560 research outputs found
CMB Constraints on Primordial non-Gaussianity from the Bispectrum (f_{NL}) and Trispectrum (g_{NL} and \tau_{NL}) and a New Consistency Test of Single-Field Inflation
We outline the expected constraints on non-Gaussianity from the cosmic
microwave background (CMB) with current and future experiments, focusing on
both the third (f_{NL}) and fourth-order (g_{NL} and \tau_{NL}) amplitudes of
the local configuration or non-Gaussianity. The experimental focus is the
skewness (two-to-one) and kurtosis (two-to-two and three-to-one) power spectra
from weighted maps. In adition to a measurement of \tau_{NL} and g_{NL} with
WMAP 5-year data, our study provides the first forecasts for future constraints
on g_{NL}. We describe how these statistics can be corrected for the mask and
cut-sky through a window function, bypassing the need to compute linear terms
that were introduced for the previous-generation non-Gaussianity statistics,
such as the skewness estimator. We discus the ratio A_{NL} =
\tau_{NL}/(6f_{NL}/5)^2 as an additional test of single-field inflationary
models and discuss the physical significance of each statistic. Using these
estimators with WMAP 5-Year V+W-band data out to l_{max}=600 we constrain the
cubic order non-Gaussianity parameters \tau_{NL}, and g_{NL} and find -7.4 <
g_{NL}/10^5 < 8.2 and -0.6 < \tau_{NL}/10^4 < 3.3 improving the previous
COBE-based limit on \tau_{NL} < 10^8 nearly four orders of magnitude with WMAP.Comment: 15 pages. 14 figure
Exploiting neutron-rich radioactive ion beams to constrain the symmetry energy
The Modular Neutron Array (MoNA) and 4 Tm Sweeper magnet were used to measure
the free neutrons and heavy charged particles from the radioactive ion beam
induced 32Mg + 9Be reaction. The fragmentation reaction was simulated with the
Constrained Molecular Dynamics model(CoMD), which demonstrated that the
of the heavy fragments and free neutron multiplicities were observables
sensitive to the density dependence of the symmetry energy at sub-saturation
densities. Through comparison of these simulations with the experimental data
constraints on the density dependence of the symmetry energy were extracted.
The advantage of radioactive ion beams as a probe of the symmetry energy is
demonstrated through examination of CoMD calculations for stable and
radioactive beam induced reactions
Search for unbound 15Be states in the 3n+12Be channel
15Be is expected to have low-lying 3/2+ and 5/2+ states. A first search did
not observe the 3/2+ [A. Spyrou et al., Phys. Rev. C 84, 044309 (2011)],
however, a resonance in 15Be was populated in a second attempt and determined
to be unbound with respect to 14Be by 1.8(1) MeV with a tentative spin-parity
assignment of 5/2+ [J. Snyder et al., Phys. Rev. C 88, 031303(R) (2013)].
Search for the predicted 15Be 3/2+ state in the three-neutron decay channel. A
two-proton removal reaction from a 55 MeV/u 17C beam was used to populate
neutron-unbound states in 15Be. The two-, three-, and four-body decay energies
of the 12Be + neutron(s) detected in coincidence were reconstructed using
invariant mass spectroscopy. Monte Carlo simulations were performed to extract
the resonance and decay properties from the observed spectra. The low-energy
regions of the decay energy spectra can be described with the first excited
unbound state of 14Be (E_x=1.54 MeV, E_r=0.28 MeV). Including a state in 15Be
that decays through the first excited 14Be state slightly improves the fit at
higher energies though the cross section is small. A 15Be component is not
needed to describe the data. If the 3/2+ state in 15Be is populated, the decay
by three-neutron emission through 14Be is weak, less than or equal to 11% up to
4 MeV. In the best fit, 15Be is unbound with respect to 12Be by 1.4 MeV
(unbound with respect to $14Be by 2.66 MeV) with a strength of 7%.Comment: 6 pages, 5 figures, accepted in Physical Review
Three-body correlations in the ground-state decay of 26O
Background: Theoretical calculations have shown that the energy and angular
correlations in the three-body decay of the two-neutron unbound O26 can provide
information on the ground-state wave function, which has been predicted to have
a dineutron configuration and 2n halo structure.
Purpose: To use the experimentally measured three-body correlations to gain
insight into the properties of O26, including the decay mechanism and
ground-state resonance energy.
Method: O26 was produced in a one-proton knockout reaction from F27 and the
O24+n+n decay products were measured using the MoNA-Sweeper setup. The
three-body correlations from the O26 ground-state resonance decay were
extracted. The experimental results were compared to Monte Carlo simulations in
which the resonance energy and decay mechanism were varied.
Results: The measured three-body correlations were well reproduced by the
Monte Carlo simulations but were not sensitive to the decay mechanism due to
the experimental resolutions. However, the three-body correlations were found
to be sensitive to the resonance energy of O26. A 1{\sigma} upper limit of 53
keV was extracted for the ground-state resonance energy of O26.
Conclusions: Future attempts to measure the three-body correlations from the
ground-state decay of O26 will be very challenging due to the need for a
precise measurement of the O24 momentum at the reaction point in the target
First Observation of 15Be
The neutron-unbound nucleus 15Be was observed for the first time. It was populated using neutron transfer from a deuterated polyethylene target with a 59 MeV/u 14Be beam. Neutrons were measured in coincidence with outgoing 14Be particles and the reconstructed decay energy spectrum exhibits a resonance at 1.8(1) MeV. This corresponds to 15Be being unbound by 0.45 MeV more then 16Be thus significantly hindering the sequential two-neutron decay of 16Be to 14Be through this state
Exploring the neutron dripline two neutrons at a time: The first observations of the 26O and 16Be ground state resonances
The two-neutron unbound ground state resonances of O and Be
were populated using one-proton knockout reactions from F and B
beams. A coincidence measurement of 3-body system (fragment + n + n) allowed
for the decay energy of the unbound nuclei to be reconstructed. A low energy
resonance, 200 keV, was observed for the first time in the O + n + n
system and assigned to the ground state of O. The Be ground state
resonance was observed at 1.35 MeV. The 3-body correlations of the Be +
n + n system were compared to simulations of a phase-space, sequential, and
dineutron decay. The strong correlations in the n-n system from the
experimental data could only be reproduced by the dineutron decay simulation
providing the first evidence for a dineutron-like decay.Comment: Invited Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
First observation of Li ground state
The ground state of neutron-rich unbound Li was observed for the first
time in a one-proton removal reaction from Be at a beam energy of 53.6
MeV/u. The Li ground state was reconstructed from Li and two
neutrons giving a resonance energy of 120 keV. All events
involving single and double neutron interactions in the Modular Neutron Array
(MoNA) were analyzed, simulated, and fitted self-consistently. The three-body
(Li+) correlations within Jacobi coordinates showed strong
dineutron characteristics. The decay energy spectrum of the intermediate
Li system (Li+) was described with an s-wave scattering length
of greater than -4 fm, which is a smaller absolute value than reported in a
previous measurement.Comment: Accepted for publication in Phys. Rev. C as a Rapid Communicatio
Spectroscopy of neutron-unbound F
The ground state of F has been observed as an unbound resonance
keV above the ground state of F. Comparison of this
result with USDA/USDB shell model predictions leads to the conclusion that the
F ground state is primarily dominated by -shell configurations. Here
we present a detailed report on the experiment in which the ground state
resonance of F was first observed. Additionally, we report the first
observation of a neutron-unbound excited state in F at an excitation
energy of keV.Comment: 10 pages, 11 figures, Accepted for publication in Phys. Rev.
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