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1.
Cell ; 184(11): 3056-3074.e21, 2021 05 27.
Artículo en Inglés | MEDLINE | ID: mdl-33932339

RESUMEN

The choroid plexus (ChP) in each brain ventricle produces cerebrospinal fluid (CSF) and forms the blood-CSF barrier. Here, we construct a single-cell and spatial atlas of each ChP in the developing, adult, and aged mouse brain. We delineate diverse cell types, subtypes, cell states, and expression programs in epithelial and mesenchymal cells across ages and ventricles. In the developing ChP, we predict a common progenitor pool for epithelial and neuronal cells, validated by lineage tracing. Epithelial and fibroblast cells show regionalized expression by ventricle, starting at embryonic stages and persisting with age, with a dramatic transcriptional shift with maturation, and a smaller shift in each aged cell type. With aging, epithelial cells upregulate host-defense programs, and resident macrophages upregulate interleukin-1ß (IL-1ß) signaling genes. Our atlas reveals cellular diversity, architecture and signaling across ventricles during development, maturation, and aging of the ChP-brain barrier.


Asunto(s)
Plexo Coroideo/embriología , Plexo Coroideo/metabolismo , Factores de Edad , Envejecimiento/fisiología , Animales , Barrera Hematoencefálica/metabolismo , Encéfalo/metabolismo , Encéfalo/fisiología , Encefalopatías/genética , Encefalopatías/fisiopatología , Diferenciación Celular/genética , Linaje de la Célula/genética , Plexo Coroideo/fisiología , Células Epiteliales/metabolismo , Femenino , Masculino , Ratones/embriología , Ratones Endogámicos C57BL , Transducción de Señal , Análisis de la Célula Individual
2.
Phys Rev Lett ; 128(13): 132003, 2022 Apr 01.
Artículo en Inglés | MEDLINE | ID: mdl-35426713

RESUMEN

The ratio of the nucleon F_{2} structure functions, F_{2}^{n}/F_{2}^{p}, is determined by the MARATHON experiment from measurements of deep inelastic scattering of electrons from ^{3}H and ^{3}He nuclei. The experiment was performed in the Hall A Facility of Jefferson Lab using two high-resolution spectrometers for electron detection, and a cryogenic target system which included a low-activity tritium cell. The data analysis used a novel technique exploiting the mirror symmetry of the two nuclei, which essentially eliminates many theoretical uncertainties in the extraction of the ratio. The results, which cover the Bjorken scaling variable range 0.19

3.
J Geriatr Psychiatry Neurol ; 34(4): 274-279, 2021 07.
Artículo en Inglés | MEDLINE | ID: mdl-34219522

RESUMEN

Parkinson's disease (PD) is the second most common neurodegenerative disease seen in older adults after Alzheimer's disease, with increasing prevalence worldwide. Parkinson's disease psychosis (PDP) is a common, non-motor feature of PD, which increases caregiver stress and is a risk-factor for nursing home placement. In this paper we review PDP epidemiology, features, diagnosis, and treatment. PDP most often presents with sequential development of minor and then increasingly complex visual hallucinations mediated by dopaminergic-serotonergic interactions activating the mesolimbic pathway, with contributions from other structures and neurotransmitters. Appropriate evaluation of differential diagnoses for psychosis is vital before diagnosing PDP. Initial treatment should involve non-pharmacologic approaches. If these are unsuccessful and PDP symptoms significantly impact the patient's and or their caregivers' quality of life and functions, then pharmacotherapy is indicated. Pimavanserin is a recently FDA-approved pharmacologic treatment for PDP with a better profile of balanced effectiveness and safety compared to previous use of atypical antipsychotics. Early diagnosis and safer, more effective treatments for PDP should help reduce caregiver burden and enable caregivers to continue to provide care at home versus institutionalization.


Asunto(s)
Antipsicóticos , Enfermedades Neurodegenerativas , Enfermedad de Parkinson , Trastornos Psicóticos , Anciano , Antipsicóticos/uso terapéutico , Cuidadores , Humanos , Enfermedad de Parkinson/tratamiento farmacológico , Enfermedad de Parkinson/epidemiología , Trastornos Psicóticos/diagnóstico , Trastornos Psicóticos/tratamiento farmacológico , Trastornos Psicóticos/epidemiología , Calidad de Vida
4.
Phys Rev Lett ; 124(21): 212501, 2020 May 29.
Artículo en Inglés | MEDLINE | ID: mdl-32530643

RESUMEN

We report the first measurement of the (e,e^{'}p) three-body breakup reaction cross sections in helium-3 (^{3}He) and tritium (^{3}H) at large momentum transfer [⟨Q^{2}⟩≈1.9 (GeV/c)^{2}] and x_{B}>1 kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta 40≤p_{miss}≤500 MeV/c that, in the QE limit with no rescattering, equals the initial momentum of the probed nucleon. The measured cross sections are compared with state-of-the-art ab initio calculations. Overall good agreement, within ±20%, is observed between data and calculations for the full p_{miss} range for ^{3}H and for 100≤p_{miss}≤350 MeV/c for ^{3}He. Including the effects of rescattering of the outgoing nucleon improves agreement with the data at p_{miss}>250 MeV/c and suggests contributions from charge-exchange (SCX) rescattering. The isoscalar sum of ^{3}He plus ^{3}H, which is largely insensitive to SCX, is described by calculations to within the accuracy of the data over the entire p_{miss} range. This validates current models of the ground state of the three-nucleon system up to very high initial nucleon momenta of 500 MeV/c.

5.
Microvasc Res ; 122: 71-77, 2019 03.
Artículo en Inglés | MEDLINE | ID: mdl-30481493

RESUMEN

Pulmonary alveolar septal capillaries receive their perfusion from a web of larger surrounding acinar vessels. Using 4 µm diam. Latex particles, we showed that positive pressure ventilation narrowed the acinar vessels as evidenced by venous 4 µm particle concentrations and perfusate flows <50% of particle concentrations in negative pressure ventilated lungs. We aimed to understand the effects of positive and negative pressure ventilation on flows of larger particles through the lung. Isolated, ventilated rat lungs (air, transpulmonary pressures of 15/5 cm H2O, 25 breaths/min) were perfused with a hetastarch solution at Ppulm art/PLA pressures of 10/0 cm H2O. Red latex 7 µm (2.5 mg, 4.8 × 106) or 15 µm (2.5 mg, 5.5 × 105) particles were infused into each lung during positive or negative pressure ventilation. An equal number of green particles was infused 20 min later. Flows through lungs infused with 7 µm and 15 µm particles were not different from flows through lungs infused with 4 µm particles (p = 0.811). Venous particle concentrations of 7 µm particles relative to infused particles were lower in positive pressure lungs (0.03 ±â€¯0.03%) compared to negative pressure lungs (0.17 ±â€¯0.12%) (p = 0.041). Venous particle concentrations of 15 µm particles were not different between positive (2.3 ±â€¯1.9%) and negative (3.3 ±â€¯1.8%) pressure ventilation (p = 0.406). Together with our previous study, we conclude that 4 µm and 7 µm particles both enter acinar vessels but that the 7 µm particles are too large to flow through those vessels. In contrast, we conclude that 15 µm particles bypass the acinar vessels, flowing instead through larger intrapulmonary vessels to enter the venous outflow. These findings suggest that intrapulmonary vessels are organized as a web that allows bypass of the acinar vessels by large particles and, that these bypass vessels are not compressed by positive pressure ventilation.


Asunto(s)
Microcirculación , Microvasos/fisiología , Respiración con Presión Positiva , Alveolos Pulmonares/irrigación sanguínea , Circulación Pulmonar , Ventiladores de Presión Negativa , Animales , Velocidad del Flujo Sanguíneo , Colorantes Fluorescentes/administración & dosificación , Masculino , Microesferas , Tamaño de la Partícula , Ratas Sprague-Dawley , Flujo Sanguíneo Regional , Respiración , Factores de Tiempo
6.
Phys Rev Lett ; 119(18): 182501, 2017 Nov 03.
Artículo en Inglés | MEDLINE | ID: mdl-29219591

RESUMEN

We report the measurement of the beam-vector and tensor asymmetries A_{ed}^{V} and A_{d}^{T} in quasielastic (e[over →],e^{'}p) electrodisintegration of the deuteron at the MIT-Bates Linear Accelerator Center up to missing momentum of 500 MeV/c. Data were collected simultaneously over a momentum transfer range 0.1

7.
J Infect Dis ; 213(10): 1562-72, 2016 May 15.
Artículo en Inglés | MEDLINE | ID: mdl-26704612

RESUMEN

BACKGROUND: A safe, effective tetravalent dengue vaccine is a global health priority. The safety and immunogenicity of a live attenuated, recombinant tetravalent dengue vaccine candidate (TDV) were evaluated in healthy volunteers from dengue-endemic countries. METHODS: This multicenter, double-blind, phase 2 study was conducted in Puerto Rico, Colombia, Singapore, and Thailand. During stage I, 148 volunteers aged 1.5-45 years were sequentially enrolled into 4 age-descending groups and randomized at a ratio of 2:1 to receive TDV or placebo. In stage II (group 5), 212 children aged 1.5-11 years were randomized at a ratio of 3:1 to receive TDV or placebo. Participants received a subcutaneous injection of TDV or placebo on days 0 and 90 and were followed for analysis of safety, seropositivity, and neutralizing antibodies to DENV-1-4. RESULTS: Injection site pain, itching, and erythema (mostly mild) were the only solicited adverse events more frequently reported with TDV than with placebo in all age groups. After 2 TDV doses, seropositivity was >95% in all 5 groups for DENV-1-3 and 72.7%-100% for DENV-4; geometric mean titers ranged from 582 to 1187 for DENV-1, from 582 to 1187 for DENV-2, from 196 to 630 for DENV-3, and from 41 to 210 for DENV-4 among the 5 groups. CONCLUSIONS: TDV was well tolerated and immunogenic in volunteers aged 1.5-45 years, irrespective of prevaccination dengue exposure.


Asunto(s)
Anticuerpos Antivirales/inmunología , Vacunas contra el Dengue/inmunología , Virus del Dengue/inmunología , Dengue/prevención & control , Adolescente , Adulto , Anticuerpos Neutralizantes/inmunología , Niño , Preescolar , Colombia , Dengue/inmunología , Vacunas contra el Dengue/administración & dosificación , Vacunas contra el Dengue/normas , Método Doble Ciego , Femenino , Humanos , Lactante , Inyecciones Subcutáneas , Masculino , Persona de Mediana Edad , Puerto Rico , Seguridad , Singapur , Tailandia , Vacunas Atenuadas/administración & dosificación , Vacunas Atenuadas/inmunología , Vacunas Atenuadas/normas , Adulto Joven
8.
Phys Rev Lett ; 115(17): 172502, 2015 Oct 23.
Artículo en Inglés | MEDLINE | ID: mdl-26551107

RESUMEN

We report the first measurement of the target single-spin asymmetry, A(y), in quasielastic scattering from the inclusive reaction (3)He(↑)(e,e') on a (3)He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A nonzero A(y) can arise from the interference between the one- and two-photon exchange processes which is sensitive to the details of the substructure of the nucleon. An experiment recently completed at Jefferson Lab yielded asymmetries with high statistical precision at Q(2)=0.13, 0.46, and 0.97 GeV(2). These measurements demonstrate, for the first time, that the (3)He asymmetry is clearly nonzero and negative at the 4σ-9σ level. Using measured proton-to-(3)He cross-section ratios and the effective polarization approximation, neutron asymmetries of -(1-3)% were obtained. The neutron asymmetry at high Q(2) is related to moments of the generalized parton distributions (GPDs). Our measured neutron asymmetry at Q(2)=0.97 GeV(2) agrees well with a prediction based on two-photon exchange using a GPD model and thus provides a new, independent constraint on these distributions.

9.
Phys Rev Lett ; 114(19): 192503, 2015 May 15.
Artículo en Inglés | MEDLINE | ID: mdl-26024167

RESUMEN

New results are reported from a measurement of π^{0} electroproduction near threshold using the p(e,e^{'}p)π^{0} reaction. The experiment was designed to determine precisely the energy dependence of s- and p-wave electromagnetic multipoles as a stringent test of the predictions of chiral perturbation theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a two-spectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the ϕ_{π}^{*} and θ_{π}^{*} angles in the pπ^{0} center of mass was obtained for invariant energies above threshold from 0.5 up to 15 MeV. The 4-momentum transfer Q^{2} coverage ranges from 0.05 to 0.155 (GeV/c)^{2} in fine steps. A simple phenomenological analysis of our data shows strong disagreement with p-wave predictions from ChPT for Q^{2}>0.07 (GeV/c)^{2}, while the s-wave predictions are in reasonable agreement.

10.
Phys Rev Lett ; 113(2): 022002, 2014 Jul 11.
Artículo en Inglés | MEDLINE | ID: mdl-25062166

RESUMEN

Double-spin asymmetries and absolute cross sections were measured at large Bjorken x (0.25≤x≤0.90), in both the deep-inelastic and resonance regions, by scattering longitudinally polarized electrons at beam energies of 4.7 and 5.9 GeV from a transversely and longitudinally polarized (3)He target. In this dedicated experiment, the spin structure function g(2)((3)He) was determined with precision at large x, and the neutron twist-3 matrix element d(2)(n) was measured at ⟨Q(2)⟩ of 3.21 and 4.32 GeV(2)/c(2), with an absolute precision of about 10(-5). Our results are found to be in agreement with lattice QCD calculations and resolve the disagreement found with previous data at ⟨Q(2)⟩=5 GeV(2)/c(2). Combining d(2)(n) and a newly extracted twist-4 matrix element f(2)(n), the average neutron color electric and magnetic forces were extracted and found to be of opposite sign and about 30 MeV/fm in magnitude.

11.
Phys Rev Lett ; 113(2): 022501, 2014 Jul 11.
Artículo en Inglés | MEDLINE | ID: mdl-25062168

RESUMEN

We studied simultaneously the (4)He(e,e'p), (4)He(e,e'pp), and (4)He(e,e'pn) reactions at Q(2)=2(GeV/c)(2) and x(B)>1, for an (e,e'p) missing-momentum range of 400 to 830 MeV/c. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A=2 system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum, in a region where the nucleon-nucleon (NN) force is expected to change from predominantly tensor to repulsive. The abundance of neutron-proton pairs is reduced as the nucleon momentum increases beyond ∼500 MeV/c. The extracted fraction of proton-proton pairs is small and almost independent of the missing momentum. Our data are compared with calculations of two-nucleon momentum distributions in (4)He and discussed in the context of probing the elusive repulsive component of the NN force.

12.
Phys Rev Lett ; 113(2): 022502, 2014 Jul 11.
Artículo en Inglés | MEDLINE | ID: mdl-25062169

RESUMEN

We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction 3)He(↑)(e,e')X on a polarized (3)He gas target. Assuming time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be nonzero if two-photon-exchange contributions are included. The experiment, conducted at Jefferson Lab using a 5.89 GeV electron beam, covers a range of 1.72 GeV, which is nonzero at the 2.89σ level. Our measured asymmetry agrees both in sign and magnitude with a two-photon-exchange model prediction that uses input from the Sivers transverse momentum distribution obtained from semi-inclusive deep-inelastic scattering.

13.
Phys Rev Lett ; 113(23): 232505, 2014 Dec 05.
Artículo en Inglés | MEDLINE | ID: mdl-25526124

RESUMEN

We present a precise measurement of double-polarization asymmetries in the ^{3}He[over →](e[over →],e^{'}d) reaction. This particular process is a uniquely sensitive probe of hadron dynamics in ^{3}He and the structure of the underlying electromagnetic currents. The measurements have been performed in and around quasielastic kinematics at Q^{2}=0.25(GeV/c)^{2} for missing momenta up to 270 MeV/c. The asymmetries are in fair agreement with the state-of-the-art calculations in terms of their functional dependencies on p_{m} and ω, but are systematically offset. Beyond the region of the quasielastic peak, the discrepancies become even more pronounced. Thus, our measurements have been able to reveal deficiencies in the most sophisticated calculations of the three-body nuclear system, and indicate that further refinement in the treatment of their two-and/or three-body dynamics is required.

14.
Biol Psychiatry ; 96(1): 34-43, 2024 Jul 01.
Artículo en Inglés | MEDLINE | ID: mdl-38141910

RESUMEN

BACKGROUND: Depression, a common psychiatric illness and global public health problem, remains poorly understood across different life stages, which hampers the development of novel treatments. METHODS: To identify new candidate genes for therapeutic development, we performed differential gene expression analysis of single-nucleus RNA sequencing data from the dorsolateral prefrontal cortex of older adults (n = 424) in relation to antemortem depressive symptoms. Additionally, we integrated genome-wide association study results for depression (n = 500,199) along with genetic tools for inferring the expression of 14,048 unique genes in 7 cell types and 52 cell subtypes to perform a transcriptome-wide association study of depression followed by Mendelian randomization. RESULTS: Our single-nucleus transcriptome-wide association study analysis identified 68 candidate genes for depression and showed the greatest number being in excitatory and inhibitory neurons. Of the 68 genes, 53 were novel compared to previous studies. Notably, gene expression in different neuronal subtypes had varying effects on depression risk. Traits with high genetic correlations with depression, such as neuroticism, shared more transcriptome-wide association study genes than traits that were not highly correlated with depression. Complementing these analyses, differential gene expression analysis across 52 neocortical cell subtypes showed that genes such as KCNN2, SCAI, WASF3, and SOCS6 were associated with late-life depressive symptoms in specific cell subtypes. CONCLUSIONS: These 2 sets of analyses illustrate the utility of large single-nucleus RNA sequencing data both to uncover genes whose expression is altered in specific cell subtypes in the context of depressive symptoms and to enhance the interpretation of well-powered genome-wide association studies so that we can prioritize specific susceptibility genes for further analysis and therapeutic development.


Asunto(s)
Estudio de Asociación del Genoma Completo , Transcriptoma , Humanos , Masculino , Femenino , Anciano , Depresión/genética , Corteza Prefontal Dorsolateral , Predisposición Genética a la Enfermedad/genética , Persona de Mediana Edad , Análisis de la Aleatorización Mendeliana , Neuronas/metabolismo
15.
medRxiv ; 2023 Mar 29.
Artículo en Inglés | MEDLINE | ID: mdl-37034737

RESUMEN

Background: Depression is a common psychiatric illness and global public health problem. However, our limited understanding of the biological basis of depression has hindered the development of novel treatments and interventions. Methods: To identify new candidate genes for therapeutic development, we examined single-nucleus RNA sequencing (snucRNAseq) data from the dorsolateral prefrontal cortex (N=424) in relation to ante-mortem depressive symptoms. To complement these direct analyses, we also used genome-wide association study (GWAS) results for depression (N=500,199) along with genetic tools for inferring the expression of 22,159 genes in 7 cell types and 55 cell subtypes to perform transcriptome-wide association studies (TWAS) of depression followed by Mendelian randomization (MR). Results: Our single-nucleus TWAS analysis identified 71 causal genes in depression that have a role in specific neocortical cell subtypes; 59 of 71 genes were novel compared to previous studies. Depression TWAS genes showed a cell type specific pattern, with the greatest enrichment being in both excitatory and inhibitory neurons as well as astrocytes. Gene expression in different neuron subtypes have different directions of effect on depression risk. Compared to lower genetically correlated traits (e.g. body mass index) with depression, higher correlated traits (e.g., neuroticism) have more common TWAS genes with depression. In parallel, we performed differential gene expression analysis in relation to depression in 55 cortical cell subtypes, and we found that genes such as ANKRD36, MADD, TAOK3, SCAI and CHUK are associated with depression in specific cell subtypes. Conclusions: These two sets of analyses illustrate the utility of large snucRNAseq data to uncover both genes whose expression is altered in specific cell subtypes in the context of depression and to enhance the interpretation of well-powered GWAS so that we can prioritize specific susceptibility genes for further analysis and therapeutic development.

16.
Nat Neurosci ; 26(7): 1267-1280, 2023 07.
Artículo en Inglés | MEDLINE | ID: mdl-37336975

RESUMEN

The role of different cell types and their interactions in Alzheimer's disease (AD) is a complex and open question. Here, we pursued this question by assembling a high-resolution cellular map of the aging frontal cortex using single-nucleus RNA sequencing of 24 individuals with a range of clinicopathologic characteristics. We used this map to infer the neocortical cellular architecture of 638 individuals profiled by bulk RNA sequencing, providing the sample size necessary for identifying statistically robust associations. We uncovered diverse cell populations associated with AD, including a somatostatin inhibitory neuronal subtype and oligodendroglial states. We further identified a network of multicellular communities, each composed of coordinated subpopulations of neuronal, glial and endothelial cells, and we found that two of these communities are altered in AD. Finally, we used mediation analyses to prioritize cellular changes that might contribute to cognitive decline. Thus, our deconstruction of the aging neocortex provides a roadmap for evaluating the cellular microenvironments underlying AD and dementia.


Asunto(s)
Enfermedad de Alzheimer , Disfunción Cognitiva , Neocórtex , Humanos , Enfermedad de Alzheimer/metabolismo , Células Endoteliales/metabolismo , Encéfalo/metabolismo , Envejecimiento/patología , Disfunción Cognitiva/patología , Neocórtex/patología
17.
Cancer ; 118(17): 4098-104, 2012 Sep 01.
Artículo en Inglés | MEDLINE | ID: mdl-22281842

RESUMEN

BACKGROUND: Serum and plasma levels of vascular endothelial growth factor (VEGF) correlate with prognosis in patients with metastatic breast cancer (MBC). VEGF binds to 2 receptors on endothelial cells, VEGFR-1 and VEGFR-2. RPI.4610 (Angiozyme0) is an antiangiogenic ribozyme targeting the VEGFR-1 mRNA. Preclinical and phase 1 studies suggested that RPI.4610 is a well-tolerated agent with clinical activity in solid tumors. The authors' trial evaluated the efficacy of RPI.4610 in the treatment of patients with progressive MBC. METHODS: This phase 2, multicenter, single-arm study was designed to assess the objective response rate of RPI.4610 in patients with MBC who had experienced disease progression with at least 1 course of chemotherapy for MBC. Patients received daily subcutaneous injections of RPI.4610 100 mg/m(2) for 12 weeks. RESULTS: Most patients (93%) had received at least 2 lines of chemotherapy previously; 69% of patients had received at least 3 lines of chemotherapy. Median follow-up was 2.76 months (range, 0.89-36.6 months). No partial responses nor complete responses were found. Median progression-free survival was 1.41 months (95% confidence interval [CI], 1.35-1.45). The median overall survival from start of treatment was 11.89 months (95% CI, 4.11-23.66). Treatment-related adverse events (AEs) were primarily grade 1 to 2 in intensity. Most common AEs were: injection site reactions, abdominal pain, anorexia, chromaturia, constipation, dyspnea, fatigue, headache, pain at the injection site, nausea, vomiting, and fever. CONCLUSIONS: Although RPI.4610 demonstrated a well-tolerated safety profile, its lack of clinical efficacy precludes this drug from further development.


Asunto(s)
Inhibidores de la Angiogénesis/uso terapéutico , Neoplasias de la Mama/tratamiento farmacológico , ARN Catalítico/uso terapéutico , Adulto , Anciano , Neoplasias de la Mama/patología , Neoplasias de la Mama/secundario , Supervivencia sin Enfermedad , Femenino , Humanos , Persona de Mediana Edad , ARN Catalítico/efectos adversos , Receptor 1 de Factores de Crecimiento Endotelial Vascular/antagonistas & inhibidores
18.
Phys Rev Lett ; 108(5): 052001, 2012 Feb 03.
Artículo en Inglés | MEDLINE | ID: mdl-22400926

RESUMEN

We report the first measurement of the double-spin asymmetry A{LT} for charged pion electroproduction in semi-inclusive deep-inelastic electron scattering on a transversely polarized {3}He target. The kinematics focused on the valence quark region, 0.16

19.
Phys Rev Lett ; 108(22): 222004, 2012 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-23180491

RESUMEN

We present new data for the polarization observables of the final state proton in the (1)H(γ,p)π(0) reaction. These data can be used to test predictions based on hadron helicity conservation and perturbative QCD. These data have both small statistical and systematic uncertainties and were obtained with beam energies between 1.8 and 5.6 GeV and for π(0) scattering angles larger than 75° in the center-of-mass frame. The data extend the polarization measurements database for neutral pion photoproduction up to E(γ)=5.6 GeV. The results show a nonzero induced polarization above the resonance region. The polarization transfer components vary rapidly with the photon energy and π(0) scattering angle in the center-of-mass frame. This indicates that hadron helicity conservation does not hold and that the perturbative QCD limit is still not reached in the energy regime of this experiment.

20.
Phys Rev Lett ; 106(13): 132501, 2011 Apr 01.
Artículo en Inglés | MEDLINE | ID: mdl-21520982

RESUMEN

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, G(E)/G(M), obtained separately from cross section and polarization transfer measurements. One possible explanation for this difference is a two-photon-exchange 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 H(e[over →],e(')p[over →]) reaction for three different beam energies at a Q(2)=2.5 GeV(2), spanning a wide range of the kinematic parameter ε. The ratio R, which equals µ(p)G(E)/G(M) in the Born approximation, is found to be independent of ε at the 1.5% level. The ε dependence of the longitudinal polarization transfer component P(ℓ) shows an enhancement of (2.3±0.6)% relative to the Born approximation at large ε.

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