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Abstract:

The flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of √s = 13 TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model tt¯ events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained.

Abstract:

The Einstein Telescope (ET), the European project for a third-generation gravitational-wave detector, has a reference configuration based on a triangular shape consisting of three nested detectors with 10 km arms, where each detector has a 'xylophone' configuration made of an interferometer tuned toward high frequencies, and an interferometer tuned toward low frequencies and working at cryogenic temperature. Here, we examine the scientific perspectives under possible variations of this reference design. We perform a detailed evaluation of the science case for a single triangular geometry observatory, and we compare it with the results obtained for a network of two L-shaped detectors (either parallel or misaligned) located in Europe, considering different choices of arm-length for both the triangle and the 2L geometries. We also study how the science output changes in the absence of the low-frequency instrument, both for the triangle and the 2L configurations. We examine a broad class of simple 'metrics' that quantify the science output, related to compact binary coalescences, multi-messenger astronomy and stochastic backgrounds, and we then examine the impact of different detector designs on a more specific set of scientific objectives.

Abstract:

It has been proposed that core-collapse supernovae (CCSNe) can take place along with the generation of a jet that fails to emerge from the stellar envelope of the progenitor star, i.e., a choked jet. Although the fraction of CCSNe that harbour such jets is unknown, it remains as an interesting possibility that can give rise to the production of high-energy neutrinos. In this work, we focus on the particular case of the recent type II supernova, SN 2023ixf, the closest of its class in the last decade. We describe the particle distributions of protons, pions, and muons in a putative jet applying a simple model to account for the relevant interactions, which are synchrotron cooling and interactions with the soft photon field in the ambient. After evaluating the produced fluence for different values of the viewing angle $i_{\rm j}$ with respect to the jet axis, and comparing with the upper bound by IceCube, we conclude that the generation of a choked jet in SN 2023ixf can not be ruled out. Specifically, for typical jet Lorentz factors of the jet $Γ=100$, the jet could have been produced with an half-opening angle $θ_{\rm op}=0.2\,{\rm rad}$ but for a viewing angle $i_{\rm j}\gtrsim θ_{\rm op}$, no significant Doppler boosting would take place along this direction. Therefore, the choked jet scenario in SN 2023ixf still remains compatible with observations provided our line of sight corresponds to an off-axis view of the jet.16 pages, 7 figures. Matches published versio