Report from Working Group 3: Beyond the standard model physics at the HL-LHC and HE-LHC

This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as $3$ ab$^{-1}$ of data taken at a centre-of-mass energy of 14 TeV, and of a possible future upgrade, the High Energy (HE) LHC, defined as $15$ ab$^{-1}$ of data at a centre-of-mass energy of 27 TeV. We consider a large variety of new physics models, both in a simplified model fashion and in a more model-dependent one. A long list of contributions from the theory and experimental (ATLAS, CMS, LHCb) communities have been collected and merged together to give a complete, wide, and consistent view of future prospects for BSM physics at the considered colliders. On top of the usual standard candles, such as supersymmetric simplified models and resonances, considered for the evaluation of future collider potentials, this report contains results on dark matter and dark sectors, long lived particles, leptoquarks, sterile neutrinos, axion-like particles, heavy scalars, vector-like quarks, and more. Particular attention is placed, especially in the study of the HL-LHC prospects, to the detector upgrades, the assessment of the future systematic uncertainties, and new experimental techniques. The general conclusion is that the HL-LHC, on top of allowing to extend the present LHC mass and coupling reach by $20-50\%$ on most new physics scenarios, will also be able to constrain, and potentially discover, new physics that is presently unconstrained. Moreover, compared to the HL-LHC, the reach in most observables will, generally more than double at the HE-LHC, which may represent a good candidate future facility for a final test of TeV-scale new physics

Welcome to Twin Particles: From Novel ZZ Estimate to Searches for Supersymmetric Sleptons and Higgsinos using the ATLAS Run-2 Data and at the High-Luminosity LHC

After the Higgs boson discovery by the ATLAS and CMS collaborations at CERN, one of the main goals of the Large Hadron Collider programme is to find Beyond the Standard Model particles. This thesis focuses on the search for supersymmetric partners of the leptons (sleptons) and presents the prospects of a search for the supersymmetric partners of the electroweak gauge bosons and the Higgs boson (higgsinos). The detectable final state for both signatures consists of two electrons or muons with opposite electric charge. The search for the sleptons is performed using the full Run-2 data collected by the ATLAS detector, corresponding to an integrated luminosity of $139~\text{fb}^{-1}$ at $\sqrt{s} = 13~\text{TeV}$. In the regions sensitive to the slepton signal, the selected events are found to be consistent with the Standard Model predictions. The higgsino search is developed in the context of the next major upgrade of the LHC, the High-Luminosity LHC (HL-LHC). The thesis assesses the sensitivity reach on the search for higgsinos by the end of the HL-LHC era, by which the ATLAS detector is expected to have recorded an integrated luminosity of $3000~\text{fb}^{-1}$ at $\sqrt{s} = 14~\text{TeV}$. The results obtained show that using the full HL-LHC dataset, higgsinos with masses of about $200~\text{GeV}$ could be discovered, and masses up to $350~\text{GeV}$ could be excluded. The thesis also discusses the possibility of estimating the Standard Model $ZZ$ process using $Z\gamma$ events from data in Beyond the Standard Model searches, showing that theoretical uncertainties of about $4\%$ can be achieved. In addition to the LHC data analyses, the thesis reports on the design of a cooling setup with the aim of testing the silicon modules that will be placed in the upgraded ATLAS Inner Detector

Search for Dark Photons with the FASER detector at the LHC

The FASER experiment at the LHC is designed to search for light, weakly-interacting particles produced in proton-proton collisions at the ATLAS interaction point that travel in the far-forward direction. The first results from a search for dark photons decaying to an electron-positron pair, using a dataset corresponding to an integrated luminosity of $27.0~\mathrm{fb}^{-1}$ collected at center-of-mass energy $\sqrt{s} = 13.6$ TeV in 2022 in LHC Run 3, are presented. No events are seen in an almost background-free analysis, yielding world-leading constraints on dark photons with couplings $\epsilon \sim 2 \times 10^{-5} - 1 \times 10^{-4}$ and masses $\sim 17~\text{MeV}- 70~\text{MeV}$. The analysis is also used to probe the parameter space of a massive gauge boson from a U(1)$_{B-L}$ model, with couplings $g_{B-L} \sim 5\times10^{-6} - 2\times10^{-5}$ and masses $\sim 15~\text{MeV} - 40~\text{MeV}$ excluded for the first time.The FASER experiment at the LHC is designed to search for light, weakly-interacting particles produced in proton-proton collisions at the ATLAS interaction point that travel in the far-forward direction. The first results from a search for dark photons decaying to an electron-positron pair, using a dataset corresponding to an integrated luminosity of 27.0 fb$^{-1}$ collected at center-of-mass energy $\sqrt{s} = 13.6$ TeV in 2022 in LHC Run 3, are presented. No events are seen in an almost background-free analysis, yielding world-leading constraints on dark photons with couplings $\epsilon \sim 2 \times 10^{-5} - 1 \times 10^{-4}$ and masses $\sim$ 17 MeV - 70 MeV. The analysis is also used to probe the parameter space of a massive gauge boson from a U(1)$_{B-L}$ model, with couplings $g_{B-L} \sim 5 \times 10^{-6} - 2 \times 10^{-5}$ and masses $\sim$ 15 MeV - 40 MeV excluded for the first time

The risk of COVID-19 death is much greater and age dependent with type I IFN autoantibodies

International audienceSignificance There is growing evidence that preexisting autoantibodies neutralizing type I interferons (IFNs) are strong determinants of life-threatening COVID-19 pneumonia. It is important to estimate their quantitative impact on COVID-19 mortality upon SARS-CoV-2 infection, by age and sex, as both the prevalence of these autoantibodies and the risk of COVID-19 death increase with age and are higher in men. Using an unvaccinated sample of 1,261 deceased patients and 34,159 individuals from the general population, we found that autoantibodies against type I IFNs strongly increased the SARS-CoV-2 infection fatality rate at all ages, in both men and women. Autoantibodies against type I IFNs are strong and common predictors of life-threatening COVID-19. Testing for these autoantibodies should be considered in the general population

The risk of COVID-19 death is much greater and age dependent with type I IFN autoantibodies

International audienceSignificance There is growing evidence that preexisting autoantibodies neutralizing type I interferons (IFNs) are strong determinants of life-threatening COVID-19 pneumonia. It is important to estimate their quantitative impact on COVID-19 mortality upon SARS-CoV-2 infection, by age and sex, as both the prevalence of these autoantibodies and the risk of COVID-19 death increase with age and are higher in men. Using an unvaccinated sample of 1,261 deceased patients and 34,159 individuals from the general population, we found that autoantibodies against type I IFNs strongly increased the SARS-CoV-2 infection fatality rate at all ages, in both men and women. Autoantibodies against type I IFNs are strong and common predictors of life-threatening COVID-19. Testing for these autoantibodies should be considered in the general population