303 research outputs found
Quantitative determination of spatial resolution and linearity of position-sensitive LG-SiPMs at sub-millimeter scale via Ricean distribution fitting
No full textPosition-sensitive SiPMs are useful in all light detection applications requiring a small number of readout channels while preserving the information about the incoming light’s interaction position. Focusing on a 2 × 2 array of LG-SiPMs covering an area of ∼ 15.5 × 15.5 mm2 with just 6 readout channels, we proposed a quantitative method to evaluate the image reconstruction performance. The method is based on a statistical approach to assess the device’s precision (spatial resolution) and accuracy (linearity) in reconstructing the light spot center of gravity. This evaluation is achieved through a Rice probability distribution function fitting. We obtained an average sensor spatial resolution of 81 ± 3 μm (standard deviation) with a corresponding accuracy of 231 ± 4 μm
Detection of the Geminga pulsar at energies down to 20 GeV with the LST-1 of CTAO
No full text Context. Geminga is the third gamma-ray pulsar firmly detected by imaging atmospheric Cherenkov telescopes (IACTs) after the Crab and the Vela pulsars. Most of its emission is expected at tens of giga-electronvolts, and, out of the planned telescopes of the upcoming Cherenkov Telescope Array Observatory (CTAO), the Large-Sized Telescopes (LSTs) are the only ones with optimised sensitivity at these energies.
Aims. We aim to characterise the gamma-ray pulse shape and spectrum of Geminga as observed by the first LST (hereafter LST-1) of the Northern Array of CTAO. Furthermore, this study confirms the great performance and the improved energy threshold of the telescope, as low as 10 GeV for pulsar analysis, with respect to current-generation Cherenkov telescopes.
Methods. We analysed 60 hours of good-quality data taken by the LST-1 between December 2022 and March 2024 at zenith angles below 50°. Additionally, a new Fermi -LAT analysis of 16.6 years of data was carried out to extend the spectral analysis down to 100 MeV. Lastly, a detailed study of the systematic effects was performed.
Results. We report the detection of Geminga in the energy range between 20 and 65 GeV. Of the two peaks of the phaseogram, the second one, P2, is detected with a significance of 12.2 σ , while the first (P1) reaches a significance level of 2.6 σ . The best-fit model for the spectrum of P2 was found to be a power law with a spectral index of Γ = (4.5 ± 0.4 stat ) −0.6 sys +0.2 sys , compatible with the previous results obtained by the MAGIC Collaboration. No evidence of curvature is found in the LST-1 energy range. The joint fit with Fermi -LAT data confirms a preference for a sub-exponential cut-off over a pure exponential, even though both models fail to reproduce the data above several tens of giga-electronvolts. The overall results presented in this paper prove that the LST-1 is an excellent telescope for the observation of pulsars, and improved sensitivity is expected to be achieved with the full CTAO Northern Array. </p
Maximum Likelihood Estimation: a Method for Calibration, Reconstruction and Data Analysis of Cherenkov Telescopes
No full textPlusieurs des questions fondamentales adressées après la première observation du rayonnement cosmique n'ont pas trouvé de réponses. Bien que théorisées, l'accélération, l'interaction et la propagation des rayons cosmiques à travers l'univers sont toujours sujet à débat. Cette thèse se concentre sur deux expériences d'astrophysique des hautes énergies: le CTA et IceCube. Ce travail analyse des données et simulations à plusieurs niveaux de reconstruction. Les méthodes de reconstructions sont toutes basées sur l'estimation du maximum de vraisemblance. La calibration du prototype de la caméra SST-1M est relatée. Une nouvelle méthode de paramétrisation des images utilisant un maximum de vraisemblance a été développée. Elle utilise des contraintes spatiales et temporelles qui découlent du développement de la lumière Cherenkov dans les gerbes atmosphériques. Finalement, des évènements de neutrinos de l'observatoire IceCube ont été utilisés dans le cadre d'une étude de corrélation avec les rayons cosmiques à très hautes énergies. L'analyse compte le nombre de rayons cosmiques à très hautes énergies étant corrélés avec les neutrinos d'IceCube
All-flavor constraints on nonstandard neutrino interactions and generalized matter potential with three years of IceCube DeepCore data
No full textWe report constraints on nonstandard neutrino interactions (NSI) from the observation of atmospheric neutrinos with IceCube, limiting all individual coupling strengths from a single dataset. Furthermore, IceCube is the first experiment to constrain flavor-violating and nonuniversal couplings simultaneously. Hypothetical NSI are generically expected to arise due to the exchange of a new heavy mediator particle. Neutrinos propagating in matter scatter off fermions in the forward direction with negligible momentum transfer. Hence the study of the matter effect on neutrinos propagating in the Earth is sensitive to NSI independently of the energy scale of new physics. We present constraints on NSI obtained with an all-flavor event sample of atmospheric neutrinos based on three years of IceCube DeepCore data. The analysis uses neutrinos arriving from all directions, with reconstructed energies between 5.6 GeV and 100 GeV. We report constraints on the individual NSI coupling strengths considered singly, allowing for complex phases in the case of flavor-violating couplings. This demonstrates that IceCube is sensitive to the full NSI flavor structure at a level competitive with limits from the global analysis of all other experiments. In addition, we investigate a generalized matter potential, whose overall scale and flavor structure are also constrained
Velocity Independent Constraints on Spin-Dependent DM-Nucleon Interactions from IceCube and PICO
No full textAdopting the Standard Halo Model (SHM) of an isotropic Maxwellian velocity distribution for dark matter (DM) particles in the Galaxy, the most stringent current constraints on their spin-dependent scattering cross-section with nucleons come from the IceCube neutrino observatory and the PICO-60 superheated bubble chamber experiments. The former is sensitive to high energy neutrinos from the self-annihilation of DM particles captured in the Sun, while the latter looks for nuclear recoil events from DM scattering off nucleons. Although slower DM particles are more likely to be captured by the Sun, the faster ones are more likely to be detected by PICO. Recent N-body simulations suggest significant deviations from the SHM for the smooth halo component of the DM, while observations hint at a dominant fraction of the local DM being in substructures. We use the method of Ferrer et al. (JCAP 1509: 052, 2015) to exploit the complementarity between the two approaches and derive conservative constraints on DM-nucleon scattering. Our results constrain () at C.L. for a DM particle of mass 1 TeV annihilating into () with a local density of . The constraints scale inversely with and are independent of the DM velocity distribution
eV-Scale Sterile Neutrino Search Using Eight Years of Atmospheric Muon Neutrino Data from the IceCube Neutrino Observatory
No full textThe results of a 3+1 sterile neutrino search using eight years of data from the IceCube Neutrino Observatory are presented. A total of 305 735 muon neutrino events are analyzed in reconstructed energy-zenith space to test for signatures of a matter-enhanced oscillation that would occur given a sterile neutrino state with a mass-squared differences between 0.01 and 100 eV2. The best-fit point is found to be at sin2(2θ24)=0.10 and Δm412=4.5 eV2, which is consistent with the no sterile neutrino hypothesis with a p value of 8.0%
Development of an analysis to probe the neutrino mass ordering with atmospheric neutrinos using three years of IceCube DeepCore data
No full textThe Neutrino Mass Ordering (NMO) remains one of the outstanding questions in the field of neutrino physics. One strategy to measure the NMO is to observe matter effects in the oscillation pattern of atmospheric neutrinos above , as proposed for several next-generation neutrino experiments. Moreover, the existing IceCube DeepCore detector can already explore this type of measurement. We present the development and application of two independent analyses to search for the signature of the NMO with three years of DeepCore data. These analyses include a full treatment of systematic uncertainties and a statistically-rigorous method to determine the significance for the NMO from a fit to the data. Both analyses show that the dataset is fully compatible with both mass orderings. For the more sensitive analysis, we observe a preference for normal ordering with a p-value of and for the inverted ordering hypothesis, while the experimental results from both analyses are consistent within their uncertainties. Since the result is independent of the value of and obtained from energies , it is complementary to recent results from long-baseline experiments. These analyses set the groundwork for the future of this measurement with more capable detectors, such as the IceCube Upgrade and the proposed PINGU detector
Reconstruction of extensive air shower images of the first Large Size Telescope prototype of CTA using a novel likelihood technique
No full textGround-based gamma-ray astronomy aims at reconstructing the energy and
direction of gamma rays from the extensive air showers they initiate in the
atmosphere. Imaging Atmospheric Cherenkov Telescopes (IACT) collect the
Cherenkov light induced by secondary charged particles in extensive air showers
(EAS), creating an image of the shower in a camera positioned in the focal
plane of optical systems. This image is used to evaluate the type, energy and
arrival direction of the primary particle that initiated the shower. This
contribution shows the results of a novel reconstruction method based on
likelihood maximization. The novelty with respect to previous likelihood
reconstruction methods lies in the definition of a likelihood per single camera
pixel, accounting not only for the total measured charge, but also for its
development over time. This leads to more precise reconstruction of shower
images. The method is applied to observations of the Crab Nebula acquired with
the Large Size Telescope prototype (LST-1) deployed at the northern site of the
Cherenkov Telescope Array.Comment: Proceedings of the 37th International Cosmic Ray Conference (ICRC
2021), Berlin, Germany. https://pos.sissa.it/395/71
The POSiCS handheld gamma-ray camera for radio-guided surgery
No full textIntraoperative imaging techniques such as Sentinel Lymph Node Biopsy (SLNB) and Radio Occult Lesion Localization (ROLL) are adopted as a standard in breast cancer and melanoma surgery. Traditional 1D gamma probes, while widely used, lack spatial imaging capability, limiting their effectiveness near injection sites. To address this, we present POSiCS: a compact, wireless gamma camera designed for real-time intraoperative imaging. POSiCS employs a high-density scintillator and novel position-sensitive SiPMs developed by FBK, enabling sub-millimeter spatial resolution with only 8 readout channels. The device supports interchangeable collimators for adjustable sensitivity and resolution, and is optimized for detection of 99mTc. Performance tests demonstrate a spatial resolution of 1.4 mm and a sensitivity of up to 481 cps/MBq, as well as reliable energy discrimination at 140 keV. Phantom studies confirm the system’s ability to resolve closely spaced sources with low activity levels, reinforcing its suitability for SLNB and ROLL. With a patent filed and promising initial results, POSiCS offers a portable, high-performance solution that enhances surgical precision and reduces procedure time
Compact and Handheld SiPM-Based Gamma Camera for Radio-Guided Surgery and Medical Imaging
No full textIn the continuous pursuit of minimally invasive interventions while ensuring a radical excision of lesions, Radio-Guided Surgery (RGS) has been for years the standard for image-guided surgery procedures, such as the Sentinel Lymph Node biopsy (SLN), Radio-guided Seed Localization (RSL), etc. In RGS, the lesion has to be identified precisely, in terms of position and extension. In such a context, going beyond the current one-point probes, introducing portable but high-resolution cameras, handholdable by the surgeon, would be highly beneficial. We developed and tested a novel compact, low-power, handheld gamma camera for radio-guided surgery. This is based on a particular position-sensitive Silicon Photomultiplier (SiPM) technology—the FBK linearly graded SiPM (LG-SiPM). Within the camera, the photodetector is made up of a 3 × 3 array of 10 × 10 mm2 SiPM chips having a total area of more than 30 × 30 mm2. This is coupled with a pixelated scintillator and a parallel-hole collimator. With the LG-SiPM technology, it is possible to significantly reduce the number of readout channels to just eight, simplifying the complexity and lowering the power consumption of the readout electronics while still preserving a good position resolution. The novel gamma camera is light (weight), and it is made to be a fully stand-alone system, therefore featuring wireless communication, battery power, and wireless recharge capabilities. We designed, simulated (electrically), and tested (functionally) the first prototypes of the novel gamma camera. We characterized the intrinsic position resolution (tested with pulsed light) as being ~200 µm, and the sensitivity and resolution when detecting gamma rays from Tc-99m source measured between 134 and 481 cps/MBq and as good as 1.4–1.9 mm, respectively
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