Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session H12: Collider Physics I |
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Sponsoring Units: DPF Chair: Young-Kee Kim, University of Chicago Room: Marquette III - 2nd Floor |
Sunday, April 16, 2023 1:30PM - 1:42PM |
H12.00001: A Search for Stealth and R-Parity Violating SUSY using a Neural Network Based ABCD Method Bryan Crossman The Compact Muon Solenoid (CMS) collaboration is responsible for many searches for supersymmetry using collision data from the Large Hadron Collider (LHC). Most of these searches assume that the lightest supersymmetric particle (LSP) is stable and does not leave a direct signature in our detector. However, some theories predict that supersymmetry could be "stealthy" and evade previous search techniques by decaying to SM particles. Two such candidate theories are the R-Parity violating (RPV) and Stealth SYY SUSY models which result in supersymmetric quark decays to SM particles with little to no missing energy. We have performed a search for RPV and Stealth SYY-like decays of top squarks (stops) in LHC collision data using the full LHC Run 2 dataset (137 /fb) with center of mass energy √s=13 TeV. This analysis presents a particularly challenging problem in that these decays are almost indistinguishable from those of top-antitop production, a common LHC background. Through the use of a neural network (NN) in conjunction with the ABCD background estimation method, following the "Double DisCo" approach extended by an additional NN loss term minimizing the ABCD non-closure directly, we are able to establish a data-driven background estimation in the search for these supersymmetric decays. This novel approach can be applied to a wide range of particle physics analyses. |
Sunday, April 16, 2023 1:42PM - 1:54PM |
H12.00002: Prospects of Collider Searches for DFSZ Axinos Jan T Offermann, David W Miller, Ben Rosser, Kristin M Dona, Gabe Hoshino, Bianca J Pol, Keisuke Harigaya Prospects for direct collider searches for the QCD axion -- a dark matter candidate that presents a solution to the strong CP problem -- are limited at best. However, in the context of supersymmetry (SUSY), existing collider experiments may be sensitive to the axion's super-partner, the axino. We will discuss a physics model that incorporates both DFSZ axions and axinos, in which the axino is the lightest supersymmetric particle (LSP). Such a model gives rise to processes in which heavier supersymmetric particles may decay to an axino and a Higgs boson, or vector bosons (W/Z). The lifetime of the decay in these cases will be proportional to the axion mass. For a wide range of model parameters ranging from with micro-eV to milli-eV axion masses, we show that the decaying particle is long-lived and gives rise to detector signatures including displaced vertices and missing energy. We will present the prospects for searches for these axion-axino models at detectors such as the ATLAS and CMS experiments at CERN. |
Sunday, April 16, 2023 1:54PM - 2:06PM |
H12.00003: Search for B-L R-Parity-Violating Scalar Top Decays with ATLAS Lauren Osojnak A search is presented for the direct pair production of scalar tops, which each decay through an R-parity-violating coupling to a charged lepton and a b quark. The final state has two resonances formed by the lepton-jet pairs. Expected sensitivity will be shown for the dataset consisting of an integrated luminosity of 139fb−1 of proton-proton collisions at a center-of-mass energy of √s=13 TeV, collected between 2015 and 2018 by the ATLAS detector at the LHC. Supersymmetry is able to resolve many questions left unanswered by the Standard Model, such as the hierarchy problem. This search is inspired by the minimal supersymmetric B-L extension of the Standard Model, which has spontaneous R-parity violation that allows violation of lepton number. |
Sunday, April 16, 2023 2:06PM - 2:18PM |
H12.00004: Di-track search for heavy, charged particles with high ionization energy loss with the ATLAS detector Marija Glisic, Laura Jeanty, Ismet Siral, dEdx Analysis Team In the search for Beyond-Standard-Model particles, long-lived particles (LLPs) offer an exciting sector yet to be fully explored. Some Supersymmetric models suggest massive, charged, long-lived particles, such as R-Hadrons and staus, may be produced at the Large Hadron Collider (LHC) in proton-proton collisions of sqrt(s) = 13 TeV. These LLPs would present as high-momentum tracks with high ionization energy relative to the minimum-ionizing SM particles of similar momenta, and are detectable using ATLAS's Pixel Detector to measure ionization energy loss. These massive particles do not have simple SM backgrounds which can be easily simulated, but rather can be mimicked by detector effects and mis-reconstructions. As such, a data-driven method is formed to estimate the background. A previous study for single-track events set strong limits on the possible masses for long-lived charginos and R-Hadrons. We present an extension to the previous analysis which requires two candidate tracks per event. The di-track selection has greater sensitivity for pair-produced staus with lifetimes of 10 ns or longer. This analysis utilizes the full ATLAS Run 2 dataset with integrated luminosity of 139 fb^-1. |
Sunday, April 16, 2023 2:18PM - 2:30PM |
H12.00005: Estimates of Lepton Backgrounds for Slepton Searches in Compressed Mass Scenarios at the ATLAS Experiment Thomas Gosart Supersymmetry (SUSY) is a highly motivated extension of the Standard Model (SM) that can solve many of the outstanding problems in the SM. A search for for selectrons ($widetilde{e}$) and smuons ($widetilde{mu}$) in models with compressed mass spectra is currently underway at the ATLAS collaboration at CERN. The model assumes $R$-parity conserving supersymmetry where the lightest supersymmetric partner (LSP) is a neutralino with a mass that is very close to that of the slepton. Specifically, the mass-splitting between the $widetilde{e}$ or $widetilde{mu}$ and the LSP is on the order of 20-70 GeV. The smuon search is particularly motivated, as it could provide a SUSY explanation to the muon $g-2$ anomaly. |
Sunday, April 16, 2023 2:30PM - 2:42PM |
H12.00006: Search for single and pair production of vector-like quarks with leptonic and hadronic final states in ATLAS Avik Roy Vector-like quarks (VLQs), hypothetical fermions with identical electroweak representation for left and right chiralities, are telltale signatures of a number of theories that address the naturalness problem of the Higgs boson's mass. This talk reports results from a number of analyses searching for single and pair production of VLQs with 139~$fb^{-1}$ data from $pp$ collisions at $sqrt{s} = 13$~TeV center of mass energy at the ATLAS detector at the LHC. In these results, VLQs are assumed to dominantly interact with the third generation of the standard model quarks alone. These searches look for VLQs in fully hadronic and leptonic final states and present generalized interpretations of statistical limits obtained from them. |
Sunday, April 16, 2023 2:42PM - 2:54PM |
H12.00007: Search for H→aa→bbbb boosted events in 2018 CMS data using neural networks Brooks C McMaster This talk will present the results and methods of a search for pseudoscalar a, predicted under two-higgs doublet extensions to the standard model, at a 20 GeV theoretical mass point. The decay path H->aa->bbbb in highly boosted jets was specifically targeted, and a binary classification neural network was developed to perform the search using data collected by the CMS experiment in 2018. Upper limits on the existence of a will be presented, and much of the talk will be dedicated to covering neural network techniques (including the use of focal and distance-correlation loss) and lessons in network development learned along the way. |
Sunday, April 16, 2023 2:54PM - 3:06PM |
H12.00008: Probing EFT models using ttX in multiple lepton final states Furong Yan A search for new physics in top quark production with additional final-state leptons is performed with 138 fb-1 of proton-proton collisions at √s = 13 TeV, collected by the CMS detector during 2016, 2017, and 2018. Using the framework of effective field theory (EFT), potential new physics effects are parametrized in terms of 26 dimension-six EFT operators. The data are divided into several categories based on lepton multiplicity, total lepton charge, jet multiplicities, and b tagged jet multiplicities. Kinematic variables corresponding to the leading pT pair of leptons and jets as well as the pT of on-shell Z bosons are used to extract the 95% confidence intervals of the 26 dimension-six EFT operators. No significant deviation with respect to the SM prediction was found. |
Sunday, April 16, 2023 3:06PM - 3:18PM |
H12.00009: Determining the CP Property of htt Coupling via a Novel Jet Substructure Observable Zhite Yu, Kirtimaan A Mohan, C.-P. Yuan Determining the CP property of the Higgs boson is important for a precision test of the Standard Model as well as for the search for new physics. We propose a novel jet substructure observable based on the azimuthal anisotropy in a linearly polarized gluon jet that is produced in association with a Higgs boson at hadron colliders, and demonstrate that it provides a new CP-odd observable for determining the CP property of the Higgs-top interaction. We introduce a factorization formalism to define a polarized gluon jet function with the insertion of an infrared-safe azimuthal observable to capture the linear polarization. |
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