119237581
Determination of astrophysical 12N(p,g)13O reaction rate from the 2H(12N, 13O)n reaction and its astrophysical implications
The evolution of massive stars with very low-metallicities depends critically on the amount of CNO nuclides which they produce. The $^{12}$N($p$,\,$\gamma$)$^{13}$O reaction is an important branching point in the rap-processes, which are believed to be alternative paths to the slow 3$\alpha$ process for producing CNO seed nuclei and thus could change the fate of massive stars. In the present work, the angular distribution of the $^2$H($^{12}$N,\,$^{13}$O)$n$ proton transfer reaction at $E_{\mathrm{c.m.}}$ = 8.4 MeV has been measured for the first time. Based on the Johnson-Soper approach, the square of the asymptotic normalization coefficient (ANC) for the virtual decay of $^{13}$O$_\mathrm{g.s.}$ $\rightarrow$ $^{12}$N + $p$ was extracted to be 3.92 $\pm$ 1.47 fm$^{-1}$ from the measured angular distribution and utilized to compute the direct component in the $^{12}$N($p$,\,$\gamma$)$^{13}$O reaction. The direct astrophysical S-factor at zero energy was then found to be 0.39 $\pm$ 0.15 keV b. By considering the direct capture into the ground state of $^{13}$O, the resonant capture via the first excited state of $^{13}$O and their interference, we determined the total astrophysical S-factors and rates of the $^{12}$N($p$,\,$\gamma$)$^{13}$O reaction. The new rate is two orders of magnitude slower than that from the REACLIB compilation. Our reaction network calculations with the present rate imply that $^{12}$N($p,\,\gamma$)$^{13}$O will only compete successfully with the $\beta^+$ decay of $^{12}$N at higher ($\sim$two orders of magnitude) densities than initially predicted.
119276160
New determination of the 13C(a, n)16O reaction rate and its influence on the s-process nucleosynthesis in AGB stars
We present a new measurement of the $\alpha$-spectroscopic factor ($S_\alpha$) and the asymptotic normalization coefficient (ANC) for the 6.356 MeV 1/2$^+$ subthreshold state of $^{17}$O through the $^{13}$C($^{11}$B, $^{7}$Li)$^{17}$O transfer reaction and we determine the $\alpha$-width of this state. This is believed to have a strong effect on the rate of the $^{13}$C($\alpha$, $n$)$^{16}$O reaction, the main neutron source for {\it slow} neutron captures (the $s$-process) in asymptotic giant branch (AGB) stars. Based on the new width we derive the astrophysical S-factor and the stellar rate of the $^{13}$C($\alpha$, $n$)$^{16}$O reaction. At a temperature of 100 MK our rate is roughly two times larger than that by \citet{cau88} and two times smaller than that recommended by the NACRE compilation. We use the new rate and different rates available in the literature as input in simulations of AGB stars to study their influence on the abundances of selected $s$-process elements and isotopic ratios. There are no changes in the final results using the different rates for the $^{13}$C($\alpha$, $n$)$^{16}$O reaction when the $^{13}$C burns completely in radiative conditions. When the $^{13}$C burns in convective conditions, as in stars of initial mass lower than $\sim$2 $M_\sun$ and in post-AGB stars, some changes are to be expected, e.g., of up to 25% for Pb in our models. These variations will have to be carefully analyzed when more accurate stellar mixing models and more precise observational constraints are available.
126327724
New determination of the proton spectroscopic factor in Be-9 from the C-13 (Be-9, Li-8) N-14 angular distribution
119976206
Current progress of nuclear astrophysical reaction and decay study at CIAE
Presented here was current progress of the study of nuclear astrophysical reaction and decay at CIAE. We studied astrophysical 12N(p,γ)13O reaction through the measurement of the 12N(d,n)13O angular distribution in inverse kinematics. Our result is in agreement with that from the 14N(12N,13O)13C reaction and two shell model calculations. We also measured the angular distributions of single neutron transfer reaction of 7Li(6Li,7Li)6Li, and derived the reaction cross section for 6Li(n,γ)7Li by using the present spectroscopic factor. The astrophysical reaction rate is found to be higher by a factor of 1.7 than the value adopted in previous reaction network calculations. In addition, half-life of 147Sm in metal samarium and Sm2O3 was measured. No significant change has been observed within the experimental uncertainty.
18591049
Probing the evolution of the dark energy density with future supernova surveys
The time dependence of the dark energy density can be an important clue to the nature of dark energy in the universe. We show that future supernova data from dedicated telescopes (such as SNAP), when combined with data of nearby supernovae, can be used to determine how the dark energy density ρX(z) depends on redshift, if ρX(z )i s not too closeto a constant. For quantitative comparison, we have done an extensive study of a number of dark energy models. Based on these models we have simulated data sets in order to show that we can indeed reconstruct the correct sign of the time dependence of the dark energy density, outside of a degeneracy region centred on 1 + w0 �− w1zmax/ 3( where zmax is the maximum redshift of the survey; for example, zmax =1 . 7f or SNAP).
22730544
Revised rates for the stellar triple-alpha process from measurement of 12C nuclear resonances.
In the centres of stars where the temperature is high enough, three alpha-particles (helium nuclei) are able to combine to form 12C because of a resonant reaction leading to a nuclear excited state. (Stars with masses greater than approximately 0.5 times that of the Sun will at some point in their lives have a central temperature high enough for this reaction to proceed.) Although the reaction rate is of critical significance for determining elemental abundances in the Universe, and for determining the size of the iron core of a star just before it goes supernova, it has hitherto been insufficiently determined. Here we report a measurement of the inverse process, where a 12C nucleus decays to three alpha-particles. We find a dominant resonance at an energy of approximately 11 MeV, but do not confirm the presence of a resonance at 9.1 MeV (ref. 3). We show that interference between two resonances has important effects on our measured spectrum. Using these data, we calculate the triple-alpha rate for temperatures from 10(7) K to 10(10) K and find significant deviations from the standard rates. Our rate below approximately 5 x 10(7) K is higher than the previous standard, implying that the critical amounts of carbon that catalysed hydrogen burning in the first stars are produced twice as fast as previously believed. At temperatures above 10(9) K, our rate is much less, which modifies predicted nucleosynthesis in supernovae.
123359096
Charge Independent(CI) and Charge Dependent(CD) correlations as a function of Centrality formed from Delta phi imum Delta eta Charged Pair Correlations in Minimum Bias Au+Au Collisions at s(NN)**(1/2) = 200-GeV
16580300
Observation of electron-antineutrino disappearance at Daya Bay.
The Daya Bay Reactor Neutrino Experiment has measured a nonzero value for the neutrino mixing angle θ(13) with a significance of 5.2 standard deviations. Antineutrinos from six 2.9 GWth reactors were detected in six antineutrino detectors deployed in two near (flux-weighted baseline 470 m and 576 m) and one far (1648 m) underground experimental halls. With a 43,000 ton-GWth-day live-time exposure in 55 days, 10,416 (80,376) electron-antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to expected number of antineutrinos at the far hall is R=0.940±0.011(stat.)±0.004(syst.). A rate-only analysis finds sin(2)2θ(13)=0.092±0.016(stat.)±0.005(syst.) in a three-neutrino framework.
120279709
Level-0 trigger algorithms for the ALICE PHOS detector
Abstract The PHOS level-0 trigger provides a minimum bias trigger for p–p collisions and information for a level-1 trigger at both p–p and Pb–Pb collisions. There are two level-0 trigger generating algorithms under consideration: the Direct Comparison algorithm and the Weighted Sum algorithm. In order to study trigger algorithms via simulation, a simplified equivalent model is extracted from the trigger electronics to derive the waveform function of the Analog-or signal as input to the trigger algorithms. Simulations shown that the Weighted Sum algorithm can achieve higher trigger efficiency and provide more precise single channel energy information than the direct compare algorithm. An energy resolution of 9.75 MeV can be achieved with the Weighted Sum algorithm at a sampling rate of 40 Msps (mega samples per second) at 1 GeV. The timing performance at a sampling rate of 40 Msps with the Weighted Sum algorithm is better than that at a sampling rate of 20 Msps with both algorithms. The level-0 trigger can be delivered to ALICE CTP within 800 ns with a timing uncertainty of 2 LHC bunch crossing cycles.