Μελέτες για την ανακάλυψη νέων θεμελιωδών αλληλεπιδράσεων με γεγονότα πολλαπλών πιδάκων σωματίων στο πείραμα CMS του LHC (Doctoral thesis)

Παράδας, Ευάγγελος


A study for the search of two hypothetical vector bosons, called Coloron and Axigluon, is presented, and their possible existence is a signature of new fundamental strong interactions beyond the standard model. According to the theory, their production refers to a resonance and their decay leads to the production of two massive intermediate particles (hyper – pion and sigma, accordingly), while the latter are forced to decay further to two gluons, resulting in a final state of eight jets. The mass range of the vector bosons is set between for the Coloron and for the Axigluon, in steps of . The mass of the intermediate massive scalar particles, is set to be equal to ¼ and 1/3 of the vector boson’s mass. The mass width of the vector boson is set to be equal to 10% and 20% resulting to four scenarios. This study is based on events from proton – proton collisions, collected by the CMS detector, at the LHC. The collected data correspond to a total recorded luminosity of with energy in the center of the mass. The main background for the above process is QCD events. The estimation of the background is done (a) using simulated Monte Carlo events from MadGraph + Pythia6 generator and (b) using data – driven techniques. Two different methods used in this analysis (MultiVariate Analysis method and Cut & Count method), without observing any significant difference between the data and the background. Thus, we calculated the upper limits for every mass point with the results depending on the method and scenario. For the Coloron, the lowest excluded mass is while the highest is between (Cut & Count method) and (Multi Variate Analysis method), depending on the scenario. For the Axigluon, the lowest excluded mass is while the highest is between (Cut & Count method) and (Multi Variate Analysis method), depending on the scenario. All the upper limits refer to 95% confidence level and have been published to the arXiv (1608.01224v1) . In addition to the above, a High Level Trigger is built, dedicated to multijet events, called HLT_PFHT750_4JetPt50. Its special characteristic is the lower threshold of the scalar sum of all the transverse momenta, , but also the high acceptance (in comparison to the previous multijet triggers). The new trigger is working during the new LHC RUNII at 13 TeV center of the mass energy collecting data for various analyses.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Φυσικής
Subject classification: Μποζόνια
Keywords: Φυσική στοιχειωδών σωματιδίων,Coloron,Axigluon
URI: http://olympias.lib.uoi.gr/jspui/handle/123456789/27809
Appears in Collections:Διδακτορικές Διατριβές

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