cosmic-ray collisions observed on earth, TPS $c\overline{c}$-pair cross sections equal the total p-Air inelastic cross section.

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D. dEnterria and A. Snigirev
Wed, 28 Dec 16
45/46

Comments: 6 pages, 4 figures. arXiv admin note: text overlap with arXiv:1612.05582

Impact of $(α,n)$ reactions on neutrino-driven wind nucleosynthesis [SSA]

http://arxiv.org/abs/1612.02435

After a successful core-collapse supernova, a neutrino-driven wind develops where it is possible to synthesize lighter heavy elements ($30<Z<45$). In the early galaxy, the origin of these elements is associated to the r-process and to an additional process. Here we assume the additional process corresponds to the weak r-process or alpha-process taking place in neutrino-driven winds. Based on a trajectory obtained from hydrodynamical simulations we study the astrophysics and nuclear physics uncertainties with our main focus on the \alphan reactions. These are critical to redistribute the matter and allow to further move it from light to heavy elements after nuclear statistical equilibrium freezes out. In this first sensitivity study, we vary all \alphan reactions by given constant factors which are justified based on the uncertainties of the statistical model and its nuclear physics input, mainly alpha optical potentials under the conditions found in the wind. Our results show that \alphan reactions are indeed very important to predict abundances. Therefore, further studies will follow to identify individual critical reactions. Since the nucleosynthesis path is close to stability, these reactions can be measured in the near future. This will uniquely allow to reduce the nuclear physics uncertainties and thus to use observations to constrain and understand the astrophysical conditions in the wind.

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J. Bliss, A. Arcones, F. Montes, et. al.
Fri, 9 Dec 16
19/62

Comments: 15 pages, 8 figures

Precise measurement of the thermal and stellar $^{54}$Fe($n, γ$)$^{55}$Fe cross sections via AMS [CL]

http://arxiv.org/abs/1611.09006

The detection of long-lived radionuclides through ultra-sensitive single atom counting via accelerator mass spectrometry (AMS) offers opportunities for precise measurements of neutron capture cross sections, e.g. for nuclear astrophysics. The technique represents a truly complementary approach, completely independent of previous experimental methods. The potential of this technique is highlighted at the example of the $^{54}$Fe($n, \gamma$)$^{55}$Fe reaction. Following a series of irradiations with neutrons from cold and thermal to keV energies, the produced long-lived $^{55}$Fe nuclei ($t_{1/2}=2.744(9)$ yr) were analyzed at the Vienna Environmental Research Accelerator (VERA). A reproducibility of about 1% could be achieved for the detection of $^{55}$Fe, yielding cross section uncertainties of less than 3%. Thus, the new data can serve as anchor points to time-of-flight experiments. We report significantly improved neutron capture cross sections at thermal energy ($\sigma_{th}=2.30\pm0.07$ b) as well as for a quasi-Maxwellian spectrum of $kT=25$ keV ($\sigma=30.3\pm1.2$ mb) and for $E_n=481\pm53$ keV ($\sigma= 6.01\pm0.23$ mb). The new experimental cross sections have been used to deduce improved Maxwellian average cross sections in the temperature regime of the common $s$-process scenarios. The astrophysical impact is discussed using stellar models for low-mass AGB stars.

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A. Wallner, T. Belgya, K. Buczak, et. al.
Tue, 29 Nov 16
73/77

Comments: N/A

Parity-Even and Time-Reversal-Odd Neutron Optical Potential in Spinning Matter Induced by Gravitational Torsion [CL]

http://arxiv.org/abs/1611.08172

Recent theoretical work has shown that spin $1/2$ particles moving through unpolarized matter which sources torsion fields experience a new type of parity-even and time-reversal-odd optical potential if the matter is spinning in the lab frame. This new type of optical potential can be sought experimentally using the helicity dependence of the total cross sections for longitudinally polarized neutrons moving through a rotating cylindrical target. In combination with recent experimental constraints on short-range P–odd, T–even torsion interactions derived from polarized neutron spin rotation in matter one can derive separate constraints on the time components of scalar and pseudoscalar torsion fields in matter. We estimate the sensitivity achievable in such an experiment and briefly outline some of the potential sources of systematic error to be considered in any future experimental search for this effect.

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A. Ivanov and W. Snow
Mon, 28 Nov 16
17/75

Comments: 5 pages, no figures, to appear in Physics Letters B

A study of raining influence on the environmental radiation background spectra with HXMT/HE [CL]

http://arxiv.org/abs/1611.08357

Full functional and performance tests were performed many times before the Hard X-ray Modulation Telescope (HXMT) launch. During one of the tests, the count rate curves of the 18 High Energy Detectors (HED) have been found increased consistently within an interval of time. A further study on the correlation between the count rate and rainfall was carried out,and the increased net spectrum was also analyzed. The analysis results indicate that the short-lived 222Rn decay products (214Pb and 214Bi) in rainwater were responsible for the transient changes of the background radiation spectra in HEDs. The results show that the HXMT/HEDs have a good detection sensitivity on X/gamma rays, and the detector calibration results are effective.

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X. Li, C. Liu, Y. Zhang, et. al.
Mon, 28 Nov 16
60/75

Comments: 6 pages,6 figures (2subplot in fig.2), submitted to Chinese Physics C

Nuclear Fusion in Laser-Driven Counter-Streaming Collisionless Plasmas [CL]

http://arxiv.org/abs/1611.03951

Nuclear fusion reactions are the most important processes in nature to power stars and produce new elements, and lie at the center of the understanding of nucleosynthesis in the universe. It is critically important to study the reactions in full plasma environments that are close to true astrophysical conditions. By using laser-driven counter-streaming collisionless plasmas, we studied the fusion D$+$D$\rightarrow n +^3$He in a Gamow-like window around 27 keV. The results show that astrophysical nuclear reaction yield can be modulated significantly by the self-generated electromagnetic fields and the collective motion of the plasma. This plasma-version mini-collider may provide a novel tool for studies of astrophysics-interested nuclear reactions in plasma with tunable energies in earth-based laboratories.

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X. Zhang, J. Zhao, D. Yuan, et. al.
Tue, 15 Nov 16
68/86

Comments: 5 pages; 4figures

The e-ASTROGAM mission (exploring the extreme Universe in the MeV-GeV range) [HEAP]

http://arxiv.org/abs/1611.02232

e-ASTROGAM (`enhanced ASTROGAM’) is a breakthrough Observatory mission dedicated to the study of the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. In the largely unexplored MeV-GeV domain, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on Galactic ecosystems. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA, ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and the promise of eLISA.
Keywords: High-energy gamma-ray astronomy, High-energy astrophysics, Nuclear Astrophysics, Compton and Pair creation telescope, Gamma-ray bursts, Active Galactic Nuclei, Jets, Outflows, Multiwavelength observations of the Universe, Counterparts of gravitational waves, Fermi, Dark Matter, Nucleosynthesis, Early Universe, Supernovae, Cosmic Rays, Cosmic antimatter.

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A. Angelis, V. Tatischeff, M. Tavani, et. al.
Tue, 8 Nov 16
6/75

Comments: N/A

Theoretical photo-disintegration of $^{16}$O [CL]

http://arxiv.org/abs/1611.02057

The photodisintegration of $^{16}$O is predicted to be dominated by $E$2 excitation in the vicinity of the $\alpha$-particle threshold.
The reaction rates of $^{12}$C($\alpha$,$\gamma$)$^{16}$O are expected to be determined from this reaction.

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M. Katsuma
Tue, 8 Nov 16
62/75

Comments: 3 pages, 2 figures, Proceedings of Nuclei in the Cosmos (NIC-XIV). 19-24 June 2016, Niigata, Japan

The effect of dark matter velocity profile on directional detection of dark matter [CEA]

http://arxiv.org/abs/1610.08632

Directional detection is an important way to detect dark matter. An input to these experiments is the dark matter velocity distribution. Recent hydrodynamical simulations have shown that the dark matter velocity distribution differs substantially from the Standard Halo Model. We study the impact of some of these updated velocity distribution in dark matter directional detection experiments. We calculate the ratio of events required to confirm the forward-backward asymmetry and the existence of the ring of maximum recoil rate using different dark matter velocity distributions for $^{19}$F and Xe targets. We show that with the use of updated dark matter velocity profiles, the forward-backward asymmetry and the ring of maximum recoil rate can be confirmed using a factor of $\sim$2 — 3 less events when compared to that using the Standard Halo Model.

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R. Laha
Fri, 28 Oct 16
25/73

Comments: v1: 8 pages, 6 figures. Comments welcome

Dependence of X-ray Burst Models on Nuclear Masses [HEAP]

http://arxiv.org/abs/1610.07596

X-ray burst model predictions of light curves and final composition of the nuclear ashes are affected by uncertain nuclear physics. Nuclear masses play an important role. Significant progress has been made in measuring the masses of very neutron deficient rare isotopes along the path of the rapid proton capture process (rp-process) in X-ray bursts. This paper identifies the remaining nuclear mass uncertainties in X-ray burst models using a one zone model that takes into account the changes in temperature and density evolution caused by changes in the nuclear physics. Two types of bursts are investigated – a typical mixed H/He burst with a limited rp-process and an extreme mixed H/He burst with an extended rp-process. Only three remaining nuclear mass uncertainties affect the light curve predictions of a typical H/He burst, and only three additional masses affect the composition strongly. A larger number of mass uncertainties remains to be addressed for the extreme H/He burst. Mass uncertainties of better than 10~keV need to be achieved. For one of the identified masses, $^{27}$P, we use the isobaric mass multiplet equation (IMME) to improve the mass uncertainty, obtaining an atomic mass excess of -716(7) keV. The results provide a roadmap for future experiments at advanced rare isotope beam facilities, where all the identified nuclides are expected to be within reach for precision mass measurements.

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H. Schatz and W. Ong
Wed, 26 Oct 16
55/63

Comments: 12 pages, submitted to Ap. J

Sensitivity of stellar electron-capture rates to parent neutron number: A case study on a continuous chain of twenty Vanadium isotopes [CL]

http://arxiv.org/abs/1610.06992

Gamow-Teller (GT) strength distributions (B(GT)) in electron-capture (EC) daughters stemming from the parent ground state are computed with the shell-model in the full pf-shell space, with quasi-particle random-phase approximation (QRPA) in the formalism of Krumlinde and M\”oller and with an Approximate Method (AM) for assigning an effective B(GT). These are compared to data available from decay and charge-exchange (CE) experiments across titanium isotopes in the pf-shell from A=43 to A=62, the largest set available for any chain of isotopes in the pf-shell. The present study is the first to examine B(GT) and the associated EC rates across a particular chain of isotopes with the purpose of examining rate sensitivities as neutron number increases. EC rates are also computed for a wide variety of stellar electron densities and temperatures providing concise estimates of the relative size of rate sensitivities for particular astrophysical scenarios. This work underscores the astrophysical motivation for CE experiments in inverse kinematics for nuclei away from stability at the luminosities of future Radioactive Ion Beam Facilities.

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G. Hitt, S. Gupta, R. Zegers, et. al.
Tue, 25 Oct 16
30/69

Comments: 12 pages, 9 figures, submitted to Physical Review C

Production Uncertainties of p-Nuclei in the $γ$-Process in Massive Stars Using a Monte Carlo Approach [HEAP]

http://arxiv.org/abs/1610.04339

Proton-rich nuclei, the so-called p-nuclei, are made in photodisintegration processes in outer shells of massive stars in the course of the final supernova explosion. Nuclear uncertainties in the production of these nuclei have been quantified in a Monte Carlo procedure. Bespoke temperature-dependent uncertainties were assigned to different types of reactions involving nuclei from Fe to Bi and all rates were varied randomly within the uncertainties. The resulting total production uncertainties of the p-nuclei are below a factor of two, with few exceptions. Key reactions dominating the final uncertainties have been identified in an automated procedure using correlations between rate and abundance uncertainties. Our results are compared to those of a previous study manually varying reaction rates.

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T. Rauscher, N. Nishimura, R. Hirschi, et. al.
Mon, 17 Oct 16
11/53

Comments: 4 pages, 2 figures; to appear in the Proceedings of “Nuclei in the Cosmos” 2016

Direct measurement of low-energy $^{22}$Ne(p,$γ$)$^{23}$Na resonances [CL]

http://arxiv.org/abs/1610.00925

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.

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R. Depalo, F. Cavanna, M. Aliotta, et. al.
Wed, 5 Oct 16
48/66

Comments: Submitted to Phys. Rev. C

Origins and Impacts of High-Density Symmetry Energy [CL]

http://arxiv.org/abs/1610.00549

What is nuclear symmetry energy? Why is it important? What do we know about it? Why is it so uncertain especially at high densities? Can the total symmetry energy or its kinetic part be negative? What are the effects of three-body and/or tensor force on symmetry energy? How can we probe the density dependence of nuclear symmetry energy with terrestrial nuclear experiments? What observables of heavy-ion reactions are sensitive to the high-density behavior of nuclear symmetry energy? How does the symmetry energy affect properties of neutron stars, gravitational waves and our understanding about the nature of strong-field gravity? In this lecture, we try to answer these questions as best as we can based on some of our recent work and/or understanding of research done by others. This note summarizes the main points of the lecture.

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B. Li
Tue, 4 Oct 16
45/81

Comments: Invited lecture given at the Carpathian Summer School of Physics 2016, Exotic Nuclei and Nuclear Astrophysics (VI), Sinaia, Romania, June 26 to July 9, 2016

Reevaluation of thermonuclear reaction rate of 50Fe(p,gamma)51Co [CL]

http://arxiv.org/abs/1609.09165

The thermonuclear rate of the 50Fe(p,gamma)51Co reaction in the Type I X-ray bursts (XRBs) temperature range has been reevaluated based on a recent precise mass measurement at CSRe lanzhou, where the proton separation energy Sp=142+/-77 keV has been determined firstly for the 51Co nucleus. Comparing to the previous theoretical predictions, the experimental Sp value has much smaller uncertainty. Based on the nuclear shell model and mirror nuclear structure information, we have calculated two sets of thermonuclear rates for the 50Fe(p,gamma)51Co reaction by utilizing the experimental Sp value. It shows that the statistical-model calculations are not ideally applicable for this reaction primarily because of the low density of low-lying excited states in 51Co. In this work, we recommend that a set of new reaction rate based on the mirror structure of 51Cr should be incorporated in the future astrophysical network calculations.

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L. Zhang, J. He, W. Chai, et. al.
Fri, 30 Sep 16
51/75

Comments: 7 pages, 2 figures and 5 tables

Primordial Nucleosynthesis [CEA]

http://arxiv.org/abs/1609.06048

Primordial or big bang nucleosynthesis (BBN) is now a parameter free theory whose predictions are in good overall agreement with observations. However, the 7Li calculated abundance is significantly higher than the one deduced from spectroscopic observations. Most solutions to this lithium problem involve a source of extra neutrons that inevitably leads to an increase of the deuterium abundance. This seems now to be excluded by recent deuterium observations that have drastically reduced the uncertainty on D/H and also calls for improved precision on thermonuclear reaction rates.

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A. Coc
Wed, 21 Sep 16
2/53

Comments: Invited review at the 14th International Symposium on Nuclei in the Cosmos XIV (Niigata)

Experimental study of the astrophysical gamma-process reaction 124Xe(alpha,gamma)128Ba [CL]

http://arxiv.org/abs/1609.05612

The synthesis of heavy, proton rich isotopes in the astrophysical gamma-process proceeds through photodisintegration reactions. For the improved understanding of the process, the rates of the involved nuclear reactions must be known. The reaction 128Ba(g,a)124Xe was found to affect the abundance of the p nucleus 124Xe. Since the stellar rate for this reaction cannot be determined by a measurement directly, the aim of the present work was to measure the cross section of the inverse 124Xe(a,g)128Ba reaction and to compare the results with statistical model predictions. Of great importance is the fact that data below the (a,n) threshold was obtained. Studying simultaneously the 124Xe(a,n)127Ba reaction channel at higher energy allowed to further identify the source of a discrepancy between data and prediction. The 124Xe + alpha cross sections were measured with the activation method using a thin window 124Xe gas cell. The studied energy range was between E = 11 and 15 MeV close above the astrophysically relevant energy range. The obtained cross sections are compared with statistical model calculations. The experimental cross sections are smaller than standard predictions previously used in astrophysical calculations. As dominating source of the difference, the theoretical alpha width was identified. The experimental data suggest an alpha width lower by at least a factor of 0.125 in the astrophysical energy range. An upper limit for the 128Ba(g,a)124Xe stellar rate was inferred from our measurement. The impact of this rate was studied in two different models for core-collapse supernova explosions of 25 solar mass stars. A significant contribution to the 124Xe abundance via this reaction path would only be possible when the rate was increased above the previous standard value. Since the experimental data rule this out, they also demonstrate the closure of this production path.

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Z. Halasz, E. Somorjai, G. Gyurky, et. al.
Tue, 20 Sep 16
72/74

Comments: Accepted for publication in Phys. Rev. C

Isospin dependence of nucleon effective masses in neutron-rich matter [CL]

http://arxiv.org/abs/1609.01324

In this talk, we first briefly review the isospin dependence of the total nucleon effective mass $M^{\ast}_{J}$ inferred from analyzing nucleon-nucleus scattering data within an isospin dependent non-relativistic optical potential model, and the isospin dependence of the nucleon E-mass $M^{\ast,\rm{E}}_{J}$ obtained from applying the Migdal-Luttinger theorem to a phenomenological single-nucleon momentum distribution in nuclei constrained by recent electron-nucleus scattering experiments. Combining information about the isospin dependence of both the nucleon total effective mass and E-mass, we then infer the isospin dependence of nucleon k-mass using the well-known relation $M^{\ast}_{J}=M^{\ast,\rm{E}}_{J}\cdot M^{\ast,\rm{k}}_{J}$. Implications of the results on the nucleon mean free path (MFP) in neutron-rich matter are discussed.

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B. Li, B. Cai, L. Chen, et. al.
Wed, 7 Sep 16
41/61

Comments: An invited talk given at the 5th International Workshop on Nuclear Dynamics in Heavy-Ion Reactions (IWND2016), Xinxiang, China, May 15-20, 2016

Dark Sectors 2016 Workshop: Community Report [CL]

http://arxiv.org/abs/1608.08632

This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years.

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J. Alexander, M. Battaglieri, B. Echenard, et. al.
Thu, 1 Sep 16
38/74

Comments: 66 pages, 15 figures, 3 tables. Workshop website and agenda: this http URL this https URL Editors: J. Alexander, M. Battaglieri, B. Echenard, R. Essig, M. Graham, E. Izaguirre, J. Jaros, G. Krnjaic, J. Mardon, D. Morrissey, T. Nelson, M. Perelstein, M. Pyle, A. Ritz, P. Schuster, B. Shuve, N. Toro, R. Van De Water

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

http://arxiv.org/abs/1608.03588

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.

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B. Scholz, A. Chavarria, J. Collar, et. al.
Mon, 15 Aug 16
40/43

Comments: 7 pages, 6 figures

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

http://arxiv.org/abs/1608.03348

“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 $T_p\leq 100$ 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.

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E. Kafexhiu
Fri, 12 Aug 16
32/38

Comments: 18 pages, 15 figures submitted to PRC

Analysis of Neutron Stars Observations Using a Correlated Fermi Gas Model [CL]

http://arxiv.org/abs/1608.00487

Background: The nuclear symmetry energy is a fundamental ingredient in determining the equation of state (EOS) of neutron stars (NS). Recent terrestrial experiments constrain both its value and slope at nuclear saturation density, however, its value at higher densities is unknown. Assuming a Free Fermi-gas (FFG) model for the kinetic symmetry energy, the high-density extrapolation depends on a single parameter, the density dependence of the potential symmetry energy. The Correlated Fermi-gas (CFG) model improves on the FFG model by including the effects of short-range, correlated, high-momentum, nucleons in nuclear matter. Using the CFG model for the kinetic symmetry energy along with constraints from terrestrial measurements leads to a much softer density dependence for the potential symmetry energy. Purpose: Examine the ability of the FFG and CFG models to describe NS observables that are directly sensitive to the symmetry energy at high-density. Specifically, examine the ability of the CFG model, with its softer density dependence of the potential symmetry energy, to describe a two solar-mass NS. Methods: Using a Bayesian analysis of NS observables we compare the CFG and FFG models and examine the resulting parameters in the NS EOS and the density dependence of the potential symmetry energy. Results: Despite the large difference in the density dependence of the potential part of the symmetry energy, both models can describe the NS data and support a two solar-mass NS. The different density dependences has only a small effect on the NS EOS. Conclusions: While sensitive to the high-density values of the symmetry energy, NS observables alone are not enough to distinguish between the CFG and FFG models. This indicates that the NS EOS, obtain from Bayesian analysis of NS observables, is robust and is not sensitive to the exact nuclear model used for the kinetic symmetry energy.

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O. Hen, A. Steiner, E. Piasetzky, et. al.
Thu, 4 Aug 16
28/70

Comments: 5 pages, 3 figures

Nuclear Data for Astrophysical Modeling [IMA]

http://arxiv.org/abs/1608.00596

Nuclear physics has been playing an important role in modern astrophysics and cosmology. Since the early 1950’s it has been successfully applied for the interpretation and prediction of astrophysical phenomena. Nuclear physics models helped to explain the observed elemental and isotopic abundances and star evolution and provided valuable insights on the Big Bang theory. Today, the variety of elements observed in stellar surfaces, solar system and cosmic rays, and isotope abundances are calculated and compared with the observed values. Consequently, the overall success of the modeling critically depends on the quality of underlying nuclear data that helps to bring physics of macro and micro scales together. To broaden the scope of traditional nuclear astrophysics activities and produce additional complementary information, I will investigate applicability of the U.S. Nuclear Data Program (USNDP) databases for astrophysical applications. EXFOR (Experimental Nuclear Reaction Data) and ENDF (Evaluated Nuclear Data File) libraries have large astrophysics potential; the former library contains experimental data sets while the latter library includes evaluated neutron cross sections. ENSDF (Evaluated Nuclear Structure Data File) database is a primary depository of nuclear structure and decay rates information. The decay rates are essential in stellar nucleosynthesis calculations, and these rates are evaluated using nuclear structure codes. The structure evaluation codes are pure mathematical procedures that can be applied to diverse data samples. A brief review of astrophysical nuclear data needs has been presented. Several opportunities and the corresponding computer tools have been identified. Further work will include extensive analysis of nuclear databases and computer procedures for astrophysical calculations.

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B. Pritychenko
Wed, 3 Aug 16
32/54

Comments: 20 pages, 10 figures, 2 tables, Brookhaven National Laboratory Report. arXiv admin note: text overlap with arXiv:1506.02978, arXiv:1110.1076

Analysis of Neutron Stars Observations Using a Correlated Fermi Gas Model [CL]

http://arxiv.org/abs/1608.00487

Background: The nuclear symmetry energy is a fundamental ingredient in determining the equation of state (EOS) of neutron stars (NS). Recent terrestrial experiments constrain both its value and slope at nuclear saturation density, however, its value at higher densities is unknown. Assuming a Free Fermi-gas (FFG) model for the kinetic symmetry energy, the high-density extrapolation depends on a single parameter, the density dependence of the potential symmetry energy. The Correlated Fermi-gas (CFG) model improves on the FFG model by including the effects of short-range, correlated, high-momentum, nucleons in nuclear matter. Using the CFG model for the kinetic symmetry energy along with constraints from terrestrial measurements leads to a much softer density dependence for the potential symmetry energy. Purpose: Examine the ability of the FFG and CFG models to describe NS observables that are directly sensitive to the symmetry energy at high-density. Specifically, examine the ability of the CFG model, with its softer density dependence of the potential symmetry energy, to describe a two solar-mass NS. Methods: Using a Bayesian analysis of NS observables we compare the CFG and FFG models and examine the resulting parameters in the NS EOS and the density dependence of the potential symmetry energy. Results: Despite the large difference in the density dependence of the potential part of the symmetry energy, both models can describe the NS data and support a two solar-mass NS. The different density dependences has only a small effect on the NS EOS. Conclusions: While sensitive to the high-density values of the symmetry energy, NS observables alone are not enough to distinguish between the CFG and FFG models. This indicates that the NS EOS, obtain from Bayesian analysis of NS observables, is robust and is not sensitive to the exact nuclear model used for the kinetic symmetry energy.

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O. Hen, A. Steiner, E. Piasetzky, et. al.
Tue, 2 Aug 16
33/80

Comments: 5 pages, 3 figures

Large-scale deformed quasiparticle random-phase approximation calculations of the $γ$-ray strength function using the Gogny force [CL]

http://arxiv.org/abs/1607.08483

Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we present large-scale calculations of the $E1$ $\gamma$-ray strength function obtained in the framework of the axially-symmetric deformed QRPA based on the finite-range Gogny force. This approach is applied to even-even nuclei, the strength function for odd nuclei being derived by interpolation. The convergence with respect to the adopted number of harmonic oscillator shells and the cut-off energy introduced in the 2-quasiparticle (2-$qp$) excitation space is analyzed. The calculations performed with two different Gogny interactions, namely D1S and D1M, are compared. A systematic energy shift of the $E1$ strength is found for D1M relative to D1S, leading to a lower energy centroid and a smaller energy-weighted sum rule for D1M. When comparing with experimental photoabsorption data, the Gogny-QRPA predictions are found to overestimate the giant dipole energy by typically $\sim$2 MeV. Despite the microscopic nature of our self-consistent Hartree-Fock-Bogoliubov plus QRPA calculation, some phenomenological corrections need to be included to take into account the effects beyond the standard 2-$qp$ QRPA excitations and the coupling between the single-particle and low-lying collective phonon degrees of freedom. For this purpose, three prescriptions of folding procedure are considered and adjusted to reproduce experimental photoabsorption data at best. All of them are shown to lead to rather similar predictions of the $E1$ strength, both at low energies and for exotic neutron-rich nuclei. Predictions of $\gamma$-ray strength functions and Maxwellian-averaged neutron capture rates for the whole Sn isotopic chain are also discussed and compared with previous theoretical calculations.

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M. Martini, S. Peru, S. Hilaire, et. al.
Fri, 29 Jul 16
30/44

Comments: N/A

Nuclear Physics Meets the Sources of the Ultra-High Energy Cosmic Rays [HEAP]

http://arxiv.org/abs/1607.07989

We study the implications of nuclear data and models for cosmic-ray astrophysics, which involves the photodisintegration of nuclei up to iron in astrophysical environments. We demonstrate that data on photo-absorption cross sections are sparse in that mass range by screening nuclear databases, such as EXFOR; these cross sections are needed to compute the photodisintegration rates. We also test the prediction power of models, such as TALYS, and find uncertainties of the order of a factor two. If however the radiation fields are strong enough such that the nuclear cascade in the astrophysical source can develop, we find that differences among different models average out — unless there is a systematic offset in the interaction model. We conclude with an isotope chart describing which information is in principle necessary to describe nuclear interactions, supported by simulating the entire disintegration chain in a gamma-ray burst. We also point out that a first consistency check may be the measurement of the absorption cross section for different isobars.

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D. Boncioli, A. Fedynitch and W. Winter
Thu, 28 Jul 16
29/57

Comments: 11 pages, 6 figures

From the Coulomb breakup of halo nuclei to neutron radiative capture [CL]

http://arxiv.org/abs/1607.06791

Coulomb breakup is used to infer radiative-capture cross sections at astrophysical energies. We test theoretically the accuracy of this indirect technique in the particular case of 15C, for which both the Coulomb breakup to ^{14}C+n and the radiative capture 14C(n,{\gamma})15C have been measured. We analyse the dependance of Coulomb-breakup calculations on the projectile description in both its initial bound state and its continuum. Our calculations depend not only on the Asymptotic Normalisation Coefficient (ANC) of the 15C ground state, but also on the 14C-n continuum. This questions the method proposed by Summers and Nunes [Phys. Rev. C 78, 011601 (2008), ibid. 78, 069908 (2008)], which assumes that an ANC can be directly extracted from the comparison of calculations to breakup data. Fortunately, the sensitivity to the continuum description can be absorbed in a normalisation constant obtained by a simple {\chi}2 fit of our calculations to the measurements. By restricting this fit to low 14C-n energy in the continuum, we can achieve a better agreement between the radiative-capture cross sections inferred from the Coulomb-breakup method and the exact ones. This result revives the Coulomb-breakup technique to infer neutron radiative-capture capture to loosely-bound states, which would be very useful for r- and s-process modelling in explosive stellar environments.

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P. Capel and Y. Nollet
Mon, 25 Jul 16
24/55

Comments: 8 pages, 7 figures, contribution to the proceedings of the 54th International Winter Meeting on Nuclear Physics (25-29 January 2016, Bormio, Italy)

Detecting supernova neutrinos with iron and lead detectors [HEAP]

http://arxiv.org/abs/1607.05591

Supernova (SN) neutrinos can excite the nuclei of various detector materials beyond their neutron emission thresholds through charged current (CC) and neutral current (NC) interactions. The emitted neutrons, if detected, can be a signal for the supernova event. Here we present the results of our study of SN neutrino detection through the neutron channel in lead ($^{208} {\rm Pb}$) and iron ($^{56} {\rm Fe}$) detectors for realistic neutrino fluxes and energies given by the recent Basel/Darmstadt simulations for a 18 solar mass progenitor SN at a distance of 10 kpc. We find that, in general, the number of neutrons emitted per kTon of detector material for the neutrino luminosities and average energies of the different neutrino species as given by the Basel/Darmstadt simulations are significantly lower than those estimated in previous studies based on the results of earlier SN simulations. At the same time, we highlight the fact that, although the total number of neutrons produced per kTon in a iron detector is more than an order of magnitude lower than that for lead, the dominance of the flavor blind NC events in the case of iron, as opposed to dominance of $\nu_e$ induced CC events in the case of lead, offers a complementarity between the two detector materials so that simultaneous detection of SN neutrinos in a lead and a sufficiently large iron detector suitably instrumented for neutron detection may allow estimating the fraction of the total $\mu$ and $\tau$ flavored neutrinos in the SN neutrino flux and thereby probing the emission mechanism as well as flavor oscillation scenarios of the SN neutrinos.

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A. Bandyopadhyay, P. Bhattacharjee, S. Chakraborty, et. al.
Wed, 20 Jul 16
50/66

Comments: 9 pages, LaTex, 10 figures

Nuclear constraints on gravitational waves from deformed pulsars [CL]

http://arxiv.org/abs/1607.05373

The recent direct detection of gravitational waves (GWs) from binary black hole mergers (2016, Phys. Rev. Lett. 116, no. 6, 061102; no. 24, 241103) opens up an entirely new non-electromagnetic window into the Universe making it possible to probe physics that has been hidden or dark to electromagnetic observations. In addition to cataclysmic events involving black holes, GWs can be triggered by physical processes and systems involving neutron stars. Properties of neutron stars are largely determined by the equation of state (EOS) of neutron-rich matter, which is the major ingredient in calculating the stellar structure and properties of related phenomena, such as gravitational wave emission from elliptically deformed pulsars and neutron star binaries. Although the EOS of neutron-rich matter is still rather uncertain mainly due to the poorly known density dependence of nuclear symmetry energy at high densities, significant progress has been made recently in constraining the symmetry energy using data from terrestrial nuclear laboratories. These constraints could provide useful information on the limits of GWs expected from neutron stars. Here after briefly reviewing our previous work on constraining gravitational radiation from elliptically deformed pulsars with terrestrial nuclear laboratory data in light of the recent gravitational wave detection, we estimate the maximum gravitational wave strain amplitude, using an optimistic value for the breaking strain of the neutron star crust, for 15 pulsars at distances 0.16 kpc to 0.91 kpc from Earth, and find it to be in the range of $\sim[0.2-31.1]\times 10^{-24}$, depending on the details of the EOS used to compute the neutron star properties. Implications are discussed.

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P. Krastev and B. Li
Wed, 20 Jul 16
66/66

Comments: 16 pages, 6 figures and 2 tables. Invited article by Nova Science Publishers for the edited collection “Gravitational Waves: Exploration, Insights and Detection”. In press

Measurement of the cosmogenic activation of germanium detectors in EDELWEISS-III [CEA]

http://arxiv.org/abs/1607.04560

We present a measurement of the cosmogenic activation in the germanium cryogenic detectors of the EDELWEISS III direct dark matter search experiment. The decay rates measured in detectors with different exposures to cosmic rays above ground are converted into production rates of different isotopes. The measured production rates in units of nuclei/kg/day are 82 $\pm$ 21 for $^3$H, 2.8 $\pm$ 0.6 for $^{49}$V, 4.6 $\pm$ 0.7 for $^{55}$Fe, and 106 $\pm$ 13 for $^{65}$Zn. These results are the most accurate for these isotopes. A lower limit on the production rate of $^{68}$Ge of 74 nuclei/kg/day is also presented. They are compared to model predictions present in literature and to estimates calculated with the ACTIVIA code.

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EDELWEISS. Collaboration, E. Armengaud, Q. Arnaud, et. al.
Mon, 18 Jul 16
2/50

Comments: N/A

Dark matter search in a Beam-Dump eXperiment (BDX) at Jefferson Lab [CL]

http://arxiv.org/abs/1607.01390

MeV-GeV dark matter (DM) is theoretically well motivated but remarkably unexplored. This proposal presents the MeV-GeV DM discovery potential for a $\sim$1 m$^3$ segmented CsI(Tl) scintillator detector placed downstream of the Hall A beam-dump at Jefferson Lab, receiving up to 10$^{22}$ electrons-on-target (EOT) in 285 days. This experiment (Beam-Dump eXperiment or BDX) would be sensitive to elastic DM-electron and to inelastic DM scattering at the level of 10 counts per year, reaching the limit of the neutrino irreducible background. The distinct signature of a DM interaction will be an electromagnetic shower of few hundreds of MeV, together with a reduced activity in the surrounding active veto counters. A detailed description of the DM particle $\chi$ production in the dump and subsequent interaction in the detector has been performed by means of Monte Carlo simulations. Different approaches have been used to evaluate the expected backgrounds: the cosmogenic background has been extrapolated from the results obtained with a prototype detector running at INFN-LNS (Italy), while the beam-related background has been evaluated by GEANT4 Monte Carlo simulations. The proposed experiment will be sensitive to large regions of DM parameter space, exceeding the discovery potential of existing and planned experiments in the MeV-GeV DM mass range by up to two orders of magnitude.

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M. Battaglieri, A. Bersani, B. Caiffi, et. al.
Thu, 7 Jul 16
30/43

Comments: Proposal submitted to the 44th JLab PAC. 125 pages, 60 figures

Proton-skins in momentum and neutron-skins in coordinate in heavy nuclei [CL]

http://arxiv.org/abs/1606.08045

Liouville’s theorem and Heisenberg’s uncertainty principle together require that nucleons’ root-mean-square (RMS) radii in momentum and coordinate are inversely correlated. An analysis of this inverse correlation within an extended Thomas-Fermi (ETF$^+$) approximation incorporating effects of the nucleon-nucleon short-range correlation (SRC) reveals generally that on average protons move faster than neutrons in neutron-skins of heavy nuclei. Namely, the proton-skin in momentum (k-space) and neutron-skin in coordinate (r-space) in heavy nuclei coexist and are naturally correlated. Using $^{208}$Pb as an example, we show that combining information about its proton-skin in momentum extracted from recent SRC experiments at Jefferson Laboratory (JLAB) with a specified size of its neutron-skin in coordinate can more stringently constrain nuclear many-body theories.

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B. Cai, B. Li and L. Chen
Tue, 28 Jun 16
58/58

Comments: 5 pages including 4 figures

Search for electron antineutrinos associated with gravitational wave events GW150914 and GW151226 using KamLAND [HEAP]

http://arxiv.org/abs/1606.07155

We present a search for low energy antineutrino events coincident with the gravitational wave events GW150914 and GW151226, and the candidate event LVT151012 using KamLAND, a kiloton-scale antineutrino detector. We find no inverse beta-decay neutrino events within $\pm 500$ seconds of either gravitational wave signal. This non-detection is used to constrain the electron antineutrino fluence and the luminosity of the astrophysical sources.

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KamLAND. Collaboration, A. Gando, Y. Gando, et. al.
Fri, 24 Jun 16
25/47

Comments: 4 figures, 10 pages