The pre-LHC Higgs hunt.

Enormous efforts at accelerators and experiments all around the world have gone into the search for the long-sought Higgs boson, postulated almost five decades ago. This search has culminated in the discovery of a Higgs-like particle by the ATLAS and CMS experiments at CERN's Large Hadron Collider in 2012. Instead of describing this widely celebrated discovery, in this article I will rather focus on earlier attempts to discover the Higgs boson, or to constrain the range of possible masses by interpreting precise data in the context of the Standard Model of particle physics. In particular, I will focus on the experimental efforts carried out during the last two decades, at the Large Electron Positron collider, CERN, Geneva, Switzerland, and the Tevatron collider, Fermilab, near Chicago, IL, USA.

A Monte-Carlo based model of the AX-PET demonstrator and its experimental validation.

AX-PET is a novel PET detector based on axially oriented crystals and orthogonal wavelength shifter (WLS) strips, both individually read out by silicon photo-multipliers. Its design decouples sensitivity and spatial resolution, by reducing the parallax error due to the layered arrangement of the crystals. Additionally the granularity of AX-PET enhances the capability to track photons within the detector yielding a large fraction of inter-crystal scatter events. These events, if properly processed, can be included in the reconstruction stage further increasing the sensitivity. Its unique features require dedicated Monte-Carlo simulations, enabling the development of the device, interpreting data and allowing the development of reconstruction codes. At the same time the non-conventional design of AX-PET poses several challenges to the simulation and modeling tasks, mostly related to the light transport and distribution within the crystals and WLS strips, as well as the electronics readout. In this work we present a hybrid simulation tool based on an analytical model and a Monte-Carlo based description of the AX-PET demonstrator. It was extensively validated against experimental data, providing excellent agreement.

Precise determination of the strong coupling constant at NNLO in QCD from the three-jet rate in electron-positron annihilation at LEP.

We present the first determination of the strong coupling constant from the three-jet rate in e{+}e{-} annihilation at LEP, based on a next-to-next-to-leading-order (NNLO) perturbative QCD prediction. More precisely, we extract alpha{s}(M{Z}) by fitting perturbative QCD predictions at O(alpha{s}{3}) to data from the ALEPH experiment at LEP. Over a large range of the jet-resolution parameter y{cut}, this observable is characterized by small nonperturbative corrections and an excellent stability under renormalization scale variation. We find alpha{s}(M{Z})=0.1175+/-0.0020(expt)+/-0.0015(theor), which is more accurate than the values of alpha{s}(M{Z}) from e{+}e{-} event-shape data currently used in the world average.