Comparative overview of differential measurements at ATLAS and CMS

The study of the top quark has a central role for both the ATLAS and CMS experiments. The measurement of the $t\bar{t}$ production differential cross section, in particular, is sensitive to existence of new resonances, it is a stringent test of perturbative QCD calculations and it is used to improve the modelling of $t\bar{t}$ production. ATLAS and CMS provided a large number of results during the last years at $\sqrt{s}$=7, 8, 13 TeV, in different regions of the phase space, considering different channels and topology and measuring the cross section as a function of the kinematic variables of the $t\bar{t}$ system, the top quarks and/or their decay products. Even if the individual steps are dependent on the specific analysis all the differential cross section measurements proceed through the same workflow: the event selection, the background determination, the reconstruction of the $t\bar{t}$ system, the definition of the fiducial phase space, the unfolding applied to remove the effect of limited acceptance and resolution of the detector and the evaluation of the systematic uncertainties. In the following I will focus on the techniques used by ATLAS and CMS to perform some of these steps while presenting a selection of recent results by the two experiments.Comment: 7 pages, 9 figures, proceedings of a contribution at the 11th International Workshop on Top Quark Physics (TOP 2018

Constraining scalar resonances with top-quark pair production at the LHC

Constraints on models which predict resonant top-quark pair production at the LHC are provided via a reinterpretation of the Standard Model (SM) particle level measurement of the top-anti-top invariant mass distribution, $m(t\bar{t})$. We make use of state-of-the-art Monte Carlo event simulation to perform a direct comparison with measurements of $m(t\bar{t})$ in the semi-leptonic channels, considering both the boosted and the resolved regime of the hadronic top decays. A simplified model to describe various scalar resonances decaying into top-quarks is considered, including CP-even and CP-odd, color-singlet and color-octet states, and the excluded regions in the respective parameter spaces are provided.Comment: 34 pages, 17 figure

3D Reconstruction of the Poggio Sommavilla Territory (Sabina Tiberina, Rieti- Italy) A new approach to the knowledge of the archeological evidences

[EN] The area object of this paper is located in the Middle Tiber Valley and comprises a wide stretch of land within the loop of the river Tiber between the municipalities of Magliano Sabina and Ponzano. A study about this region was published in the volume 44 of the Series Forma Italiae, as it has played an important role in the reconstruction of the cultural and historical aspects of the Sabine Tiber Valley in ancient time. Its geological structure has produced a characteristic wavy landscape wich has determined the country life from time to time. Therefore, the 3D reconstruction of this area appears an important aid to the knowledge of the territory shape and its evolution. In fact the 3D model of this area has been developed in order to better understand its geological, hydrographical and anthropological conformation.[ES] El área objeto de este articulo está localizada en el Valle Medio del Tevere y comprende una amplia extensión de tierra dentro del meandro del rio Tevere entre las municipalidades de Magliano Sabina y Ponzano. Un estudio sobre esta región fue publicado en el volumen 44 de la Serie Forma Italiae, y ha jugado un importante papel en la reconstrucción de los aspectos culturales e históricos del Valle Sabina Tiberina en la antigüedad. Su estructura geológica ha producido un paisaje ondulado característico el cual ha determinado la vida del país de vez en vez. Por lo tanto, la reconstrucción 3D de esta área parece una importante ayuda para el conocimiento de la forma del territorio y su evolución. De hecho el modelo 3D de esta área ha sido desarrollado con el fin de entender mejor su conformación hidrográfica y antropológica.Verga, F.; Fabbri, F. (2011). 3D Reconstruction of the Poggio Sommavilla Territory (Sabina Tiberina, Rieti- Italy) A new approach to the knowledge of the archeological evidences. Virtual Archaeology Review. 2(3):23-26. https://doi.org/10.4995/var.2011.4578OJS23262

Measurement of the differential cross section of ttbar production, using data collected by the ATLAS detector at √s=13 TeV.

The study of the top quark physics covers a large part of the ATLAS experiment physics program and represents an active research field for the theoretical community. In this thesis, the measurement of the differential cross-sections of top quark pair production in proton proton collisions at a centre of mass energy of √s=13 TeV is presented. The measurement is performed in a fiducial phase-space, as a function of top quark and ttbar system kinematic observables, and the data set corresponds to an integrated luminosity of 3.2 fb^(-1), recorded in 2015 with the ATLAS detector at the CERN Large Hadron Collider. Only events with exactly one electron or muon in the final state are retained and the analysis employs two separate selections and top quark reconstruction techniques, focusing on different regions of the top quark momentum spectra. The measured spectra are corrected for detector effects and are compared to several theoretical Monte Carlo simulations through χ^2 and p-values calculations. The measured spectra provide stringent tests of perturbative QCD and can be used to tune the Monte Carlo simulations and re-interpreted to set limits on the existence of processes beyond the standard model. Finally, new techniques that will improve the sensitivity of future analysis in the region where the top quark is produced with high transverse momentum are presented

Periodic Structural Defects in Graphene Sheets Engineered via Electron Irradiation

Artificially-induced defects in the lattice of graphene are a powerful tool for engineering the properties of the crystal, especially if organized in highly-ordered structures such as periodic arrays. A method to deterministically induce defects in graphene is to irradiate the crystal with low-energy (<20 keV) electrons delivered by a scanning electron microscope. However, the nanometric precision granted by the focused beam can be hindered by the pattern irradiation itself due to the small lateral separation among the elements, which can prevent the generation of sharp features. An accurate analysis of the achievable resolution is thus essential for practical applications. To this end, we investigated patterns generated by low-energy electron irradiation combining atomic force microscopy and micro-Raman spectroscopy measurements. We proved that it is possible to create well-defined periodic patterns with precision of a few tens of nanometers. We found that the defected lines are influenced by electrons back-scattered by the substrate, which limit the achievable resolution. We provided a model that takes into account such substrate effects. The findings of our study allow the design and easily accessible fabrication of graphene devices featuring complex defect engineering, with a remarkable impact on technologies exploiting the increased surface reactivity

Isolating semi-leptonic H → WW∗ decays for Bell inequality tests

We present a method for identifying H→WW∗→ℓνjj events in the presence of large Standard Model backgrounds and illustrate how this decay mode may be applied to the study of Bell-type Inequalities. Our findings reveal the feasibility of complete reconstruction of such Higgs decays and the efficacy of our suggested combination of selection criteria in effectively mitigating the otherwise overwhelming backgrounds. Our approach is based on a combination of bottom and charm tagging, alongside innovative reconstruction techniques. A realistic simulation based on publicly available object identification, reconstruction, and tagging efficiencies from the ATLAS experiment is used to explore the potential sensitivity to violations of the Collins-Gisin-Linden-Massar-Popescu (CGLMP) inequality in existing and expected future data collected at the Large Hadron Collider (LHC). It is found that, the proposed method provides a powerful means of distinguishing the Higgs decay mode from the background, allowing us to achieve an expectation of approximately 3σ significance in detecting violations of these inequalities with 300 fb-1 of data, soon-to-be collected by the LHC

Deterministic Covalent Organic Functionalization of Monolayer Graphene with 1,3-Dipolar Cycloaddition Via High Resolution Surface Engineering

Spatially-resolved organic functionalization of monolayer graphene is successfully achieved by combining low-energy electron beam irradiation with 1,3-dipolar cycloaddition of azomethine ylide. Indeed, the modification of the graphene honeycomb lattice obtained via electron beam irradiation yields to a local increase of the graphene chemical reactivity. As a consequence, thanks to the high-spatially resolved generation of structural defects (~ 100 nm), chemical reactivity patterning has been designed over the graphene surface in a well-controlled way. Atomic force microscopy and Raman spectroscopy allow to investigate the two-dimensional spatial distribution of the structural defects and the new features that arise from the 1,3-dipolar cycloaddition, confirming the spatial selectivity of the graphene functionalization achieved via defect engineering. The Raman signature of the functionalized graphene is investigated both experimentally and via ab initio molecular dynamics simulations, computing the power spectrum. Furthermore, the organic functionalization is shown to be reversible thanks to the desorption of the azomethine ylide induced by focused laser irradiation. The selective and reversible functionalization of high quality graphene using 1,3-dipolar cycloaddition is a significant step towards the controlled synthesis of graphene-based complex structures and devices at the nanoscale.Comment: 11 pages, 7 figure