At the Large Hadron Collider (LHC), protons are collided at the highest possible energy to generate subatomic elementary particles. We use the results of these collisions to understand our universe at the most fundamental level. Many theorists believe that new physics exists at a very high energy. The top quark is the heaviest elementary particle known to date with unique properties. It is therefore naturally suspected to have hidden connections with new physics. The simultaneous production of four top-quarks (tttt) is the most energetic process accessible with the LHC, making it a unique place to search for heavy new physics, which are less likely to appear elsewhere. The first evidence of these extremely rare events was only revealed last year, and we know very little about them. With the world-record energy at LHC Run3 (13.6 TeV), we expect 20% higher tttt events production rate. This offers a timely opportunity to further study this process. With an aim to find new physics, we will study tttt events in unprecedented detail with the ATLAS experiment at the LHC. We will measure the inclusive production rate and the kinematic properties of these events. We will use the measured results to probe new physics, with unique approaches that do not rely on new physics predictions made upon specific assumptions (which could be wrong). The results have the potential to reveal new physics that are too energetic and beyond the reach of the LHC. This will be the first time this is done for tttt events. The measured tttt event kinematics will be corrected to remove effects from the detector resolution and acceptance. This allows theorists to directly test their new physics predictions against the experimental results, continuously generating impact in the relevant scientific community. We will combine the results of tttt events with those of other types of events containing top quarks to build a global picture of the top quark in terms of its subtle connections to new physics.

Time-of-flight positron emission tomography (TOF-PET) is the standard-of-care in cancer detection. TOF-PET scanners’ performance is dependent on the radiation detectors they use. Improving time and spatial detection features in such detectors will dramatically impact the diagnostic capacity of TOF-PET systems. The goal of this project is to build a gamma detector concept for TOF-PET able to improve the time resolution and spatial segmentation of state-of-the-art detectors by a factor of up to 7 and 10, respectively, without additional production costs. CHLOE-PET is a forward-looking gamma detector design for TOF-PET able to exploit the new photodetector technologies that are currently under development and will become available within the next 5-to-10 years. The novelty of the proposed design lies in using Cherenkov light as a prompt time source, using an innovative geometry optimized to maximize light collection, and employing photodetectors with small pixel pitch. This project is the first attempt to build a detector module scalable to a full-size system that can be used in a hospital setting. The CHLOE-PET detector will consist of bismuth germanate (BGO) crystals with 12 mm thickness and will combine the readout of scintillation and Cherenkov light. CHLOE-PET will provide an effective 3D segmentation of 2x2x2 mm3, an intrinsic photon time spread of 20 ps, and no intrinsic radiation background (unlike state-of-the-art TOF-PET detectors). Such improvements will allow increasing the signal-to-noise ratio of images by >2-fold, to be able to detect lesions of 2 mm size (>3 times the current performance), to build portable high-performance organ-dedicated TOF-PET systems, and to universalize the use of dynamic TOF-PET studies. The combination of these outcomes will provide significantly better diagnostic capabilities in a range of fields such as oncology, neurology, or cardiology, among others, and ultimately boost treatment efficacy and patient comfort.