1,358 research outputs found
Gravitationally enhanced depolarization of ultracold neutrons in magnetic-field gradients
Trapped ultracold neutrons (UCN) have for many years been the mainstay of experiments to search for the electric dipole moment (EDM) of the neutron, a critical parameter in constraining scenarios of new physics beyond the Standard Model. Because their energies are so low, UCN preferentially populate the lower region of their physical enclosure, and do not sample uniformly the ambient magnetic field throughout the storage volume. This leads to a substantial increase in the rate of depolarization, as well as to shifts in the measured frequency of the stored neutrons. Consequences for EDM measurements are discussed
Determination of polarized parton distribution functions with recent data on polarization asymmetries
Global analysis has been performed within the next-to-leading order in
Quantum Chromodynamics (QCD) to determine polarized parton distributions with
new experimental data in spin asymmetries. The new data set includes JLab,
HERMES, and COMPASS measurements on spin asymmetry A_1 for the neutron and
deuteron in lepton scattering. Our new analysis also utilizes the double-spin
asymmetry for pi^0 production in polarized pp collisions, A_{LL}^{pi^0},
measured by the PHENIX collaboration. Because of these new data, uncertainties
of the polarized PDFs are reduced. In particular, the JLab, HERMES, and COMPASS
measurements are valuable for determining Delta d_v(x) at large x and Delta
qbar(x) at x~0.1. The PHENIX pi^0 data significantly reduce the uncertainty of
Delta g(x). Furthermore, we discuss a possible constraint on Delta g(x) at
large x by using the HERMES data on g_1^d in comparison with the COMPASS ones
at x~0.05.Comment: 11 pages, REVTeX, 13 eps files, Phys. Rev. D in pres
Particle Physics in the LHC era
This book gives a modern introduction to particle physics. The main mathematical tools required for the rest of the book are developed in Chapter 2. A quantitative introduction to accelerator physics is presented in Chapter 3. Chapter 4 covers detector physics, with an emphasis on fundamental physical principles. Chapter 5 covers the static quark model, with applications to light mesons and baryons as well as heavier states containing charm and beauty quarks. Chapter 6 introduces relativistic quantum mechanics and uses spinors to relate Lorentz invariance to the Dirac equation. Chapter 7 covers the basics of the electroweak theory based on broken SU(2) × U(1) symmetry. Chapter 8 reviews some of the key experiments that led to the development of the electroweak theory. Chapter 9 explains the importance of deep inelastic scattering data for providing direct evidence for the existence of quarks. It also gives a brief introduction to quantum chromodynamics (QCD). Chapter 10 considers flavour oscillations in the quark sector and then discusses the evidence for CP violation. Chapter 11 examines the theory of neutrino oscillations as well as the evidence for these oscillations. Chapter 12 gives an elementary introduction to the Higgs mechanism as well as a careful explanation of the experimental evidence for the existence of a Higgs boson. Chapter 13 looks at LHC physics and explains how searches for Beyond the Standard Model Physics are performed. It concludes with a discussion of the evidence for dark matter and dark energy
What did HERA teach us about the structure of the proton?
Starting in 2008 the H1 and ZEUS experiments have been combining their data
in order to provide the most complete and accurate set of deep-inelastic data
as the legacy of HERA. The present review presents these combinations, both
published and preliminary, and explores how they have been used to give
information on the structure of the proton. The HERAPDF parton distribution
functions (PDFs) are presented and compared with other current PDFs and with
data from the Tevatron and LHC colliders.Comment: 49 pages, 49 figures, to be published in J.Phys.
Particle Physics in the LHC era
This book gives a modern introduction to particle physics. The main mathematical tools required for the rest of the book are developed in Chapter 2. A quantitative introduction to accelerator physics is presented in Chapter 3. Chapter 4 covers detector physics, with an emphasis on fundamental physical principles. Chapter 5 covers the static quark model, with applications to light mesons and baryons as well as heavier states containing charm and beauty quarks. Chapter 6 introduces relativistic quantum mechanics and uses spinors to relate Lorentz invariance to the Dirac equation. Chapter 7 covers the basics of the electroweak theory based on broken SU(2) × U(1) symmetry. Chapter 8 reviews some of the key experiments that led to the development of the electroweak theory. Chapter 9 explains the importance of deep inelastic scattering data for providing direct evidence for the existence of quarks. It also gives a brief introduction to quantum chromodynamics (QCD). Chapter 10 considers flavour oscillations in the quark sector and then discusses the evidence for CP violation. Chapter 11 examines the theory of neutrino oscillations as well as the evidence for these oscillations. Chapter 12 gives an elementary introduction to the Higgs mechanism as well as a careful explanation of the experimental evidence for the existence of a Higgs boson. Chapter 13 looks at LHC physics and explains how searches for Beyond the Standard Model Physics are performed. It concludes with a discussion of the evidence for dark matter and dark energy
Clustering aspects in nuclear structure functions
For understanding an anomalous nuclear effect experimentally observed for the
beryllium-9 nucleus at the Thomas Jefferson National Accelerator Facility
(JLab), clustering aspects are studied in structure functions of deep inelastic
lepton-nucleus scattering by using momentum distributions calculated in
antisymmetrized (or fermionic) molecular dynamics (AMD) and also in a simple
shell model for comparison. According to the AMD, the Be-9 nucleus consists of
two alpha-like clusters with a surrounding neutron. The clustering produces
high-momentum components in nuclear wave functions, which affects nuclear
modifications of the structure functions. We investigated whether clustering
features could appear in the structure function F_2 of Be-9 along with studies
for other light nuclei. We found that nuclear modifications of F_2 are similar
in both AMD and shell models within our simple convolution description although
there are slight differences in Be-9. It indicates that the anomalous Be-9
result should be explained by a different mechanism from the nuclear binding
and Fermi motion. If nuclear-modification slopes d(F_2^A/F_2^D)/dx are shown by
the maximum local densities, the Be-9 anomaly can be explained by the AMD
picture, namely by the clustering structure, whereas it certainly cannot be
described in the simple shell model. This fact suggests that the large nuclear
modification in Be-9 should be explained by large densities in the clusters.
For example, internal nucleon structure could be modified in the high-density
clusters. The clustering aspect of nuclear structure functions is an unexplored
topic which is interesting for future investigations.Comment: 11 pages, LaTeX, 10 eps files, Physical Review C in pres
The generalised relativistic Lindhard functions
We present here analytic expressions for the generalised Lindhard function,
also referred to as Fermi Gas polarisation propagator, in a relativistic
kinematic framework and in the presence of various resonances and vertices.
Particular attention is payed to its real part, since it gives rise to
substantial difficulties in the definition of the currents entering the
dynamics.Comment: 48 pages, 2 figures, to be published in EPJ
Estimating ecological metrics for holistic conservation management in a biodiverse but information‐poor tropical region
Conservation ecologists face the dual challenge of working with difficult‐to‐study species and providing ecological metrics that support conservation management at global, regional, and local levels. We present metrics identifying distributions, site‐level and global abundance, site‐contextualized habitat requirements, and threats for seven dry forest endemic birds (two threatened, one Near Threatened) in the globally important Tumbes region of Peru. Extents of occurrence ranged from 36,000 to 152,000 km2, and while broad distributions were generally congruent, nearly half of species overlapped 150,000. Site‐level population estimates varied hugely, reflecting size of site and extreme variation in local abundances. Large tree girths and dense low cover generally promoted bird abundance, but stem density acted in opposite directions for different species, implying the need for site‐ and species‐specific habitat management. Habitat quality varied across sites, further complicating management options at the local level (e.g., reduced grazing). We highlight the suitability of our methods in providing useful conservation metrics for data‐poor regions, and demonstrate their application. Importantly, we propose key sites and priority actions for the region, including extensions of existing protected areas
A Brief Report: Community Supportiveness May Facilitate Participation of Children With Autism Spectrum Disorder in Their Community and Reduce Feelings of Isolation in Their Caregivers
Children with autism spectrum disorder (ASD) participate at lower rates in their community, and their caregivers experience higher levels of stress, in comparison to families of typically developing (TD) children. The social model of disability positions the environment as the central issue when children with disabilities are unable to participate, yet little is known about the relationship between poor community support, reduced community participation in children with ASD, and caregiver stress. This study examined caregiver perceptions of community supportiveness for the community participation of 48 children with ASD (aged 5–12 years), alongside caregiver-reported child ASD symptom severity, adaptive functioning, and caregiver stress. Community supportiveness predicted child involvement, but not attendance, when child characteristics were held constant. Caregiver perceptions of low community supportiveness significantly predicted caregiver feelings of isolation. The importance of modifying community programs to better support inclusion of children with ASD is discussed
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