Preparation to the Higgs self-coupling measurement using the HH -> bbyy channel.

Stage numéro : M2-2021-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 :Elisabeth Petit - 0033.4.91.82.72.63 - petit@cppm.in2p3.fr

Thématique : Physique des particules

Eight years after the discovery of the Higgs boson the precision measurement of its properties is a key goal of the LHC and Future Colliders in order to test the Standard Model. In particular the measurement of the Higgs self-coupling is one parameter not measured yet, that can be probed through the HH production. Even if the cross-section of the HH production is too small to be observed with the data expected to be collected by the ATLAS detector by the end of the LHC Phase 1, the corresponding analyses will bring the best existing constraints on the Higgs self-coupling, in addition to setting baselines for the analyses to be performed with the dataset to be collected during the HL-LHC running.

The current 95% CL expected limit on the HH production cross-section is 10 times the predicted Standard Model cross-section. The dataset collected up to now is expected to double during Run 3 of the LHC (2021-2024). The team has already been highly involved in the HH->bbgammagamma analysis channel. In order to discover the HH process a good understanding of the background processes is necessary, in particular the Z(->bb)H(->gammagamma) process which is an important background to the analysis and has a similar final state. We plan to measure it since it could be detected with the dataset collected during Run 3 and it is a benchmark to test the analysis strategy.

The student will work with MC simulation and real data to prepare for this measurement.

Desired skills: C++, ROOT