276 research outputs found
Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection
The precise value of the mean neutron lifetime, τ_n, plays an important role in nuclear and particle physics and cosmology. It is used to predict the ratio of protons to helium atoms in the primordial universe and to search for physics beyond the Standard Model of particle physics. We eliminated loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls. As a result of this approach and the use of an in situ neutron detector, the lifetime reported here [877.7 ± 0.7 (stat) +0.4/–0.2 (sys) seconds] does not require corrections larger than the quoted uncertainties
Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection
The precise value of the mean neutron lifetime, τ_n, plays an important role in nuclear and particle physics and cosmology. It is used to predict the ratio of protons to helium atoms in the primordial universe and to search for physics beyond the Standard Model of particle physics. We eliminated loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls. As a result of this approach and the use of an in situ neutron detector, the lifetime reported here [877.7 ± 0.7 (stat) +0.4/–0.2 (sys) seconds] does not require corrections larger than the quoted uncertainties
A next-generation inverse-geometry spallation-driven ultracold neutron source
The physics model of a next-generation spallation-driven high-current
ultracold neutron (UCN) source capable of delivering an extracted UCN rate of
around an-order-of-magnitude higher than the strongest proposed sources, and
around three-orders-of-magnitude higher than existing sources, is presented.
This UCN-current-optimized source would dramatically improve cutting-edge UCN
measurements that are currently statistically limited. A novel "Inverse
Geometry" design is used with 40 L of superfluid He (He-II), which acts as
a converter of cold neutrons (CNs) to UCNs, cooled with state-of-the-art
sub-cooled cryogenic technology to 1.6 K. Our design is optimized for a
100 W maximum heat load constraint on the He-II and its vessel. In our
geometry, the spallation target is wrapped symmetrically around the UCN
converter to permit raster scanning the proton beam over a relatively large
volume of tungsten spallation target to reduce the demand on the cooling
requirements, which makes it reasonable to assume that water edge-cooling only
is sufficient. Our design is refined in several steps to reach
s under our other restriction of 1 MW maximum
available proton beam power. We then study effects of the He-II scattering
kernel as well as reductions in due to pressurization to reach
s. Finally, we provide a design for the UCN
extraction system that takes into account the required He-II heat transport
properties and implementation of a He-II containment foil that allows UCN
transmission. We estimate a total useful UCN current from our source of
s from a 18 cm diameter guide 5 m from the source.
Under a conservative "no return" approximation, this rate can produce an
extracted density of cm in 1000~L external experimental
volumes with a Ni (335 neV) cut-off potential.Comment: Submitted to Journal of Applied Physic
A high-field adiabatic fast passage ultracold neutron spin flipper for the UCNA experiment
The UCNA collaboration is making a precision measurement of the β asymmetry (A) in free neutron decay using polarized ultracold neutrons (UCN). A critical component of this experiment is an adiabatic fast passage neutron spin flipper capable of efficient operation in ambient magnetic fields on the order of 1 T. The requirement that it operate in a high field necessitated the construction of a free neutron spin flipper based, for the first time, on a birdcage resonator. The design, construction, and initial testing of this spin flipper prior to its use in the first measurement of A with UCN during the 2007 run cycle of the Los Alamos Neutron Science Center's 800 MeV proton accelerator is detailed. These studies determined the flipping efficiency of the device, averaged over the UCN spectrum present at the location of the spin flipper, to be ϵ(overbar) = 0.9985(4)
Measurement of the half-life of the T= mirror decay of Ne and its implication on physics beyond the standard model
The superallowed mixed mirror decay
of Ne to F is excellently suited for high precision studies of
the weak interaction. However, there is some disagreement on the value of the
half-life. In a new measurement we have determined this quantity to be
= s, which differs
from the previous world average by 3 standard deviations. The impact of this
measurement on limits for physics beyond the standard model such as the
presence of tensor currents is discussed.Comment: 5 pages, 3 figures, 1 tabl
Women candidates and councillors in Scottish local government, 1974-2012
While significant attention has been paid to the levels of representation of women in both the Westminster Parliament and the Scottish Parliament, much less considered has been given to the position within local government. This article addresses that deficit for Scotland. It shows that for twenty-five years following the reorganisation of local government in Scotland in 1974 there was a slow but relatively steady increase in the numbers of female candidates and councillors, although more recently this appears to have since plateaued somewhat, together with a similar increase in the number of women councillors taking up more senior roles in Scotland’s councils. The article analyses the representation of women in Scottish local government over the period from 1974 to 2012 against the backdrop of significant change in Scotland, including a further restructuring of local government and the introduction of the Single Transferable Vote for council elections, the creation of the Scottish Parliament, the rise of the SNP and the decline of the Conservative Party
Determination of the Axial-Vector Weak Coupling Constant with Ultracold Neutrons
A precise measurement of the neutron decay -asymmetry has been
carried out using polarized ultracold neutrons (UCN) from the pulsed spallation
UCN source at the Los Alamos Neutron Science Center (LANSCE). Combining data
obtained in 2008 and 2009, we report , from which we determine the ratio of the
axial-vector to vector weak coupling of the nucleon .Comment: 5 pages, 2 figure
Electoral bias at the 2015 general election: reducing Labour’s electoral advantage
Electoral bias results in an asymmetrical seat distribution between parties with similar vote shares. Over recent British general elections Labour held an advantage because it efficiently converted votes into seats. Following the 2015 election result this advantage has reduced considerably, principally because Labour’s vote distribution saw it accumulate more ineffective votes, particularly where electoral support was not converted into seats. By contrast, the vote distribution of the Conservative party is now superior to that of Labour because it acquired fewer wasted votes although Labour retains a modest advantage overall because it benefits from inequalities in electorate size and differences in voter turnout. Features of the 2015 election, however, raise general methodological challenges for decomposing electoral bias. The analysis, therefore, considers the effect of substituting the Liberal Democrats as the third party with the United Kingdom Independence Party. It also examines the outcome in Scotland separately from that in England and Wales. Following this analysis it becomes clear that the method for decomposing electoral bias requires clearer guidelines for its application in specific settings
Search for the Neutron Decay n X+ where X is a dark matter particle
In a recent paper submitted to Physical Review Letters, Fornal and Grinstein
have suggested that the discrepancy between two different methods of neutron
lifetime measurements, the beam and bottle methods can be explained by a
previously unobserved dark matter decay mode, n X+ where X
is a dark matter particle. We have performed a search for this decay mode over
the allowed range of energies of the monoenergetic gamma ray for X to be a dark
matter particle. We exclude the possibility of a sufficiently strong branch to
explain the lifetime discrepancy with greater than 4 sigma confidence.Comment: 6 pages 3 figure
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