Measurement of the Higgs boson Spin and CP quantum numbers with ATLAS/LHC
IDPASC Portugal - PHD Programme 2016
2016 / 2017
Theoretical Particle Physics | Experimental Particle Physics
Patricia Conde Muino
Faculdade de Ciências - Universidade de Lisboa
Laboratório de Instrumentação e Física Experimental de Partículas
The Standard Model of Particle Physics (SM) is a very successful theory that describes the fundamental constituents of matter and their interactions. It is, however, incomplete since there are many questions it cannot explain, like the origin of Dark Matter in the Universe or why matter dominates over anti-matter. One of the missing pieces of the SM that has not been fully probed by experiments up to now is the mechanism through which the fundamental particles acquire mass, so-called Higgs mechanism. In the SM, the mechanism predicts one fundamental scalar particle, the Higgs boson. The discovery of a Higgs boson at CERN by the ATLAS and CMS experiments in 2012 was a very important milestone in this quest. The focus of both collaborations is now on the precise measurement of all the properties of this new particle, to probe its nature, testing the SM predictions and searching for new physics if deviations from the SM predictions are found. This project will start with a detailed survey of the best processes to probe the CP-nature and the spin of a fundamental scalar at the LHC. The experiments most important task for the future is to determine the CP-nature of the Higgs boson and the nature of its couplings. In particular, the Yukawa couplings are largely unknown at the moment. Furthermore, if more scalars are found we need to be prepared to study their CP-nature and spin. A promising channel to study the Higgs Spin and CP quantum numbers is the associated production with a W boson, when the Higgs decays to b-quark pairs and the W boson to a lepton and a neutrino. The spin and CP quantum numbers of the Higgs leave their footprint in the angles of the decay products of the Higgs and the W boson. The student will explore kinematical observables, like angular variables, capable of separating the different spin and CP component on the production vertex. The work will continue with the analysis of the Run II ATLAS data (13/14 TeV pp collisions). Analysis algorithms that use the standard ATLAS software tools will be developed to identify the Higgs boson in the selected channel and to study the observables that are sensitive to its spin and CP properties. Comparisons with theoretical models, using Monte Carlo simulation, will be performed. In addition, the student will participate in the ATLAS data taking and physics analysis activities, with frequent trips to CERN to participate in shifts and in collaboration meetings.