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Search for new phenomena in the dilepton final state at LHC

Resonant searches in the dilepton (dielectron and dimuon) final state have a long and illustrious history with the discovery of the J/ψ meson in 1974 and Υ meson in 1977 as well as the Z boson in 1983. As these were key steps which led to the establishment of the Standard Model (SM) of particle physics, the study of the same final state could help to pave the way to a better understanding of the physics processes beyond it. A common theme in many beyond SM theories is a presence of the new neutral gauge bosons (Z’) with mass at a TeV scale. They have been extensively searched for at the Large Hadron Collider (LHC). The most recent lower limit on the mass of the Z’SSM decaying to dileptons was set by the ATLAS experiment to be 5.1TeV.

The searches to date assume that a Z’ boson is produced through quark-anti-quark annihilation. But if the coupling of the Z’ boson to the SM quarks is small, the dominant production channel becomes vector-boson-fusion (VBF). Its signature is a resonance in the dilepton spectrum combined with a presence of two back-to-back jets in the event. There are also models in which a Z’DM boson is produced in association with invisible dark matter particles, signature for which is missing transverse momentum in the detector. The current inclusive searches do not have sensitivity to such models and they might have eluded the detection up to now. These are first searches of this kind at the LHC.

o Level : Master 2 internship, can be followed by a PhD

o Date of the internship : spring 2021

o Supervisor : Tetiana Berger-Hryn’ova

o Phone : 04 50 09 16 77

o e-mail : hrynova@lapp.in2p3.fr

o Team members : C. Adam-Bourdarios, N. Berger, M. Delmastro, L. Di Ciaccio, C. Goy, T. Guillemin,T. Hryn’ova, S. Jézéquel, I. Koletsou, J. Lévêque, N. Lorenzo Martinez, E. Sauvan

Detailed description :