University of Zagreb. Faculty of Science. Department of Physics.
Abstract
Visokoenergetski sudari teških iona pružaju mogućnost proučavanja svojstava vruće i guste nuklearne materije. U uvjetima ekstremne temperature i/ili gustoće kvarkovi i gluoni, inače vezani unutar hadrona, postaju slobodni i formiraju stanje materije koje nazovamo kvark-gluon plazmom. Elektronpozitron parovi, dielektroni, nastaju tijekom čitave prostorno-vremenske evolucije sudara, a budući da ne interagiraju jakim silama, nose informaciju o svojstvima materije u vremenu svoga nastavka. Ovaj se rad temelji na analizi e +e − parova iz Au+Au sudara na √ sNN = 62 GeV, prema podacima koji su prikupljeni tijekom 2010. godine u PHENIX eksperimentu na Relativistic Heavy Ion Collideru (RHIC). Za potrebe analize i korištenja informacija o vremenu proleta čestica u identifikaciji elektrona napravljena je kalibracija vremenskog odaziva Elektromagnetskog Kalorimetra. Prethodno analizi su iz PHENIX akceptancije uklonjena neaktivna i nefunkcionalna područja Driftne komore te je napravljena selekcija događaja na temelju kvalitete rekonstrukcije signala. Navedenim je postupkom osiguran konzistentan odaziv detektora koji su korišteni u analizi. Na temelju fizikalnog očekivanja odaziva čestica u detektorima napravljena je selekcija elektronskog uzorka te je procijenjen udio hadronske kontaminacije u uzorku (∼ 15%). Iz elektronskog uzorka su tada formirani e +e − parovi i promatran je spektar nakon oduzimanja pozadine. Diskutirani su opaženi doprinosi spektru invarijantne mase dielektrona te je dan pregled koraka koji bi sljedili kao nastavak analize iznesene u ovom radu.High-energy heavy ion collisions provide an opportunity to study the properties of the hot and dense nuclear matter. In the conditions of extreme temperature and/or density, quarks and gluons, normally confined inside hadronic matter, become deconfined and form a state of matter which we call the quark-gluon plasma. Electron-positron pairs, dielectrons, are created during the whole space-time evolution of the system. Since they don’t interact strongly and leave the medium without final state interactions, dielectrons carry information about the properties of matter at the time of their production. In this thesis the analysis of e+e- pairs from Au+Au collisions at √sNN = 62 GeV was presented, for data collected during 2010 in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). Prior to analysis, the Drift Chamber fiducal cuts were defined and the timing callibration of the Electromagnetic Calorimeter was done. The obtained time-of-flight information was used to define the mass squared variable of the particle, which was then sigmatized as a function of transverse momentum and used in electron identification (eID). After applying eID cuts on the trajectories from runs which have passed the QA (quality assurance) analysis, an electron sample was obtained, with an estimated hadronic background of 15%. Trajectories from the sample were used to form e+e- pairs. After background subtraction, the dielectron invariant mass spectrum was obtained and contributions to the spectrum were discussed. In conclusion, an overlook for the further analysis was given
