1,034 research outputs found
Measurement of the analyzing power of proton-carbon elastic scattering in the CNI region at RHIC
The single transverse spin asymmetry, A_N, of the p-carbon elastic scattering
process in the Coulomb Nuclear Interference (CNI) region was measured using an
ultra thin carbon target and polarized proton beam in the Relativistic Heavy
Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). In 2004, data were
collected to calibrate the p-carbon process at two RHIC energies (24 GeV, 100
GeV). A_N was obtained as a function of momentum transfer -t. The results were
fit with theoretical models which allow us to assess the contribution from a
hadronic spin flip amplitude.Comment: Contribution to the proceedings of the 16th International Spin
Physics Symposium, spin2004 (Trieste
Measurement of the analyzing power in pp elastic scattering in the peak CNI region at RHIC
We report the first measurements of the A_N absolute value and shape in the
-t range from 0.0015 to 0.010GeV/c^2 with a precision better than 0.005 for
each A_N data point using a polarized atomic hydrogen gas jet target and the
100 GeV RHIC proton beam.Comment: 4 pages, 5 figure
Measurement of quasi-elastic 12C(p,2p) scattering at high momentum transfer
We measured the high-momentum quasi-elastic 12C(p,2p) reaction (at center of
mass angle near 90 degrees) for 6 and 7.5 GeV/c incident protons. The
three-momentum components of both final state protons were measured and the
missing energy and momentum of the target proton in the nucleus were
determined.
The validity of the quasi-elastic picture was verified up to Fermi momenta of
about 450 MeV/c, where it might be questionable. Transverse and longitudinal
Fermi momentum distributions of the target proton were measured and compared to
independent particle models which do not reproduce the large momentum tails. We
also observed that the transverse Fermi distribution gets wider as the
longitudinal component increases in the beam direction, in contrast to a simple
Fermi gas model.Comment: 4 pages including 3 figure
RHIC polarimetry
Polarimeters were developed to measure the polarization of the proton beam at RHIC in relative scale through the asymmetry measurement of the elastic proton-carbon scattering. Recoil carbon ions with kinetic energy of 400 ≤ E ≤ 900 keV were detected by silicon strip detectors installed at 90° with respect to the beam. The absolute polarization is given by normalizing against another polarimeter implemented at RHIC, namely a polarized hydrogen gas jet polarimeter. In this report, the details of polarization measurements, data analysis, and systematic uncertainties are discussed based on the data taken during ∫s = 200 GeV operation of Run 05 at RHIC
Oribatid mites show how climate and latitudinal gradients in organic matter can drive large-scale biodiversity patterns of soil communities
Aim: The factors determining spatial distributions and diversity of terrestrial invertebrates are typically investigated at small scales. Large‐scale studies are lacking for soil animals, which control microbial communities and represent one of the most diverse yet poorly known animal assemblages. Here, we analyzed a major group (Oribatida) to test whether belowground macroecological patterns can be predicted by climatic variables, vegetation and large‐scale variation in key soil properties.
Location: We modelled the multivariate distribution of more than 100 species using biodiversity data collected across Great Britain in the framework of the Countryside Survey (http://www.countrysidesurvey.org.uk).
Methods: We analyzed species‐level data from 582 samples collected across 162 hectads (10 × 10 km) covering the largest possible range of vegetation types, soil properties and climatic conditions within GB. We created the first large‐scale maps of soil animal diversity metrics at the GB scale, including novel estimates of metrics of phylogenetic diversity (PD). Using structural equation modelling, we quantified the direct and indirect effects of location (latitude, longitude), plant community structure and abiotic factors such as precipitation on species composition, richness and PD.
Results: We found that variation in species composition follows a latitudinal gradient with diversity generally increasing northward. The latitudinal variation in species composition drives PD via changes in both species richness and phylogenetic distance between species. This gradient is mostly determined by latitudinal variation in precipitation and organic matter, which were very good predictors of species composition. Precipitation and organic matter were, however, relatively weak while statistically significant predictors of diversity metrics.
Conclusions: Past studies have emphasized the unpredictability of species distributions and variation in species composition in hyper diverse soil animal communities. However, past studies were conducted at small scales, where stochastic factors may weaken the signal of deterministic factors. Oribatid mites in our study show for the first time that the large scale latitudinal gradients in climate and organic matter predict not only variation in species composition but also taxonomic and PD of soil animal communities
IMF dependence of Saturn's auroras: modelling study of HST and Cassini data from 12–15 February 2008
To gain better understanding of auroral processes in
Saturn's magnetosphere, we compare ultraviolet (UV) auroral images obtained
by the Hubble Space Telescope (HST) with the position of the open-closed
field line boundary in the ionosphere calculated using a magnetic field
model that employs Cassini measurements of the interplanetary magnetic field
(IMF) as input. Following earlier related studies of pre-orbit insertion
data from January 2004 when Cassini was located ~ 1300 Saturn radii
away from the planet, here we investigate the interval 12–15 February
2008, when UV images of Saturn's southern dayside aurora were obtained by
the HST while the Cassini spacecraft measured the IMF in the solar wind just
upstream of the dayside bow shock. This configuration thus provides an
opportunity, unique to date, to determine the IMF impinging on Saturn's
magnetosphere during imaging observations, without the need to take account
of extended and uncertain interplanetary propagation delays. The paraboloid
model of Saturn's magnetosphere is then employed to calculate the
magnetospheric magnetic field structure and ionospheric open-closed field
line boundary for averaged IMF vectors that correspond, with appropriate
response delays, to four HST images. We show that the IMF-dependent open
field region calculated from the model agrees reasonably well with the area
lying poleward of the UV emissions, thus supporting the view that the
poleward boundary of Saturn's auroral oval in the dayside ionosphere lies
adjacent to the open-closed field line boundary
Cassini observations of the variation of Saturn's ring current parameters with system size
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