Calendario Dottorato

Ph.D in Physics

Journal Club Seminari 2024

28/10/2024  
aula 108 - primo piano- V. della Vasca Navale n. 84

ore: 14:30	Romano Orlandini DOTTORATO IN FISICA	Study of a kinematic fit algorithm in the context of HDBS in the final state at the ATLAS detector.
		Abstract: The Higgs Di-Boson Searches (HDBS) are a fundamental step for the study and comprehension of the Higgs field potential, responsible for the electro-weak spontaneous symmetry breaking. In fact, observing the production of Higgs bosons pairs at the LHC would allow us to finally measure the tri-linear self-coupling term of the Higgs and, subsequently, to determine the cubic term of the potential. However, due to the low number of events expected, one of the current objectives in this field of research is to develop and optimize analysis tools able to increase experimental sensitivity to such events. In this talk I will discuss the implementation and some results of a very promising kinematic fit based algorithm, used in the context of the decay of two Higgs bosons in photons and -jets pairs. This tool is in fact able to substantially improve the energetic resolution of the hadronic component of the decay channel thanks to the imposition of kinematic constraints. As such, its application should increase our ability to reject the non-resonant  background, allowing us to determine more stringent confident intervals on the tri-linear self-coupling value.

ore: 15:00	Francesco Borra DOTTORATO IN FISICA	Search for neutrinoless double beta decay with LEGEND
		Abstract: Neutrinoless double beta decay (0vββ) is a hypothetical process which, if observed, would prove the neutrino to be a Majorana particle. This process is not predicted by the Standard Model, and violates the lepton number. Its experimental signature is a sharp peak at the end-point of the double beta spectrum (Qββ). The experimental strategy consists in collecting the spectrum from the sum of the energies of the two emitted electrons while minimizing the physics backgrounds from (especially) radiogenic processes in the Qββ region. This presentation will illustrate the LEGEND project, which aims to search for 0vββ in 76Ge. The technique relies on high-purity germanium (HPGe) detectors that serve both as the source of the decaying isotope and as detectors for the emitted electrons. To increase the experimental exposure, the germanium crystals are enriched in 76Ge mass concentration to over 90%. The Q-value for 0vββ in 76Ge is 2039 keV. Ge detectors offer excellent energy resolution, dropping below 3 keV FWHM at Qββ. The LEGEND experiment (Large Enriched Germanium Experiment for Neutrinoless double beta Decay) is currently in its first phase, with the LEGEND-200 detector collecting physics data at the Gran Sasso National Laboratories. In this phase, the goal is to achieve a sensitivity for the half-life of the 76Ge 0vββ decay of 1027 years. In its next phase, LEGEND-1000 aims to explore half-lives around 1028 years. To achieve the design sensitivity for the 0vββ half-life, it is necessary to suppress radiogenic and cosmogenic backgrounds as much as possible. For this purpose, LEGEND-200 employs a combined strategy based on Pulse Shape Discrimination and two active vetoes: a muon veto and a liquid argon veto. The talk will therefore focus on the technological aspects and background reduction strategies in view of LEGEND-1000 and will show the first results from LEGEND-200

ore: 15:30	Ilaria Villani DOTTORATO IN FISICA	Shedding X-ray light on the formation sites of high-z Hot Dust Obscured luminous quasars: the case of W0410-09 at z~ 3.6
		Abstract: Hot Dust Obscured Galaxies (Hot DOGs) represent a transitional, heavily dust-enshrouded phase in the merger-driven, feedback-dominated evolutionary sequence of luminous (Lbol > 1e47 erg/s) QSOs. Due to the presence of large amount of dust, this phase is thought to be a key stage of BH growth and AGN evolution. Galaxy formation models predict these systems to grow via mergers, that can deliver large amounts of gas toward their centers, induce intense bursts of star formation and feed their supermassive black holes. The Hot DOG W0410-09 (z ~ 3.6) is one of the brightest (L_IR > 1e14 Lsun) and most gas-rich (> 1e11 Msun) star-forming (> 1000 Msun/yr) galaxies discovered so far. MUSE revealed that W0410−09 is surrounded by an exceptional swarm of Lyα-emitting galaxies making this circumgalactic environment (≈ 400 kpc) one of the densest regions in the Universe observed so far. However, the Lyα nebula around W0410−09 shows an extension of only ~ 30 kpc, much smaller than typically found (up to hundreds of kpc) around luminous, unobscured QSOs at z~2-4. ALMA observations of W0410-09 detected a massive rotationally supported fast rotating molecular disk, which challenge our current understanding of dust-enshrouded BH growth via major mergers. I will present a study of the nuclear properties of W0410-09 based on a deep Chandra (~ 300 ks) observation, to complement the information from MUSE and ALMA. The X-ray spectral analysis was very challenging due to the high level of intrinsic obscuration and, remarkably, resulted into the discovery of the most absorbed (Nh ~ 1e24 cm-2) luminous (Lx > 1e45 erg/s) QSO at z>3.5. This heavy Compton-thick absorber might account for the lack of "standard" Lyα nebula around W0410-09. As a matter of fact, X-ray data hints to the presence of multiple obscured AGN activity among companion galaxies, which is likely promoted by the exceptional evolutionary stage in a dense environment undergone by Hot DOGs. The Chandra analysis coupled with the multiwavelength MUSE and ALMA coverage allows us to shed light on the close environment of this peculiar high-z QSO.