Journal Club

(DOTTORATO IN FISICA)

Study of a kinematic fit algorithm in the context of HDBS in the final state at the ATLAS detector.

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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.
 

 

(DOTTORATO IN FISICA)

Search for neutrinoless double beta decay with LEGEND

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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

 

 

(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

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            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.
 

 

(DOTTORATO IN FISICA)

Towards a Lagrangian Double Copy for Supergravity

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In 2008 Bern, Carrasco and Johansson introduced the so-called Double Copy relations, which are correspondences between gravitational and Yang-Mills theories which allow one to compute tree-level n-graviton amplitudes from tree-level n-gluon ones. These relations provided tremendous simplifications in the computations for graviton scattering, thus allowing for a greater insight on (super)gravitational theories. One of the topics of main interest concerning the Double Copy is the search for a possible Lagrangian origin to the relations, i.e. a possible connection between the Lagrangians of Yang-Mills theories with those of gravitational theories which justifies the correspondence found for the amplitudes. In this contribution, we present our strategy for the Double Copy construction of perturbative Lagrangians for gravitational theories by discussing the examples of the free Lagrangians of N=0 Supergravity and of N=1 Supergravity coupled to a chiral multiplet.

 

 

(DOTTORATO IN FISICA)

Evolution and dust production by AGB stars in Andromeda

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The stars evolving through the Asymptotic Giant Branch (AGB) are generally regarded as highly efficient dust
manufactures, owing to the thermodynamic properties of their wind, which prove extremely favourable to
the condensation process of gas molecules into solid grains. In this talk, I will describe the dust and
mineralogy of the dust formed in the surroundings of this class of stars, outlining the role of mass and
metallicity, and the importance of these studies for the characterization of evolved stellar populations in
galaxies. In detail, I will focus on one of the most interesting and well investigated galaxies: Andromeda
(M31). The scope of this study is to analyze the AGB population of M31, in order to obtain a full
characterization of the sources of the progenitors, and the current evolutionary stage and dust production
rate.

 

(DOTTORATO IN FISICA)

Estimating the physical properties of the snow cover in the Apennines through GPR and FDR techniques

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Data and simulations show a significant reduction in the snow cover extension due to global warming, and this is particularly evident in the Central Italian Apennines (CIA). Due to its high spatial and temporal variability, it is necessary to use satellite data that allow constant and large-scale monitoring of snow cover: in this context, the SMIVIA project aimed to integrate Synthetic Aperture Radar (SAR) data and in situ measurements to characterize snow physical parameters in the CIA region. The aim of this research work is to use geophysical techniques for carrying out in situ measurements of snow cover properties and to characterize the accuracy and precision of the estimates. For this purpose, two electromagnetic techniques are employed: Ground Penetrating Radar (GPR) and Frequency Domain Reflectometry (FDR) via Vector Network Analyzer (VNA). GPR technique, based on the emission of electromagnetic pulses into the snow layer, exploits the dielectric contrasts in the subsurface and provides data on its physical properties and stratigraphy in a non-invasive way. FDR technique uses high-frequency signals that propagates along an open-ended transmission line to estimate dielectric parameters like permittivity and conductivity, that allow to obtain density and water content via empirical relations. The results of the measurements, carried out for two winter seasons in two sites located in the CIA, show that GPR allows an accurate reconstruction of the snow-soil interface and the thickness of the snow cover, while VNA measurements, performed by inserting the probes horizontally inside a trench dug in the snow, allows to estimate the snow density and water content: the comparison with gravimetric measurements shows a good agreement within the uncertainties, especially in the case of wet snow. In conclusion, this work has shown that combining GPR and FDR technique represents a promising tool to characterize snowpacks and their stratigraphy, allowing a continuous monitoring fundamental for the validation of satellite measurements.
 

 

(DOTTORATO IN FISICA)

X-ray study of optically selected dual AGN

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Galaxy merging phenomena at pc−tens of kpc scales are subjects of interest in modern Astrophysics, since they could cause the triggering of the Active Galactic Nuclei (AGNs) and the formation of Super Massive Black Holes (SMBHs) at the center of the galaxies, as several studies suggest. When two interacting galaxies host two AGNs (one each), we refer to them as dual AGN. However, multi-waveband observations are needed in order to properly identify and characterize dual AGNsystems. X-rays are a powerful method with which we can detect AGNs and study their properties, such as the absorption caused by a dusty material which obscures the inner regions of the AGN. Here we present the X-ray study of 28 dual AGN candidates optically selected or via a double-peaked [OIII]λ5007Å line profile, or via the photometrically resolved image of the two nuclei. By performing a detailed spectral analysis of 17 sources of our sample, we find that ∼70%of the sources seems to be in an absorption regime (Hydrogen column density nH > 1022cm−2). This absorption regime is confirmed by several diagnostics, such as the L[OIII]−Lintr X (2−10keV) and the FX(2−10keV)/νFν(22µm) relations, the latter also highlighting a fraction of ∼ 20% of Compton-Thick (nH > 1024 cm−2) sources. These results suggest that the fraction of obscured sources is significantly higher when looking at dual systems, with respect to isolated AGN (where the fraction of absorbed sources is ∼ 45%).

 

 

(DOTTORATO IN FISICA)

A simplest flavor model for leptons: the revival of modular S3

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In the recent past, substantial effort has been devoted to exploring flavor symmetries to understand neutrino masses and mixing. However, traditional flavor symmetry models proved to be quite unsatisfactory. In 2017, a new 'bottom-up' approach based on modular invariance was suggested, wherein the Yukawa couplings of the Standard Model become modular forms of level N. Within this framework, we addressed the following question: is it possible to employ the lowest level and most minimal modular group S3 to construct predictive lepton mass models? As demonstrated in our work, the answer is affirmative if we assume a certain set of guiding principles that fully exploit modular invariance. Among other observables, the model is able to predict a normal ordering of neutrino masses and a Dirac CP-phase near maximal violation.

 

 

(DOTTORATO IN FISICA)

The DISSHARTA - 2 Experiment at DAONE

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QCD is the theory that describes the strong interaction. In this theory the mediators (gluons) are self-interacting. This peculiarity reflects in a particular running of the coupling constant as a function of the energy scale: at high momentum transfer (Q²) the coupling of the strong interaction (αs) is decreasing, and the quarks and gluons behave almost as free particles enabling the treatment of QCD by using the perturbation theory. At low Q² below energies of ∼1 GeV), on the other hand, αs diverges making QCD non-treatable perturbatively. For this reason, phenomenological models are an appropriate method to understand how hadrons interact at low energy.
In this framework, the exotic atoms with hadrons (atoms in which a negatively charged hadron replaces an electron and bounds to a nucleus) represent a unique experimental tool to test and provide inputs to phenomenological models on strong interactions at threshold.
Particularly, the experimental studies on kaonic atoms play a key role since they can directly probe the non-perturbative regime of the QCD in the strangeness sector.
The DAΦΝE collider at INFN-LNF represents an ideal machine to perform kaonic atoms measurements, thanks to the low-energetic and almost monochromatic beam of kaons generated.
The precise measurement of the shift and the width induced on the 1s level of kaonic hydrogen, two important observables strictly liked to the iso-scalar and iso-vector antikaon-nucleon scattering lenghts, was achieved by the SIDDHARTA experiment. To fully disentangle the iso-scalar and iso-vector scattering lengths, the measurement of kaonic deuterium is necessary as well.
The SIDDHARTA-2 experiment, now taking data at the DAΦΝE collider, aims to fulfill the need of this measurement, providing important constraints to models on low-energy strong interactions. Furthermore, the collaboration is exploring the possibility to perform future kaonic atoms experiments crucial for a deeper understanding of the kaon-nucleons interactions in function of the nuclear density, developing X-ray detector systems beyond the current state-of-art.
The collaboration also aims to solve the kaon mass puzzle, that alters many measurements in particle physics.