Higgs property measurements with the ATLAS detector at LHC

Stage numéro : M2-1819-AT-02
Laboratoire :Centre de Physique des Particules de Marseille Case 902
 163 avenue de Luminy - 13288 Marseille Cedex 9
Directeur :Cristinel Diaconu - 04.91.82.72.01 - diaconu@cppm.in2p3.fr
Correspondant :William Gillard - 04.91.82.72.67 - gillard@cppm.in2p3.fr
Groupe d'accueil :Atlas
Chef de groupe :Marlon Barbero - 04.91.82.76.58 - barbero@cppm.in2p3.fr
Responsable de stage :Emmanuel Monnier - 04 91 82 72 69 - monnier@cppm.in2p3.fr

Thématique : Physique des particules

Physics at the Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research) is the high priority research field of the Particle Physics community worldwide. ATLAS is one of the two general purpose experiments installed at the LHC that discovered a Higgs boson in July 2012, key piece for the understanding of the fundamental interactions and the origin of elementary particle mass. Its physics program extends beyond Higgs property measurements to the search for signs of physics beyond the Standard Model of particle physics.

The ATLAS group of the “Centre de Physique des Particules de Marseille” (CPPM) is deeply involved in this scientific program, in particular linked to its expertise of the electromagnetic calorimeter. The latter is a key component for the identification and energy measurement of electrons and photons, which were at the core of the Higgs boson discovery. It is also at the forefront of this boson studies and of the supersymmetry searches in the ongoing data taking campaign, so called “Run 2”, with major consequences in several analyses with leptons in their final states. Moreover, for the upgrade of the accelerator performances foreseen in 2021, this calorimeter has a major ongoing development program to dramatically upgrade its trigger and readout to which the CPPM group actively contributes.

In the Standard Model, the Higgs boson is highly coupled to the top quark, the known particle with the largest mass. The only way to directly measure this Higgs-top coupling (called top Yukawa coupling) is to observe the associated production of a Higgs boson with top quarks. This will be accessible for the first time with the “Run 2” data taken between 2015 and 2018 from LHC proton-proton collision at a 13 TeV center of mass energy. This key measurement,

and more generally the Higgs properties studies are of high importance since they would allow to confirm that the observed boson is the Standard Model Higgs boson, or could reveal New Physics.

The subject of this M2 internship is to participate in the measurement of the properties of the Higgs boson in the final states with several leptons (electrons or muons) in particular by relying on multivariate analysis tools. These studies will be done on the “Run 2” data set. This should lead, by summer 2019, to get the best sensitivity on some of the Higgs properties in particular

its Yukawa coupling. Furthermore, depending on the interests of the student, participation in the study of a prototype installed on the detector in early 2018 as part of the electromagnetic calorimeter upgrade program is also possible.

In this framework, the student may have to go to CERN and the research work will combine physics analysis on real and simulated data as well as studies and operation of experimental systems. This internship can naturally then evolve to a thesis