Search for electroweak production of supersymmetric partciles at the LHC Run 3 with the ATLAS detector

Stage numéro : Doctorat-2023-AT-02
Laboratoire :Centre de Physique des Particules de Marseille Case 902
 163 avenue de Luminy - 13288 Marseille Cedex 9
Directeur :Cristinel Diaconu - -
Correspondant :William Gillard - -
Groupe d'accueil :Atlas
Chef de groupe :Marlon Barbero - -
Directeur de thèse :Steve Muanza - -

Thématique : Physique des particules

After the culminating triumph of the Standard Model (SM) in 2012 with the discovery of the Higgs boson by the ATLAS and CMS in the data collected at the LHC Run 1, the main focuses of these two experiments are the precision measurements of the Higgs boson properties and the pursue of direct signs of physics beyond the SM.

We propose a PhD topic to continue to search for an electroweak (EW) production of supersymmetric

(SUSY) particles at the LHC Run 3 with the ATLAS detector. At the Run 1 we participated to the irst ATLAS search for pp→~χ±1~χ02→ W±(→l±ν)h0125(→ bb). We continued this search with the first data of Run 2 (L=36/fb from 2015-2016) and we are currently extending this search

with the analysis of the full Run 2 dataset (L=140/fb) to search for pp→~χ±1~χ02→ W±(→l±ν)Z0(→ qq/bb).

Compared to the LHC Run2, Run 3 will have pp collisions reaching √s=14 TeV, the nominal center-of-mass energy of the LHC, and should collect an integrated luminosity

of about 150/fb. Therefore the sensitivity to the signals should increase significantly and open new search channels like to vector boson production (VBF) mode of the above chargino-neutralino production. We intend to pursue the pp→~χ±1~χ02→ W±(→l±ν)Z0(→ qq/bb) signal and possibly to start explointing the VBF production of pp→~χ±1~χ02→ W±(→l±ν)h0125(→ bb) (accompanied by a forward jet and a backward jet).

In addition to the increased center-of-mass energy and integrated luminosity, we'll continue to develop new approaches to the analysis that we are currently introducing in the W+Z+mET

analysis. All of these SUSY analyses he search topology is 1L+(2/3)jets+mET, where L and mET stand for charged lepton and missing transverse momentum, respectively. In the 1L+3jets+mET events (about half of the signal events), we designed a new method which distinguishes efficiently the initial-state-radiations from the final-state-radiations, and enables an improved reconstruction of the hadronic boson decay. Our aim is to combine this with existing algorithms that enables to split into two hemispheres the 2-vector contributions

to the mET, so as to reconstruct completely the pattern of the SUSY decays.

The selected student will take part into the data analysis of Run 3 as decsribed above. Prior to this, within his/her first year, he/she contribute to the studies of the performance

of the jet flavour tagging algorithms used by the ATLAS collaboration.