| 1. |
- Basagni, Andrea, et al.
(författare)
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On-surface photo-dissociation of C-Br bonds: towards room temperature Ullmann coupling
- 2015
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1364-548X .- 1359-7345. ; 51:63, s. 12593-12596
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Tidskriftsartikel (refereegranskat)abstract
- The surface-assisted synthesis of gold-organometallic hybrids on the Au(111) surface both by thermo-and light-initiated dehalogenation of bromo-substituted tetracene is reported. Combined X-ray photoemission (XPS) and scanning tunneling microscopy (STM) data reveal a significant increase of the surface order when mild reaction conditions are combined with 405 nm light irradiation.
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| 2. |
- Di Mauro, Mattia, et al.
(författare)
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Multimessenger constraints on the dark matter interpretation of the Fermi-LAT Galactic Center excess
- 2021
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 103:12
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Tidskriftsartikel (refereegranskat)abstract
- An excess of gamma rays in the data measured by the Fermi Large Area Telescope in the direction of the Galactic Center has been reported in several publications. This excess, labeled as the Galactic Center excess (GCE), is detected analyzing the data with different interstellar emission models, point source catalogs and analysis techniques. The characteristics of the GCE, recently measured with unprecedented precision, are all compatible with dark matter particles (DM) annihilating in the main halo of our Galaxy, even if other interpretations are still not excluded. We investigate the DM candidates that fit the observed GCE spectrum and spatial morphology. We assume a simple scenario with DM annihilating into a single channel but we inspect also more complicated models with two and three channels. We perform a search for a gamma-ray flux from a list of 48 Milky Way dwarf spheroidal galaxies (dSphs) using state-of-the-art estimation of the DM density in these objects. Since we do not find any significant signal from the dSphs, we put upper limits on the annihilation cross section that result to be compatible with the DM candidate that fits the GCE. However, we find that the GCE DM signal is excluded at the 95% confidence level by the AMS-02 (p) over bar flux data for all purely hadronic (semihadronic) channels unless the diffusive halo size L is smaller than 1.7 kpc (2.6 kpc). Such a small diffusion halo is at the 2 sigma significance lower limit for the results inferred from fluxes of radioactive cosmic rays and is in some tension with results from analyses performed with radio and gamma-ray data. Furthermore, AMS-02 e(+) data rule out the GCE DM interpretation with pure or partial annihilation into e(+)e(-). The only DM candidate that fits the GCE spectrum and fulfills all constraints obtained with the combined dSphs analysis and the AMS-02 (p) over bar and e(+) data annihilates purely (or very dominantly) into mu(+)mu(-), has a mass of similar to 60 GeV and roughly a thermal cross section.
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| 3. |
- Di Mauro, Mattia, et al.
(författare)
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Novel prediction for secondary positrons and electrons in the Galaxy
- 2023
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 108:6
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Tidskriftsartikel (refereegranskat)abstract
- The Galactic flux of cosmic-ray (CR) positrons in the GeV to TeV energy range is very likely due to different Galactic components. One of these is the inelastic scattering of CR nuclei with the atoms of the interstellar medium. The precise amount of this component determines the eventual contribution from other sources. We present here a new estimation of the secondary CR positron flux by incorporating the latest results for the production cross sections of e± from hadronic scatterings calibrated on collider data. All the reactions for CR nuclei up to silicon scattering on both hydrogen and helium are included. The propagation models are derived consistently by fits on primary and secondary CR nuclei data. Models with a small halo size (L≤2 kpc) are disfavored by the nuclei data although the current uncertainties on the beryllium nuclear cross sections may impact this result. The resulting positron flux shows a strong dependence on the Galactic halo size, increasing up to factor 1.5 moving L from 8 kpc to 2 kpc. Within the most reliable propagation models, the positron flux matches the data for energies below 1 GeV. We verify that secondary positrons contribute less than 70% of the data above a few GeV, corroborating that an excess of positrons is already present at very low energies. At larger energies, our predictions are below the data with the discrepancy becoming more and more pronounced. Our results are provided together with uncertainties due to propagation and hadronic cross sections. The former uncertainties are below 5% at fixed L, while the latter are about 7% almost independently of the propagation scheme. In addition to the predictions of positrons, we provide new predictions also for the secondary CR electron flux.
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| 4. |
- Orusa, Luca, et al.
(författare)
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New determination of the production cross section for secondary positrons and electrons in the Galaxy
- 2022
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 105:12
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Tidskriftsartikel (refereegranskat)abstract
- The cosmic-ray fluxes of electrons and positrons (e±) are measured with high precision by the space-borne particle spectrometer AMS-02. To infer a precise interpretation of the production processes for e± in our Galaxy, it is necessary to have an accurate description of the secondary component, produced by the interaction of cosmic-ray proton and helium with the interstellar medium atoms. We determine new analytical functions of the Lorentz invariant cross section for the production of π± and K± by fitting data from collider experiments. We also evaluate the invariant cross sections for several other channels, involving for example hyperon decays, contributing at the few % level on the total cross section. For all these particles, the relevant 2 and 3 body decay channels are implemented, with the polarized μ± decay computed with next-to-leading order corrections. The cross section for scattering of nuclei heavier than protons is modeled by fitting data on p+C collisions. The total differential cross section dσ/dTe±(p+p→e±+X) is predicted from 10 MeV up to 10 TeV of e± energy with an uncertainty of about 5–7% in the energies relevant for AMS-02 positron flux, thus dramatically reducing the precision of the theoretical model with respect to the state of the art. Finally, we provide a prediction for the secondary Galactic e± source spectrum with an uncertainty of the same level. As a service for the scientific community, we provide numerical tables and a script to calculate energy-differential cross sections.
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| 5. |
- Orusa, Luca, et al.
(författare)
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New determination of the production cross section for γ rays in the Galaxy
- 2023
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 107:8
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Tidskriftsartikel (refereegranskat)abstract
- The flux of γ rays is measured with unprecedented accuracy by the Fermi Large Area Telescope from 100 MeV to almost 1 TeV. In the future, the Cherenkov Telescope Array will have the capability to measure photons up to 100 TeV. To accurately interpret this data, precise predictions of the production processes, specifically the cross section for the production of photons from the interaction of cosmic-ray protons and helium with atoms of the ISM, are necessary. In this study, we determine new analytical functions describing the Lorentz-invariant cross section for γ-ray production in hadronic collisions. We utilize the limited total cross section data for π0 production channels and supplement this information by drawing on our previous analyses of charged pion production to infer missing details. In this context, we highlight the need for new data on π0 production. Our predictions include the cross sections for all production channels that contribute down to the 0.5% level of the final cross section, namely η, K+, K−, K0S, and K0L mesons as well as Λ, Σ, and Ξ baryons. We determine the total differential cross section dσ(p+p→γ+X)/dEγ from 10 MeV to 100 TeV with an uncertainty of 10% below 10 GeV of γ-ray energies, increasing to 20% at the TeV energies. We provide numerical tables and a script for the community to access our energy-differential cross sections, which are provided for incident proton (nuclei) energies from 0.1 GeV to 107 GeV (GeV/n).
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