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Accueil du site > Formation > Thèses - Stages de M2

Search for a new phenomena in the dilepton final state

While the Standard Model (SM) has proven tremendously successful, much experimental evidence points to it not being a complete description of our universe. The searches for new phenomena (BSM) are therefore an important component of the experimental program of the Large Hadron Collider at CERN, Geneva. While there is no direct evidence for BSM phenomena at the LHC, measurements of beauty hadron decays display a seemingly coherent pattern of deviations with respect to the SM predictions, which suggest that new physics couples differently to three generations of matter. This pattern points towards new effects at mass scales not much above 10 TeV.

Scientific description

While the Standard Model (SM) has proven tremendously successful, much experimental evidence points to it not being a complete description of our universe. The searches for new phenomena (BSM) are therefore an important component of the experimental program of the Large Hadron Collider at CERN, Geneva. While there is no direct evidence for BSM phenomena at the LHC, measurements of beauty hadron decays display a seemingly coherent pattern of deviations with respect to the SM predictions, which suggest that new physics couples differently to three generations of matter. This pattern points towards new effects at mass scales not much above 10 TeV.

Note that the quark-level processes responsible for these so-called ‘B anomalies’, b → sll and b → cτv transitions, could be connected to bs̄ → ll and bc̄ → lv → ll and bc̄ → lv and bc̄ → lv → lv scattering processes by crossing symmetry. These latter Drell-Yan processes could be studied in the proton-proton collisions collected by ATLAS experiment at the LHC and also sensitive to any new phenomena which affect the B meson decays. This project will focus on a search for deviation from the SM prediction in the cross-sections of the Drell-Yan process, for all three lepton families consistently : dielectrons, dimuons and ditaus. As the searched phenomena would be beyond the kinematic reach of the LHC, they have to be explored in the framework of SM effective field theories (SMEFT). The ongoing ATLAS experiment measurements of the double-differential cross-section of the Drell-Yan process on Run 2 LHC data set collected in 2015-2018 would be optimized to improve their sensitivity to the new phenomena through EFT effects.

This work will be done in the ATLAS group at LAPP in Annecy. LAPP is located 50 km from CERN. The candidates should contact internship supervisors by email.

Optional information on a possible PhD subject :

The M2 internship can be expanded into a PhD based on studies described above focusing on preparation of Run 3 (2022-2024) and High Luminosity LHC (2027+) ATLAS Drell-Yan measurements. Final states with additional bjets will also be explored. The technical part of the thesis will be related to the construction of the new inner tracking pixel detector (ITK- pixel) for the High Luminosity LHC (2027+), involving work on the set up and the operation of the system test for the ITK modules assembled at LAPP. The duration of the thesis is three years. An extended stay in CERN is possible during the PhD thesis. The geographical proximity of LAPP to CERN facilitates the direct implication of the student in the life of the experiment including shifts and collaboration meetings. The contacts with theoreticians are also facilitated by the presence of the theoretical physics laboratory LAPTh in the same building.

o Niveau : Master 2

o Responsable : Tetiana Berger- Hryn’ova, Eleonora Rossi

o Téléphone : 04 50 09 16 77

o e-mail : hrynova@lapp.in2p3.fr jeleonora.rossi@lapp.in2p3.fr

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