The η-meson photoproduction cross sections have been measured on C and Cu targets for the photon energies between 600 and 1100 MeV to investigate the behavior of the S11(1535) resonance in a nucleus. ...The excitation functions of the cross section as well as the angular and momentum distributions of η-mesons are in quantitative agreement with the Quantum Molecular Dynamics (QMD) model calculations in which the η-meson emission processes other than the S11(1535) resonance are also incorporated. It is shown that the η production in the γN→πηN reaction and the D15(1675) resonance formation in the γn→ηn reaction play an important role for Eγ>900 MeV.
Shock accelerated nonthermal particles are thought to contribute to modify the shock structure. Here we present two such cases at two strong interplanetary shocks in 1994 and 2003, and try to see how ...the nonlinear feature depend on the shock parameters, such as Mach number and shock angle.
In this paper, we present the measurement of the energy spectra of carbon and oxygen in cosmic rays based on observations with the Calorimetric Electron Telescope on the International Space Station ...from October 2015 to October 2019. Analysis, including the detailed assessment of systematic uncertainties, and results are reported. The energy spectra are measured in kinetic energy per nucleon from 10 GeV/n to 2.2 TeV/n with an all-calorimetric instrument with a total thickness corresponding to 1.3 nuclear interaction length. The observed carbon and oxygen fluxes show a spectral index change of ∼0.15 around 200 GeV/n established with a significance > 3σ. They have the same energy dependence with a constant C/O flux ratio 0.911 ± 0.006 above 25 GeV/n. The spectral hardening is consistent with that measured by AMS-02, but the absolute normalization of the flux is about 27% lower, though in agreement with observations from previous experiments including the PAMELA spectrometer and the calorimetric balloon-borne experiment CREAM.
Energetic ions are at times observed in the upstream region of the Earth's bow shock, and their origin is considered to be in the interaction with the shock front. While the energy of the solar wind ...ions is a few keV at most, the energy of the back streaming ions ranges from ∼5 keV to several MeV. In the present study we investigate back streaming energetic ions in the upstream of the Earth's bow shock observed by Geotail during two coronal mass ejection events. The observed local magnetic field rotated significantly during the events. Using the bow shock model and the observed magnetic field data, we found that the energetic ions appeared only when the upstream magnetic field was connected to the bow shock. The energetic ions showed two distinct distribution function characteristics, namely, the field‐aligned beam (FAB) and the loss cone–shaped distribution. While the former is occasionally detected, the latter having higher energies (30 keV to several hundred keV, compared to <18 keV for FAB) has not been reported before. Using a bow shock model, we can also estimate the shock angle at the point on the shock surface that the upstream field line is connected to and find that the distribution function shape transits from the FAB to the loss cone–shaped distribution as the shock angle becomes larger (transition at ΘBn = 70°–80°). We discuss the possible mechanisms responsible for the production of the newly found member of the energetic upstream ion family.
We have successfully detected solar neutrons at ground level in association with the X17.0 solar flare that occurred on 2005 September 7. Observations were made with the solar neutron telescopes and ...neutron monitors located in Bolivia and Mexico. In this flare, large fluxes of hard X-rays and γ-rays were observed by the
GEOTAIL and the
INTEGRAL satellites. The
INTEGRAL observations include the 4.4
MeV line γ-rays of
12C. The data suggest that solar neutrons were produced at the same time as these hard electromagnetic radiations. We have however found an apparent discrepancy between the observed and the expected time profiles. This fact suggests a possible extended neutron emission.
The kaon photo-production process on 12C has been studied by measuring neutral kaons in the photon energy range of 0.8–1.1 GeV. Neutral kaons were identified by the invariant mass constructed from ...two charged pions emitted in the KS0→π+π− decay channel. The differential and integrated cross sections in the threshold photon energy region were obtained. The obtained momentum spectra were compared with a Spectator model calculation using elementary amplitudes of kaon photo-production given by recent isobar models. The present results provide the first information on the n(γ,K0)Λ reaction, which is expected to play an important role in constructing models of strangeness production by electromagnetic interactions. The experimental results show that the cross section of C12(γ,K0) is of the same order as that of C12(γ,K+) and suggest that a slightly backward K0 angular distribution is favored in the γn→K0Λ process.
Increased event statistics will be required to definitively answer the question of the origin(s) of Ultra-High Energy Cosmic Rays (UHECR). Using current technologies however, achieving the necessary ...statistics may be financially and practically impossible. We describe the status and plans of the TARA project, an effort to detect Ultra-High-Energy Cosmic Rays by their forward scattered or "bistatic" radar signature. Bistatic radar holds promise as a new remote sensing technique for UHECR, without the duty cycle limitations of nitrogen fluorescence detectors. Such a technique could prove key in advancing the study of UHECR beyond the constraints of the current generation of cosmic ray observatories. TARA consists of a low-VHF television transmitter illuminating the air above the Telescope Array (TA), and a set of radio receivers on the far side of TA approximately 50 km distant from the transmitter. We have collected radar data since April 2011 using a 2 kW transmitter at 54.1 MHz. Recently, we received permission to increase our broadcast power to 40 kW and our effective radiated power (ERP) to 6 MW. On the receiver end, we are employing software-defined radio receivers and developing real-time trigger algorithms based on the expected air shower radar echo. In addition to presenting an overview of the project status and future plans, we will present the most recent results of searches for coincidences between radar echoes and Telescope Array air shower events.
After ionization in the solar wind, He+ pickup ions of the interstellar origin are expected to be accelerated at heliospheric shocks (the termination shock, CIR (co‐rotating interaction region) ...shocks, and planetary bow shocks), and to become the seed population for anomalous cosmic rays. Although there are many theoretical attempts to treat the 'injection' process of the helium pickup ions at these shocks, there has been little direct observational evidence. In this report we present in situ identification of the initial acceleration process of pickup He+ at the bow shock.
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