Laura Pereira Sanchez

The correct identification of b-initiated jets against c-initiated, hadronic tau-initiated and u-, d-, s-initiated jets is primordial for ATLAS Collaboration searches and precision measurements e.g.t t and single-top measurements, supersymmetry, Higgs boson.In consequence, the ATLAS Collaboration has developed several so-called b-tagging algorithms to discriminate b-jets against other flavour jets.Expected performance is evaluated on Monte Carlo events, but due to some inaccuracies in the simulation, it might differ from the performance in real data events.These algorithms are calibrated to account for differences between data and simulated events in the b-tagging efficiency for b-jets and mis-tagging efficiency in cand light-jets.The b-jet efficiency calibration is performed on two-lepton t t events in order to exploit the large purity of this final state in b-jets.The c-jet mis-tag rate is measured on one-lepton t t events, which allow the presence of an hadronically decaying W-jet enriched in c-jets.Both calibrations adopt a combinatorial likelihood approach to retrieve the efficiency of the jet for a given flavour.Finally, due to the large light-jet rejection of b-tagging algorithms, the calibration of light-jets mis-tag rate is performed on a Z+jet sample since t t doesn't allow for a pure enough light-jet sample.This proceeding presents an overview of the DL1r b-tagging algorithm and the calibration techniques explained above.Results in the form of data -Monte Carlo scale-factors are obtained for the b-jet efficiency and cand light-jet mis-tag rate with 140 fb -1 of data recorded by the ATLAS detector from 2015 to 2018.

This poster presents the latest results on searches for pair production of supersymmetric partners of the top and bottom quarks using the LHC proton-proton collision data, recorded by the ATLAS detector at a centre of mass energy of √ s = 13 TeV from 2015 to 2018, corresponding to an integrated luminosity of 139 fb -1 .Three main analyses are presented; a search for top squark pair production in events with Z bosons, a search for bottom squark pair production in events with two Higgs bosons and a search for top squark pair production in events with a three body decay.The ATLAS Collaboration has also published new results which offer interpretations with third generation squarks and extend the current exclusion limits.

Measuring Higgs pair production (HH) will provide information about the Higgs self coupling, which is key to determine the shape of the Higgs potential at higher order.The leading HH production mode at the Large Hadron Collider is gluon gluon fusion and the sub-leading production mode is vector boson fusion.Given the small cross section, Higgs pair production has not yet been observed.However, competitive upper limits on the HH production cross section and Higgs self coupling modifier κ λ are set by the ATLAS and CMS Collaborations.Searches for HH production in a final state where one Higgs boson decays to a pair of b quarks, and the other Higgs boson decays either to two photons, two b quarks or four leptons, with the full Run 2 proton-proton collision data set at √ s = 13 TeV from the ATLAS and CMS experiments, are presented.Combinations of HH searches and Higgs self coupling measurements with partial Run 2 data are also presented.Competitive upper limits on the HH cross section are obtained by the ATLAS and CMS HH searches in the b bγγ final state.However, the CMS HH search in the b bb b final state sets the current most stringent observed upper limit on the HH production cross section of 3.6 times the Standard Model expectation at 95% confidence level.The current most stringent limits on κ λ are obtained by the ATLAS HH search in the b bγγ final state, which sets observed (expected) limits of -1.5 (-2.4) < κ λ < 6.7 (7.7) at 95% confidence level.