Measurement of single top t-channel production cross section through the t $\rightarrow$ Wb $\rightarrow$ $\mu \nu$b decay in 7TeV proton-proton collisions with the Compact Muon Solenoid detector at the Large Hadron Collider

In my PhD I actively participated the Compact Muon Solenoid (CMS) experiment at theLarge Hadron Collider (LHC) of CERN. My work over the three years of the PhD encompassed several aspects of the experiment, including participation to data taking activities,performance studies of the detector and data analysis finalized to the measurement ofsingle top quark production. During the first year of my Ph.D. program I had the chanceto participate in the commissioning effort of the CMS Muon System, studying the performances of the Resistive Plate Chambers detectors using cosmic ray data collected in2008-2009 and early collision data taken in 2010. The second and third years of my Ph.D.program were devoted to the study of the production of single-top events in proton-protoncollisions at LHC. The LHC has been successfully running since the end of 2009 and isproviding 7 TeV center of mass proton-proton collision data since March 2010, collectingdata corresponding to an integrated luminosity of 36.1 pb−1 . With the data taking of2011, the instantaneous luminosity of the machine was constantly upgraded, allowing tocollect 5.73 f b−1 of integrated luminosity. The CMS detector has successfully collectedcollision data through 2010 and 2011, collecting a total integrated luminosity of 5.22 f b−1 .The LHC is often considered to be a “top quark factory”, allowing for a production of¯top quarks through several mechanisms: tt pair production, mainly occurring throughprocesses which involve the strong interaction, and single top quark production, whichoccurs through electroweak interactions and has been object of study of my thesis. Thereare three mechanisms of production of single top, known as t,s, and tW channels. Thestudy of single top processes provides the unique opportunity to explore the electroweaksector of top quark physics, allowing for example a direct measurement of Vtb as well as thestudy of Flavour Changing Neutral Currents. On the other hand single top channels offer awindow for searches for physics beyond standard model, being for instance sensitive toW resonances. Amongst the three channels, I focused my work on the t channel, whichyields a production cross section of 64.6 pb, the highest amongst the single top processes.I developed and deployed an analysis which focused on the top quark decay channelt → W b → µνb aiming at early observation of single top events with the 2010 dataset. Iwas successful in achieving the first experimental evidence of single top at the LHC, whichresulted in a paper published on PRL . With 2011 data incoming, I developed and deployeda new analysis, adapting the strategy to a different goal: the new analysis should haveminimized the systematic uncertainty and at the same time be model-independent to allowfor further studies of single top polarization and beyond standard model physics searches.The results have been updated with a luminosity of 1299 pb−1 , and a combination with theelectron channel results has been performed to increase the precision of the measurement.