A search for Supersymmetry in the compressed mass spectrum in events with three soft leptons and missing transverse momentum with the CMS experiment at the LHC.

Στην παρούσα διατριβή διερευνάται η ύπαρξη Υπερσυμμετρίας (SUSY) με μοντέλα συμπιεσμένου φάσματος μάζας μεταξύ των υπερσυμμετρικών σωματιδίων, τα οποία προβλέπουν παρατηρήσιμες τελικές καταστάσεις που περιλαμβάνουν σωματίδια του Καθιερωμένου Προτύπου (SM) χαμηλής εγκάρσιας ορμής και εγκάρσια ελλείπουσα ενέργεια (MET). Η ανάλυση επικεντρώνεται σε τελικές καταστάσεις με δύο ή τρία λεπτόνια (ηλεκτρόνια ή μιόνια), οι οποίες έχουν συνολικά μικρότερο υπόβαθρο από διεργασίες του SM σε σύγκριση με τις αδρονικές τελικές καταστάσεις που προβλέπουν αυτά τα μοντέλα. Το κύριο υπόβαθρο στις λεπτονικές τελικές καταστάσεις που εξετάζονται προέρχεται από εσφαλμένη ταυτοποίηση λεπτονίων που είτε δεν είναι γνήσια (αδρόνια που έχουν κατά λάθος αναγνωριστεί ως λεπτόνια) είτε δεν προέρχονται από το σημείο κύριας αλληλεπίδρασης όπου μπορούν να παραχθούν υπερσυμμετρικά σωματίδια. Στη διατριβή εφαρμόζονται προωθημένες τεχνικές εκτίμησης αυτού του υπόβαθρου, εκτιμώνται οι συνεισφορές από όλες τις διεργασίες του SM που παράγουν τις διερευνώμενες τελικές καταστάσεις και οι εκτιμήσεις συγκρίνονται με τα δεδομένα του πειράματος με βάση επιλεγμένες κατανομές κινηματικών μεταβλητών ευαίσθητων σε διασπάσεις υπερσυμμετρικών σωματιδίων. Δεν παρατηρείται κατά τη σύγκριση κάποια συνεισφορά τέτοιων διασπάσεων, οπότε με στατιστική συμπερασματολογία εξάγονται όρια αποκλεισμού των εξεταζόμενων μοντέλων συναρτήσει των μαζών των υπερσυμμετρικών σωματιδίων.Thε dissertation presents a search for Supersymmetry (SUSY) in models with compressed mass spectrum of the supersymmetric particles, which predict observable final states containing Standard Model (SM) particles of low transverse momentum and missing transverse energy (MET). The analysis focuses on final states with two or three leptons (electrons or muons), which have an overall lower background from SM processes comparing with hadronic final states predicted by these models. The main background in the examined leptonic final states originates from lepton misidentification, when either the lepton is not genuine (a hadron misidentified as a lepton) or it does not come from the primary interaction vertex where supersymmetric particles can be produced. Advanced techniques of estimating this background are applied in the dissertation, then the contributions are estimated from all SM processes producing the final states under consideration, and the estimates are compared with the experimental data based on the distributions of selected kinematic variables which are sensitive to supersymmetric particle decays. No contribution from such decays is observed in the comparison, therefore exclusion limits on the supersymmetric particle masses of the examined models are extracted using statistical inference

Measurement of t(t)over-bar normalised multi-differential cross sections in pp collisions at root s=13 TeV, and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

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MUSiC : a model-unspecific search for new physics in proton-proton collisions at root s=13TeV

Results of the Model Unspecific Search in CMS (MUSiC), using proton-proton collision data recorded at the LHC at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1), are presented. The MUSiC analysis searches for anomalies that could be signatures of physics beyond the standard model. The analysis is based on the comparison of observed data with the standard model prediction, as determined from simulation, in several hundred final states and multiple kinematic distributions. Events containing at least one electron or muon are classified based on their final state topology, and an automated search algorithm surveys the observed data for deviations from the prediction. The sensitivity of the search is validated using multiple methods. No significant deviations from the predictions have been observed. For a wide range of final state topologies, agreement is found between the data and the standard model simulation. This analysis complements dedicated search analyses by significantly expanding the range of final states covered using a model independent approach with the largest data set to date to probe phase space regions beyond the reach of previous general searches.Peer reviewe

Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

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Probing effective field theory operators in the associated production of top quarks with a Z boson in multilepton final states at root s=13 TeV

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