25 research outputs found
Polarization transfer in wide-angle Compton scattering and single-pion photoproduction from the proton
Wide-angle exclusive Compton scattering and single-pion photoproduction from the proton have been investigated via measurement of the polarization transfer from a circularly polarized photon beam to the recoil proton. The wide-angle Compton scattering polarization transfer was analyzed at an incident photon energy of 3.7 GeV at a proton scattering angle of θpcm=70°. The longitudinal transfer KLL, measured to be 0.645±0.059±0.048, where the first error is statistical and the second is systematic, has the same sign as predicted for the reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton. However, the observed value is ∼3 times larger than predicted by the generalized-parton-distribution-based calculations, which indicates a significant unknown contribution to the scattering amplitude
Recoil Polarization Measurements of the Proton Electromagnetic Form Factor Ratio to Q^2 = 8.5 GeV^2
Among the most fundamental observables of nucleon structure, electromagnetic
form factors are a crucial benchmark for modern calculations describing the
strong interaction dynamics of the nucleon's quark constituents; indeed, recent
proton data have attracted intense theoretical interest. In this letter, we
report new measurements of the proton electromagnetic form factor ratio using
the recoil polarization method, at momentum transfers Q2=5.2, 6.7, and 8.5
GeV2. By extending the range of Q2 for which GEp is accurately determined by
more than 50%, these measurements will provide significant constraints on
models of nucleon structure in the non-perturbative regime
Measurements of Non-Singlet Moments of the Nucleon Structure Functions and Comparison to Predictions from Lattice QCD for
We present extractions of the nucleon non-singlet moments utilizing new
precision data on the deuteron structure function at large Bjorken-
determined via the Rosenbluth separation technique at Jefferson Lab
Experimental Hall C. These new data are combined with a complementary set of
data on the proton previously measured in Hall C at similar kinematics and
world data sets on the proton and deuteron at lower measured at SLAC and
CERN. The new Jefferson Lab data provide coverage of the upper third of the
range, crucial for precision determination of the higher moments. In contrast
to previous extractions, these moments have been corrected for nuclear effects
in the deuteron using a new global fit to the deuteron and proton data. The
obtained experimental moments represent an order of magnitude improvement in
precision over previous extractions using high data. Moreover, recent
exciting developments in Lattice QCD calculations provide a first ever
comparison of these new experimental results with calculations of moments
carried out at the physical pion mass, as well as a new approach which first
calculates the quark distributions directly before determining moments
Search for effects beyond the Born approximation in polarization transfer observables in elastic scattering
Intensive theoretical and experimental efforts over the past decade have
aimed at explaining the discrepancy between data for the proton electric to
magnetic form factor ratio, , obtained separately from cross
section and polarization transfer measurements. One possible explanation for
this difference is a two-photon-exchange (TPEX) contribution. In an effort to
search for effects beyond the one-photon-exchange or Born approximation, we
report measurements of polarization transfer observables in the elastic
reaction for three different beam energies at a fixed
squared momentum transfer GeV, spanning a wide range of the
virtual photon polarization parameter, . From these measured
polarization observables, we have obtained separately the ratio , which
equals in the Born approximation, and the longitudinal
polarization transfer component , with statistical and systematic
uncertainties of \Delta R \approx \pm 0.01 \mbox{(stat)} \pm 0.013
\mbox{(syst)} and \Delta P_\ell/P^{Born}_{\ell} \approx \pm 0.006
\mbox{(stat)}\pm 0.01 \mbox{(syst)}. The ratio is found to be independent
of at the 1.5% level, while the dependence of
shows an enhancement of relative to the Born approximation at
large
Exclusive photoproduction of pi degrees up to large values of Mandelstam variables s, t, and u with CLAS
Exclusive photoproduction cross sections have been measured for the process
with the Dalitz decay final state
using tagged photon energies in the range of GeV.
The complete angular distribution of the final state , for the entire
photon energy range up to large values of and , has been measured for
the first time. The data obtained show that the cross section , at
mid to large angles, decreases with energy as . This is in
agreement with the perturbative QCD quark counting rule prediction of . Paradoxically, the size of angular distribution of measured cross sections
is greatly underestimated by the QCD based Generalized Parton Distribution
mechanism at highest available invariant energy GeV. At the same
time, the Regge exchange based models for photoproduction are more
consistent with experimental data.Comment: 7 pages, 6 figure
Table_1_Soluble biomarkers of HIV-1-related systemic immune activation are associated with high plasma levels of growth factors implicated in the pathogenesis of Kaposi sarcoma in adults.docx
BackgroundHuman Herpesvirus-8 (HHV-8) is the etiologic agent of Kaposi’s sarcoma (KS), a multicentric angio-proliferative cancer commonly associated with Human Immunodeficiency Virus (HIV) infection. KS pathogenesis is a multifactorial condition hinged on immune dysfunction yet the mechanisms underlying the risk of developing KS in HHV-8 seropositive adults remains unclear. Here we explored whether soluble markers of HIV-1-related systemic immune activation (SIA) and angiogenesis (VEGF and FGF acidic) are involved in the pathogenesis of KS in adults with HHV8.MethodologyBlood samples from 99 HIV-1 infected and 60 HIV-1 uninfected adults were collected in Yaoundé, Cameroon. CD3+/CD4+ T cell counts and HIV-1 plasma viral load were determined using the Pima Analyzer and the RT-PCR technique, respectively. Plasma levels of SIA biomarkers (sCD163, sCD25/IL-2Rα, and sCD40/TNFRSF5) and biomarkers of progression to KS (VEGF and FGF acidic) were measured using the Luminex assay. Seropositivity (IgG) for HHV-8 was determined using the ELISA method.ResultsOverall, 20.2% (20/99) of HIV-1 infected and 20% (12/60) of HIV-1 uninfected participants were seropositive for HHV8. Levels of sCD163, sCD25/IL-2Rα, sCD40/TNFRSF5, and FGF acidic were higher in the HIV-1 and HHV8 co-infection groups compared to the HIV-1 and HHV8 uninfected groups (all P s = 0.58, P =0.0067) and sCD40/TNFRSF5 (rs = 0.59, P = 0.0064), while FGF acidic levels correlated with sCD40/TNFRSF5 (rs = 0.51, P = 0.022) in co-infected. In HIV-1 mono-infected donors, VEGF and FGF acidic levels correlated with sCD163 (rs =0.25, P = 0.03 and rs = 0.30, P = 0.006 respectively), sCD25/IL-2Rα (rs = 0.5, P s = 0.55, P s = 0.7, P s = 0.59, P s = 0.39, P = 0.012 and rs = 0.53, P = 0.0004 respectively) and sCD40/TNFRSF5 (rs = 0.81, P s = 0.44, P = 0.0045 respectively).ConclusionOur findings suggest that although the development of KS in PLWH is multifactorial, HIV-associated SIA might be among the key drivers in coinfections with HHV8 and is independent of the patients’ viremic status.</p