Search for SUSY Electroweak production at LHC Run 2 and study of CMOS sensor performance for ITK replacement in second-half of HL-LHC.

• Ngoc Khanh Vu

There are two dedicated searches for the SUSY Electroweak production performed at ATLAS-CPPM. The first one is a search for the direct production of chargino and neutralino, where the neutralino decays into a Z boson and the lightest SUSY particle, and the chargino into a W boson and the LSP. The second search is for the chargino pair production, where each chargino decays into W boson and the LSP. In both searches, we focus on the scenario where the W boson decays leptonically while the other W or Z boson decays hadronically. The final states are therefore characterized by the presence of one isolated lepton, jets and missing transverse momentum. The two analyses via this one-lepton channel are conducted for the first time at LHC and target an integrated luminosity of 139 fb-1 corresponding to the full ATLAS Run-2 (2015-2018) collected data. The High Luminosity Large Hadron Collider (HL-LHC) is an upgrade to the LHC, that will be operational in 2027 and aim to increase the luminosity by a factor of 10 in order to allow better studies of known mechanisms and boost the potential for new discoveries as well. The B-Layer and IBL, which were installed during LHC Run-1 and Run-2 and designed to work effectively with a fluence up to 10^15 and 2×10^15 1-MeV neutrons per cm2, respectively, will suffer during Run-3 and not be able to withstand the HL-LHC radiation levels. Consequently, they will be replaced by a new full silicon tracker (ITK) in the LHC LS3 (2025- 2026) for the HL-LHC. The innermost layer of ITK can withstand up to 10^16 n(1 MeV)/cm2 which is only a half of the total dose foreseen for the entire lifetime of HL-LHC, thereby leading to a replacement for ITK by the HL-LHC half-life. One of the potential candidates for ITK replacement is the CMOS technology which has shown up many advantages in the electronic industry for 20 years. With smaller pixel size and monolithic design, CMOS sensors will provide a better spatial resolution and a reduction of the detector cost as well. Our group is contributing to the R&D effort to make CMOS sensors radiation- hard enough for the HL-LHC and also investigating what can be gained from the ITK replacement.

Testing lepton flavor universality with the B0 -> K* tau+ tau- decay at LHCb

• Jacopo Cerasoli (Aix Marseille Univ, CNRS/IN2P3, CPPM, Marseille, France)

Lepton flavor universality is a property of the Standard Model of particle physics according to which the coupling constants of the three families of leptons to the weak bosons are the same. The difference between the leptons is consequently due only to their masses. Even though this property has been experimentally tested, recently some tensions between the predictions of the theory and measured values have arisen, pointing in the direction of a violation of lepton flavor universality. Modes with 𝜏 leptons in the final state are experimentally challenging and still largely unexplored, with lots of room left for possible new physics effects. In particular the 𝐵0→𝐾∗𝜏+𝜏− decay is expected to be suppressed in the SM, with a predicted branching ratio of 10^−7, but which could be enhanced by up to factors of 1000 in new models, especially those involving the existence of leptoquarks.