Soutenance publique de thèse - Laurent Forthomme - Measurement of exclusive two-photon processes with dilepton final states in pp collisions at the LHC

by Mr Laurent Forthomme (CP3)

Monday 25 Apr 2016, 14:00 → 16:00 Europe/Brussels

CYCL 01 (Cyclotron)

The unification of the electromagnetic and weak forces is a cornerstone of the standard theory of elementary particles and fundamental interactions. At the Large Hadron Collider the processes of pair production via fusion of two exchanged photons provide a unique laboratory both for testing the standard theory and for search of new phenomena in high-energy physics. In this thesis such a two-photon exclusive pair production in pp collisions has been studied experimentally, at two centre of mass energies using the data collected with the CMS experiment during LHC's Run-1.
 Thanks to large, effective photon fluxes and the outstanding performance of the CMS apparatus clean two-photon signal samples could be extracted. The novel track-based exclusivity selection was instrumental for making successful measurements in an extremely demanding LHC environment. In particular, the “reference” two-photon production of lepton pairs has been measured and investigated in detail, including extended phenomenological studies. A new formalism has been implemented in Monte Carlo simulations using the so-called kT factorisation scheme.
 Finally, the two-photon production of weak boson pairs has been studied through the analysis of the data collected with CMS at 7 and 8 TeV. Beside the first observation ever made experimentally of the γγ→WW process, the measured production rate has been used to extract the best world limits on anomalous behaviour of the γγWW as well as the γγZZ quartic gauge boson couplings. In addition, the Precision Proton Spectrometer project has been also portrayed – the PPS detectors will allow to measure forward scattered protons, and hence to tag two-photon processes. In particular, one of the possible, ultrafast timing detectors to be installed in the spectrometer is characterised: the GasToF Cerenkov time of flight detector.

Slides publicdefence.pdf