Mon·Jun 22, 2015Monday·June 22, 2015

1. 01*

   The 23Na({\alpha},p) 26Mg reaction rate at astrophysically relevant energies

   A.M. Howard · M. Munch🇩🇰 · H.O.U. Fynbo🇩🇰 · O.S. Kirsebom🇩🇰 · K.L. Laursen · C.Aa. Diget · N.J. Hubbard

   The production of 26 Al in massive stars is sensitive to the 23 Na(a,p) 26 Mg cross section. Recent experimental data suggest the currently recommended cross sections are underestimated by a factor of 40. We present here differential cross sections for the 23 Na(a,p) 26 Mg reaction measured in the energy range E c.m. = 1.7 - 2.5 MeV. Concurrent measurements of Rutherford scattering provide absolute normalisations which are independent of variations in target properties. Angular distributions were measured for both p 0 and p 1 permitting the determination of total cross sections. The results show no significant deviation from the statistical model calculations upon which the recommended rates are based. We therefore retain the previous recommendation without the increase in cross section and resulting stellar reaction rates of a factor of 40, impacting on the 26 Al yield from massive stars by more than a factor of three.

   nucl-exPRL(2015)·12 citations
2. 02*

   Lifetime measurement of excited low-spin states via the $(p,p^{\prime }\gamma$) reaction

   A. Hennig🇩🇪 · V. Derya🇩🇪 · M. N. Mineva · P. Petkov · S. G. Pickstone🇩🇪 · M. Spieker🇩🇪 · A. Zilges🇩🇪

   In this article a method for lifetime measurements in the sub-picosecond regime via the Doppler-shift attenuation method (DSAM) following the inelastic proton scattering reaction is presented. In a pioneering experiment we extracted the lifetimes of 30 excited low-spin states of ${}^{96}$Ru, taking advantage of the coincident detection of scattered protons and de-exciting $\gamma$-rays as well as the large number of particle and $\gamma$-ray detectors provided by the SONIC@HORUS setup at the University of Cologne. The large amount of new experimental data shows that this technique is suited for the measurement of lifetimes of excited low-spin states, especially for isotopes with a low isotopic abundance, where $(n,n^{\prime }\gamma$) or - in case of investigating dipole excitations - ($\gamma ,{\gamma }^{\prime }$) experiments are not feasible due to the lack of sufficient isotopically enriched target material.

   nucl-exNucl.Instrum.Meth.A(2015)·11 citations
3. 03*

   Determination of gamma-ray widths in ${}^{15}$N using nuclear resonance fluorescence

   T. Szücs🇩🇪 · D. Bemmerer🇩🇪 · A. Caciolli🇮🇹 · Zs. Fülöp🇭🇺 · R. Massarczyk🇺🇸 · C. Michelagnoli🇫🇷 · T. P. Reinhardt🇩🇪 · R. Schwengner🇩🇪 · M. P. Takács🇩🇪 · C. A. Ur🇮🇹 · A. Wagner🇩🇪 · L. Wagner🇩🇪

   The stable nucleus ${}^{15}$N is the mirror of ${}^{15}$O, the bottleneck in the hydrogen burning CNO cycle. Most of the ${}^{15}$N level widths below the proton emission threshold are known from just one nuclear resonance fluorescence (NRF) measurement, with limited precision in some cases. A recent experiment with the AGATA demonstrator array determined level lifetimes using the Doppler Shift Attenuation Method (DSAM) in ${}^{15}$O. As a reference and for testing the method, level lifetimes in ${}^{15}$N have also been determined in the same experiment. The latest compilation of ${}^{15}$N level properties dates back to 1991. The limited precision in some cases in the compilation calls for a new measurement in order to enable a comparison to the AGATA demonstrator data. The widths of several ${}^{15}$N levels have been studied with the NRF method. The solid nitrogen compounds enriched in ${}^{15}$N have been irradiated with bremsstrahlung. The $\gamma$-rays following the deexcitation of the excited nuclear levels were detected with four HPGe detectors. Integrated photon-scattering cross sections of ten levels below the proton emission threshold have been measured. Partial gamma-ray widths of ground-state transitions were deduced and compared to the literature. The photon scattering cross sections of two levels above the proton emission threshold, but still below other particle emission energies have also been measured, and proton resonance strengths and proton widths were deduced. Gamma and proton widths consistent with the literature values were obtained, but with greatly improved precision.

   nucl-exPRC(2015)·3 citations
4. 04*

   Result of the search for neutrinoless double-$\beta$ decay in ${}^{100}$Mo with the NEMO-3 experiment

   R. Arnold · C. Augier · J.D. Baker · A.S. Barabash · A. Basharina-Freshville · S. Blondel · S. Blot · M. Bongrand · V. Brudanin · J. Busto · A.J. Caffrey · S. Calvez and 78 other authors

   The NEMO-3 detector, which had been operating in the Modane Underground Laboratory from 2003 to 2010, was designed to search for neutrinoless double $\beta$ ($0\nu \beta \beta$) decay. We report final results of a search for $0\nu \beta \beta$ decays with $6.914$ kg of ${}^{100}$Mo using the entire NEMO-3 data set with a detector live time of $4.96$ yr, which corresponds to an exposure of 34.3 kg$\cdot$yr. We perform a detailed study of the expected background in the $0\nu \beta \beta$ signal region and find no evidence of $0\nu \beta \beta$ decays in the data. The level of observed background in the $0\nu \beta \beta$ signal region $[2.8-3.2]$ MeV is $0.44\pm 0.13$ counts/yr/kg, and no events are observed in the interval $[3.2-10]$ MeV. We therefore derive a lower limit on the half-life of $0\nu \beta \beta$ decays in ${}^{100}$Mo of $T_{1/2}(0\nu \beta \beta )>1.1\times 10^{24}$ yr at the $90\%$ Confidence Level, under the hypothesis of light Majorana neutrino exchange. Depending on the model used for calculating nuclear matrix elements, the limit for the effective Majorana neutrino mass lies in the range $⟨m_{\nu }⟩<0.33$--$0.62$ eV. We also report constraints on other lepton-number violating mechanisms for $0\nu \beta \beta$ decays.

   ↳ hep-exnucl-exphysics.ins-detPRD(2015)·230 citations
5. 05*

   Relativistic and Nuclear Medium Effects on the Coulomb Sum Rule

   Ian C. Cloët🇺🇸 · Wolfgang Bentz🇯🇵 · Anthony W. Thomas🇦🇺

   In light of the forthcoming high precision quasielastic electron scattering data from Jefferson Lab, it is timely for the various approaches to nuclear structure to make robust predictions for the associated response functions. With this in mind, we focus here on the longitudinal response function and the corresponding Coulomb sum rule for isospin-symmetric nuclear matter at various baryon densities. Using a quantum field-theoretic quark-level approach which preserves the symmetries of quantum chromodynamics, as well as exhibiting dynamical chiral symmetry breaking and quark confinement, we find a dramatic quenching of the Coulomb sum rule for momentum transfers $\left|\mathbf{q}\right|\gtrsim 0.5$GeV. The main driver of this effect lies in changes to the proton Dirac form factor induced by the nuclear medium. Such a dramatic quenching of the Coulomb sum rule was not seen in a recent quantum Monte Carlo calculation for carbon, suggesting that the Jefferson Lab data may well shed new light on the explicit role of QCD in nuclei.

   ↳ nucl-thhep-phnucl-exPRL(2016)·40 citations
6. 06*

   Subtraction method in the second random--phase approximation: first applications with a Skyrme energy functional

   D. Gambacurta🇮🇹 · M. Grasso🇫🇷 · J. Engel🇺🇸

   We make use of a subtraction procedure, introduced to overcome double--counting problems in beyond--mean--field theories, in the second random--phase--approximation (SRPA) for the first time. This procedure guarantees the stability of SRPA (so that all excitation energies are real). We show that the method fits perfectly into nuclear density--functional theory. We illustrate applications to the monopole and quadrupole response and to low--lying $0^{+}$ and $2^{+}$ states in the nucleus ${}^{16}$O. We show that the subtraction procedure leads to: (i) results that are weakly cutoff dependent; (ii) a considerable reduction of the SRPA downwards shift with respect to the random--phase approximation (RPA) spectra (systematically found in all previous applications). This implementation of the SRPA model will allow a reliable analysis of the effects of 2 particle--2 hole configurations ($2p2h$) on the excitation spectra of medium--mass and heavy nuclei.

   ↳ nucl-thnucl-exPRC(2015)·73 citations
7. 07*

   Combination of Measurements of Inclusive Deep Inelastic $e^{\pm }p$ Scattering Cross Sections and QCD Analysis of HERA Data

   H1 · ZEUS Collaborations

   A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current $e^{\pm }p$ scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb${}^{-1}$ and span six orders of magnitude in negative four-momentum-transfer squared, $Q^2$, and Bjorken $x$. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixed-flavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in ${\alpha }_s(M_Z)=0.1183\pm 0.0009(\exp )\pm 0.0005(model/parameterisation)\pm 0.0012{(\mathrm{hadronisation})}_{-0.0030}^{+0.0037}(\mathrm{scale})$. An extraction of $x{F}_3^{\gamma Z}$ and results on electroweak unification and scaling violations are also presented.

   ↳ hep-exhep-phnucl-exnucl-thEPJC(2015)·1156 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.