The Dalitz decay η→γe+e− has been measured using the combined Crystal Ball and TAPS photon detector setup at the electron accelerator MAMI-C. Compared to the most recent transition form-factor ...measurement in the e+e− channel, statistics have been improved by one order of magnitude. The e+e− invariant mass distribution shows a deviation from the QED prediction for a point-like particle, which can be described by a form-factor. Using the usual monopole transition form-factor parameterization, F(m2)=(1−m2/Λ2)−1, a value of Λ−2=(1.92±0.35(stat)±0.13(syst)) GeV−2 has been determined. This value is in good agreement with a recent measurement of the η Dalitz decay in the μ+μ− channel and with recent form-factor calculations. An improved value of the branching ratio BR(η→γe+e−)=(6.6±0.4(stat)±0.4(syst))⋅10−3 has been determined.
We present a search for axion-like particles, \(a\), produced in photon-proton collisions at a center-of-mass energy of approximately 4 GeV, focusing on the scenario where the \(a\)-gluon coupling is ...dominant. The search uses \(a\to\gamma\gamma\) and \(a\to\pi^+\pi^-\pi^0\) decays, and a data sample corresponding to an integrated luminosity of 168 pb\(^{-1}\) collected with the GlueX detector. The search for \(a\to\gamma\gamma\) decays is performed in the mass range of \(180 < m_a < 480\) MeV, while the search for \(a\to\pi^+\pi^-\pi^0\) decays explores the \(600 < m_a < 720\) MeV region. No evidence for a signal is found, and 90% confidence-level exclusion limits are placed on the \(a\)-gluon coupling strength. These constraints are the most stringent to date over much of the mass ranges considered.
The cross section for coherent omega-meson photoproduction off the deuteron has been measured for the first time as a function of the momentum transfer t=(P-gamma - P-omega)(2) and photon energy ...E-gamma using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cross sections are measured in the energy range 1.4 < E-gamma < 3.4GeV. A model based on omega- N rescattering is consistent with the data at low and intermediate momentum transfer, vertical bar t vertical bar. For 2.8 < E-gamma < 3.4GeV, the total cross-section of omega - N scattering, based on fits within the framework of the Vector Meson Dominance model, is in the range of 30-40 mb.
We present studies of single-spin asymmetries for neutral pion electroproduction in semi-inclusive deep-inelastic scattering of 5.776 GeV polarized electrons from an unpolarized hydrogen target, ...using the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. A substantial sinϕh amplitude has been measured in the distribution of the cross section asymmetry as a function of the azimuthal angle ϕh of the produced neutral pion. The dependence of this amplitude on Bjorken x and on the pion transverse momentum is extracted with significantly higher precision than previous data and is compared to model calculations.
Quasi-free photoproduction of πη-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross ...sections, angular distributions, invariant-mass distributions of the πη and meson-nucleon pairs, and beam helicity asymmetries have been measured for the reactions γp → pπ0η, γn → nπ0η, γp → nπ+η, and γn → pπ–η from nucleons bound inside the deuteron. For the γp initial-state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of π0η pairs from nucleons bound in 3He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost 4π covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential Δ *3/2– → ηΔ(1232) → πηN decay chain, mainly with Δ(1700)3/2– and Δ(1940)3/2–. The ratios of the magnitude of the total cross sections also agree with this assumption. Furthermore, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data.
Results are presented for the first measurement of the double-polarization helicity asymmetry E for the η photoproduction reaction γ p → η p. Data were obtained using the FROzen Spin Target (FROST) ...with the CLAS spectrometer in Hall B at Jefferson Lab, covering a range of center-of-mass energy W from threshold to 2.15 GeV and a large range in center-of-mass polar angle. As an initial application of these data, the results have been incorporated into the J\"ulich model to examine the case for the existence of a narrow Ν* resonance between 1.66 and 1.70 GeV. The addition of these data to the world database results in marked changes in the predictions for the E observable using that model. As a result, further comparison with several theoretical approaches indicates these data will significantly enhance our understanding of nucleon resonances.
The burden of skin disease in the United States Lim, Henry W., MD; Collins, Scott A.B., MD; Resneck, Jack S., MD ...
Journal of the American Academy of Dermatology,
05/2017, Letnik:
76, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Since the publication of the last US national burden of skin disease report in 2006, there have been substantial changes in the practice of dermatology and the US health care system. These include ...the development of new treatment modalities, marked increases in the cost of medications, increasingly complex payer rules and regulations, and an aging of the US population. Recognizing the need for up-to-date data to inform researchers, policy makers, public stakeholders, and health care providers about the impact of skin disease on patients and US society, the American Academy of Dermatology produced a new national burden of skin disease report. Using 2013 claims data from private and governmental insurance providers, this report analyzed the prevalence, cost, and mortality attributable to 24 skin disease categories in the US population. In this first of 3 articles, the presented data demonstrate that nearly 85 million Americans were seen by a physician for at least 1 skin disease in 2013. This led to an estimated direct health care cost of $75 billion and an indirect lost opportunity cost of $11 billion. Further, mortality was noted in half of the 24 skin disease categories.
Photoproduction of the f1(1285) meson Schumacher, R. A.; Adhikari, K. P.; Akbar, Z. ...
Physical review. C,
06/2016, Letnik:
93, Številka:
6
Journal Article
Recenzirano
Odprti dostop
The f1 (1285) meson with mass 1281.0 ± 0.8 MeV/c2 and width 18.4 ± 1.4 MeV (full width at half maximum) was measured for the first time in photoproduction from a proton target using CLAS at Jefferson ...Lab. Differential cross sections were obtained via the ηπ + π -, K+ K0 π -, and K-K0 π+ decay channels from threshold up to a center-of-mass energy of 2.8 GeV. The mass, width, and an amplitude analysis of the ηπ + π- final-state Dalitz distribution are consistent with the axial-vector JP = 1+ f1 (1285) identity, rather than the pseudoscalar 0-η (1295). The production mechanism is more consistent with s -channel decay of a high-mass N * state and not with t -channel meson exchange. Decays to η π π go dominantly via the intermediate a$^±_0$ (980) π ∓ states, with the branching ratio Γ a0π (no $\overline{K}K$) / Γ ηππ (all) = 0.74 ± 0.09 . The branching ratios Γ ($\overline{K}K$ π )/ Γ (ηππ) = 0.216 ± 0.033 and Γ (γρ0) / Γ (ηππ) = 0.047 ± 0.018 were also obtained. The first is in agreement with previous data for the f1 (1285), while the latter is lower than the world average.
Photoproduction of the f1(1285) meson Schumacher, R. A.; Adhikari, K. P.; Akbar, Z. ...
Physical review. C,
06/2016, Letnik:
93, Številka:
6
Journal Article
Recenzirano
The f(1)(1285) meson withmass 1281.0 +/- 0.8MeV/c(2) and width 18.4 +/- 1.4MeV (full width at half maximum) was measured for the first time in photoproduction from a proton target using CLAS at ...Jefferson Lab. Differential cross sections were obtained via the eta pi(+)pi(-), K+(K) over bar (0) pi(-), and (K-K0)pi(+) decay channels from threshold up to a center-of-mass energy of 2.8 GeV. The mass, width, and an amplitude analysis of the eta pi(+)pi(-) final-state Dalitz distribution are consistent with the axial-vector J(P) = 1(+) f(1)(1285) identity, rather than the pseudoscalar 0(-) eta(1295). The production mechanism is more consistent with s-channel decay of a high-mass N* state and not with t-channel meson exchange. Decays to eta pi pi go dominantly via the intermediate a(0)(+/-) (980)pi(-/+) states, with the branching ratio Gamma a(0)pi (no (K) over barK)/Gammaeta pi pi (all) = 0.74 +/- 0.09. The branching ratios Gamma (K (K) over bar pi)/Gamma(eta pi pi) = 0.216 +/- 0.033 and Gamma (gamma rho(0))/Gamma(eta pi pi) = 0.047 +/- 0.018 were also obtained. The first is in agreement with previous data for the f(1)(1285), while the latter is lower than the world average.
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