Measurement of the ZZ production cross section and limits on anomalous neutral triple gauge couplings with ATLAS

The main work of this thesis concerns the measurement of the production cross section using LHC 2011 data collected at a center-of-mass energy equal to 7 TeV by the ATLAS detector and resulting in a total integrated luminosity of 4.6 inverse fb. The ZZ total cross section is finally compared with the NLO prediction calculated with modern Monte Carlo generators. In addition, the three differential distributions (∆φ(l,l), ZpT and M4l) are shown unfolded back to the underlying distributions using a Bayesian iterative algorithm. Finally, the transverse momentum of the leading Z is used to provide limits on anoumalus triple gauge couplings forbidden in the Standard Model.

Evidence for a new boson in the search for the Standard Model Higgs particle decaying to four leptons at CMS

One of the main targets of the CMS experiment is to search for the Standard Model Higgs boson. The 4-lepton channel (from the Higgs decay h->ZZ->4l, l = e,mu) is one of the most promising. The analysis is based on the identification of two opposite-sign, same-flavor lepton pairs: leptons are required to be isolated and to come from the same primary vertex. The Higgs would be statistically revealed by the presence of a resonance peak in the 4-lepton invariant mass distribution. The 4-lepton analysis at CMS is presented, spanning on its most important aspects: lepton identification, variables of isolation, impact parameter, kinematics, event selection, background control and statistical analysis of results. The search leads to an evidence for a signal presence with a statistical significance of more than four standard deviations. The excess of data, with respect to the background-only predictions, indicates the presence of a new boson, with a mass of about 126 GeV/c2 , decaying to two Z bosons, whose characteristics are compatible with the SM Higgs ones.

Measurement of the differential cross section of tt pairs in pp collision at sqrt(s) = 7TeV with the ATLAS detector at the LHC

In this thesis three measurements of top-antitop differential cross section at an energy in the center of mass of 7 TeV will be shown, as a function of the transverse momentum, the mass and the rapidity of the top-antitop system. The analysis has been carried over a data sample of about 5/fb recorded with the ATLAS detector. The events have been selected with a cut based approach in the "one lepton plus jets" channel, where the lepton can be either an electron or a muon. The most relevant backgrounds (multi-jet QCD and W+jets) have been extracted using data driven methods; the others (Z+ jets, diboson and single top) have been simulated with Monte Carlo techniques. The final, background-subtracted, distributions have been corrected, using unfolding methods, for the detector and selection effects. At the end, the results have been compared with the theoretical predictions. The measurements are dominated by the systematic uncertainties and show no relevant deviation from the Standard Model predictions.

Il discorso politico culturale del Deutscher Geist in Gefahr di Ernst Robert Curtius

Nel 1932 Ernst Robert Curtius pubblica il pamphlet politico culturale Deutscher Geist in Gefahr nel quale chiarisce il suo pensiero di fronte alla grave crisi in cui versa la Germania. Egli si schiera contro le posizioni di destra del suo tempo, delle quali critica apertamente la boria nazionalista, il rozzo antisemitismo e la creazione di un mito nazionale elaborato come strumento di manipolazione dell’opinione pubblica. Ritiene inoltre inaccettabili le posizioni rivoluzionarie, tanto di destra quanto di sinistra, che vogliono liberarsi della tradizione umanistica europea e disprezzano la Zivilisation francese; allo stesso modo rifiuta l’ideale di un germanesimo eroico avulso dalla storia europea e respinge infine tutte le forme di nichilismo che si risolvono in un atteggiamento di indifferenza nei confronti della realtà, dei valori e della storia. Curtius accetta il sistema democratico come unica soluzione e ritiene che le decisioni politiche debbano mirare al bene di tutti i ceti sociali indipendentemente dagli interessi di partiti e di singoli gruppi. Rifiuta qualunque forma, anche culturale, di supremazia della Germania, aspira a un’Europa cosmopolita, le cui nazioni siano valorizzate nelle loro caratteristiche specifiche, ed è convinto che per la costruzione della pace gli europei debbano vivere, studiare e lavorare insieme imparando gli uni le lingue degli altri. Per Curtius l’Umanesimo della tradizione classica e la letteratura del Medioevo sono parte integrante della vita di ogni europeo e fonte di energie spirituali per affrontare in modo creativo il presente e il futuro.