Seminari & Eventi

Hunting the Higgs boson at high energy using the ATLAS detector at the LHC

Speaker:
Dr. Francesco di Bello
University of Geneva
When: Tuesday, April 30, 2019 - 14:30
Where: Dipartimento di Fisica - Aula 500

Abstract:

Seminario di Fenomenologia delle Particelle Elementari

With the discovery of the Higgs boson in 2012, an extensive physics program has been carried out by the ATLAS experiment to characterize its properties. Among them, one of the most important is the coupling between the Higgs boson and the fermion, known as Yukawa coupling. Of particular interest is the coupling with the b-quark, the heaviest lepton accessible in the direct decay of the Higgs boson and therefore the one with highest branching ratio. Due to the overwhelming QCD background, an inclusive search for H- >bbar has tought to be impossible. However, with the development of theoretical and experimental techniques for boosted object, it was possible to find a strategy to probe the Higgs boson at high transverse momentum. During the seminar, I will discuss an inclusive search for the standard model Higgs boson produced with high transverse momentum decaying to a bottom-antibottom quark pair using a data-set of pp collisions at a center-ofmass energy of 13 TeV collected with the ATLAS experiment at the LHC. The data sample corresponds to an integrated luminosity of 80.5 fb−1. This is the first time the analysis is ever been performed within the ATLAS experiment. The analysis also provided a measurement of W/Z+jets processes in boosted regime with b-quarks final states observed at a significance of 5 standard deviation. A small excess, compatible at 1.6 sigma with the background-only hypothesis, is observed at 125 GeV. In addition, exclusions limits for dark matter resonant model are placed. The seminar will give an overview of the analysis along with its future perspective.


Impact of small-x resummation on HERA data

Speaker:
Dr. Francesco Giuli
Roma Due
When: Tuesday, May 7, 2019 - 13:45
Where: Dipartimento di Fisica - Aula 500

Abstract:

Seminario di Fenomenologia delle Particelle Elementari

Fits to the final combined HERA deep-inelastic scattering cross-section data within the conventional DGLAP framework of QCD have shown some tension at low-x and low-Q2 . A resolution of this tension incorporating ln(1/x)- resummation into the HERAPDF fits is investigated using the xFitter program. Such resummation not only gives a better description of the data, but it also results in a gluon PDF which is steeply rising at low x for low scales, contrary to the fixed-order result. Then, a new parametrization for PDFs designed to be flexible in the small-x region has been studied and new fits to HERA data have been performed. The new parametrization leads to a better fit quality, both at fixed order and at resummed level, and thus removes a signficant bias present in the previously used parametrizations. The benefits of including small-x resummation remains signficant also with the new more flexible parametrization, thus giving more robustness to the previous results.


Hot TOP(phys)ics

Speaker:
Dr. Yvonne Peters
University of Manchester
When: Monday, May 13, 2019 - 14:30
Where: Dipartimento di Fisica - Aula 500

Abstract:

Seminario di Fenomenologia delle Particelle Elementari

The heaviest known elementary particle, the top quark, provides an interesting area of research. Its high mass and short lifetime make it to be of special interest in the hunt for physics beyond the standard model. In my talk I will present a potpourri of recent analyses in the top sector, using LHC protonproton collision data at 13TeV centre-of-mass energy, recorded with the ATLAS detector. The presented analyses are a new result on top quark spin correlations, a study of QCD colour-flow in top events, and the connection of the top to the Higgs boson. 


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