124 research outputs found
Exploring the âmiddle groundâ between state and market: the example of China
Studies of housing systems lying in the âmiddle groundâ between state and market are subject to three important shortcomings. First, the widely used Esping-Andersen (EA) approach assesses only a subset of the key housing outcomes and may be less helpful for describing changes in housing policy regimes. Second, there is too much emphasis on tenure transitions, and an assumed close correspondence between tenure labels and effective system functioning may not be valid. Third, due attention has not been given to the spatial dimensions in which housing systems operate, in particular when housing policies have a significant devolved or localised emphasis. Updating EAâs framework, we suggest a preliminary list of housing system indicators in order to capture the nature of the housing systems being developed and devolved. We verified the applicability of this indicator system with the case of China. This illustrates clearly the need for a more nuanced and systematic basis for categorising differences and changes in welfare and housing policies
A new direct detection electron scattering experiment to search for the X17 particle
A new electron scattering experiment (E12-21-003) to verify and understand
the nature of hidden sector particles, with particular emphasis on the
so-called X17 particle, has been approved at Jefferson Lab. The search for
these particles is motivated by new hidden sector models introduced to account
for a variety of experimental and observational puzzles: excess in
pairs observed in multiple nuclear transitions, the 4.2 disagreement
between experiments and the standard model prediction for the muon anomalous
magnetic moment, and the small-scale structure puzzle in cosmological
simulations. The aforementioned X17 particle has been hypothesized to account
for the excess in pairs observed from the Be M1, He M0, and,
most recently, C E1 nuclear transitions to their ground states observed
by the ATOMKI group. This experiment will use a high resolution electromagnetic
calorimeter to search for or set new limits on the production rate of the X17
and other hidden sector particles in the MeV mass range via their
decay (or decay with limited tracking). In these
models, the MeV mass range is particularly well-motivated and the
lower part of this range still remains unexplored. Our proposed direct
detection experiment will use a magnetic-spectrometer-free setup (the PRad
apparatus) to detect all three final state particles in the visible decay of a
hidden sector particle for an effective control of the background and will
cover the proposed mass range in a single setting. The use of the
well-demonstrated PRad setup allows for an essentially ready-to-run and
uniquely cost-effective search for hidden sector particles in the MeV
mass range with a sensitivity of 8.910 - 5.810 to
, the square of the kinetic mixing interaction constant between
hidden and visible sectors.Comment: 6 pages, 7 figures. arXiv admin note: substantial text overlap with
arXiv:2108.1327
Beam Charge Asymmetries for Deeply Virtual Compton Scattering on the Proton at CLAS12
The parameterization of the nucleon structure through Generalized Parton
Distributions (GPDs) shed a new light on the nucleon internal dynamics. For its
direct interpretation, Deeply Virtual Compton Scattering (DVCS) is the golden
channel for GPDs investigation. The DVCS process interferes with the
Bethe-Heitler (BH) mechanism to constitute the leading order amplitude of the
process. The study of the reaction with polarized
positron and electron beams gives a complete set of unique observables to
unravel the different contributions to the cross section. This
separates the different reaction amplitudes, providing a direct access to their
real and imaginary parts which procures crucial constraints on the model
dependences and associated systematic uncertainties on GPDs extraction. The
real part of the BH-DVCS interference amplitude is particularly sensitive to
the -term which parameterizes the Gravitational Form Factors of the nucleon.
The separation of the imaginary parts of the interference and DVCS amplitudes
provides insights on possible higher-twist effects. We propose to measure the
unpolarized and polarized Beam Charge Asymmetries (BCAs) of the process on an unpolarized hydrogen target with {\tt
CLAS12}, using polarized positron and electron beams at 10.6~GeV. The azimuthal
and -dependences of the unpolarized and polarized BCAs will be measured over
a large phase space using a 100 day run with a luminosity of
0.66cms.Comment: Proposal to the Jefferson Lab Program Advisory Committee (PAC51
First Measurement of Electroproduction off Nuclei in the Current and Target Fragmentation Regions
We report results of hyperon production in semi-inclusive
deep-inelastic scattering off deuterium, carbon, iron, and lead targets
obtained with the CLAS detector and the Continuous Electron Beam Accelerator
Facility 5.014~GeV electron beam. These results represent the first
measurements of the multiplicity ratio and transverse momentum
broadening as a function of the energy fraction~() in the current and target
fragmentation regions. The multiplicity ratio exhibits a strong suppression at
high~~and~an enhancement at~low~. The measured transverse momentum
broadening is an order of magnitude greater than that seen for light mesons.
This indicates that the propagating entity interacts very strongly with the
nuclear medium, which suggests that propagation of diquark configurations in
the nuclear medium takes place at least part of the time, even at high~. The
trends of these results are qualitatively described by the Giessen
Boltzmann-Uehling-Uhlenbeck transport model, particularly for the multiplicity
ratios. These observations will potentially open a new era of studies of the
structure of the nucleon as well as of strange baryons.Comment: 14 pages, 6 figure
Observation of azimuth-dependent suppression of hadron pairs in electron scattering off nuclei
We present the first measurement of di-hadron angular correlations in
electron-nucleus scattering. The data were taken with the CLAS detector and a
5.0 GeV electron beam incident on deuterium, carbon, iron, and lead targets.
Relative to deuterium, the nuclear yields of charged-pion pairs show a strong
suppression for azimuthally opposite pairs, no suppression for azimuthally
nearby pairs, and an enhancement of pairs with large invariant mass. These
effects grow with increased nuclear size. The data are qualitatively described
by the GiBUU model, which suggests that hadrons form near the nuclear surface
and undergo multiple-scattering in nuclei. These results show that angular
correlation studies can open a new way to elucidate how hadrons form and
interact inside nucleiComment: 6 pages, 4 figure
First Measurement of Hard Exclusive Ï- Î++ Electroproduction Beam-Spin Asymmetries off the Proton
The polarized cross-section ratio ÏLTâČ/Ï0 from hard exclusive Ï-Î++ electroproduction off an unpolarized hydrogen target has been extracted based on beam-spin asymmetry measurements using a 10.2 GeV/10.6 GeV incident electron beam and the CLAS12 spectrometer at Jefferson Lab. The study, which provides the first observation of this channel in the deep-inelastic regime, focuses on very forward-pion kinematics in the valence regime, and photon virtualities ranging from 1.5 GeV2 up to 7 GeV2. The reaction provides a novel access to the d-quark content of the nucleon and to pâÎ++ transition generalized parton distributions. A comparison to existing results for hard exclusive Ï+n and Ï0p electroproduction is provided, which shows a clear impact of the excitation mechanism, encoded in transition generalized parton distributions, on the asymmetry
Observation of Azimuth-Dependent Suppression of Hadron Pairs in Electron Scattering Off Nuclei
We present the first measurement of dihadron angular correlations in electron-nucleus scattering. The data were taken with the CLAS detector and a 5.0 GeV electron beam incident on deuterium, carbon, iron, and lead targets. Relative to deuterium, the nuclear yields of charged-pion pairs show a strong suppression for azimuthally opposite pairs, no suppression for azimuthally nearby pairs, and an enhancement of pairs with large invariant mass. These effects grow with increased nuclear size. The data are qualitatively described by the gibuu model, which suggests that hadrons form near the nuclear surface and undergo multiple scattering in nuclei. These results show that angular correlation studies can open a new way to elucidate how hadrons form and interact inside nuclei
Measurement of the helicity asymmetry E for the Îłâ pâ â pÏ reaction in the resonance region: The CLAS Collaboration
The double-spin-polarization observable E for Îłâ pâ â pÏ has been measured with the CEBAF Large Acceptance Spectrometer (CLAS) at photon beam energies EÎł from 0.367 to 2.173GeV (corresponding to center-of-mass energies from 1.240 to 2.200GeV) for pion center-of-mass angles, cosΞÏ0c.m. , between - 0.86 and 0.82. These new CLAS measurements cover a broader energy range and have smaller uncertainties compared to previous CBELSA data and provide an important independent check on systematics. These measurements are compared to predictions as well as new global fits from The George Washington University, Mainz, and Bonn-Gatchina groups. Their inclusion in multipole analyses will allow us to refine our understanding of the single-pion production contribution to the Gerasimov-Drell-Hearn sum rule and improve the determination of resonance properties, which will be presented in a future publication
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