Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at s = 8 TeV

Abstract: The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb−1 for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (F0), left-handed (FL), or right-handed (FR) polarizations. The resulting combined measurements of the polarization fractions are F0 = 0.693 ± 0.014 and FL = 0.315 ± 0.011. The fraction FR is calculated from the unitarity constraint to be FR = −0.008 ± 0.007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F0 (FL) with respect to the most precise single measurement. A limit on anomalous right-handed vector (VR), and left- and right-handed tensor (gL, gR) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [−0.11, 0.16] for VR, [−0.08, 0.05] for gL, and [−0.04, 0.02] for gR, at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived

Search for electroweak production of charginos and neutralinos in multileptonic final states with the ATLAS experiment

Supersymmetry, or SUSY, is one of the proposed extensions of the Standard Model which represents a solution to some of the limitations of the latter, such as the hierarchy problem. It introduces new particle states which may be produced at the ATLAS experiment taking data at sqrt(s)=13 TeV at the Large Hadron Collider (LHC). Due to existing constraints on the value of the masses of strongly coupled SUSY particles, the electroweak production of weakly interacting sparticles may become the key mechanism to search for beyond-the-Standard-Model physics at the LHC. A search for electroweak production of charginos and neutralinos decaying to multileptonic final states using Run-2 data collected with the ATLAS experiment is presented. Results are interpreted is the context of simplified models in which charginos and neutralinos undergo R-parity-conserving decays via intermediate production of gauge and Higgs bosons

Searches for electroweak production of supersymmetric particles with the ATLAS detector

The direct production of electroweak SUSY particles, including sleptons, charginos, and neutralinos, is a particularly interesting area with connections to dark matter and the naturalness of the Higgs mass. The small production cross-sections and challenging experimental signatures, often involving compressed spectra, lead to difficult searches. This talk will highlight the most recent results of searches performed by the ATLAS experiment for supersymmetric particles produced via electroweak processes, including analyses targeting small mass splittings between SUSY particles, and including both in R-parity-conserving and R-parity-violating scenarios. Recent results involving the combination of searches are also presented

Search for electroweak production of charginos and neutralinos in final states with three leptons and missing transverse momentum with the ATLAS experiment

Supersymmetry, or SUSY, is a viable extension to the Standard Model, and resolves important limitations latter such as those arising from the hierarchy problem. It introduces new particle states which may be produced at the ATLAS experiment taking data at \sqrt{s}=13 TeV at the Large Hadron Collider (LHC). Due to existing constraints on the value of the masses of strongly coupled SUSY particles, the electroweak production of weakly interacting sparticles may become the key mechanism to search for beyond-the-Standard-Model physics at the LHC. A new search for electroweak production of charginos and neutralinos decaying to final states with three light leptons – electrons or muons – and missing transverse momentum is presented, based on the analysis of the full Run-2 data sample collected with the ATLAS experiment. Results are interpreted is the context of R-parity-conserving simplified models in which charginos and neutralinos undergo decays via the intermediate production of W and Z bosons or W and Higgs (h) bosons. These new results significantly extend previously published constraints on relevant sparticle masses

EW SUSY searches at ATLAS and CMS (including charginos, neutralino and sleptons, soft susy)

Supersymmetry, or SUSY, is one of the proposed extensions of the Standard Model which represents a solution to some of the limitations of the latter, such as the hierarchy problem. It introduces new particle states which may be produced at the ATLAS experiment taking data at $\sqrt{s}=13$ TeV at the Large Hadron Collider (LHC). Due to existing constraints on the value of the masses of strongly coupled SUSY particles, the electroweak production of weakly interacting sparticles may become the key mechanism to search for beyond-the-Standard-Model physics at the LHC. In this talk the latest results from the ATLAS and CMS Collaborations are presented in the context of the search for electroweak production of SUSY particles at the LHC

Searches for chargino and neutralino production in multileptonic final states using s\sqrt{s} = 13 TeV proton-proton collisions with the ATLAS detector

This thesis presents the work of the Candidate during his PhD on three analyses targeting the Electroweak Supersymmetry production of charginos and neutralinos decaying into multilptonic final states. Only electrons and muons are considered along with R-Parity-conserving decays. These analyses all use from $\sqrt{s}$ = 13 TeV proton-proton collisions collected by the ATLAS experiment at the Large Hadron Collider in the 2015-2018 period for a total of 139 $fb^{−1}$. Firstly, the analysis targeting final states with two leptons of the same electrical charge and intermediate $W$ and Higgs on-shell bosons is presented. The results show no significant excess from the Standard Model predictions and new constraints on the masses of charginos and neutralinos are obtained for this model, significantly extending the known bounds from previous searches. Secondly, results of another analysis targeting intermediate states with on-shell $W Z$ and $W h$ bosons and three-lepton final states are also presented. Once again, no significant deviation from the Standard Model prediction is observed and exclusion limits on the masses of charginos and neutralinos are set for these models. Finally, the statistical combination of these searches with those of other analyses targeting the same electroweak Supersymmetry production mechanism with different final states is also presented in this thesis. The final results show how such combination can be used to further improve the constraints on the masses of the charginos and neutralinos. Moreover, the details of a technical task concerning the characterisation of the performance of the Inner Detector Trigger tracking of electrons and muons in the ATLAS experiment through the usage of the Tag-and-Probe technique is also discussed. The final result show a significant improvement in the accuracy of the measured Trigger tracking efficiencies with respect to those obtained by means of the previously used procedure

Search for electroweak production of charginos and neutralinos in final states with three leptons and missing transverse momentum with the ATLAS experiment

A new search for electroweak production of charginos and neutralinos decaying to final states with three light leptons - electrons or muons - and missing transverse momentum is presented. The analysis is performed by using the full Run-2 data sample - corresponding to an integrated luminosity $L=139\,fb^{-1}$ - collected with the ATLAS experiment. Results are interpreted in the context of an $R$-parity-conserving simplified model in which charginos and neutralinos decay via the intermediate production of $W$ and $Z$ bosons or $W$ and Higgs ($h$) bosons. The new results significantly extend published constraints on relevant sparticle masses