Etude du calorimètre électromagnétique silicium-tungstène du concept de détecteur ILD pour l'ILC et mesure de la masse du boson de Higgs dans le canal e+e−→ Z H → e+e− + X

The International Linear Collider (ILC) is an e+e− linear collider that operates at a centre-of-mass energy between 90~GeV and 1~TeV. One of the detector concepts for the ILC is the International Large Detector (ILD) concept. It is optimised for the Particle Flow Approach. A reference option for the electromagnetic calorimeter is a high granularity sampling calorimeter with tungsten as radiator and silicon diodes as sensitive material. A limited in size but full depth "physics prototype" has been already constructed and tested in test beam areas at CERN and FNAL. In this work, the relative energy resolution of the calorimeter as a function of the beam energy, E, was measured. It was parametrized as a quadratic sum of a stochastic and a constant term. The result of a fit to data, ΔE/E(%)=(17,96±0,7)/E(GeV)‾‾‾‾‾‾‾√⊕(0,8±0,06), was compared to Monte Carlo predictions. Various methods were applied to compensate for the non-instrumented areas. The measured value of the position resolution of the prototype, ΔX(mm)=(3,32±0,06)/E(GeV)‾‾‾‾‾‾‾√⊕(9,0±0,07)/E(GeV)⊕(0,9±0,01), is well within the ILC Reference Design Report requirements. In the thesis, the mass decline for the decay channel, e+e−→ZH→e+e−+X, as measured by the ILD detector was studied. For an integrated luminosity of 250~fb−1, the accuracy of the reconstruction and the good knowledge of the initial state allow for the measurement of the Higgs boson mass with a precision better than 130~MeV.