Session G19: BSM Searches at the LHC

Live

Model-independent searches for physics beyond the Standard Model typically focus on invariant masses of two objects (jets, leptons or photons). In this study we explore opportunities for similar model-agnostic searches using multi-body invariant masses. In particular, we will discuss physics cases when new physics can be observed in a model-independent way in three- and four-body invariant masses of jets and leptons while two-body invariant masses, that have been extensively explored at collider experiments in the past, cannot provide sufficient signatures for experimental observations. A number of models beyond the Standard Models leading to signals in multi-body invariant masses are discussed.   

Live

In this talk we present the current status of a W+gamma resonance search in the leptonic channel, using the full LHC Run II data set of 13TeV proton-proton collisions collected with the CMS detector, corresponding to an integrated luminosity of 137 $fb^{-1}$. Final states with a W boson and a photon are interesting as they can be used to test several Beyond the Standard Model (BSM) theories including charged Higgs and folded supersymmetry models. The leptonic final state is expected to set improved limits for masses below 1TeV compared to searches in the hadronic channel due to a smaller backgrounds. To better model backgrounds due to misidentifications, we employ data-based methods to estimate electron-to-photon misidentification and jet-to-photon misidentification. We will present the expected limits including systematic uncertainties for the combined 2016 - 2018 LHC running period.   

Live

This presentation describes a search for dark matter candidates produced in association with a Standard Model Higgs boson, with a focus on the $ H \rightarrow b\bar{b}$ decay channel. The search utilises a dataset of $pp$ collisions at $\sqrt{s}=$ 13 TeV corresponding to an integrated luminosity of 139 fb$^{-1}$, recorded by the ATLAS detector. The results are interpreted in the context of the 2-Higgs doublet model with an extra vector or pseudoscalar mediator. The 2-Higgs doublet model is an example of the so-called Higgs portal models, in which dark matter particles interact with the SM particles only through their couplings with the Higgs sector of the theory.   

Not Participating

Some two Higgs doublet models predict the decay of the Higgs boson to two spin-zero bosons, where the dominant decay mode is to two bottom quarks. The channel remains a significant challenge for the LHC, due to the enormous hadronic background and challenge defining trigger strategies. We present a preliminary analysis of Monte Carlo simulations of this process, focusing on the VBF production mechanism with an additional associated photon.   

Live

Effective Field Theories such as HEFT, organized as momentum expansions, are a controllable approximation to strong dynamics only near threshold, as they miss exact elastic unitarity, reducing their predictive power at a higher scale if small separations from the Standard Model are found at the LHC or elsewhere. Unitarized chiral perturbation theory extends their reach to saturation of unitarity but, generally, with unknown systematics. Our contribution follows the derivation of the Inverse Amplitude Method (IAM), a serious unitarization procedure, quantifying the uncertainty introduced at each step. Provided a check for zeroes of the amplitude is performed and, if appropriate, they are taken into account, we find that the IAM extension of EFT partial wave amplitudes can be assigned a limited uncertainty band up to and including the first resonance or structure of the amplitude, and if none appears, up to energies of the order of $(4\pi F)$, nominal validity limit of the EFT.   

Not Participating

The idea of with EW-$\nu_R$ model with additional GeV scale mirror fermions with large displaced vertices and extended Scalar sector is very appealing from the Collider perspective. The presence of a complex singlet scalar in this model helps to solve the strong-CP problem, satisfying the constraint coming from the present absence of neutron electric dipole moment, and without need of an axion. Based on this model, in this work, we study the detailed scalar mass spectrum, having $\sim 125$ GeV Higgs-like scalar, which allowed by signal strength and lepton flavor violating constraints data. Besides explaining the $\sim 125$ GeV Higgs-like scalar, this scenario can also accommodate a non-thermal scalar dark matter which can satisfy the relic density data. The imaginary part of the complex singlet scalar in this model serve as a viable non-thermal feebly interacting massive particle (FIMP) dark matter candidate. We identify the region of the parameter space for the freeze-in scenario, which is consistent with all the bounds from relic density and direct-indirect searches and discuss the possible future implications of this scenario.   

Live

A data sample containing top-antitop quark pair associated with a boosted Z or Higgs boson is used to search for signs of new physics within the framework of effective field theory (EFT). The samples correspond to an integrated luminosity of $137\,\text{fb}^{−1}$ of proton-proton collisions produced in 2016, 2017, and 2018 at a center-of-mass energy of 13 TeV at the LHC and collected by the CMS experiment. The sample is selected by requiring events with a single lepton, jets identified as bottom quarks, and a jet with high transverse momentum ($p_{\text{T}}$). A template is constructed from event kinematics centered around the boosted Z/H candidate, and a neural network trained to discriminate $\text{t}\bar{\text{t}}\text{Z}$ and $\text{t}\bar{\text{t}}\text{H}$ from $\text{t}\bar{\text{t}}$ events. To probe EFT effects directly, a parameterization of the signal rate in terms of the Wilson coefficients of the EFT operators is derived, and a fit is performed simultaneously of the 9 Wilson coefficients to the data. Limits on the values of the Wilson coefficients are presented.   

Live

Searches are presented for resonances with mass between 0.6 and 1.8 TeV decaying to dijet final states in proton-proton collisions at sqrt(s)$=$13 TeV. The searches are performed with dijets that are reconstructed from calorimeter information in the trigger using data corresponding to an integrated~luminosity of 122 /fb. The dijet mass spectrum is compared to a smooth parameterization of the QCD background and simulations of resonance signals decaying into parton pairs. Upper limits at 95{\%} CL are presented on the production cross section of narrow quark-quark, quark-gluon, and gluon-gluon resonances.   

Live

An Effective Field Theory (EFT) re-interpretation of the differential measurement of Vector Boson Fusion Higgs production and decay to two W bosons will be reported. The analysis used the full Run-2 data in 2015--2018 of $pp$ collisions at $\sqrt{s}=$13 TeV with the ATLAS detector at the LHC, which correspond to an integrated luminosity of 139 fb$^{-1}$. Events with an electron and a muon from the decay of the W bosons and two energetic jets in the final state are considered as signals. At particle level, Standard Model predictions can be modified by expressing the differential cross section of various observables as a function of parameters that represent new phenomena predicted by EFT. The background subtracted and unfolded data are used to set limits on these new physics parameters.