Mass measurements of J/Ψ and Z at ATLAS Experiment

Αραμπατζή, Μιχαέλα; Arampatzi, Michaela

dc.contributor.author	Αραμπατζή, Μιχαέλα	el
dc.contributor.author	Arampatzi, Michaela	en
dc.date.accessioned	2023-10-23T09:39:05Z
dc.date.available	2023-10-23T09:39:05Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/58232
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.25928
dc.description	Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Φυσική και Τεχνολογικές Εφαρμογές”	el
dc.rights	Αναφορά Δημιουργού-Μη Εμπορική Χρήση-Όχι Παράγωγα Έργα 3.0 Ελλάδα	*
dc.rights.uri	http://creativecommons.org/licenses/by-nc-nd/3.0/gr/	*
dc.subject	ATLAS	en
dc.subject	CERN	en
dc.subject	Mass Measurements	en
dc.subject	Armenteros-Podolanski plots	en
dc.subject	Boson Z and meson J/Ψ	en
dc.subject	Διαγράμματα Armenteros-Podolanski	el
dc.subject	Στοιχειώδη σωματίδια	el
dc.subject	Πείραμα ATLAS	el
dc.subject	Μέτρηση μάζας μποζονίου Ζ και μεσονίου J/Ψ	el
dc.subject	Μιαδικασία fit	el
dc.title	Mass measurements of J/Ψ and Z at ATLAS Experiment	en
heal.type	masterThesis
heal.classification	High Energy Physics/Particle Physics	en
heal.language	en
heal.access	free
heal.recordProvider	ntua	el
heal.publicationDate	2023-06-30
heal.abstract	The present thesis was written in the context of my master’s studies and is an introduction to data analysis in order to study the mass of the boson Z and the J/ψ meson. In the first four chapters, a theoretical introduction of some basic concepts and a brief description of the ATLAS experiment is given, necessary for the understanding of the analysis carried out in this thesis. Then, the analysis is divided into two parts. In the first part, i.e. chapter 5, the mass distribution of the boson Z, through the decay Z → µ + µ − , is studied in order to find the functions describing it. Firstly, Monte Carlo data are used to make the Z mass histogram, through which it is found that the signal is satisfactorily described by a Crystal Ball and a Gaussian distribution, while a second-degree Chebyshev polynomial is used for the background. Although visually the fit seems to correspond to the mass distribution, the goodness-of-fit tests, i.e. χ 2 /ndf , p-value and pull distribution, reveal the opposite. However, knowing that the detector does not have the same resolution in all its parts and expecting that separating the data according to their pseudorapidity, η, will improve the fit procedure, we divide the detector into 11 η-regions between [-1.1,1.1]. So, because each of the two muons can be detected in any of the 11-η-regions, 11 × 11 mass histograms and their corresponding fit are produced. This idea was confirmed as after performing the η separation of the muons, the fit procedure improved significantly for all combinations of η-regions, where the two produced muons can be detected, i.e. for all 11 × 11 histograms. The next step was to examine whether the separation of the data into 11 η-regions affects the statistics of the analysis, which was confirmed. Last, we studied the relationship between the fitted parameters and the η regions where the two muons from the Z boson decay are detected, which revealed a systematic error. After carrying out all the analysis on the MC data, we apply the same model and the same methodology to the data in order to compare the results with MC’s ones. In some results there are differences which logically indicate that the MC data need some improvements. In the second part of the analysis, i.e. chapter 6, the objective is to contribute to the attempt to measure precisely the mass of the boson Z, through the decay Z → µ + µ − . The pursuit of a precise mea- surement has led studies to focus on improving the calibration of muon energy. In this context, a new calibration method is suggested, based on the Armenteros-Podolanski plots. The Armenteros-Podolanski plot is a representation of the transverse momentum of a two-body decay versus the asymmetry of the longitudinal momentum of the decay products. The method is based on the determination of the masses of the final state particles and for this reason it is proposed as a method because it is believed that it allows a significantly more accurate calibration of the momentum than using only the parent parti- cles, since the masses of the final particles are known more precisely than those of the parent particles. Firstly, the mathematical expression of the Armenteros-Podolanski plots is demonstrated and then its behaviour for small and large masses is examined, using J/ψ and Z data respectively. Once the behavior of the equation has been understood, we apply two tests to the Armenteros-Podolanski plots to check whether the plots successfully respond to them, which is achieved. Therefore, it is inferred that the Armenteros-Podolanski plots could, after further research, be a method to be used for the calibration of the detector and even provide a significantly more accurate calibration.	en
heal.advisorName	Αλεξόπουλος, Θεόδωρος	el
heal.committeeMemberName	Μαλτέζος, Σταύρος	el
heal.committeeMemberName	Γαζής, Ευάγγελος	el
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Εφαρμοσμένων Μαθηματικών και Φυσικών Επιστημών. Τομέας Φυσικής	el
heal.academicPublisherID	ntua
heal.numberOfPages	91 σ.	el
heal.fullTextAvailability	false