Potraga za rezonancijama u konačnim stanjima s dva hadronska mlaza na masama ispod 1 TeV u proton-proton sudarima na energiji centra mase od 13 TeV na Velikom hadronskom sudarivaču

master's thesis

• Title (english): Search for dijet resonances at masses below 1 TeV in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider
• Author: Lucija Bajan
• Mentor: Dinko Ferenček (mentor)
• Mentor: Damir Bosnar (mentor)
• Committee member: Damir Bosnar (predsjednik povjerenstva)
• Committee member: Dinko Ferenček (član povjerenstva)
• Committee member: Krešimir Kumerički (član povjerenstva)
• Committee member: Vuko Brigljević (član povjerenstva)
• Committee member: Davor Horvatić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2016-07-08, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

Krajem 2015. godine kolaboracije CMS i ATLAS objavile su rezultate analize spektra mase dva fotona koji ukazuju na moguće postojanje nove čestice na masi od oko 750 GeV. Analizirani podaci prikupljeni su u sudarima protona na energiji centra mase od 13 TeV tijekom 2015. godine u drugoj fazi rada Velikog hadronskog sudarivača. Iako globalna signifikantnost opaženog viška dogadaja na masi od 750 GeV na svakom od eksperimenata zasebno nije bila vrlo visoka, činjenica da se pojavila kod oba eksperimenta pobudila je veliko zanimanje u znanstvenoj zajednici. Indikacije za novu česticu dosad su uočene samo u kanalu raspada s dva fotona. Medutim, izgledno je da bi se nova čestica, ukoliko postoji, trebala raspadati i u hadronska konačna stanja, primarno u dva hadronska mlaza. U ovom radu prezentirana je potraga za rezonancijama koje se raspadaju na dva hadronska mlaza u konačnom stanju. Analizirani podaci prikupljeni su CMS detektorom u sudarima protona na energiji centra mase od 13 TeV tijekom 2015. godine korištenjem takozvane scouting tehnike prikupljanja podataka te odgovaraju integriranom luminozitetu od 1.9 fb^-1. Kako bi provjerili postoje li naznake nove fizike, proučen je spektar invarijantne mase dva hadronska mlaza, čija je glatkoća potom provjerena. Postavljene su gornje granice na udarne presjeke signala s razinom pouzdanosti od 95 %, te su isključeni rasponi masa čestica predvidenih raznim teorijskim modelima. Koristeći metodu b-označavanja, proučili smo konačna stanja obogaćena b mlazovima.

Abstract (english)

At the end of 2015, the CMS and ATLAS collaborations announced the results of an analysis of a diphoton mass spectrum which indicated possible existence of a new particle at a mass of about 750 GeV. The analyzed data were collected in proton collisions at a center-of-mass energy of 13 TeV during Run 2 of the LHC in 2015. Although the global significance of the observed excess of events at a mass of 750 GeV in each of the experiments individually was not very high, the fact that it occurred in both experiments has generated significant interest in the scientific community. Indications for the new particle have been observed only in the diphoton channel. However, it is likely that the new particle, if it exists, should decay to hadronic final state, primarily dijets. In this thesis we present a search for resonances decaying into dijet final states. The analyzed data were collected by the CMS detector in proton collisions at a center-of-mass energy of 13 TeV during 2015 using the so-called scouting technique of data collection. It corresponds to an integrated luminosity of 1.9 fb^1. To check for indications of new physics, the dijet mass spectrum is studied and its smoothness is tested. We set 95% confidence level upper limits on the signal cross section and exclude specific mass ranges for particles predicted by various theoretical models. Using b-tagging methods, we have also studied the final states enriched in b jets.

• Keywords: proton-proton sudari
• Keywords (english): proton-proton collisions
• Language: croatian
• URN:NBN: urn:nbn:hr:217:993394
• Study programme: Title: Physics; specializations in: Research; Course: Research; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra fizike (magistar/magistra fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-03-02 19:54:29