Measurement of the Z boson pair-production cross section in proton-proton collisions at 7 and 8 TeV, and ECAL timing studies for the phase-2 upgrade of the CMS experiment

A measurement of the Z boson pair production cross section using proton-proton collisions at 7 and 8 TeV center-of-mass energy, recorded by the CMS experiment, is presented. The ZZ production cross section is measured via the decay channel ZZ → 2l2ν. The data used for the analysis have been recorded in years 2011 and 2012 by CMS and correspond to an integrated luminosity of about 5.1 fb−1 at 7 TeV and 19.6 fb−1 at 8 TeV. We measure σ(pp → ZZ) = 5.1 +1.5 −1.4 (stat) +1.4 −1.1 (syst) ± 0.1 (lumi) pb at 7 TeV, and 7.2 +0.8 −0.8 (stat) +1.9 −1.5 (syst) ± 0.2 (lumi) pb at 8 TeV, in good agreement with the SM next-to-leading-order predictions. The selected data were also analyzed to search for anomalous triple gauge couplings (aTGC) involving the ZZ final state, and subsequently combined with the ZZ → 2l2l 0 final state data, in order to increase the sensitivity. In the absence of signs of new physics we set limits on the relevant aTGC parameters. The last part of the thesis discusses the possible use of timing to mitigate the pileup contribution in object reconstruction, in the contest of the High Luminosity phase of LHC. Timing is included in different reconstruction algorithms, proving that a time resolution of about 30 ps could allow to reconstruct the z position of the hard vertex with a O(cm) resolution, and to reject jets coming from pileup interactions with a rejection factor of about three