How will our knowledge of short gamma-ray bursts affect the distance measurement of binary neutron stars?

Gravitational waves from binary neutron stars associated with short gamma-ray bursts have drawn considerable attention due to their prospect in cosmology. For such events, the sky locations of sources can be pinpointed with techniques such as identifying the host galaxies. However, the cosmological applications of these events still suffer from the problem of degeneracy between luminosity distance and inclination angle. To address this issue, a technique was proposed in previous study, i.e., using the collimation property of short gamma-ray bursts. Based on the observations, we assume that the cosine of inclination follows a Gaussian distribution, which may act as a prior in the Bayes analysis to break the degeneracy. This paper investigates the effects of different Gaussian priors and detector configurations on distance measurement and cosmological research. We first derive a simplified Fisher information matrix for demonstration, and then conduct quantitative analyses via simulation. By varying the number of third-generation detectors and the scale of prior, we generate four catalogs of 1000 events. It is shown that, in the same detecting period, a network of detectors can recognize more and farther events than a single detector. Besides, adopting tighter prior and employing multiple detectors both decrease the error of luminosity distance. Also considered is the performance of a widely adopted formula in the error budget, which turns out to be a conservative choice in each case. As for cosmological applications, for the ΛCDM model, 500, 200, 600, and 300 events are required for the four configurations to achieve 1% H0 accuracy. With all 1000 events in each catalog, H0 and Ωm can be constrained to (0.66%, 0.37%, 0.76%, 0.49%), and (0.010, 0.006, 0.013, 0.010), respectively. The results of the Gaussian process also show that the gravitational wave standard siren can serve as a probe of cosmology at high redshifts.

Study of Multi-Pixel Scintillator Detector Configurations for Measuring Polarized Gamma Radiation

When a positron annihilates, two gamma photons are created with orthogonal polarizations. It is possible to use coincidence measurements where both photons undergo Compton scattering to estimate their initial relative polarization orientation. This information is of great interest in gamma imaging systems, such as Positron Emission Tomography, where it may be used as an additional tool to distinguish true coincidence events from scatter and random background. The successful utilization of this principle critically depends on the detector’s angular and energy resolution, which determine its polarimetric performance. In this study, we use Monte Carlo simulations based on the Geant4 toolkit to model two multi-pixel detector configurations identified as prospective for the measurement of gamma-ray polarization in PET. One is based on 2 mm × 2 mm × 20 mm LYSO scintillators and the other is based on 3 mm × 3 mm × 20 mm GAGG scintillators. Each configuration has a pair of modules, each consisting of 64 crystals set up in a single 8 × 8 matrix, where both the recoil electron and the Compton-scattered photon are absorbed. We simulate positron annihilation by generating two back-to-back gamma photons of 511 keV with orthogonal polarizations. The Compton scattering is successfully identified and the modulation of the azimuthal angle difference is clearly observed. The configuration based on GAGG crystals demonstrates slightly better polarimetric performance than the one based on LYSO crystals, reflected in the more pronounced azimuthal modulation.

Anomaly Detection based on Compressed Data: an Information Theoretic Characterization

<div>We analyze the effect of lossy compression in the processing of sensor signals that must be used to detect anomalous events in the system under observation. The intuitive relationship between the quality loss at higher compression and the possibility of telling anomalous behaviours from normal ones is formalized in terms of information-theoretic quantities. Some analytic derivations are made within the Gaussian framework and possibly in the asymptotic regime for what concerns the stretch of signals considered.</div><div>Analytical conclusions are matched with the performance of practical detectors in a toy case allowing the assessment of different compression/detector configurations.</div>

Anomaly Detection based on Compressed Data: an Information Theoretic Characterization

<div>We analyze the effect of lossy compression in the processing of sensor signals that must be used to detect anomalous events in the system under observation. The intuitive relationship between the quality loss at higher compression and the possibility of telling anomalous behaviours from normal ones is formalized in terms of information-theoretic quantities. Some analytic derivations are made within the Gaussian framework and possibly in the asymptotic regime for what concerns the stretch of signals considered.</div><div>Analytical conclusions are matched with the performance of practical detectors in a toy case allowing the assessment of different compression/detector configurations.</div>

Improving the Measurement Quality of Small Satellite Star Trackers

Recent demand from the small satellite community has led to the development of a new series of star trackers that are specifically designed for small satellites. These units represent substantial improvements in mass, power consumption and cost over traditional star trackers, but suffer slightly in terms of accuracy and availability performance. The primary factors inhibiting their performance are the use of significantly smaller optics, and commercial off the shelf components (COTS). This thesis presents a series of strategies for improving the performance of small satellite star trackers (SSSTs). These goals are realized through the development of offline calibration procedures, flight software, validation tests, and optical trade studies to guide future development. This thesis begins with the development of a target-based focusing procedure that enables precision control over the focus of the sensor optics. This improves the detection performance for dim stars, and ultimately increases the availability of the attitude solution. Flight software is developed to compensate for the effects of electronic rolling shutters, which reside on most COTS image detectors. Combined with a developed camera calibration procedure, these tools reduce the uncertainty with which a star tracker can measure the direction vectors to stars in view, ultimately increasing sensor accuracy. Integrated tests are performed to validate detection performance in dynamic conditions. These tests specifically examine the effect of slew rate on star tracker detection, and availability performance. Lastly, this thesis presents a series of optical trades studies that seek to identify design requirements for high performance SSSTs. The trends in availability and accuracy performance are examined as a function of different lens/detector configurations as well dual/triple-head sensor configurations. Together, these strategies represent tools that aim to improve small satellite star tracker performance and guide future sensor development.

Improving the Measurement Quality of Small Satellite Star Trackers

Recent demand from the small satellite community has led to the development of a new series of star trackers that are specifically designed for small satellites. These units represent substantial improvements in mass, power consumption and cost over traditional star trackers, but suffer slightly in terms of accuracy and availability performance. The primary factors inhibiting their performance are the use of significantly smaller optics, and commercial off the shelf components (COTS). This thesis presents a series of strategies for improving the performance of small satellite star trackers (SSSTs). These goals are realized through the development of offline calibration procedures, flight software, validation tests, and optical trade studies to guide future development. This thesis begins with the development of a target-based focusing procedure that enables precision control over the focus of the sensor optics. This improves the detection performance for dim stars, and ultimately increases the availability of the attitude solution. Flight software is developed to compensate for the effects of electronic rolling shutters, which reside on most COTS image detectors. Combined with a developed camera calibration procedure, these tools reduce the uncertainty with which a star tracker can measure the direction vectors to stars in view, ultimately increasing sensor accuracy. Integrated tests are performed to validate detection performance in dynamic conditions. These tests specifically examine the effect of slew rate on star tracker detection, and availability performance. Lastly, this thesis presents a series of optical trades studies that seek to identify design requirements for high performance SSSTs. The trends in availability and accuracy performance are examined as a function of different lens/detector configurations as well dual/triple-head sensor configurations. Together, these strategies represent tools that aim to improve small satellite star tracker performance and guide future sensor development.

Simplified fast detector simulation in MadAnalysis 5

We introduce a new simplified fast detector simulator in the MadAnalysis 5 platform. The Python-like interpreter of the programme has been augmented by new commands allowing for a detector parametrisation through smearing and efficiency functions. On run time, an associated C++ code is automatically generated and executed to produce reconstructed-level events. In addition, we have extended the MadAnalysis 5 recasting infrastructure to support our detector emulator, and we provide predefined LHC detector configurations. We have compared predictions obtained with our approach to those resulting from the usage of the Delphes 3 software, both for Standard Model processes and a few new physics signals. Results generally agree to a level of about 10% or better, the largest differences in the predictions stemming from the different strategies that are followed to model specific detector effects. Equipped with these new functionalities, MadAnalysis 5 now offers a new user-friendly way to include detector effects when analysing collider events, the simulation of the detector and the analysis being both handled either through a set of intuitive Python commands or directly within the C++ core of the platform.

GPU simulation with Opticks: The future of optical simulations for LZ

The LZ collaboration aims to directly detect dark matter by using a liquid xenon Time Projection Chamber (TPC). In order to probe the dark matter signal, observed signals are compared with simulations that model the detector response. The most computationally expensive aspect of these simulations is the propagation of photons in the detector’s sensitive volume. For this reason, we propose to offload photon propagation modelling to the Graphics Processing Unit (GPU), by integrating Opticks into the LZ simulations workflow. Opticks is a system which maps Geant4 geometry and photon generation steps to NVIDIA’s OptiX GPU raytracing framework. This paradigm shift could simultaneously achieve a massive speed-up and an increase in accuracy for LZ simulations. By using the technique of containerization through Shifter, we will produce a portable system to harness the NERSC supercomputing facilities, including the forthcoming Perlmutter supercomputer, and enable the GPU processing to handle different detector configurations. Prior experience with using Opticks to simulate JUNO indicates the potential for speed-up factors over 1000× for LZ, and by extension other experiments requiring photon propagation simulations.