418 research outputs found

    The {\eta}'-carbon potential at low meson momenta

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    The production of η\eta^\prime mesons in coincidence with forward-going protons has been studied in photon-induced reactions on 12^{12}C and on a liquid hydrogen (LH2_2) target for incoming photon energies of 1.3-2.6 GeV at the electron accelerator ELSA. The η\eta^\prime mesons have been identified via the ηπ0π0η6γ\eta^\prime\rightarrow \pi^0 \pi^0\eta \rightarrow 6 \gamma decay registered with the CBELSA/TAPS detector system. Coincident protons have been identified in the MiniTAPS BaF2_2 array at polar angles of 2θp112^{\circ} \le \theta _{p} \le 11^{\circ}. Under these kinematic constraints the η\eta^\prime mesons are produced with relatively low kinetic energy (\approx 150 MeV) since the coincident protons take over most of the momentum of the incident-photon beam. For the C-target this allows the determination of the real part of the η\eta^\prime-carbon potential at low meson momenta by comparing with collision model calculations of the η\eta^\prime kinetic energy distribution and excitation function. Fitting the latter data for η\eta^\prime mesons going backwards in the center-of-mass system yields a potential depth of V = -(44 ±\pm 16(stat)±\pm15(syst)) MeV, consistent with earlier determinations of the potential depth in inclusive measurements for average η\eta^\prime momenta of \approx 1.1 GeV/cc. Within the experimental uncertainties, there is no indication of a momentum dependence of the η\eta^\prime-carbon potential. The LH2_2 data, taken as a reference to check the data analysis and the model calculations, provide differential and integral cross sections in good agreement with previous results for η\eta^\prime photoproduction off the free proton.Comment: 9 pages, 13 figures. arXiv admin note: text overlap with arXiv:1608.0607

    Experimental constraints on the ω\omega-nucleus real potential

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    In a search for ω\omega mesic states, the production of ω\omega-mesons in coincidence with forward going protons has been studied in photon induced reactions on 12^{12}C for incident photon energies of 1250 - 3100 MeV. The π0γ\pi^0 \gamma pairs from decays of bound or quasi-free ω\omega-mesons have been measured with the CBELSA/TAPS detector system in coincidence with protons registered in the MiniTAPS forward array. Structures in the total energy distribution of the π0γ\pi^0 \gamma pairs, which would indicate the population and decay of bound ω 11\omega~^{11}B states, are not observed. The π0γ\pi^0 \gamma cross section of 0.3 nb/MeV/sr observed in the bound state energy regime between -100 and 0 MeV may be accounted for by yield leaking into the bound state regime because of the large in-medium width of the ω\omega-meson. A comparison of the measured total energy distribution with calculations suggests the real part V0V_0 of the ω 11\omega~^{11}B potential to be small and only weakly attractive with V0(ρ=ρ0)=15±V_0(\rho=\rho_0) = -15\pm 35(stat) ±\pm20(syst) MeV in contrast to some theoretical predictions of attractive potentials with a depth of 100 - 150 MeV.Comment: 13 pages, 8 figure

    The polarization observables T, P, and H and their impact on γppπ0\gamma p \to p\pi^0 multipoles

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    Data on the polarization observables T, P, and H for the reaction γppπ0\gamma p\to p\pi^0 are reported. Compared to earlier data from other experiments, our data are more precise and extend the covered range in energy and angle substantially. The results were extracted from azimuthal asymmetries measured using a transversely polarized target and linearly polarized photons. The data were taken at the Bonn electron stretcher accelerator ELSA with the CBELSA/TAPS detector. Within the Bonn-Gatchina partial wave analysis, the new polarization data lead to a significant narrowing of the error band for the multipoles for neutral-pion photoproduction

    Detailed spectral and morphological analysis of the shell type SNR RCW 86

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    Aims: We aim for an understanding of the morphological and spectral properties of the supernova remnant RCW~86 and for insights into the production mechanism leading to the RCW~86 very high-energy gamma-ray emission. Methods: We analyzed High Energy Spectroscopic System data that had increased sensitivity compared to the observations presented in the RCW~86 H.E.S.S. discovery publication. Studies of the morphological correlation between the 0.5-1~keV X-ray band, the 2-5~keV X-ray band, radio, and gamma-ray emissions have been performed as well as broadband modeling of the spectral energy distribution with two different emission models. Results:We present the first conclusive evidence that the TeV gamma-ray emission region is shell-like based on our morphological studies. The comparison with 2-5~keV X-ray data reveals a correlation with the 0.4-50~TeV gamma-ray emission.The spectrum of RCW~86 is best described by a power law with an exponential cutoff at Ecut=(3.5±1.2stat)E_{cut}=(3.5\pm 1.2_{stat}) TeV and a spectral index of Γ\Gamma~1.6±0.21.6\pm 0.2. A static leptonic one-zone model adequately describes the measured spectral energy distribution of RCW~86, with the resultant total kinetic energy of the electrons above 1 GeV being equivalent to \sim0.1\% of the initial kinetic energy of a Type I a supernova explosion. When using a hadronic model, a magnetic field of BB~100μ\muG is needed to represent the measured data. Although this is comparable to formerly published estimates, a standard E2^{-2} spectrum for the proton distribution cannot describe the gamma-ray data. Instead, a spectral index of Γp\Gamma_p~1.7 would be required, which implies that ~7×1049/ncm37\times 10^{49}/n_{cm^{-3}}erg has been transferred into high-energy protons with the effective density ncm3=n/1n_{cm^{-3}}=n/ 1 cm^-3. This is about 10\% of the kinetic energy of a typical Type Ia supernova under the assumption of a density of 1~cm^-3.Comment: accepted for publication by A&

    The N(1520) 3/2- helicity amplitudes from an energy-independent multipole analysis based on new polarization data on photoproduction of neutral pions

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    New data on the polarization observables T, P, and H for the reaction γppπ0\gamma p \to p\pi^0 are reported. The results are extracted from azimuthal asymmetries when a transversely polarized butanol target and a linearly polarized photon beam are used. The data were taken at the Bonn electron stretcher accelerator ELSA using the CBELSA/TAPS detector. These and earlier data are used to perform a truncated energy-independent partial wave analysis in sliced-energy bins. This energy-independent analysis is compared to the results from energy-dependent partial wave analyses

    Detection of variable VHE gamma-ray emission from the extra-galactic gamma-ray binary LMC P3

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    Context. Recently, the high-energy (HE, 0.1-100 GeV) γ\gamma-ray emission from the object LMC P3 in the Large Magellanic Cloud (LMC) has been discovered to be modulated with a 10.3-day period, making it the first extra-galactic γ\gamma-ray binary. Aims. This work aims at the detection of very-high-energy (VHE, >100 GeV) γ\gamma-ray emission and the search for modulation of the VHE signal with the orbital period of the binary system. Methods. LMC P3 has been observed with the High Energy Stereoscopic System (H.E.S.S.); the acceptance-corrected exposure time is 100 h. The data set has been folded with the known orbital period of the system in order to test for variability of the emission. Energy spectra are obtained for the orbit-averaged data set, and for the orbital phase bin around the VHE maximum. Results. VHE γ\gamma-ray emission is detected with a statistical significance of 6.4 σ\sigma. The data clearly show variability which is phase-locked to the orbital period of the system. Periodicity cannot be deduced from the H.E.S.S. data set alone. The orbit-averaged luminosity in the 1101-10 TeV energy range is (1.4±0.2)×1035(1.4 \pm 0.2) \times 10^{35} erg/s. A luminosity of (5±1)×1035(5 \pm 1) \times 10^{35} erg/s is reached during 20% of the orbit. HE and VHE γ\gamma-ray emissions are anti-correlated. LMC P3 is the most luminous γ\gamma-ray binary known so far.Comment: 5 pages, 3 figures, 1 table, accepted for publication in A&

    The exceptionally powerful TeV gamma-ray emitters in the Large Magellanic Cloud

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    The Large Magellanic Cloud, a satellite galaxy of the Milky Way, has been observed with the High Energy Stereoscopic System (H.E.S.S.) above an energy of 100 billion electron volts for a deep exposure of 210 hours. Three sources of different types were detected: the pulsar wind nebula of the most energetic pulsar known N 157B, the radio-loud supernova remnant N 132D and the largest non-thermal X-ray shell - the superbubble 30 Dor C. The unique object SN 1987A is, surprisingly, not detected, which constrains the theoretical framework of particle acceleration in very young supernova remnants. These detections reveal the most energetic tip of a gamma-ray source population in an external galaxy, and provide via 30 Dor C the unambiguous detection of gamma-ray emission from a superbubble.Comment: Published in Science Magazine (Jan. 23, 2015). This ArXiv version has the supplementary online material incorporated as an appendix to the main pape

    Photoproduction of eta mesons from the neutron: cross sections and double polarization observable E

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    Photoproduction of η\eta mesons from neutrons} \abstract{Results from measurements of the photoproduction of η\eta mesons from quasifree protons and neutrons are summarized. The experiments were performed with the CBELSA/TAPS detector at the electron accelerator ELSA in Bonn using the η3π06γ\eta\to3\pi^{0}\to6\gamma decay. A liquid deuterium target was used for the measurement of total cross sections and angular distributions. The results confirm earlier measurements from Bonn and the MAMI facility in Mainz about the existence of a narrow structure in the excitation function of γnnη\gamma n\rightarrow n\eta. The current angular distributions show a forward-backward asymmetry, which was previously not seen, but was predicted by model calculations including an additional narrow P11P_{11} state. Furthermore, data obtained with a longitudinally polarized, deuterated butanol target and a circularly polarized photon beam were analyzed to determine the double polarization observable EE. Both data sets together were also used to extract the helicity dependent cross sections σ1/2\sigma_{1/2} and σ3/2\sigma_{3/2}. The narrow structure in the excitation function of γnnη\gamma n\rightarrow n\eta appears associated with the helicity-1/2 component of the reaction

    Global mismatches in aboveground and belowground biodiversity

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    Human activities are accelerating global biodiversity change and have resulted in severely threatened ecosystem services. A large proportion of terrestrial biodiversity is harbored by soil, but soil biodiversity has been omitted from many global biodiversity assessments and conservation actions, and understanding of global patterns of soil biodiversity remains limited. In particular, the extent to which hotspots and coldspots of aboveground and soil biodiversity overlap is not clear. We examined global patterns of these overlaps by mapping indices of aboveground (mammals, birds, amphibians, vascular plants) and soil (bacteria, fungi, macrofauna) biodiversity that we created using previously published data on species richness. Areas of mismatch between aboveground and soil biodiversity covered 27% of Earth's terrestrial surface. The temperate broadleaf and mixed forests biome had the highest proportion of grid cells with high aboveground biodiversity but low soil biodiversity, whereas the boreal and tundra biomes had intermediate soil biodiversity but low aboveground biodiversity. While more data on soil biodiversity are needed, both to cover geographic gaps and to include additional taxa, our results suggest that protecting aboveground biodiversity may not sufficiently reduce threats to soil biodiversity. Given the functional importance of soil biodiversity and the role of soils in human well-being, soil biodiversity should be considered further in policy agendas and conservation actions by adapting management practices to sustain soil biodiversity and considering soil biodiversity when designing protected areas.Peer reviewe
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