Light elements were produced in the first few minutes of the Universe through a sequence of nuclear reactions known as Big Bang nucleosynthesis (BBN)
. Among the light elements produced during BBN
, ...deuterium is an excellent indicator of cosmological parameters because its abundance is highly sensitive to the primordial baryon density and also depends on the number of neutrino species permeating the early Universe. Although astronomical observations of primordial deuterium abundance have reached percent accuracy
, theoretical predictions
based on BBN are hampered by large uncertainties on the cross-section of the deuterium burning D(p,γ)
He reaction. Here we show that our improved cross-sections of this reaction lead to BBN estimates of the baryon density at the 1.6 percent level, in excellent agreement with a recent analysis of the cosmic microwave background
. Improved cross-section data were obtained by exploiting the negligible cosmic-ray background deep underground at the Laboratory for Underground Nuclear Astrophysics (LUNA) of the Laboratori Nazionali del Gran Sasso (Italy)
. We bombarded a high-purity deuterium gas target
with an intense proton beam from the LUNA 400-kilovolt accelerator
and detected the γ-rays from the nuclear reaction under study with a high-purity germanium detector. Our experimental results settle the most uncertain nuclear physics input to BBN calculations and substantially improve the reliability of using primordial abundances to probe the physics of the early Universe.
ABSTRACT
A deep survey of the Large Magellanic Cloud at ∼0.1–100 TeV photon energies with the Cherenkov Telescope Array is planned. We assess the detection prospects based on a model for the emission ...of the galaxy, comprising the four known TeV emitters, mock populations of sources, and interstellar emission on galactic scales. We also assess the detectability of 30 Doradus and SN 1987A, and the constraints that can be derived on the nature of dark matter. The survey will allow for fine spectral studies of N 157B, N 132D, LMC P3, and 30 Doradus C, and half a dozen other sources should be revealed, mainly pulsar-powered objects. The remnant from SN 1987A could be detected if it produces cosmic-ray nuclei with a flat power-law spectrum at high energies, or with a steeper index 2.3–2.4 pending a flux increase by a factor of >3–4 over ∼2015–2035. Large-scale interstellar emission remains mostly out of reach of the survey if its >10 GeV spectrum has a soft photon index ∼2.7, but degree-scale 0.1–10 TeV pion-decay emission could be detected if the cosmic-ray spectrum hardens above >100 GeV. The 30 Doradus star-forming region is detectable if acceleration efficiency is on the order of 1−10 per cent of the mechanical luminosity and diffusion is suppressed by two orders of magnitude within <100 pc. Finally, the survey could probe the canonical velocity-averaged cross-section for self-annihilation of weakly interacting massive particles for cuspy Navarro–Frenk–White profiles.
Satellite experiments for gamma-ray and cosmic-ray detection employ plastic scintillators to discriminate charged from neutral particles in order to correctly identify gamma-rays and charged nuclei. ...The High Energy Cosmic Radiation Detection (HERD) facility will be among these experiments, to be installed onboard the future Chinese Space Station (CSS), to detect cosmic-rays and gamma-rays up to TeV energies. The plastic scintillator detector (PSD) will consist of scintillator tiles or bars coupled to Silicon Photomultipliers (SiPMs). To discriminate gamma-rays from charged particles and measure the ion charge up to iron nuclei a wide dynamic range is required, from few tens up to thousands of photoelectrons. We have equipped a plastic scintillator tile prototype with SiPMs produced by Hamamatsu and AdvanSiD and coupled their analog signals to the DT5550W board based on the CITIROC ASIC, produced by CAEN SpA. The CITIROC ASIC allows both the formation of a fast trigger with a configurable threshold and the digitization of analog waveforms after a preamplification and shaping stage along two paths with different gain settings. The performance of our prototype will be shown.
Plastic scintillators are widely used for anti-coincidence systems and for the identification of charged cosmic-ray nuclei in satellite experiments. For this reason, a plastic scintillator detector ...(PSD) should have a high detection efficiency for charged cosmic rays and a very good capability of measuring charges. We implemented a full and customizable simulation tool to investigate the performance of a PSD coupled to Silicon Photomultipliers. The overall performance of the detector is studied by tracking optical photons produced inside the scintillator. The simulation will be used for the design of a PSD for future space experiments, such as HERD, AMEGO, e-Astrogam. In this work we investigated in detail the effect of Birks’ saturation in the discrimination of charged ions up to iron nuclei. We will show the comparison between simulations and measurements conducted on prototype scintillator tiles.
The High Energy Cosmic Radiation Detection (HERD) facility, onboard the future China’s Space Station (CSS), will provide high quality data on charged cosmic rays and gamma rays in the energy range ...from few GeV to PeV. HERD will be equipped with a fine granularity cubic crystals calorimeter and a precision tracker detector. The entire instrument will be surrounded by a Plastic Scintillator Detector (PSD) that will be used to discriminate charged from neutral particles in order to correctly identify gamma-rays and nuclei. One proposed configuration for the HERD PSD consists of tiles of plastic scintillator, optically coupled to SiPMs. In 2019-2020, two beam tests were performed at CNAO (Centro Nazionale di Adroterapia Oncologica) in Pavia (Italy), exposing some PSD tiles, equipped with SiPMs, to low-beta p and C ion beams in order to evaluate the detector response to heavy ions. Spatial and temporal resolution were also evaluated using a radioactive source.
We present a novel approach to the determination of the pointing of Imaging Atmospheric Cherenkov Telescopes (IACTs) using the trajectories of the stars in their camera’s field of view. The method ...starts with the reconstruction of the star positions from the Cherenkov camera data, taking into account the point spread function of the telescope, to achieve a satisfying reconstruction accuracy of the pointing position. A simultaneous fit of all reconstructed star trajectories is then performed with the orthogonal distance regression (ODR) method. ODR allows us to correctly include the star position uncertainties and use the time as an independent variable. Having the time as an independent variable in the fit makes it better suitable for various star trajectories. This method can be applied to any IACT and requires neither specific hardware nor interface or special data-taking mode. In this paper, we use the Large-Sized Telescope (LST) data to validate it as a useful tool to improve the determination of the pointing direction during regular data taking. The simulation studies show that the accuracy and precision of the method are comparable with the design requirements on the pointing accuracy of the LST (≤14″). With the typical LST event acquisition rate of 10 kHz, the method can achieve up to 50 Hz pointing monitoring rate, compared to ??(1) Hz achievable with standard techniques. The application of the method to the LST prototype (LST-1) commissioning data shows the stable pointing performance of the telescope.
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