3,362 research outputs found
Generalized parton distributions and rapidity gap survival in exclusive diffractive pp scattering
We propose a new approach to the problem of rapidity gap survival (RGS) in
the production of high-mass systems (H = dijet, heavy quarkonium, Higgs boson)
in double-gap exclusive diffractive pp scattering, pp -> p + (gap) + H + (gap)
+ p. It is based on the idea that hard and soft interactions proceed over
widely different time- and distance scales and are thus approximately
independent. The high-mass system is produced in a hard scattering process with
exchange of two gluons between the protons. Its amplitude is calculable in
terms of the gluon generalized parton distributions (GPDs) in the protons,
which can be measured in J/psi production in exclusive ep scattering. The hard
scattering process is modified by soft spectator interactions, which we
calculate in a model-independent way in terms of the pp elastic scattering
amplitude. Contributions from inelastic intermediate states are suppressed. A
simple geometric picture of the interplay of hard and soft interactions in
diffraction is obtained. The onset of the black-disk limit in pp scattering at
TeV energies strongly suppresses diffraction at small impact parameters and is
the main factor in determining the RGS probability. Correlations between hard
and soft interactions (e.g. due to scattering from the long-range pion field of
the proton, or due to possible short-range transverse correlations between
partons) further decrease the RGS probability. We also investigate the
dependence of the diffractive cross section on the transverse momenta of the
final-state protons ("diffraction pattern"). By measuring this dependence one
can perform detailed tests of the interplay of hard and soft interactions, and
even extract information about the gluon GPD in the proton. Such studies appear
to be feasible with the planned forward detectors at the LHC.Comment: 26 pages, 17 figures, uses revtex
Relationship between particulate matter and childhood asthma – basis of a future warning system for central Phoenix
Statistically significant correlations between increase of asthma attacks in children and elevated concentrations of particulate matter of diameter 10 microns and less (PM<sub>10</sub>) were determined for metropolitan Phoenix, Arizona. Interpolated concentrations from a five-site network provided spatial distribution of PM<sub>10</sub> that was mapped onto census tracts with population health records. The case-crossover statistical method was applied to determine the relationship between PM<sub>10</sub> concentration and asthma attacks. For children ages 5â17, a significant relationship was discovered between the two, while children ages 0â4 exhibited virtually no relationship. The risk of adverse health effects was expressed as a function of the change from the 25th to 75th percentiles of mean level PM<sub>10</sub> (36 ÎŒg m<sup>−3</sup>). This increase in concentration was associated with a 12.6% (95% CI: 5.8%, 19.4%) increase in the log odds of asthma attacks among children ages 5â17. Neither gender nor other demographic variables were significant. The results are being used to develop an asthma early warning system for the study area
A cascade of magnetic field induced spin transitions in LaCoO3
We present magnetization and magnetostriction studies of the insulating
perovskite LaCoO3 in magnetic fields approaching 100 T. In marked contrast with
expectations from single-ion models, the data reveal two distinct first-order
spin transitions and well-defined magnetization plateaux. The magnetization at
the higher plateau is only about half the saturation value expected for spin-1
Co3+ ions. These findings strongly suggest collective behavior induced by
strong interactions between different electronic -- and therefore spin --
configurations of Co3+ ions. We propose a model of these interactions that
predicts crystalline spin textures and a cascade of four magnetic phase
transitions at high fields, of which the first two account for the experimental
data.Comment: 5 pages + supplementary materials, 5 figure
Transverse Polarization of ÎŁ+ (1189) in Photoproduction on a Hydrogen Target in CLAS
Experimental results on the ÎŁ+(1189) hyperon transverse polarization in photoproduction on a hydrogen target using the CLAS detector at Jefferson Laboratory are presented. The ÎŁ+(1189) was reconstructed in the exclusive reaction Îł+pâK0S+ÎŁ+(1189) via the ÎŁ+âpÏ0 decay mode. The K0S was reconstructed in the invariant mass of two oppositely charged pions with the Ï0 identified in the missing mass of the detected pÏ+Ïâ final state. Experimental data were collected in the photon energy range EÎł=1.0 â3.5 GeV (âs range 1.66â2.73 GeV). We observe a large negative polarization of up to 95% . As the mechanism of transverse polarization of hyperons produced in unpolarized photoproduction experiments is still not well understood, these results will help to distinguish between different theoretical models on hyperon production and provide valuable information for the searches of missing baryon resonances
Monte Carlo simulation of virtual Compton scattering below pion threshold
This paper describes the Monte Carlo simulation developed specifically for
the VCS experiments below pion threshold that have been performed at MAMI and
JLab. This simulation generates events according to the (Bethe-Heitler + Born)
cross section behaviour and takes into account all relevant
resolution-deteriorating effects. It determines the `effective' solid angle for
the various experimental settings which are used for the precise determination
of photon electroproduction absolute cross section.Comment: 24 pages, 6 figures, to be published in Nuclear Instruments and
Methods in Physics Research, A One author adde
Differential Cross Sections for + p â Kâș + Y for Î and ÎŁâ° Hyperons
High-statistics cross sections for the reactions + p â Kâș + Î and + p â Kâș + ÎŁâ° have been measured using CLAS at Jefferson Lab for center-of-mass energies W between 1.6 and 2.53 GeV, and for -0.85 \u3c cos Ξ Kc.m. \u3c +0.95. In the Kâș + Î channel we confirm a resonance-like structure near W=1.9 GeV at backward kaon angles. The position and width of this structure change with angle, indicating that more than one resonance is likely playing a role. The Kâș + Î channel at forward angles and all energies is well described by a t-channel scaling characteristic of Regge exchange, whereas the same scaling applied to the Kâș + ÎŁâ° channel is less successful. Several existing theoretical models are compared to the data, but none provide a good representation of the results
Removal and Dispersal of Biofluid Films by Powered Medical Devices: Modelling Infectious Agent Spreading in Dentistry
Summary
Medical procedures can disperse infectious agents and spread disease. Particularly, dental procedures may pose a high risk of disease transmission as they use high-powered instruments operating within the oral cavity that may contain infectious microbiota or viruses. Here we assess the ability of powered dental devices in removing the biofluid films and identified mechanical, hydrodynamic, and aerodynamic forces as the main underlying mechanisms of removal and dispersal processes. Our results indicate that potentially infectious agents can be removed and dispersed immediately after dental instrument engagement with the adherent biofluid film while the degree of their dispersal is rapidly depleted due to removal of the source and dilution by the coolant water. We found that droplets, created by high-speed drill interactions typically travel ballistically while aerosol-laden air tends to flow as a current over surfaces. Our mechanistic investigation offers plausible routes for reducing the spread of infection during invasive medical procedures
Rosenbluth Separation of the Ï0 Electroproduction Cross Section Off the Neutron
We report the first longitudinal-transverse separation of the deeply virtual exclusive Ï0 electroproduction cross section off the neutron and coherent deuteron. The corresponding four structure functions dÏL/dt, dÏT/dt, dÏLT/dt, and dÏTT/dt are extracted as a function of the momentum transfer to the recoil system at Q2 = 1.75 GeV2 and xB = 0.36. The ed -\u3e edÏ0 cross sections are found compatible with the small values expected from theoretical models. The en -\u3e enÏ0 cross sections show a dominance from the response to transversely polarized photons, and are in good agreement with calculations based on the transversity generalized parton distributions of the nucleon. By combining these results with previous measurements of Ï0 electroproduction off the proton, we present a flavor decomposition of the u and d quark contributions to the cross section
Ï-Meson Photoproduction on Hydrogen in the Neutral Decay Mode
We report the first measurement of the photoproduction cross section of the Ï meson in its neutral decay mode in the reaction ÎłpâpÏ(KSKL) . The experiment was performed with a tagged photon beam of energy 1.6 †EÎł †3.6 GeV incident on a liquid hydrogen target of the CLAS spectrometer at the Thomas Jefferson National Accelerator Facility. The pÏ final state is identified via reconstruction of KS in the invariant mass of two oppositely charged pions and by requiring the missing particle in the reaction ÎłpâpKSX to be KL. The presented results significantly enlarge the existing data on Ï photoproduction. These data, combined with the data from the charged decay mode, will help to constrain different mechanisms of Ï photoproduction
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