206 research outputs found
Parity Violating Measurements of Neutron Densities
Parity violating electron nucleus scattering is a clean and powerful tool for
measuring the spatial distributions of neutrons in nuclei with unprecedented
accuracy. Parity violation arises from the interference of electromagnetic and
weak neutral amplitudes, and the of the Standard Model couples primarily
to neutrons at low . The data can be interpreted with as much confidence
as electromagnetic scattering. After briefly reviewing the present theoretical
and experimental knowledge of neutron densities, we discuss possible parity
violation measurements, their theoretical interpretation, and applications. The
experiments are feasible at existing facilities. We show that theoretical
corrections are either small or well understood, which makes the interpretation
clean. The quantitative relationship to atomic parity nonconservation
observables is examined, and we show that the electron scattering asymmetries
can be directly applied to atomic PNC because the observables have
approximately the same dependence on nuclear shape.Comment: 38 pages, 7 ps figures, very minor changes, submitted to Phys. Rev.
Combined effect of coherent Z exchange and the hyperfine interaction in atomic PNC
The nuclear spin-dependent parity nonconserving (PNC) interaction arising
from a combination of the hyperfine interaction and the coherent,
spin-independent, PNC interaction from Z exchange is evaluated using many-body
perturbation theory. For the 6s-7s transition in 133Cs, we obtain a result that
is about 40% smaller than that found previously by Bouchiat and Piketty [Phys.
Lett. B 269, 195 (1991)]. Applying this result to 133Cs, leads to an increase
in the experimental value of nuclear anapole moment and exacerbates differences
between constraints on PNC meson coupling constants obtained from the Cs
anapole moment and those obtained from other nuclear parity violating
experiments. Nuclear spin-dependent PNC dipole matrix elements, including
contributions from the combined weak-hyperfine interaction, are also given for
the 7s-8s transition in 211Fr and for transitions between ground-state
hyperfine levels in K, Rb, Cs, Ba+, Au, Tl, Fr, and Ra+.Comment: Revtex4 preprint 19 pages 4 table
High-precision determination of transition amplitudes of principal transitions in Cs from van der Waals coefficient C_6
A method for determination of atomic dipole matrix elements of principal
transitions from the value of dispersion coefficient C_6 of molecular
potentials correlating to two ground-state atoms is proposed. The method is
illustrated on atomic Cs using C_6 deduced from high-resolution Feshbach
spectroscopy. The following reduced matrix elements are determined < 6S_{1/2}
|| D || 6P_{1/2} > =4.5028(60) |e| a0 and
=6.3373(84) |e| a0 (a0= 0.529177 \times 10^{-8} cm.) These matrix elements are
consistent with the results of the most accurate direct lifetime measurements
and have a similar uncertainty. It is argued that the uncertainty can be
considerably reduced as the coefficient C_6 is constrained further.Comment: 4 pages; 3 fig
Reevaluation of the role of nuclear uncertainties in experiments on atomic parity violation with isotopic chains
In light of new data on neutron distributions from experiments with
antiprotonic atoms [ Trzcinska {\it et al.}, Phys. Rev. Lett. 87, 082501
(2001)], we reexamine the role of nuclear-structure uncertainties in the
interpretation of measurements of parity violation in atoms using chains of
isotopes of the same element. With these new nuclear data, we find an
improvement in the sensitivity of isotopic chain measurements to ``new
physics'' beyond the standard model. We compare possible constraints on ``new
physics'' with the most accurate to date single-isotope probe of parity
violation in the Cs atom. We conclude that presently isotopic chain experiments
employing atoms with nuclear charges Z < 50 may result in more accurate tests
of the weak interaction.Comment: 6 pages, 1 fig., submitted to Phys. Rev.
Nature of the quantum phase transitions in the two-dimensional hardcore boson model
We use two Quantum Monte Carlo algorithms to map out the phase diagram of the
two-dimensional hardcore boson Hubbard model with near () and next near
() neighbor repulsion. At half filling we find three phases: Superfluid
(SF), checkerboard solid and striped solid depending on the relative values of
, and the kinetic energy. Doping away from half filling, the
checkerboard solid undergoes phase separation: The superfluid and solid phases
co-exist but not as a single thermodynamic phase. As a function of doping, the
transition from the checkerboard solid is therefore first order. In contrast,
doping the striped solid away from half filling instead produces a striped
supersolid phase: Co-existence of density order with superfluidity as a single
phase. One surprising result is that the entire line of transitions between the
SF and checkerboard solid phases at half filling appears to exhibit dynamical
O(3) symmetry restoration. The transitions appear to be in the same
universality class as the special Heisenberg point even though this symmetry is
explicitly broken by the interaction.Comment: 10 pages, 14 eps figures, include
The Weak Charge of the Proton and New Physics
We address the physics implications of a precision determination of the weak
charge of the proton, QWP, from a parity violating elastic electron proton
scattering experiment to be performed at the Jefferson Laboratory. We present
the Standard Model (SM) expression for QWP including one-loop radiative
corrections, and discuss in detail the theoretical uncertainties and missing
higher order QCD corrections. Owing to a fortuitous cancellation, the value of
QWP is suppressed in the SM, making it a unique place to look for physics
beyond the SM. Examples include extra neutral gauge bosons, supersymmetry, and
leptoquarks. We argue that a QWP measurement will provide an important
complement to both high energy collider experiments and other low energy
electroweak measurements. The anticipated experimental precision requires the
knowledge of the order alpha_s corrections to the pure electroweak box
contributions. We compute these contributions for QWP, as well as for the weak
charges of heavy elements as determined from atomic parity violation.Comment: 22 pages of LaTeX, 5 figure
We All Know How, Donât We? On the Role of Scrum in IT-Offshoring
Part 2: Creating Value through Software DevelopmentInternational audienceOffshoring in the IT-industry involves dual interactions between a mother company and an external supplier, often viewed with an implicit perspective from the mother company. This article review general off shoring and IT offshoring literature, focusing on the proliferation of a globally available set of routines; Scrum and Agile. Two cases are studied; a small company and short process and a large mother company with a long process. The interactions of the set ups shows that global concepts like Scrum and Agile are far from a common platform. The âwell knownâ concepts are locally shaped and the enterprises have mixed experiences
Fine-mapping host genetic variation underlying outcomes to Mycobacterium bovis infection in dairy cows
Abstract Background Susceptibility to Mycobacterium bovis infection in cattle is governed in part by host genetics. However, cattle diagnosed as infected with M. bovis display varying signs of pathology. The variation in host response to infection could represent a continuum since time of exposure or distinct outcomes due to differing pathogen handling. The relationships between host genetics and variation in host response and pathological sequelae following M. bovis infection were explored by genotyping 1966 Holstein-Friesian dairy cows at 538,231 SNPs with three distinct phenotypes. These were: single intradermal cervical comparative tuberculin (SICCT) test positives with visible lesions (VLs), SICCT-positives with undetected visible lesions (NVLs) and matched controls SICCT-negative on multiple occasions. Results Regional heritability mapping identified three loci associated with the NVL phenotype on chromosomes 17, 22 and 23, distinct to the region on chromosome 13 associated with the VL phenotype. The region on chromosome 23 was at genome-wide significance and candidate genes overlapping the mapped window included members of the bovine leukocyte antigen class IIb region, a complex known for its role in immunity and disease resistance. Chromosome heritability analysis attributed variance to six and thirteen chromosomes for the VL and NVL phenotypes, respectively, and four of these chromosomes were found to explain a proportion of the phenotypic variation for both the VL and NVL phenotype. By grouping the M. bovis outcomes (VLs and NVLs) variance was attributed to nine chromosomes. When contrasting the two M. bovis infection outcomes (VLs vs NVLs) nine chromosomes were found to harbour heritable variation. Regardless of the case phenotype under investigation, chromosome heritability did not exceed 8% indicating that the genetic control of bTB resistance consists of variants of small to moderate effect situated across many chromosomes of the bovine genome. Conclusions These findings suggest the host genetics of M. bovis infection outcomes is governed by distinct and overlapping genetic variants. Thus, variation in the pathology of M. bovis infected cattle may be partly genetically determined and indicative of different host responses or pathogen handling. There may be at least three distinct outcomes following M. bovis exposure in dairy cattle: resistance to infection, infection resulting in pathology or no detectable pathology
Study of Z â llÎł decays at âs = 8 TeV with the ATLAS detector
This paper presents a study of Z â llÎł decays
with the ATLAS detector at the Large Hadron Collider. The
analysis uses a protonâproton data sample corresponding to
an integrated luminosity of 20.2 fbâ1 collected at a centre-ofmass energy âs = 8 TeV. Integrated fiducial cross-sections
together with normalised differential fiducial cross-sections,
sensitive to the kinematics of final-state QED radiation, are
obtained. The results are found to be in agreement with stateof-the-art predictions for final-state QED radiation. First
measurements of Z â llÎł Îł decays are also reported
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