Nuclear Seminar - Lucia Keszeghová (23.11.2022)
Wednesday 23.11.2022 at 14:00, Lecture room F1/364
Mgr. Lucia Keszeghová:
Associated production of the top-quark pair and Z boson in proton-proton collisions at the ATLAS experiment
Abstract:
Associated production of the top-quark pair and Z boson (ttZ) is a rare process predicted by the Standard Model. The study of ttZ process is possible thanks to unprecedented energies and luminosities reached in proton-proton collisions at the LHC. So far, all the measured values of ttZ cross section are consistent with the Standard Model prediction at given centre-of-mass energy (0.86+0.07−0.08(scale)±0.03(PDF+αS) pb at 13 TeV). The latest analysis published by the ATLAS experiment in August 2021 measured the inclusive ttZ cross section at 13 TeV to be 0.99 ± 0.05(stat) ± 0.08(syst) pb. This result is based on the full LHC Run II dataset with integrated luminosity of 139 fb−1. More precise experimental value is vital for more accurate confrontation with the Standard Model prediction. To achieve higher precision in the ttZ cross section measurement, the full ATLAS Run II dataset is being reanalysed. The inclusion of dilepton decay channel in the refined analysis significantly increases available statistics. However, the main improvement is the use of neural networks for separation of signal and background events. Preliminary results, which will be discussed during the seminar, indicate that neural networks significantly improve the measurement precision.